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- let 's talk about polarization of light . we know what light waves are ; they 're electromagnetic waves . so they 're made out of electric fields . and that 's not good enough . we know there 's not just electric fields . that could n't sustain itself . there 's got to be magnetic fields there , as well , that are changing . those are perpendicular , so you can kind of draw them . it 's hard , on something two-dimensional , but you can kind of imagine those looking something like this . and those magnetic fields would point at a right angle to the electric fields . but this gets really messy if i try to draw both the electric and magnetic fields at the same time . so we 're going to leave the magnetic fields out . it 's often good enough to just know the direction of the electric field when we focus on the electric field . so what does polarization mean ? polarization refers to the fact that , if this light ray was heading straight toward your eye , or a detector , over here , what would you see ? well , if i draw an axis over here , and this point here , in the middle , this is this line -- so imagine we 're looking straight down that line -- and then up and down is up and down , and then left and right , that direction i have the magnetic field , would be this way and that way . what would my eye see ? well , my eye 's only going to see electric fields that either point up or electric fields that point down . they might have different values , but i 'm only going to see electric fields that point up or down . because of that , this light ray is polarized . so polarized light is light where the electric field is only oscillating in one direction . up or down , that 's one direction -- vertically . or it could be polarized horizontally . or it could be polarized diagonally . but either way , you could have this wave polarized along any direction . i mean , a light ray like this , if we had it coming in diagonal , this light ray that 's oscillating like this , where the electric field oscillates like that , that also polarized . these are both polarized because there 's only one direction that the electric field is oscillating in . and you might thing , `` pff , how could you ever have `` a light ray that 's not polarized ? '' easy . most light that you get is not polarized . that is to say , light that 's coming from the sun , straight from the sun -- typically not polarized . light from a lightbulb , an old incandescent light bulb , this thing 's hot . you can get light polarized in any direction , all at once , all overlapping . so if we draw this case for a light bulb , just a random incandescent light bulb , you might get light , some of the light , hitting you eye , you can get some light that 's got that direction , you got light that 's got this direction , you got light in all these directions at any given moment . i mean , you 'd have to add these up to get the total , and they might not all be the same value . but what i 'm trying to say is , at any given moment , you do n't know what direction the electric field 's going to be hitting your eye at from a random source . it could be in any direction . so this is not polarized . this diagram represents light that is not polarized . at some point , the field might be pointing this way , at some later point it 's this way ; it 's just random . you never know which way the electric field 's going to be pointing . whereas these over here , these are polarized . so how could you polarize this light ? let 's say you wanted light that was polarized . you were doing an experiment . you needed polarized light . well , that 's easy . you can use what 's called a polarizer . and this is a material that lets light through , but it only lets light through in one orientation , so you 're going to have a polarizer that , for instance , only lets through vertically polarized light . so this is a polarizer . these are cheap : thin , plastic , configured in a way so that it only lets light through that 's vertically polarized . any light coming in here that 's not vertically polarized gets blocked , or absorbed . so what that means is , if you used this polarizer and held it in between your eye and this light bulb , you would only get this light . all the rest of it would get blocked . or you could just rotate this thing and imagine a polarizer that only lets through horizontal light . now it would only let through light that was this way , and so you would only get this part of the light . or you could just orient it at any angle you want and block everything but the certain angle that this polarizer is defined as letting light through . so you can do this . and once you hold this up , you get polarized light , light that 's only got one orientation . so that 's what polarization means . but why do we care about polarization ? well , let me get rid of this for a minute . you 've heard of polarized sunglasses . so imagine you 're standing near water , or maybe you 're standing on ice or snow or something reflective . there 's a problem . say the sun 's out . it 's shining . it 's a beautiful day -- except there 's going to be glare . let 's say you 're looking down at something here on the ground . it 's going to get light reflecting off of it from just ... you know , light 's coming in from all direction . but it also gets this direct light from the sun . so it gets light from reflected off the clouds and whatever , whatever 's nearby , ambient light . and there 's also this direct sunlight . that 's harsh . if that reflects straight up to your eye , that hurts . you do n't like that . it blocks our vision . it 's hard to see , it 's glare . we do n't want this glare . so what can we do ? well , it just so happens that , when light reflects off of a surface , even though the light from the sun is not polarized , once it reflects , it does get polarized or at least partially polarized . so this surface here , once this light reflects , it 's coming in at all orientations . you got electric field ... you never know what electric field you 're going to get straight from the sun . and when it reflects , though , you mostly get , upon reflection , the direction of polarization defined by the plane of the surface that it hit . so because the floor is horizontal , when this light ray hits the ground and reflects , that reflected light gets partially polarized . this horizontal component of the electric field is going to be more present than the other components . maybe not completely . sometimes it could be . it could be completely polarized , but often it 's just partially polarized . but that 's pretty cool , because now you know what we can do . i know how to block this . we should get some sunglasses . we put some sunglasses on and we make our glasses so that these are polarized . and how do we want these polarized ? i want to get rid of the glare . so what i do is , i make sure my sunglasses only let through vertically polarized light . here 's some polarizers . that way , a lot of this glare gets blocked because it does not have a vertical orientation , it has a horizontal orientation . and then we can block it . so that 's one good thing that polarization does for us , and understanding it , we can get rid of glare . also , fishermen like it because , if you 're trying to look in the water at fish , you want to see in through the water , you want to see this light from the fish getting to you . you do n't want to see the glare off of the sun getting to you . so polarized sunglasses are useful . also , we can play a trick on our eye , if we really wanted to . you could take one of these , make one eye have a vertical orientation for the polarization , have the other eye with a horizontal ... and you 're thinking , `` this is stupid . `` why would you do this for ? '' `` this eye 's going to get a lot of glare . '' we would n't use these outside , when you 're , like , skiing or fishing , but you could play a trick on your eyes if you went to the movies and you went and watched a movie . well , the reason our eyes see 3d is because they 're spaced a little bit apart . they each get a different , slightly different image . that makes us see in 3d . we can play the same trick on our eye if we have the polarization like this . if light , if some of the light from the movie theater screen is coming in with one polarization , and the other light 's coming in with the other polarization , we can send two different images to our eyes at the same time . if you took these off , it 'd look like garbage because you 'd be getting both of these slightly different images , it 'd look all blurry . and it does . if you take off your 3d glasses and look at a 3d movie , looks terrible , because now both eyes are getting both images . but if you put your glasses back on , now this eye only gets the orientation that it 's supposed to get , and this eye only gets the orientation that it 's supposed to get , and you get a 3d image . so it 's useful in many ways . let me show you one more thing here . let 's come back here . this light was polarized vertically . so that 's called linear polarization . any time ... same with these . these are all linear polarization because , just up and down , one linear direction , just diagonal . this is also linear . all of these are linear . you can get circular polarized light . so if we come back to here , we 've got our electric field pointing up , like that . now let 's say we sent in another light ray , another light ray that also had a polarization , but not in this direction . let 's say our other light ray had polarization in this direction , so it looks like this , kind of like what our magnetic field would have looked like . but this is a completely different light ray with its own polarization and its own magnetic field . so we send this in . what would happen ? well , at this point , you 'd have a electric field that points this way . at this point , you 'd have a electric field that points that way . what would your eye see if you were over here ? let 's see . if i draw our axis here . all right , when this point right here gets to your eye , what am i going to see ? well , i 'm going to have a light ray that 's one part of a light ray . one component points up . that 's this electric field . one component points left . that 's this electric field . so the total , my total electric field , would point this way . i could to the pythagorean theorem if i wanted to figure out the size of it , but i just want to know the direction for now . and then it gets to here , and look at it : they both have zero . this light ray has zero electric field , this one has zero electric fields . so then it 'd just be at zero . now what happens over here ? well , i 've got light . this one points to the right at that point , this pink one , and then this red one would be pointing down . so what would i have at that point ? i 'd have light that went this way , and it would just be doing this over and over . it would just be ... i 'd just have diagonally polarized light . this is n't giving me anything new . you might think this is dumb . why do this ? why send in two different waves to just get diagonally polarized light ? i could have just sent in one wave that was diagonally polarized and got the same thing . the reason is , if you shift this purple wave , this pink wave , by 90 degrees of phase , by pi over two in phase , something magical happens . let me show you what happens here , if we move this to here . now we do n't just get diagonally linear polarized light . what we 're going to get is ... let me get rid of this . okay , so we start off with red , right ? the red electric field points up , and then this pink wave 's electric field is zero at that point . so this is all i have . my total electric field would just be up . i 'm going to draw it right here . the green 'll be the total . now i come over to here , and at this point , there 's some red electric field that points up , but there 's some of this other electric field that points this way . so i 'd have a total electric field that would point that way . and then i get over to here , and i 'd have all of the electric field from the pink one , none from the red one . it would point all left then . look what 's happening . the polarization of this light , if i shift this , if i 'm sitting here , looking with my eye , as my eye receives this light , i 'm going to see this light rotate its polarization . the polarization i 'm going to notice swings around in a circular pattern . and because of this , we call this circular polarization . so this is another type of polarization , where the actual angle of polarization rotates smoothly as this light ray enters your eye . and you know what ? er , drrr ... all right , actually , i sent you to receive this one first . that makes no sense . you 're going to receive the ones closes to you first in this light ray going this way . so you 'd actually receive this one first , then that one , then this one , then this one . because of that , you would n't see this going in a counterclockwise way , you 'd see this going in a clockwise circularly polarized way . sorry about that . you might think , `` okay , why ? `` why even bother with circular polarization ? '' well , i kind of lied earlier . turns out , in the movie theater example , they do n't actually do it like this , typically . oftentimes in the movie theaters , we do n't have just linearly polarized sunglasses . this would be a problem because , when you look at the movie theater screen , and if you were to tilt your head just a little bit ... think about it . this one 's not really going to get the right image anymore . it 's going to get some of both . and this one 's going to get some of both . it 's going to be blurry . your head would have to be perfectly level the whole time , which might be annoying . so what we do is , instead , we create circular polarized glasses , so that this one would only get one polarization , this one would get the other direction . this way , even if you tilt your head a little bit ... shoot , clockwise is clockwise , counterclockwise is counterclockwise . by using circular polarization for 3d movies , it can make it a little easier on you eyes to see a better 3d image , even if your head 's tilted a little bit .
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okay , so we start off with red , right ? the red electric field points up , and then this pink wave 's electric field is zero at that point . so this is all i have .
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is n't the magnetic field , the vertical component in an electromagnetic wave and the electric field is perpendicular to it ?
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- let 's talk about polarization of light . we know what light waves are ; they 're electromagnetic waves . so they 're made out of electric fields . and that 's not good enough . we know there 's not just electric fields . that could n't sustain itself . there 's got to be magnetic fields there , as well , that are changing . those are perpendicular , so you can kind of draw them . it 's hard , on something two-dimensional , but you can kind of imagine those looking something like this . and those magnetic fields would point at a right angle to the electric fields . but this gets really messy if i try to draw both the electric and magnetic fields at the same time . so we 're going to leave the magnetic fields out . it 's often good enough to just know the direction of the electric field when we focus on the electric field . so what does polarization mean ? polarization refers to the fact that , if this light ray was heading straight toward your eye , or a detector , over here , what would you see ? well , if i draw an axis over here , and this point here , in the middle , this is this line -- so imagine we 're looking straight down that line -- and then up and down is up and down , and then left and right , that direction i have the magnetic field , would be this way and that way . what would my eye see ? well , my eye 's only going to see electric fields that either point up or electric fields that point down . they might have different values , but i 'm only going to see electric fields that point up or down . because of that , this light ray is polarized . so polarized light is light where the electric field is only oscillating in one direction . up or down , that 's one direction -- vertically . or it could be polarized horizontally . or it could be polarized diagonally . but either way , you could have this wave polarized along any direction . i mean , a light ray like this , if we had it coming in diagonal , this light ray that 's oscillating like this , where the electric field oscillates like that , that also polarized . these are both polarized because there 's only one direction that the electric field is oscillating in . and you might thing , `` pff , how could you ever have `` a light ray that 's not polarized ? '' easy . most light that you get is not polarized . that is to say , light that 's coming from the sun , straight from the sun -- typically not polarized . light from a lightbulb , an old incandescent light bulb , this thing 's hot . you can get light polarized in any direction , all at once , all overlapping . so if we draw this case for a light bulb , just a random incandescent light bulb , you might get light , some of the light , hitting you eye , you can get some light that 's got that direction , you got light that 's got this direction , you got light in all these directions at any given moment . i mean , you 'd have to add these up to get the total , and they might not all be the same value . but what i 'm trying to say is , at any given moment , you do n't know what direction the electric field 's going to be hitting your eye at from a random source . it could be in any direction . so this is not polarized . this diagram represents light that is not polarized . at some point , the field might be pointing this way , at some later point it 's this way ; it 's just random . you never know which way the electric field 's going to be pointing . whereas these over here , these are polarized . so how could you polarize this light ? let 's say you wanted light that was polarized . you were doing an experiment . you needed polarized light . well , that 's easy . you can use what 's called a polarizer . and this is a material that lets light through , but it only lets light through in one orientation , so you 're going to have a polarizer that , for instance , only lets through vertically polarized light . so this is a polarizer . these are cheap : thin , plastic , configured in a way so that it only lets light through that 's vertically polarized . any light coming in here that 's not vertically polarized gets blocked , or absorbed . so what that means is , if you used this polarizer and held it in between your eye and this light bulb , you would only get this light . all the rest of it would get blocked . or you could just rotate this thing and imagine a polarizer that only lets through horizontal light . now it would only let through light that was this way , and so you would only get this part of the light . or you could just orient it at any angle you want and block everything but the certain angle that this polarizer is defined as letting light through . so you can do this . and once you hold this up , you get polarized light , light that 's only got one orientation . so that 's what polarization means . but why do we care about polarization ? well , let me get rid of this for a minute . you 've heard of polarized sunglasses . so imagine you 're standing near water , or maybe you 're standing on ice or snow or something reflective . there 's a problem . say the sun 's out . it 's shining . it 's a beautiful day -- except there 's going to be glare . let 's say you 're looking down at something here on the ground . it 's going to get light reflecting off of it from just ... you know , light 's coming in from all direction . but it also gets this direct light from the sun . so it gets light from reflected off the clouds and whatever , whatever 's nearby , ambient light . and there 's also this direct sunlight . that 's harsh . if that reflects straight up to your eye , that hurts . you do n't like that . it blocks our vision . it 's hard to see , it 's glare . we do n't want this glare . so what can we do ? well , it just so happens that , when light reflects off of a surface , even though the light from the sun is not polarized , once it reflects , it does get polarized or at least partially polarized . so this surface here , once this light reflects , it 's coming in at all orientations . you got electric field ... you never know what electric field you 're going to get straight from the sun . and when it reflects , though , you mostly get , upon reflection , the direction of polarization defined by the plane of the surface that it hit . so because the floor is horizontal , when this light ray hits the ground and reflects , that reflected light gets partially polarized . this horizontal component of the electric field is going to be more present than the other components . maybe not completely . sometimes it could be . it could be completely polarized , but often it 's just partially polarized . but that 's pretty cool , because now you know what we can do . i know how to block this . we should get some sunglasses . we put some sunglasses on and we make our glasses so that these are polarized . and how do we want these polarized ? i want to get rid of the glare . so what i do is , i make sure my sunglasses only let through vertically polarized light . here 's some polarizers . that way , a lot of this glare gets blocked because it does not have a vertical orientation , it has a horizontal orientation . and then we can block it . so that 's one good thing that polarization does for us , and understanding it , we can get rid of glare . also , fishermen like it because , if you 're trying to look in the water at fish , you want to see in through the water , you want to see this light from the fish getting to you . you do n't want to see the glare off of the sun getting to you . so polarized sunglasses are useful . also , we can play a trick on our eye , if we really wanted to . you could take one of these , make one eye have a vertical orientation for the polarization , have the other eye with a horizontal ... and you 're thinking , `` this is stupid . `` why would you do this for ? '' `` this eye 's going to get a lot of glare . '' we would n't use these outside , when you 're , like , skiing or fishing , but you could play a trick on your eyes if you went to the movies and you went and watched a movie . well , the reason our eyes see 3d is because they 're spaced a little bit apart . they each get a different , slightly different image . that makes us see in 3d . we can play the same trick on our eye if we have the polarization like this . if light , if some of the light from the movie theater screen is coming in with one polarization , and the other light 's coming in with the other polarization , we can send two different images to our eyes at the same time . if you took these off , it 'd look like garbage because you 'd be getting both of these slightly different images , it 'd look all blurry . and it does . if you take off your 3d glasses and look at a 3d movie , looks terrible , because now both eyes are getting both images . but if you put your glasses back on , now this eye only gets the orientation that it 's supposed to get , and this eye only gets the orientation that it 's supposed to get , and you get a 3d image . so it 's useful in many ways . let me show you one more thing here . let 's come back here . this light was polarized vertically . so that 's called linear polarization . any time ... same with these . these are all linear polarization because , just up and down , one linear direction , just diagonal . this is also linear . all of these are linear . you can get circular polarized light . so if we come back to here , we 've got our electric field pointing up , like that . now let 's say we sent in another light ray , another light ray that also had a polarization , but not in this direction . let 's say our other light ray had polarization in this direction , so it looks like this , kind of like what our magnetic field would have looked like . but this is a completely different light ray with its own polarization and its own magnetic field . so we send this in . what would happen ? well , at this point , you 'd have a electric field that points this way . at this point , you 'd have a electric field that points that way . what would your eye see if you were over here ? let 's see . if i draw our axis here . all right , when this point right here gets to your eye , what am i going to see ? well , i 'm going to have a light ray that 's one part of a light ray . one component points up . that 's this electric field . one component points left . that 's this electric field . so the total , my total electric field , would point this way . i could to the pythagorean theorem if i wanted to figure out the size of it , but i just want to know the direction for now . and then it gets to here , and look at it : they both have zero . this light ray has zero electric field , this one has zero electric fields . so then it 'd just be at zero . now what happens over here ? well , i 've got light . this one points to the right at that point , this pink one , and then this red one would be pointing down . so what would i have at that point ? i 'd have light that went this way , and it would just be doing this over and over . it would just be ... i 'd just have diagonally polarized light . this is n't giving me anything new . you might think this is dumb . why do this ? why send in two different waves to just get diagonally polarized light ? i could have just sent in one wave that was diagonally polarized and got the same thing . the reason is , if you shift this purple wave , this pink wave , by 90 degrees of phase , by pi over two in phase , something magical happens . let me show you what happens here , if we move this to here . now we do n't just get diagonally linear polarized light . what we 're going to get is ... let me get rid of this . okay , so we start off with red , right ? the red electric field points up , and then this pink wave 's electric field is zero at that point . so this is all i have . my total electric field would just be up . i 'm going to draw it right here . the green 'll be the total . now i come over to here , and at this point , there 's some red electric field that points up , but there 's some of this other electric field that points this way . so i 'd have a total electric field that would point that way . and then i get over to here , and i 'd have all of the electric field from the pink one , none from the red one . it would point all left then . look what 's happening . the polarization of this light , if i shift this , if i 'm sitting here , looking with my eye , as my eye receives this light , i 'm going to see this light rotate its polarization . the polarization i 'm going to notice swings around in a circular pattern . and because of this , we call this circular polarization . so this is another type of polarization , where the actual angle of polarization rotates smoothly as this light ray enters your eye . and you know what ? er , drrr ... all right , actually , i sent you to receive this one first . that makes no sense . you 're going to receive the ones closes to you first in this light ray going this way . so you 'd actually receive this one first , then that one , then this one , then this one . because of that , you would n't see this going in a counterclockwise way , you 'd see this going in a clockwise circularly polarized way . sorry about that . you might think , `` okay , why ? `` why even bother with circular polarization ? '' well , i kind of lied earlier . turns out , in the movie theater example , they do n't actually do it like this , typically . oftentimes in the movie theaters , we do n't have just linearly polarized sunglasses . this would be a problem because , when you look at the movie theater screen , and if you were to tilt your head just a little bit ... think about it . this one 's not really going to get the right image anymore . it 's going to get some of both . and this one 's going to get some of both . it 's going to be blurry . your head would have to be perfectly level the whole time , which might be annoying . so what we do is , instead , we create circular polarized glasses , so that this one would only get one polarization , this one would get the other direction . this way , even if you tilt your head a little bit ... shoot , clockwise is clockwise , counterclockwise is counterclockwise . by using circular polarization for 3d movies , it can make it a little easier on you eyes to see a better 3d image , even if your head 's tilted a little bit .
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well , if i draw an axis over here , and this point here , in the middle , this is this line -- so imagine we 're looking straight down that line -- and then up and down is up and down , and then left and right , that direction i have the magnetic field , would be this way and that way . what would my eye see ? well , my eye 's only going to see electric fields that either point up or electric fields that point down .
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so if i put 2 left-eye lenses from the 3d glasses in the same frames , would i see the movie in 2d without it being fuzzy ?
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- let 's talk about polarization of light . we know what light waves are ; they 're electromagnetic waves . so they 're made out of electric fields . and that 's not good enough . we know there 's not just electric fields . that could n't sustain itself . there 's got to be magnetic fields there , as well , that are changing . those are perpendicular , so you can kind of draw them . it 's hard , on something two-dimensional , but you can kind of imagine those looking something like this . and those magnetic fields would point at a right angle to the electric fields . but this gets really messy if i try to draw both the electric and magnetic fields at the same time . so we 're going to leave the magnetic fields out . it 's often good enough to just know the direction of the electric field when we focus on the electric field . so what does polarization mean ? polarization refers to the fact that , if this light ray was heading straight toward your eye , or a detector , over here , what would you see ? well , if i draw an axis over here , and this point here , in the middle , this is this line -- so imagine we 're looking straight down that line -- and then up and down is up and down , and then left and right , that direction i have the magnetic field , would be this way and that way . what would my eye see ? well , my eye 's only going to see electric fields that either point up or electric fields that point down . they might have different values , but i 'm only going to see electric fields that point up or down . because of that , this light ray is polarized . so polarized light is light where the electric field is only oscillating in one direction . up or down , that 's one direction -- vertically . or it could be polarized horizontally . or it could be polarized diagonally . but either way , you could have this wave polarized along any direction . i mean , a light ray like this , if we had it coming in diagonal , this light ray that 's oscillating like this , where the electric field oscillates like that , that also polarized . these are both polarized because there 's only one direction that the electric field is oscillating in . and you might thing , `` pff , how could you ever have `` a light ray that 's not polarized ? '' easy . most light that you get is not polarized . that is to say , light that 's coming from the sun , straight from the sun -- typically not polarized . light from a lightbulb , an old incandescent light bulb , this thing 's hot . you can get light polarized in any direction , all at once , all overlapping . so if we draw this case for a light bulb , just a random incandescent light bulb , you might get light , some of the light , hitting you eye , you can get some light that 's got that direction , you got light that 's got this direction , you got light in all these directions at any given moment . i mean , you 'd have to add these up to get the total , and they might not all be the same value . but what i 'm trying to say is , at any given moment , you do n't know what direction the electric field 's going to be hitting your eye at from a random source . it could be in any direction . so this is not polarized . this diagram represents light that is not polarized . at some point , the field might be pointing this way , at some later point it 's this way ; it 's just random . you never know which way the electric field 's going to be pointing . whereas these over here , these are polarized . so how could you polarize this light ? let 's say you wanted light that was polarized . you were doing an experiment . you needed polarized light . well , that 's easy . you can use what 's called a polarizer . and this is a material that lets light through , but it only lets light through in one orientation , so you 're going to have a polarizer that , for instance , only lets through vertically polarized light . so this is a polarizer . these are cheap : thin , plastic , configured in a way so that it only lets light through that 's vertically polarized . any light coming in here that 's not vertically polarized gets blocked , or absorbed . so what that means is , if you used this polarizer and held it in between your eye and this light bulb , you would only get this light . all the rest of it would get blocked . or you could just rotate this thing and imagine a polarizer that only lets through horizontal light . now it would only let through light that was this way , and so you would only get this part of the light . or you could just orient it at any angle you want and block everything but the certain angle that this polarizer is defined as letting light through . so you can do this . and once you hold this up , you get polarized light , light that 's only got one orientation . so that 's what polarization means . but why do we care about polarization ? well , let me get rid of this for a minute . you 've heard of polarized sunglasses . so imagine you 're standing near water , or maybe you 're standing on ice or snow or something reflective . there 's a problem . say the sun 's out . it 's shining . it 's a beautiful day -- except there 's going to be glare . let 's say you 're looking down at something here on the ground . it 's going to get light reflecting off of it from just ... you know , light 's coming in from all direction . but it also gets this direct light from the sun . so it gets light from reflected off the clouds and whatever , whatever 's nearby , ambient light . and there 's also this direct sunlight . that 's harsh . if that reflects straight up to your eye , that hurts . you do n't like that . it blocks our vision . it 's hard to see , it 's glare . we do n't want this glare . so what can we do ? well , it just so happens that , when light reflects off of a surface , even though the light from the sun is not polarized , once it reflects , it does get polarized or at least partially polarized . so this surface here , once this light reflects , it 's coming in at all orientations . you got electric field ... you never know what electric field you 're going to get straight from the sun . and when it reflects , though , you mostly get , upon reflection , the direction of polarization defined by the plane of the surface that it hit . so because the floor is horizontal , when this light ray hits the ground and reflects , that reflected light gets partially polarized . this horizontal component of the electric field is going to be more present than the other components . maybe not completely . sometimes it could be . it could be completely polarized , but often it 's just partially polarized . but that 's pretty cool , because now you know what we can do . i know how to block this . we should get some sunglasses . we put some sunglasses on and we make our glasses so that these are polarized . and how do we want these polarized ? i want to get rid of the glare . so what i do is , i make sure my sunglasses only let through vertically polarized light . here 's some polarizers . that way , a lot of this glare gets blocked because it does not have a vertical orientation , it has a horizontal orientation . and then we can block it . so that 's one good thing that polarization does for us , and understanding it , we can get rid of glare . also , fishermen like it because , if you 're trying to look in the water at fish , you want to see in through the water , you want to see this light from the fish getting to you . you do n't want to see the glare off of the sun getting to you . so polarized sunglasses are useful . also , we can play a trick on our eye , if we really wanted to . you could take one of these , make one eye have a vertical orientation for the polarization , have the other eye with a horizontal ... and you 're thinking , `` this is stupid . `` why would you do this for ? '' `` this eye 's going to get a lot of glare . '' we would n't use these outside , when you 're , like , skiing or fishing , but you could play a trick on your eyes if you went to the movies and you went and watched a movie . well , the reason our eyes see 3d is because they 're spaced a little bit apart . they each get a different , slightly different image . that makes us see in 3d . we can play the same trick on our eye if we have the polarization like this . if light , if some of the light from the movie theater screen is coming in with one polarization , and the other light 's coming in with the other polarization , we can send two different images to our eyes at the same time . if you took these off , it 'd look like garbage because you 'd be getting both of these slightly different images , it 'd look all blurry . and it does . if you take off your 3d glasses and look at a 3d movie , looks terrible , because now both eyes are getting both images . but if you put your glasses back on , now this eye only gets the orientation that it 's supposed to get , and this eye only gets the orientation that it 's supposed to get , and you get a 3d image . so it 's useful in many ways . let me show you one more thing here . let 's come back here . this light was polarized vertically . so that 's called linear polarization . any time ... same with these . these are all linear polarization because , just up and down , one linear direction , just diagonal . this is also linear . all of these are linear . you can get circular polarized light . so if we come back to here , we 've got our electric field pointing up , like that . now let 's say we sent in another light ray , another light ray that also had a polarization , but not in this direction . let 's say our other light ray had polarization in this direction , so it looks like this , kind of like what our magnetic field would have looked like . but this is a completely different light ray with its own polarization and its own magnetic field . so we send this in . what would happen ? well , at this point , you 'd have a electric field that points this way . at this point , you 'd have a electric field that points that way . what would your eye see if you were over here ? let 's see . if i draw our axis here . all right , when this point right here gets to your eye , what am i going to see ? well , i 'm going to have a light ray that 's one part of a light ray . one component points up . that 's this electric field . one component points left . that 's this electric field . so the total , my total electric field , would point this way . i could to the pythagorean theorem if i wanted to figure out the size of it , but i just want to know the direction for now . and then it gets to here , and look at it : they both have zero . this light ray has zero electric field , this one has zero electric fields . so then it 'd just be at zero . now what happens over here ? well , i 've got light . this one points to the right at that point , this pink one , and then this red one would be pointing down . so what would i have at that point ? i 'd have light that went this way , and it would just be doing this over and over . it would just be ... i 'd just have diagonally polarized light . this is n't giving me anything new . you might think this is dumb . why do this ? why send in two different waves to just get diagonally polarized light ? i could have just sent in one wave that was diagonally polarized and got the same thing . the reason is , if you shift this purple wave , this pink wave , by 90 degrees of phase , by pi over two in phase , something magical happens . let me show you what happens here , if we move this to here . now we do n't just get diagonally linear polarized light . what we 're going to get is ... let me get rid of this . okay , so we start off with red , right ? the red electric field points up , and then this pink wave 's electric field is zero at that point . so this is all i have . my total electric field would just be up . i 'm going to draw it right here . the green 'll be the total . now i come over to here , and at this point , there 's some red electric field that points up , but there 's some of this other electric field that points this way . so i 'd have a total electric field that would point that way . and then i get over to here , and i 'd have all of the electric field from the pink one , none from the red one . it would point all left then . look what 's happening . the polarization of this light , if i shift this , if i 'm sitting here , looking with my eye , as my eye receives this light , i 'm going to see this light rotate its polarization . the polarization i 'm going to notice swings around in a circular pattern . and because of this , we call this circular polarization . so this is another type of polarization , where the actual angle of polarization rotates smoothly as this light ray enters your eye . and you know what ? er , drrr ... all right , actually , i sent you to receive this one first . that makes no sense . you 're going to receive the ones closes to you first in this light ray going this way . so you 'd actually receive this one first , then that one , then this one , then this one . because of that , you would n't see this going in a counterclockwise way , you 'd see this going in a clockwise circularly polarized way . sorry about that . you might think , `` okay , why ? `` why even bother with circular polarization ? '' well , i kind of lied earlier . turns out , in the movie theater example , they do n't actually do it like this , typically . oftentimes in the movie theaters , we do n't have just linearly polarized sunglasses . this would be a problem because , when you look at the movie theater screen , and if you were to tilt your head just a little bit ... think about it . this one 's not really going to get the right image anymore . it 's going to get some of both . and this one 's going to get some of both . it 's going to be blurry . your head would have to be perfectly level the whole time , which might be annoying . so what we do is , instead , we create circular polarized glasses , so that this one would only get one polarization , this one would get the other direction . this way , even if you tilt your head a little bit ... shoot , clockwise is clockwise , counterclockwise is counterclockwise . by using circular polarization for 3d movies , it can make it a little easier on you eyes to see a better 3d image , even if your head 's tilted a little bit .
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you might think , `` okay , why ? `` why even bother with circular polarization ? '' well , i kind of lied earlier .
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how do the 3d glasses create a circular polarization filter , and how do they select clockwise vs. counterclockwise ?
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- let 's talk about polarization of light . we know what light waves are ; they 're electromagnetic waves . so they 're made out of electric fields . and that 's not good enough . we know there 's not just electric fields . that could n't sustain itself . there 's got to be magnetic fields there , as well , that are changing . those are perpendicular , so you can kind of draw them . it 's hard , on something two-dimensional , but you can kind of imagine those looking something like this . and those magnetic fields would point at a right angle to the electric fields . but this gets really messy if i try to draw both the electric and magnetic fields at the same time . so we 're going to leave the magnetic fields out . it 's often good enough to just know the direction of the electric field when we focus on the electric field . so what does polarization mean ? polarization refers to the fact that , if this light ray was heading straight toward your eye , or a detector , over here , what would you see ? well , if i draw an axis over here , and this point here , in the middle , this is this line -- so imagine we 're looking straight down that line -- and then up and down is up and down , and then left and right , that direction i have the magnetic field , would be this way and that way . what would my eye see ? well , my eye 's only going to see electric fields that either point up or electric fields that point down . they might have different values , but i 'm only going to see electric fields that point up or down . because of that , this light ray is polarized . so polarized light is light where the electric field is only oscillating in one direction . up or down , that 's one direction -- vertically . or it could be polarized horizontally . or it could be polarized diagonally . but either way , you could have this wave polarized along any direction . i mean , a light ray like this , if we had it coming in diagonal , this light ray that 's oscillating like this , where the electric field oscillates like that , that also polarized . these are both polarized because there 's only one direction that the electric field is oscillating in . and you might thing , `` pff , how could you ever have `` a light ray that 's not polarized ? '' easy . most light that you get is not polarized . that is to say , light that 's coming from the sun , straight from the sun -- typically not polarized . light from a lightbulb , an old incandescent light bulb , this thing 's hot . you can get light polarized in any direction , all at once , all overlapping . so if we draw this case for a light bulb , just a random incandescent light bulb , you might get light , some of the light , hitting you eye , you can get some light that 's got that direction , you got light that 's got this direction , you got light in all these directions at any given moment . i mean , you 'd have to add these up to get the total , and they might not all be the same value . but what i 'm trying to say is , at any given moment , you do n't know what direction the electric field 's going to be hitting your eye at from a random source . it could be in any direction . so this is not polarized . this diagram represents light that is not polarized . at some point , the field might be pointing this way , at some later point it 's this way ; it 's just random . you never know which way the electric field 's going to be pointing . whereas these over here , these are polarized . so how could you polarize this light ? let 's say you wanted light that was polarized . you were doing an experiment . you needed polarized light . well , that 's easy . you can use what 's called a polarizer . and this is a material that lets light through , but it only lets light through in one orientation , so you 're going to have a polarizer that , for instance , only lets through vertically polarized light . so this is a polarizer . these are cheap : thin , plastic , configured in a way so that it only lets light through that 's vertically polarized . any light coming in here that 's not vertically polarized gets blocked , or absorbed . so what that means is , if you used this polarizer and held it in between your eye and this light bulb , you would only get this light . all the rest of it would get blocked . or you could just rotate this thing and imagine a polarizer that only lets through horizontal light . now it would only let through light that was this way , and so you would only get this part of the light . or you could just orient it at any angle you want and block everything but the certain angle that this polarizer is defined as letting light through . so you can do this . and once you hold this up , you get polarized light , light that 's only got one orientation . so that 's what polarization means . but why do we care about polarization ? well , let me get rid of this for a minute . you 've heard of polarized sunglasses . so imagine you 're standing near water , or maybe you 're standing on ice or snow or something reflective . there 's a problem . say the sun 's out . it 's shining . it 's a beautiful day -- except there 's going to be glare . let 's say you 're looking down at something here on the ground . it 's going to get light reflecting off of it from just ... you know , light 's coming in from all direction . but it also gets this direct light from the sun . so it gets light from reflected off the clouds and whatever , whatever 's nearby , ambient light . and there 's also this direct sunlight . that 's harsh . if that reflects straight up to your eye , that hurts . you do n't like that . it blocks our vision . it 's hard to see , it 's glare . we do n't want this glare . so what can we do ? well , it just so happens that , when light reflects off of a surface , even though the light from the sun is not polarized , once it reflects , it does get polarized or at least partially polarized . so this surface here , once this light reflects , it 's coming in at all orientations . you got electric field ... you never know what electric field you 're going to get straight from the sun . and when it reflects , though , you mostly get , upon reflection , the direction of polarization defined by the plane of the surface that it hit . so because the floor is horizontal , when this light ray hits the ground and reflects , that reflected light gets partially polarized . this horizontal component of the electric field is going to be more present than the other components . maybe not completely . sometimes it could be . it could be completely polarized , but often it 's just partially polarized . but that 's pretty cool , because now you know what we can do . i know how to block this . we should get some sunglasses . we put some sunglasses on and we make our glasses so that these are polarized . and how do we want these polarized ? i want to get rid of the glare . so what i do is , i make sure my sunglasses only let through vertically polarized light . here 's some polarizers . that way , a lot of this glare gets blocked because it does not have a vertical orientation , it has a horizontal orientation . and then we can block it . so that 's one good thing that polarization does for us , and understanding it , we can get rid of glare . also , fishermen like it because , if you 're trying to look in the water at fish , you want to see in through the water , you want to see this light from the fish getting to you . you do n't want to see the glare off of the sun getting to you . so polarized sunglasses are useful . also , we can play a trick on our eye , if we really wanted to . you could take one of these , make one eye have a vertical orientation for the polarization , have the other eye with a horizontal ... and you 're thinking , `` this is stupid . `` why would you do this for ? '' `` this eye 's going to get a lot of glare . '' we would n't use these outside , when you 're , like , skiing or fishing , but you could play a trick on your eyes if you went to the movies and you went and watched a movie . well , the reason our eyes see 3d is because they 're spaced a little bit apart . they each get a different , slightly different image . that makes us see in 3d . we can play the same trick on our eye if we have the polarization like this . if light , if some of the light from the movie theater screen is coming in with one polarization , and the other light 's coming in with the other polarization , we can send two different images to our eyes at the same time . if you took these off , it 'd look like garbage because you 'd be getting both of these slightly different images , it 'd look all blurry . and it does . if you take off your 3d glasses and look at a 3d movie , looks terrible , because now both eyes are getting both images . but if you put your glasses back on , now this eye only gets the orientation that it 's supposed to get , and this eye only gets the orientation that it 's supposed to get , and you get a 3d image . so it 's useful in many ways . let me show you one more thing here . let 's come back here . this light was polarized vertically . so that 's called linear polarization . any time ... same with these . these are all linear polarization because , just up and down , one linear direction , just diagonal . this is also linear . all of these are linear . you can get circular polarized light . so if we come back to here , we 've got our electric field pointing up , like that . now let 's say we sent in another light ray , another light ray that also had a polarization , but not in this direction . let 's say our other light ray had polarization in this direction , so it looks like this , kind of like what our magnetic field would have looked like . but this is a completely different light ray with its own polarization and its own magnetic field . so we send this in . what would happen ? well , at this point , you 'd have a electric field that points this way . at this point , you 'd have a electric field that points that way . what would your eye see if you were over here ? let 's see . if i draw our axis here . all right , when this point right here gets to your eye , what am i going to see ? well , i 'm going to have a light ray that 's one part of a light ray . one component points up . that 's this electric field . one component points left . that 's this electric field . so the total , my total electric field , would point this way . i could to the pythagorean theorem if i wanted to figure out the size of it , but i just want to know the direction for now . and then it gets to here , and look at it : they both have zero . this light ray has zero electric field , this one has zero electric fields . so then it 'd just be at zero . now what happens over here ? well , i 've got light . this one points to the right at that point , this pink one , and then this red one would be pointing down . so what would i have at that point ? i 'd have light that went this way , and it would just be doing this over and over . it would just be ... i 'd just have diagonally polarized light . this is n't giving me anything new . you might think this is dumb . why do this ? why send in two different waves to just get diagonally polarized light ? i could have just sent in one wave that was diagonally polarized and got the same thing . the reason is , if you shift this purple wave , this pink wave , by 90 degrees of phase , by pi over two in phase , something magical happens . let me show you what happens here , if we move this to here . now we do n't just get diagonally linear polarized light . what we 're going to get is ... let me get rid of this . okay , so we start off with red , right ? the red electric field points up , and then this pink wave 's electric field is zero at that point . so this is all i have . my total electric field would just be up . i 'm going to draw it right here . the green 'll be the total . now i come over to here , and at this point , there 's some red electric field that points up , but there 's some of this other electric field that points this way . so i 'd have a total electric field that would point that way . and then i get over to here , and i 'd have all of the electric field from the pink one , none from the red one . it would point all left then . look what 's happening . the polarization of this light , if i shift this , if i 'm sitting here , looking with my eye , as my eye receives this light , i 'm going to see this light rotate its polarization . the polarization i 'm going to notice swings around in a circular pattern . and because of this , we call this circular polarization . so this is another type of polarization , where the actual angle of polarization rotates smoothly as this light ray enters your eye . and you know what ? er , drrr ... all right , actually , i sent you to receive this one first . that makes no sense . you 're going to receive the ones closes to you first in this light ray going this way . so you 'd actually receive this one first , then that one , then this one , then this one . because of that , you would n't see this going in a counterclockwise way , you 'd see this going in a clockwise circularly polarized way . sorry about that . you might think , `` okay , why ? `` why even bother with circular polarization ? '' well , i kind of lied earlier . turns out , in the movie theater example , they do n't actually do it like this , typically . oftentimes in the movie theaters , we do n't have just linearly polarized sunglasses . this would be a problem because , when you look at the movie theater screen , and if you were to tilt your head just a little bit ... think about it . this one 's not really going to get the right image anymore . it 's going to get some of both . and this one 's going to get some of both . it 's going to be blurry . your head would have to be perfectly level the whole time , which might be annoying . so what we do is , instead , we create circular polarized glasses , so that this one would only get one polarization , this one would get the other direction . this way , even if you tilt your head a little bit ... shoot , clockwise is clockwise , counterclockwise is counterclockwise . by using circular polarization for 3d movies , it can make it a little easier on you eyes to see a better 3d image , even if your head 's tilted a little bit .
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it 's often good enough to just know the direction of the electric field when we focus on the electric field . so what does polarization mean ? polarization refers to the fact that , if this light ray was heading straight toward your eye , or a detector , over here , what would you see ?
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i ca n't understand the polarization please explain it to me ?
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- let 's talk about polarization of light . we know what light waves are ; they 're electromagnetic waves . so they 're made out of electric fields . and that 's not good enough . we know there 's not just electric fields . that could n't sustain itself . there 's got to be magnetic fields there , as well , that are changing . those are perpendicular , so you can kind of draw them . it 's hard , on something two-dimensional , but you can kind of imagine those looking something like this . and those magnetic fields would point at a right angle to the electric fields . but this gets really messy if i try to draw both the electric and magnetic fields at the same time . so we 're going to leave the magnetic fields out . it 's often good enough to just know the direction of the electric field when we focus on the electric field . so what does polarization mean ? polarization refers to the fact that , if this light ray was heading straight toward your eye , or a detector , over here , what would you see ? well , if i draw an axis over here , and this point here , in the middle , this is this line -- so imagine we 're looking straight down that line -- and then up and down is up and down , and then left and right , that direction i have the magnetic field , would be this way and that way . what would my eye see ? well , my eye 's only going to see electric fields that either point up or electric fields that point down . they might have different values , but i 'm only going to see electric fields that point up or down . because of that , this light ray is polarized . so polarized light is light where the electric field is only oscillating in one direction . up or down , that 's one direction -- vertically . or it could be polarized horizontally . or it could be polarized diagonally . but either way , you could have this wave polarized along any direction . i mean , a light ray like this , if we had it coming in diagonal , this light ray that 's oscillating like this , where the electric field oscillates like that , that also polarized . these are both polarized because there 's only one direction that the electric field is oscillating in . and you might thing , `` pff , how could you ever have `` a light ray that 's not polarized ? '' easy . most light that you get is not polarized . that is to say , light that 's coming from the sun , straight from the sun -- typically not polarized . light from a lightbulb , an old incandescent light bulb , this thing 's hot . you can get light polarized in any direction , all at once , all overlapping . so if we draw this case for a light bulb , just a random incandescent light bulb , you might get light , some of the light , hitting you eye , you can get some light that 's got that direction , you got light that 's got this direction , you got light in all these directions at any given moment . i mean , you 'd have to add these up to get the total , and they might not all be the same value . but what i 'm trying to say is , at any given moment , you do n't know what direction the electric field 's going to be hitting your eye at from a random source . it could be in any direction . so this is not polarized . this diagram represents light that is not polarized . at some point , the field might be pointing this way , at some later point it 's this way ; it 's just random . you never know which way the electric field 's going to be pointing . whereas these over here , these are polarized . so how could you polarize this light ? let 's say you wanted light that was polarized . you were doing an experiment . you needed polarized light . well , that 's easy . you can use what 's called a polarizer . and this is a material that lets light through , but it only lets light through in one orientation , so you 're going to have a polarizer that , for instance , only lets through vertically polarized light . so this is a polarizer . these are cheap : thin , plastic , configured in a way so that it only lets light through that 's vertically polarized . any light coming in here that 's not vertically polarized gets blocked , or absorbed . so what that means is , if you used this polarizer and held it in between your eye and this light bulb , you would only get this light . all the rest of it would get blocked . or you could just rotate this thing and imagine a polarizer that only lets through horizontal light . now it would only let through light that was this way , and so you would only get this part of the light . or you could just orient it at any angle you want and block everything but the certain angle that this polarizer is defined as letting light through . so you can do this . and once you hold this up , you get polarized light , light that 's only got one orientation . so that 's what polarization means . but why do we care about polarization ? well , let me get rid of this for a minute . you 've heard of polarized sunglasses . so imagine you 're standing near water , or maybe you 're standing on ice or snow or something reflective . there 's a problem . say the sun 's out . it 's shining . it 's a beautiful day -- except there 's going to be glare . let 's say you 're looking down at something here on the ground . it 's going to get light reflecting off of it from just ... you know , light 's coming in from all direction . but it also gets this direct light from the sun . so it gets light from reflected off the clouds and whatever , whatever 's nearby , ambient light . and there 's also this direct sunlight . that 's harsh . if that reflects straight up to your eye , that hurts . you do n't like that . it blocks our vision . it 's hard to see , it 's glare . we do n't want this glare . so what can we do ? well , it just so happens that , when light reflects off of a surface , even though the light from the sun is not polarized , once it reflects , it does get polarized or at least partially polarized . so this surface here , once this light reflects , it 's coming in at all orientations . you got electric field ... you never know what electric field you 're going to get straight from the sun . and when it reflects , though , you mostly get , upon reflection , the direction of polarization defined by the plane of the surface that it hit . so because the floor is horizontal , when this light ray hits the ground and reflects , that reflected light gets partially polarized . this horizontal component of the electric field is going to be more present than the other components . maybe not completely . sometimes it could be . it could be completely polarized , but often it 's just partially polarized . but that 's pretty cool , because now you know what we can do . i know how to block this . we should get some sunglasses . we put some sunglasses on and we make our glasses so that these are polarized . and how do we want these polarized ? i want to get rid of the glare . so what i do is , i make sure my sunglasses only let through vertically polarized light . here 's some polarizers . that way , a lot of this glare gets blocked because it does not have a vertical orientation , it has a horizontal orientation . and then we can block it . so that 's one good thing that polarization does for us , and understanding it , we can get rid of glare . also , fishermen like it because , if you 're trying to look in the water at fish , you want to see in through the water , you want to see this light from the fish getting to you . you do n't want to see the glare off of the sun getting to you . so polarized sunglasses are useful . also , we can play a trick on our eye , if we really wanted to . you could take one of these , make one eye have a vertical orientation for the polarization , have the other eye with a horizontal ... and you 're thinking , `` this is stupid . `` why would you do this for ? '' `` this eye 's going to get a lot of glare . '' we would n't use these outside , when you 're , like , skiing or fishing , but you could play a trick on your eyes if you went to the movies and you went and watched a movie . well , the reason our eyes see 3d is because they 're spaced a little bit apart . they each get a different , slightly different image . that makes us see in 3d . we can play the same trick on our eye if we have the polarization like this . if light , if some of the light from the movie theater screen is coming in with one polarization , and the other light 's coming in with the other polarization , we can send two different images to our eyes at the same time . if you took these off , it 'd look like garbage because you 'd be getting both of these slightly different images , it 'd look all blurry . and it does . if you take off your 3d glasses and look at a 3d movie , looks terrible , because now both eyes are getting both images . but if you put your glasses back on , now this eye only gets the orientation that it 's supposed to get , and this eye only gets the orientation that it 's supposed to get , and you get a 3d image . so it 's useful in many ways . let me show you one more thing here . let 's come back here . this light was polarized vertically . so that 's called linear polarization . any time ... same with these . these are all linear polarization because , just up and down , one linear direction , just diagonal . this is also linear . all of these are linear . you can get circular polarized light . so if we come back to here , we 've got our electric field pointing up , like that . now let 's say we sent in another light ray , another light ray that also had a polarization , but not in this direction . let 's say our other light ray had polarization in this direction , so it looks like this , kind of like what our magnetic field would have looked like . but this is a completely different light ray with its own polarization and its own magnetic field . so we send this in . what would happen ? well , at this point , you 'd have a electric field that points this way . at this point , you 'd have a electric field that points that way . what would your eye see if you were over here ? let 's see . if i draw our axis here . all right , when this point right here gets to your eye , what am i going to see ? well , i 'm going to have a light ray that 's one part of a light ray . one component points up . that 's this electric field . one component points left . that 's this electric field . so the total , my total electric field , would point this way . i could to the pythagorean theorem if i wanted to figure out the size of it , but i just want to know the direction for now . and then it gets to here , and look at it : they both have zero . this light ray has zero electric field , this one has zero electric fields . so then it 'd just be at zero . now what happens over here ? well , i 've got light . this one points to the right at that point , this pink one , and then this red one would be pointing down . so what would i have at that point ? i 'd have light that went this way , and it would just be doing this over and over . it would just be ... i 'd just have diagonally polarized light . this is n't giving me anything new . you might think this is dumb . why do this ? why send in two different waves to just get diagonally polarized light ? i could have just sent in one wave that was diagonally polarized and got the same thing . the reason is , if you shift this purple wave , this pink wave , by 90 degrees of phase , by pi over two in phase , something magical happens . let me show you what happens here , if we move this to here . now we do n't just get diagonally linear polarized light . what we 're going to get is ... let me get rid of this . okay , so we start off with red , right ? the red electric field points up , and then this pink wave 's electric field is zero at that point . so this is all i have . my total electric field would just be up . i 'm going to draw it right here . the green 'll be the total . now i come over to here , and at this point , there 's some red electric field that points up , but there 's some of this other electric field that points this way . so i 'd have a total electric field that would point that way . and then i get over to here , and i 'd have all of the electric field from the pink one , none from the red one . it would point all left then . look what 's happening . the polarization of this light , if i shift this , if i 'm sitting here , looking with my eye , as my eye receives this light , i 'm going to see this light rotate its polarization . the polarization i 'm going to notice swings around in a circular pattern . and because of this , we call this circular polarization . so this is another type of polarization , where the actual angle of polarization rotates smoothly as this light ray enters your eye . and you know what ? er , drrr ... all right , actually , i sent you to receive this one first . that makes no sense . you 're going to receive the ones closes to you first in this light ray going this way . so you 'd actually receive this one first , then that one , then this one , then this one . because of that , you would n't see this going in a counterclockwise way , you 'd see this going in a clockwise circularly polarized way . sorry about that . you might think , `` okay , why ? `` why even bother with circular polarization ? '' well , i kind of lied earlier . turns out , in the movie theater example , they do n't actually do it like this , typically . oftentimes in the movie theaters , we do n't have just linearly polarized sunglasses . this would be a problem because , when you look at the movie theater screen , and if you were to tilt your head just a little bit ... think about it . this one 's not really going to get the right image anymore . it 's going to get some of both . and this one 's going to get some of both . it 's going to be blurry . your head would have to be perfectly level the whole time , which might be annoying . so what we do is , instead , we create circular polarized glasses , so that this one would only get one polarization , this one would get the other direction . this way , even if you tilt your head a little bit ... shoot , clockwise is clockwise , counterclockwise is counterclockwise . by using circular polarization for 3d movies , it can make it a little easier on you eyes to see a better 3d image , even if your head 's tilted a little bit .
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one component points up . that 's this electric field . one component points left .
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regarding the e & b field , how the polarizer affect e & b field together ?
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- let 's talk about polarization of light . we know what light waves are ; they 're electromagnetic waves . so they 're made out of electric fields . and that 's not good enough . we know there 's not just electric fields . that could n't sustain itself . there 's got to be magnetic fields there , as well , that are changing . those are perpendicular , so you can kind of draw them . it 's hard , on something two-dimensional , but you can kind of imagine those looking something like this . and those magnetic fields would point at a right angle to the electric fields . but this gets really messy if i try to draw both the electric and magnetic fields at the same time . so we 're going to leave the magnetic fields out . it 's often good enough to just know the direction of the electric field when we focus on the electric field . so what does polarization mean ? polarization refers to the fact that , if this light ray was heading straight toward your eye , or a detector , over here , what would you see ? well , if i draw an axis over here , and this point here , in the middle , this is this line -- so imagine we 're looking straight down that line -- and then up and down is up and down , and then left and right , that direction i have the magnetic field , would be this way and that way . what would my eye see ? well , my eye 's only going to see electric fields that either point up or electric fields that point down . they might have different values , but i 'm only going to see electric fields that point up or down . because of that , this light ray is polarized . so polarized light is light where the electric field is only oscillating in one direction . up or down , that 's one direction -- vertically . or it could be polarized horizontally . or it could be polarized diagonally . but either way , you could have this wave polarized along any direction . i mean , a light ray like this , if we had it coming in diagonal , this light ray that 's oscillating like this , where the electric field oscillates like that , that also polarized . these are both polarized because there 's only one direction that the electric field is oscillating in . and you might thing , `` pff , how could you ever have `` a light ray that 's not polarized ? '' easy . most light that you get is not polarized . that is to say , light that 's coming from the sun , straight from the sun -- typically not polarized . light from a lightbulb , an old incandescent light bulb , this thing 's hot . you can get light polarized in any direction , all at once , all overlapping . so if we draw this case for a light bulb , just a random incandescent light bulb , you might get light , some of the light , hitting you eye , you can get some light that 's got that direction , you got light that 's got this direction , you got light in all these directions at any given moment . i mean , you 'd have to add these up to get the total , and they might not all be the same value . but what i 'm trying to say is , at any given moment , you do n't know what direction the electric field 's going to be hitting your eye at from a random source . it could be in any direction . so this is not polarized . this diagram represents light that is not polarized . at some point , the field might be pointing this way , at some later point it 's this way ; it 's just random . you never know which way the electric field 's going to be pointing . whereas these over here , these are polarized . so how could you polarize this light ? let 's say you wanted light that was polarized . you were doing an experiment . you needed polarized light . well , that 's easy . you can use what 's called a polarizer . and this is a material that lets light through , but it only lets light through in one orientation , so you 're going to have a polarizer that , for instance , only lets through vertically polarized light . so this is a polarizer . these are cheap : thin , plastic , configured in a way so that it only lets light through that 's vertically polarized . any light coming in here that 's not vertically polarized gets blocked , or absorbed . so what that means is , if you used this polarizer and held it in between your eye and this light bulb , you would only get this light . all the rest of it would get blocked . or you could just rotate this thing and imagine a polarizer that only lets through horizontal light . now it would only let through light that was this way , and so you would only get this part of the light . or you could just orient it at any angle you want and block everything but the certain angle that this polarizer is defined as letting light through . so you can do this . and once you hold this up , you get polarized light , light that 's only got one orientation . so that 's what polarization means . but why do we care about polarization ? well , let me get rid of this for a minute . you 've heard of polarized sunglasses . so imagine you 're standing near water , or maybe you 're standing on ice or snow or something reflective . there 's a problem . say the sun 's out . it 's shining . it 's a beautiful day -- except there 's going to be glare . let 's say you 're looking down at something here on the ground . it 's going to get light reflecting off of it from just ... you know , light 's coming in from all direction . but it also gets this direct light from the sun . so it gets light from reflected off the clouds and whatever , whatever 's nearby , ambient light . and there 's also this direct sunlight . that 's harsh . if that reflects straight up to your eye , that hurts . you do n't like that . it blocks our vision . it 's hard to see , it 's glare . we do n't want this glare . so what can we do ? well , it just so happens that , when light reflects off of a surface , even though the light from the sun is not polarized , once it reflects , it does get polarized or at least partially polarized . so this surface here , once this light reflects , it 's coming in at all orientations . you got electric field ... you never know what electric field you 're going to get straight from the sun . and when it reflects , though , you mostly get , upon reflection , the direction of polarization defined by the plane of the surface that it hit . so because the floor is horizontal , when this light ray hits the ground and reflects , that reflected light gets partially polarized . this horizontal component of the electric field is going to be more present than the other components . maybe not completely . sometimes it could be . it could be completely polarized , but often it 's just partially polarized . but that 's pretty cool , because now you know what we can do . i know how to block this . we should get some sunglasses . we put some sunglasses on and we make our glasses so that these are polarized . and how do we want these polarized ? i want to get rid of the glare . so what i do is , i make sure my sunglasses only let through vertically polarized light . here 's some polarizers . that way , a lot of this glare gets blocked because it does not have a vertical orientation , it has a horizontal orientation . and then we can block it . so that 's one good thing that polarization does for us , and understanding it , we can get rid of glare . also , fishermen like it because , if you 're trying to look in the water at fish , you want to see in through the water , you want to see this light from the fish getting to you . you do n't want to see the glare off of the sun getting to you . so polarized sunglasses are useful . also , we can play a trick on our eye , if we really wanted to . you could take one of these , make one eye have a vertical orientation for the polarization , have the other eye with a horizontal ... and you 're thinking , `` this is stupid . `` why would you do this for ? '' `` this eye 's going to get a lot of glare . '' we would n't use these outside , when you 're , like , skiing or fishing , but you could play a trick on your eyes if you went to the movies and you went and watched a movie . well , the reason our eyes see 3d is because they 're spaced a little bit apart . they each get a different , slightly different image . that makes us see in 3d . we can play the same trick on our eye if we have the polarization like this . if light , if some of the light from the movie theater screen is coming in with one polarization , and the other light 's coming in with the other polarization , we can send two different images to our eyes at the same time . if you took these off , it 'd look like garbage because you 'd be getting both of these slightly different images , it 'd look all blurry . and it does . if you take off your 3d glasses and look at a 3d movie , looks terrible , because now both eyes are getting both images . but if you put your glasses back on , now this eye only gets the orientation that it 's supposed to get , and this eye only gets the orientation that it 's supposed to get , and you get a 3d image . so it 's useful in many ways . let me show you one more thing here . let 's come back here . this light was polarized vertically . so that 's called linear polarization . any time ... same with these . these are all linear polarization because , just up and down , one linear direction , just diagonal . this is also linear . all of these are linear . you can get circular polarized light . so if we come back to here , we 've got our electric field pointing up , like that . now let 's say we sent in another light ray , another light ray that also had a polarization , but not in this direction . let 's say our other light ray had polarization in this direction , so it looks like this , kind of like what our magnetic field would have looked like . but this is a completely different light ray with its own polarization and its own magnetic field . so we send this in . what would happen ? well , at this point , you 'd have a electric field that points this way . at this point , you 'd have a electric field that points that way . what would your eye see if you were over here ? let 's see . if i draw our axis here . all right , when this point right here gets to your eye , what am i going to see ? well , i 'm going to have a light ray that 's one part of a light ray . one component points up . that 's this electric field . one component points left . that 's this electric field . so the total , my total electric field , would point this way . i could to the pythagorean theorem if i wanted to figure out the size of it , but i just want to know the direction for now . and then it gets to here , and look at it : they both have zero . this light ray has zero electric field , this one has zero electric fields . so then it 'd just be at zero . now what happens over here ? well , i 've got light . this one points to the right at that point , this pink one , and then this red one would be pointing down . so what would i have at that point ? i 'd have light that went this way , and it would just be doing this over and over . it would just be ... i 'd just have diagonally polarized light . this is n't giving me anything new . you might think this is dumb . why do this ? why send in two different waves to just get diagonally polarized light ? i could have just sent in one wave that was diagonally polarized and got the same thing . the reason is , if you shift this purple wave , this pink wave , by 90 degrees of phase , by pi over two in phase , something magical happens . let me show you what happens here , if we move this to here . now we do n't just get diagonally linear polarized light . what we 're going to get is ... let me get rid of this . okay , so we start off with red , right ? the red electric field points up , and then this pink wave 's electric field is zero at that point . so this is all i have . my total electric field would just be up . i 'm going to draw it right here . the green 'll be the total . now i come over to here , and at this point , there 's some red electric field that points up , but there 's some of this other electric field that points this way . so i 'd have a total electric field that would point that way . and then i get over to here , and i 'd have all of the electric field from the pink one , none from the red one . it would point all left then . look what 's happening . the polarization of this light , if i shift this , if i 'm sitting here , looking with my eye , as my eye receives this light , i 'm going to see this light rotate its polarization . the polarization i 'm going to notice swings around in a circular pattern . and because of this , we call this circular polarization . so this is another type of polarization , where the actual angle of polarization rotates smoothly as this light ray enters your eye . and you know what ? er , drrr ... all right , actually , i sent you to receive this one first . that makes no sense . you 're going to receive the ones closes to you first in this light ray going this way . so you 'd actually receive this one first , then that one , then this one , then this one . because of that , you would n't see this going in a counterclockwise way , you 'd see this going in a clockwise circularly polarized way . sorry about that . you might think , `` okay , why ? `` why even bother with circular polarization ? '' well , i kind of lied earlier . turns out , in the movie theater example , they do n't actually do it like this , typically . oftentimes in the movie theaters , we do n't have just linearly polarized sunglasses . this would be a problem because , when you look at the movie theater screen , and if you were to tilt your head just a little bit ... think about it . this one 's not really going to get the right image anymore . it 's going to get some of both . and this one 's going to get some of both . it 's going to be blurry . your head would have to be perfectly level the whole time , which might be annoying . so what we do is , instead , we create circular polarized glasses , so that this one would only get one polarization , this one would get the other direction . this way , even if you tilt your head a little bit ... shoot , clockwise is clockwise , counterclockwise is counterclockwise . by using circular polarization for 3d movies , it can make it a little easier on you eyes to see a better 3d image , even if your head 's tilted a little bit .
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so we send this in . what would happen ? well , at this point , you 'd have a electric field that points this way .
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so if we have up & down polarizer , what will happen with the left & right b field ?
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- let 's talk about polarization of light . we know what light waves are ; they 're electromagnetic waves . so they 're made out of electric fields . and that 's not good enough . we know there 's not just electric fields . that could n't sustain itself . there 's got to be magnetic fields there , as well , that are changing . those are perpendicular , so you can kind of draw them . it 's hard , on something two-dimensional , but you can kind of imagine those looking something like this . and those magnetic fields would point at a right angle to the electric fields . but this gets really messy if i try to draw both the electric and magnetic fields at the same time . so we 're going to leave the magnetic fields out . it 's often good enough to just know the direction of the electric field when we focus on the electric field . so what does polarization mean ? polarization refers to the fact that , if this light ray was heading straight toward your eye , or a detector , over here , what would you see ? well , if i draw an axis over here , and this point here , in the middle , this is this line -- so imagine we 're looking straight down that line -- and then up and down is up and down , and then left and right , that direction i have the magnetic field , would be this way and that way . what would my eye see ? well , my eye 's only going to see electric fields that either point up or electric fields that point down . they might have different values , but i 'm only going to see electric fields that point up or down . because of that , this light ray is polarized . so polarized light is light where the electric field is only oscillating in one direction . up or down , that 's one direction -- vertically . or it could be polarized horizontally . or it could be polarized diagonally . but either way , you could have this wave polarized along any direction . i mean , a light ray like this , if we had it coming in diagonal , this light ray that 's oscillating like this , where the electric field oscillates like that , that also polarized . these are both polarized because there 's only one direction that the electric field is oscillating in . and you might thing , `` pff , how could you ever have `` a light ray that 's not polarized ? '' easy . most light that you get is not polarized . that is to say , light that 's coming from the sun , straight from the sun -- typically not polarized . light from a lightbulb , an old incandescent light bulb , this thing 's hot . you can get light polarized in any direction , all at once , all overlapping . so if we draw this case for a light bulb , just a random incandescent light bulb , you might get light , some of the light , hitting you eye , you can get some light that 's got that direction , you got light that 's got this direction , you got light in all these directions at any given moment . i mean , you 'd have to add these up to get the total , and they might not all be the same value . but what i 'm trying to say is , at any given moment , you do n't know what direction the electric field 's going to be hitting your eye at from a random source . it could be in any direction . so this is not polarized . this diagram represents light that is not polarized . at some point , the field might be pointing this way , at some later point it 's this way ; it 's just random . you never know which way the electric field 's going to be pointing . whereas these over here , these are polarized . so how could you polarize this light ? let 's say you wanted light that was polarized . you were doing an experiment . you needed polarized light . well , that 's easy . you can use what 's called a polarizer . and this is a material that lets light through , but it only lets light through in one orientation , so you 're going to have a polarizer that , for instance , only lets through vertically polarized light . so this is a polarizer . these are cheap : thin , plastic , configured in a way so that it only lets light through that 's vertically polarized . any light coming in here that 's not vertically polarized gets blocked , or absorbed . so what that means is , if you used this polarizer and held it in between your eye and this light bulb , you would only get this light . all the rest of it would get blocked . or you could just rotate this thing and imagine a polarizer that only lets through horizontal light . now it would only let through light that was this way , and so you would only get this part of the light . or you could just orient it at any angle you want and block everything but the certain angle that this polarizer is defined as letting light through . so you can do this . and once you hold this up , you get polarized light , light that 's only got one orientation . so that 's what polarization means . but why do we care about polarization ? well , let me get rid of this for a minute . you 've heard of polarized sunglasses . so imagine you 're standing near water , or maybe you 're standing on ice or snow or something reflective . there 's a problem . say the sun 's out . it 's shining . it 's a beautiful day -- except there 's going to be glare . let 's say you 're looking down at something here on the ground . it 's going to get light reflecting off of it from just ... you know , light 's coming in from all direction . but it also gets this direct light from the sun . so it gets light from reflected off the clouds and whatever , whatever 's nearby , ambient light . and there 's also this direct sunlight . that 's harsh . if that reflects straight up to your eye , that hurts . you do n't like that . it blocks our vision . it 's hard to see , it 's glare . we do n't want this glare . so what can we do ? well , it just so happens that , when light reflects off of a surface , even though the light from the sun is not polarized , once it reflects , it does get polarized or at least partially polarized . so this surface here , once this light reflects , it 's coming in at all orientations . you got electric field ... you never know what electric field you 're going to get straight from the sun . and when it reflects , though , you mostly get , upon reflection , the direction of polarization defined by the plane of the surface that it hit . so because the floor is horizontal , when this light ray hits the ground and reflects , that reflected light gets partially polarized . this horizontal component of the electric field is going to be more present than the other components . maybe not completely . sometimes it could be . it could be completely polarized , but often it 's just partially polarized . but that 's pretty cool , because now you know what we can do . i know how to block this . we should get some sunglasses . we put some sunglasses on and we make our glasses so that these are polarized . and how do we want these polarized ? i want to get rid of the glare . so what i do is , i make sure my sunglasses only let through vertically polarized light . here 's some polarizers . that way , a lot of this glare gets blocked because it does not have a vertical orientation , it has a horizontal orientation . and then we can block it . so that 's one good thing that polarization does for us , and understanding it , we can get rid of glare . also , fishermen like it because , if you 're trying to look in the water at fish , you want to see in through the water , you want to see this light from the fish getting to you . you do n't want to see the glare off of the sun getting to you . so polarized sunglasses are useful . also , we can play a trick on our eye , if we really wanted to . you could take one of these , make one eye have a vertical orientation for the polarization , have the other eye with a horizontal ... and you 're thinking , `` this is stupid . `` why would you do this for ? '' `` this eye 's going to get a lot of glare . '' we would n't use these outside , when you 're , like , skiing or fishing , but you could play a trick on your eyes if you went to the movies and you went and watched a movie . well , the reason our eyes see 3d is because they 're spaced a little bit apart . they each get a different , slightly different image . that makes us see in 3d . we can play the same trick on our eye if we have the polarization like this . if light , if some of the light from the movie theater screen is coming in with one polarization , and the other light 's coming in with the other polarization , we can send two different images to our eyes at the same time . if you took these off , it 'd look like garbage because you 'd be getting both of these slightly different images , it 'd look all blurry . and it does . if you take off your 3d glasses and look at a 3d movie , looks terrible , because now both eyes are getting both images . but if you put your glasses back on , now this eye only gets the orientation that it 's supposed to get , and this eye only gets the orientation that it 's supposed to get , and you get a 3d image . so it 's useful in many ways . let me show you one more thing here . let 's come back here . this light was polarized vertically . so that 's called linear polarization . any time ... same with these . these are all linear polarization because , just up and down , one linear direction , just diagonal . this is also linear . all of these are linear . you can get circular polarized light . so if we come back to here , we 've got our electric field pointing up , like that . now let 's say we sent in another light ray , another light ray that also had a polarization , but not in this direction . let 's say our other light ray had polarization in this direction , so it looks like this , kind of like what our magnetic field would have looked like . but this is a completely different light ray with its own polarization and its own magnetic field . so we send this in . what would happen ? well , at this point , you 'd have a electric field that points this way . at this point , you 'd have a electric field that points that way . what would your eye see if you were over here ? let 's see . if i draw our axis here . all right , when this point right here gets to your eye , what am i going to see ? well , i 'm going to have a light ray that 's one part of a light ray . one component points up . that 's this electric field . one component points left . that 's this electric field . so the total , my total electric field , would point this way . i could to the pythagorean theorem if i wanted to figure out the size of it , but i just want to know the direction for now . and then it gets to here , and look at it : they both have zero . this light ray has zero electric field , this one has zero electric fields . so then it 'd just be at zero . now what happens over here ? well , i 've got light . this one points to the right at that point , this pink one , and then this red one would be pointing down . so what would i have at that point ? i 'd have light that went this way , and it would just be doing this over and over . it would just be ... i 'd just have diagonally polarized light . this is n't giving me anything new . you might think this is dumb . why do this ? why send in two different waves to just get diagonally polarized light ? i could have just sent in one wave that was diagonally polarized and got the same thing . the reason is , if you shift this purple wave , this pink wave , by 90 degrees of phase , by pi over two in phase , something magical happens . let me show you what happens here , if we move this to here . now we do n't just get diagonally linear polarized light . what we 're going to get is ... let me get rid of this . okay , so we start off with red , right ? the red electric field points up , and then this pink wave 's electric field is zero at that point . so this is all i have . my total electric field would just be up . i 'm going to draw it right here . the green 'll be the total . now i come over to here , and at this point , there 's some red electric field that points up , but there 's some of this other electric field that points this way . so i 'd have a total electric field that would point that way . and then i get over to here , and i 'd have all of the electric field from the pink one , none from the red one . it would point all left then . look what 's happening . the polarization of this light , if i shift this , if i 'm sitting here , looking with my eye , as my eye receives this light , i 'm going to see this light rotate its polarization . the polarization i 'm going to notice swings around in a circular pattern . and because of this , we call this circular polarization . so this is another type of polarization , where the actual angle of polarization rotates smoothly as this light ray enters your eye . and you know what ? er , drrr ... all right , actually , i sent you to receive this one first . that makes no sense . you 're going to receive the ones closes to you first in this light ray going this way . so you 'd actually receive this one first , then that one , then this one , then this one . because of that , you would n't see this going in a counterclockwise way , you 'd see this going in a clockwise circularly polarized way . sorry about that . you might think , `` okay , why ? `` why even bother with circular polarization ? '' well , i kind of lied earlier . turns out , in the movie theater example , they do n't actually do it like this , typically . oftentimes in the movie theaters , we do n't have just linearly polarized sunglasses . this would be a problem because , when you look at the movie theater screen , and if you were to tilt your head just a little bit ... think about it . this one 's not really going to get the right image anymore . it 's going to get some of both . and this one 's going to get some of both . it 's going to be blurry . your head would have to be perfectly level the whole time , which might be annoying . so what we do is , instead , we create circular polarized glasses , so that this one would only get one polarization , this one would get the other direction . this way , even if you tilt your head a little bit ... shoot , clockwise is clockwise , counterclockwise is counterclockwise . by using circular polarization for 3d movies , it can make it a little easier on you eyes to see a better 3d image , even if your head 's tilted a little bit .
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you were doing an experiment . you needed polarized light . well , that 's easy .
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does polarization affect the energy of the polarized light ?
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- let 's talk about polarization of light . we know what light waves are ; they 're electromagnetic waves . so they 're made out of electric fields . and that 's not good enough . we know there 's not just electric fields . that could n't sustain itself . there 's got to be magnetic fields there , as well , that are changing . those are perpendicular , so you can kind of draw them . it 's hard , on something two-dimensional , but you can kind of imagine those looking something like this . and those magnetic fields would point at a right angle to the electric fields . but this gets really messy if i try to draw both the electric and magnetic fields at the same time . so we 're going to leave the magnetic fields out . it 's often good enough to just know the direction of the electric field when we focus on the electric field . so what does polarization mean ? polarization refers to the fact that , if this light ray was heading straight toward your eye , or a detector , over here , what would you see ? well , if i draw an axis over here , and this point here , in the middle , this is this line -- so imagine we 're looking straight down that line -- and then up and down is up and down , and then left and right , that direction i have the magnetic field , would be this way and that way . what would my eye see ? well , my eye 's only going to see electric fields that either point up or electric fields that point down . they might have different values , but i 'm only going to see electric fields that point up or down . because of that , this light ray is polarized . so polarized light is light where the electric field is only oscillating in one direction . up or down , that 's one direction -- vertically . or it could be polarized horizontally . or it could be polarized diagonally . but either way , you could have this wave polarized along any direction . i mean , a light ray like this , if we had it coming in diagonal , this light ray that 's oscillating like this , where the electric field oscillates like that , that also polarized . these are both polarized because there 's only one direction that the electric field is oscillating in . and you might thing , `` pff , how could you ever have `` a light ray that 's not polarized ? '' easy . most light that you get is not polarized . that is to say , light that 's coming from the sun , straight from the sun -- typically not polarized . light from a lightbulb , an old incandescent light bulb , this thing 's hot . you can get light polarized in any direction , all at once , all overlapping . so if we draw this case for a light bulb , just a random incandescent light bulb , you might get light , some of the light , hitting you eye , you can get some light that 's got that direction , you got light that 's got this direction , you got light in all these directions at any given moment . i mean , you 'd have to add these up to get the total , and they might not all be the same value . but what i 'm trying to say is , at any given moment , you do n't know what direction the electric field 's going to be hitting your eye at from a random source . it could be in any direction . so this is not polarized . this diagram represents light that is not polarized . at some point , the field might be pointing this way , at some later point it 's this way ; it 's just random . you never know which way the electric field 's going to be pointing . whereas these over here , these are polarized . so how could you polarize this light ? let 's say you wanted light that was polarized . you were doing an experiment . you needed polarized light . well , that 's easy . you can use what 's called a polarizer . and this is a material that lets light through , but it only lets light through in one orientation , so you 're going to have a polarizer that , for instance , only lets through vertically polarized light . so this is a polarizer . these are cheap : thin , plastic , configured in a way so that it only lets light through that 's vertically polarized . any light coming in here that 's not vertically polarized gets blocked , or absorbed . so what that means is , if you used this polarizer and held it in between your eye and this light bulb , you would only get this light . all the rest of it would get blocked . or you could just rotate this thing and imagine a polarizer that only lets through horizontal light . now it would only let through light that was this way , and so you would only get this part of the light . or you could just orient it at any angle you want and block everything but the certain angle that this polarizer is defined as letting light through . so you can do this . and once you hold this up , you get polarized light , light that 's only got one orientation . so that 's what polarization means . but why do we care about polarization ? well , let me get rid of this for a minute . you 've heard of polarized sunglasses . so imagine you 're standing near water , or maybe you 're standing on ice or snow or something reflective . there 's a problem . say the sun 's out . it 's shining . it 's a beautiful day -- except there 's going to be glare . let 's say you 're looking down at something here on the ground . it 's going to get light reflecting off of it from just ... you know , light 's coming in from all direction . but it also gets this direct light from the sun . so it gets light from reflected off the clouds and whatever , whatever 's nearby , ambient light . and there 's also this direct sunlight . that 's harsh . if that reflects straight up to your eye , that hurts . you do n't like that . it blocks our vision . it 's hard to see , it 's glare . we do n't want this glare . so what can we do ? well , it just so happens that , when light reflects off of a surface , even though the light from the sun is not polarized , once it reflects , it does get polarized or at least partially polarized . so this surface here , once this light reflects , it 's coming in at all orientations . you got electric field ... you never know what electric field you 're going to get straight from the sun . and when it reflects , though , you mostly get , upon reflection , the direction of polarization defined by the plane of the surface that it hit . so because the floor is horizontal , when this light ray hits the ground and reflects , that reflected light gets partially polarized . this horizontal component of the electric field is going to be more present than the other components . maybe not completely . sometimes it could be . it could be completely polarized , but often it 's just partially polarized . but that 's pretty cool , because now you know what we can do . i know how to block this . we should get some sunglasses . we put some sunglasses on and we make our glasses so that these are polarized . and how do we want these polarized ? i want to get rid of the glare . so what i do is , i make sure my sunglasses only let through vertically polarized light . here 's some polarizers . that way , a lot of this glare gets blocked because it does not have a vertical orientation , it has a horizontal orientation . and then we can block it . so that 's one good thing that polarization does for us , and understanding it , we can get rid of glare . also , fishermen like it because , if you 're trying to look in the water at fish , you want to see in through the water , you want to see this light from the fish getting to you . you do n't want to see the glare off of the sun getting to you . so polarized sunglasses are useful . also , we can play a trick on our eye , if we really wanted to . you could take one of these , make one eye have a vertical orientation for the polarization , have the other eye with a horizontal ... and you 're thinking , `` this is stupid . `` why would you do this for ? '' `` this eye 's going to get a lot of glare . '' we would n't use these outside , when you 're , like , skiing or fishing , but you could play a trick on your eyes if you went to the movies and you went and watched a movie . well , the reason our eyes see 3d is because they 're spaced a little bit apart . they each get a different , slightly different image . that makes us see in 3d . we can play the same trick on our eye if we have the polarization like this . if light , if some of the light from the movie theater screen is coming in with one polarization , and the other light 's coming in with the other polarization , we can send two different images to our eyes at the same time . if you took these off , it 'd look like garbage because you 'd be getting both of these slightly different images , it 'd look all blurry . and it does . if you take off your 3d glasses and look at a 3d movie , looks terrible , because now both eyes are getting both images . but if you put your glasses back on , now this eye only gets the orientation that it 's supposed to get , and this eye only gets the orientation that it 's supposed to get , and you get a 3d image . so it 's useful in many ways . let me show you one more thing here . let 's come back here . this light was polarized vertically . so that 's called linear polarization . any time ... same with these . these are all linear polarization because , just up and down , one linear direction , just diagonal . this is also linear . all of these are linear . you can get circular polarized light . so if we come back to here , we 've got our electric field pointing up , like that . now let 's say we sent in another light ray , another light ray that also had a polarization , but not in this direction . let 's say our other light ray had polarization in this direction , so it looks like this , kind of like what our magnetic field would have looked like . but this is a completely different light ray with its own polarization and its own magnetic field . so we send this in . what would happen ? well , at this point , you 'd have a electric field that points this way . at this point , you 'd have a electric field that points that way . what would your eye see if you were over here ? let 's see . if i draw our axis here . all right , when this point right here gets to your eye , what am i going to see ? well , i 'm going to have a light ray that 's one part of a light ray . one component points up . that 's this electric field . one component points left . that 's this electric field . so the total , my total electric field , would point this way . i could to the pythagorean theorem if i wanted to figure out the size of it , but i just want to know the direction for now . and then it gets to here , and look at it : they both have zero . this light ray has zero electric field , this one has zero electric fields . so then it 'd just be at zero . now what happens over here ? well , i 've got light . this one points to the right at that point , this pink one , and then this red one would be pointing down . so what would i have at that point ? i 'd have light that went this way , and it would just be doing this over and over . it would just be ... i 'd just have diagonally polarized light . this is n't giving me anything new . you might think this is dumb . why do this ? why send in two different waves to just get diagonally polarized light ? i could have just sent in one wave that was diagonally polarized and got the same thing . the reason is , if you shift this purple wave , this pink wave , by 90 degrees of phase , by pi over two in phase , something magical happens . let me show you what happens here , if we move this to here . now we do n't just get diagonally linear polarized light . what we 're going to get is ... let me get rid of this . okay , so we start off with red , right ? the red electric field points up , and then this pink wave 's electric field is zero at that point . so this is all i have . my total electric field would just be up . i 'm going to draw it right here . the green 'll be the total . now i come over to here , and at this point , there 's some red electric field that points up , but there 's some of this other electric field that points this way . so i 'd have a total electric field that would point that way . and then i get over to here , and i 'd have all of the electric field from the pink one , none from the red one . it would point all left then . look what 's happening . the polarization of this light , if i shift this , if i 'm sitting here , looking with my eye , as my eye receives this light , i 'm going to see this light rotate its polarization . the polarization i 'm going to notice swings around in a circular pattern . and because of this , we call this circular polarization . so this is another type of polarization , where the actual angle of polarization rotates smoothly as this light ray enters your eye . and you know what ? er , drrr ... all right , actually , i sent you to receive this one first . that makes no sense . you 're going to receive the ones closes to you first in this light ray going this way . so you 'd actually receive this one first , then that one , then this one , then this one . because of that , you would n't see this going in a counterclockwise way , you 'd see this going in a clockwise circularly polarized way . sorry about that . you might think , `` okay , why ? `` why even bother with circular polarization ? '' well , i kind of lied earlier . turns out , in the movie theater example , they do n't actually do it like this , typically . oftentimes in the movie theaters , we do n't have just linearly polarized sunglasses . this would be a problem because , when you look at the movie theater screen , and if you were to tilt your head just a little bit ... think about it . this one 's not really going to get the right image anymore . it 's going to get some of both . and this one 's going to get some of both . it 's going to be blurry . your head would have to be perfectly level the whole time , which might be annoying . so what we do is , instead , we create circular polarized glasses , so that this one would only get one polarization , this one would get the other direction . this way , even if you tilt your head a little bit ... shoot , clockwise is clockwise , counterclockwise is counterclockwise . by using circular polarization for 3d movies , it can make it a little easier on you eyes to see a better 3d image , even if your head 's tilted a little bit .
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or you could just rotate this thing and imagine a polarizer that only lets through horizontal light . now it would only let through light that was this way , and so you would only get this part of the light . or you could just orient it at any angle you want and block everything but the certain angle that this polarizer is defined as letting light through .
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would this light have less energy than before , and why ?
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- let 's talk about polarization of light . we know what light waves are ; they 're electromagnetic waves . so they 're made out of electric fields . and that 's not good enough . we know there 's not just electric fields . that could n't sustain itself . there 's got to be magnetic fields there , as well , that are changing . those are perpendicular , so you can kind of draw them . it 's hard , on something two-dimensional , but you can kind of imagine those looking something like this . and those magnetic fields would point at a right angle to the electric fields . but this gets really messy if i try to draw both the electric and magnetic fields at the same time . so we 're going to leave the magnetic fields out . it 's often good enough to just know the direction of the electric field when we focus on the electric field . so what does polarization mean ? polarization refers to the fact that , if this light ray was heading straight toward your eye , or a detector , over here , what would you see ? well , if i draw an axis over here , and this point here , in the middle , this is this line -- so imagine we 're looking straight down that line -- and then up and down is up and down , and then left and right , that direction i have the magnetic field , would be this way and that way . what would my eye see ? well , my eye 's only going to see electric fields that either point up or electric fields that point down . they might have different values , but i 'm only going to see electric fields that point up or down . because of that , this light ray is polarized . so polarized light is light where the electric field is only oscillating in one direction . up or down , that 's one direction -- vertically . or it could be polarized horizontally . or it could be polarized diagonally . but either way , you could have this wave polarized along any direction . i mean , a light ray like this , if we had it coming in diagonal , this light ray that 's oscillating like this , where the electric field oscillates like that , that also polarized . these are both polarized because there 's only one direction that the electric field is oscillating in . and you might thing , `` pff , how could you ever have `` a light ray that 's not polarized ? '' easy . most light that you get is not polarized . that is to say , light that 's coming from the sun , straight from the sun -- typically not polarized . light from a lightbulb , an old incandescent light bulb , this thing 's hot . you can get light polarized in any direction , all at once , all overlapping . so if we draw this case for a light bulb , just a random incandescent light bulb , you might get light , some of the light , hitting you eye , you can get some light that 's got that direction , you got light that 's got this direction , you got light in all these directions at any given moment . i mean , you 'd have to add these up to get the total , and they might not all be the same value . but what i 'm trying to say is , at any given moment , you do n't know what direction the electric field 's going to be hitting your eye at from a random source . it could be in any direction . so this is not polarized . this diagram represents light that is not polarized . at some point , the field might be pointing this way , at some later point it 's this way ; it 's just random . you never know which way the electric field 's going to be pointing . whereas these over here , these are polarized . so how could you polarize this light ? let 's say you wanted light that was polarized . you were doing an experiment . you needed polarized light . well , that 's easy . you can use what 's called a polarizer . and this is a material that lets light through , but it only lets light through in one orientation , so you 're going to have a polarizer that , for instance , only lets through vertically polarized light . so this is a polarizer . these are cheap : thin , plastic , configured in a way so that it only lets light through that 's vertically polarized . any light coming in here that 's not vertically polarized gets blocked , or absorbed . so what that means is , if you used this polarizer and held it in between your eye and this light bulb , you would only get this light . all the rest of it would get blocked . or you could just rotate this thing and imagine a polarizer that only lets through horizontal light . now it would only let through light that was this way , and so you would only get this part of the light . or you could just orient it at any angle you want and block everything but the certain angle that this polarizer is defined as letting light through . so you can do this . and once you hold this up , you get polarized light , light that 's only got one orientation . so that 's what polarization means . but why do we care about polarization ? well , let me get rid of this for a minute . you 've heard of polarized sunglasses . so imagine you 're standing near water , or maybe you 're standing on ice or snow or something reflective . there 's a problem . say the sun 's out . it 's shining . it 's a beautiful day -- except there 's going to be glare . let 's say you 're looking down at something here on the ground . it 's going to get light reflecting off of it from just ... you know , light 's coming in from all direction . but it also gets this direct light from the sun . so it gets light from reflected off the clouds and whatever , whatever 's nearby , ambient light . and there 's also this direct sunlight . that 's harsh . if that reflects straight up to your eye , that hurts . you do n't like that . it blocks our vision . it 's hard to see , it 's glare . we do n't want this glare . so what can we do ? well , it just so happens that , when light reflects off of a surface , even though the light from the sun is not polarized , once it reflects , it does get polarized or at least partially polarized . so this surface here , once this light reflects , it 's coming in at all orientations . you got electric field ... you never know what electric field you 're going to get straight from the sun . and when it reflects , though , you mostly get , upon reflection , the direction of polarization defined by the plane of the surface that it hit . so because the floor is horizontal , when this light ray hits the ground and reflects , that reflected light gets partially polarized . this horizontal component of the electric field is going to be more present than the other components . maybe not completely . sometimes it could be . it could be completely polarized , but often it 's just partially polarized . but that 's pretty cool , because now you know what we can do . i know how to block this . we should get some sunglasses . we put some sunglasses on and we make our glasses so that these are polarized . and how do we want these polarized ? i want to get rid of the glare . so what i do is , i make sure my sunglasses only let through vertically polarized light . here 's some polarizers . that way , a lot of this glare gets blocked because it does not have a vertical orientation , it has a horizontal orientation . and then we can block it . so that 's one good thing that polarization does for us , and understanding it , we can get rid of glare . also , fishermen like it because , if you 're trying to look in the water at fish , you want to see in through the water , you want to see this light from the fish getting to you . you do n't want to see the glare off of the sun getting to you . so polarized sunglasses are useful . also , we can play a trick on our eye , if we really wanted to . you could take one of these , make one eye have a vertical orientation for the polarization , have the other eye with a horizontal ... and you 're thinking , `` this is stupid . `` why would you do this for ? '' `` this eye 's going to get a lot of glare . '' we would n't use these outside , when you 're , like , skiing or fishing , but you could play a trick on your eyes if you went to the movies and you went and watched a movie . well , the reason our eyes see 3d is because they 're spaced a little bit apart . they each get a different , slightly different image . that makes us see in 3d . we can play the same trick on our eye if we have the polarization like this . if light , if some of the light from the movie theater screen is coming in with one polarization , and the other light 's coming in with the other polarization , we can send two different images to our eyes at the same time . if you took these off , it 'd look like garbage because you 'd be getting both of these slightly different images , it 'd look all blurry . and it does . if you take off your 3d glasses and look at a 3d movie , looks terrible , because now both eyes are getting both images . but if you put your glasses back on , now this eye only gets the orientation that it 's supposed to get , and this eye only gets the orientation that it 's supposed to get , and you get a 3d image . so it 's useful in many ways . let me show you one more thing here . let 's come back here . this light was polarized vertically . so that 's called linear polarization . any time ... same with these . these are all linear polarization because , just up and down , one linear direction , just diagonal . this is also linear . all of these are linear . you can get circular polarized light . so if we come back to here , we 've got our electric field pointing up , like that . now let 's say we sent in another light ray , another light ray that also had a polarization , but not in this direction . let 's say our other light ray had polarization in this direction , so it looks like this , kind of like what our magnetic field would have looked like . but this is a completely different light ray with its own polarization and its own magnetic field . so we send this in . what would happen ? well , at this point , you 'd have a electric field that points this way . at this point , you 'd have a electric field that points that way . what would your eye see if you were over here ? let 's see . if i draw our axis here . all right , when this point right here gets to your eye , what am i going to see ? well , i 'm going to have a light ray that 's one part of a light ray . one component points up . that 's this electric field . one component points left . that 's this electric field . so the total , my total electric field , would point this way . i could to the pythagorean theorem if i wanted to figure out the size of it , but i just want to know the direction for now . and then it gets to here , and look at it : they both have zero . this light ray has zero electric field , this one has zero electric fields . so then it 'd just be at zero . now what happens over here ? well , i 've got light . this one points to the right at that point , this pink one , and then this red one would be pointing down . so what would i have at that point ? i 'd have light that went this way , and it would just be doing this over and over . it would just be ... i 'd just have diagonally polarized light . this is n't giving me anything new . you might think this is dumb . why do this ? why send in two different waves to just get diagonally polarized light ? i could have just sent in one wave that was diagonally polarized and got the same thing . the reason is , if you shift this purple wave , this pink wave , by 90 degrees of phase , by pi over two in phase , something magical happens . let me show you what happens here , if we move this to here . now we do n't just get diagonally linear polarized light . what we 're going to get is ... let me get rid of this . okay , so we start off with red , right ? the red electric field points up , and then this pink wave 's electric field is zero at that point . so this is all i have . my total electric field would just be up . i 'm going to draw it right here . the green 'll be the total . now i come over to here , and at this point , there 's some red electric field that points up , but there 's some of this other electric field that points this way . so i 'd have a total electric field that would point that way . and then i get over to here , and i 'd have all of the electric field from the pink one , none from the red one . it would point all left then . look what 's happening . the polarization of this light , if i shift this , if i 'm sitting here , looking with my eye , as my eye receives this light , i 'm going to see this light rotate its polarization . the polarization i 'm going to notice swings around in a circular pattern . and because of this , we call this circular polarization . so this is another type of polarization , where the actual angle of polarization rotates smoothly as this light ray enters your eye . and you know what ? er , drrr ... all right , actually , i sent you to receive this one first . that makes no sense . you 're going to receive the ones closes to you first in this light ray going this way . so you 'd actually receive this one first , then that one , then this one , then this one . because of that , you would n't see this going in a counterclockwise way , you 'd see this going in a clockwise circularly polarized way . sorry about that . you might think , `` okay , why ? `` why even bother with circular polarization ? '' well , i kind of lied earlier . turns out , in the movie theater example , they do n't actually do it like this , typically . oftentimes in the movie theaters , we do n't have just linearly polarized sunglasses . this would be a problem because , when you look at the movie theater screen , and if you were to tilt your head just a little bit ... think about it . this one 's not really going to get the right image anymore . it 's going to get some of both . and this one 's going to get some of both . it 's going to be blurry . your head would have to be perfectly level the whole time , which might be annoying . so what we do is , instead , we create circular polarized glasses , so that this one would only get one polarization , this one would get the other direction . this way , even if you tilt your head a little bit ... shoot , clockwise is clockwise , counterclockwise is counterclockwise . by using circular polarization for 3d movies , it can make it a little easier on you eyes to see a better 3d image , even if your head 's tilted a little bit .
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you 're going to receive the ones closes to you first in this light ray going this way . so you 'd actually receive this one first , then that one , then this one , then this one . because of that , you would n't see this going in a counterclockwise way , you 'd see this going in a clockwise circularly polarized way .
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why do the glasses that we use to watch 3-d movies have blue color on one side and red on the other if all that one needs to use is a pair of circular polarisers ?
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- let 's talk about polarization of light . we know what light waves are ; they 're electromagnetic waves . so they 're made out of electric fields . and that 's not good enough . we know there 's not just electric fields . that could n't sustain itself . there 's got to be magnetic fields there , as well , that are changing . those are perpendicular , so you can kind of draw them . it 's hard , on something two-dimensional , but you can kind of imagine those looking something like this . and those magnetic fields would point at a right angle to the electric fields . but this gets really messy if i try to draw both the electric and magnetic fields at the same time . so we 're going to leave the magnetic fields out . it 's often good enough to just know the direction of the electric field when we focus on the electric field . so what does polarization mean ? polarization refers to the fact that , if this light ray was heading straight toward your eye , or a detector , over here , what would you see ? well , if i draw an axis over here , and this point here , in the middle , this is this line -- so imagine we 're looking straight down that line -- and then up and down is up and down , and then left and right , that direction i have the magnetic field , would be this way and that way . what would my eye see ? well , my eye 's only going to see electric fields that either point up or electric fields that point down . they might have different values , but i 'm only going to see electric fields that point up or down . because of that , this light ray is polarized . so polarized light is light where the electric field is only oscillating in one direction . up or down , that 's one direction -- vertically . or it could be polarized horizontally . or it could be polarized diagonally . but either way , you could have this wave polarized along any direction . i mean , a light ray like this , if we had it coming in diagonal , this light ray that 's oscillating like this , where the electric field oscillates like that , that also polarized . these are both polarized because there 's only one direction that the electric field is oscillating in . and you might thing , `` pff , how could you ever have `` a light ray that 's not polarized ? '' easy . most light that you get is not polarized . that is to say , light that 's coming from the sun , straight from the sun -- typically not polarized . light from a lightbulb , an old incandescent light bulb , this thing 's hot . you can get light polarized in any direction , all at once , all overlapping . so if we draw this case for a light bulb , just a random incandescent light bulb , you might get light , some of the light , hitting you eye , you can get some light that 's got that direction , you got light that 's got this direction , you got light in all these directions at any given moment . i mean , you 'd have to add these up to get the total , and they might not all be the same value . but what i 'm trying to say is , at any given moment , you do n't know what direction the electric field 's going to be hitting your eye at from a random source . it could be in any direction . so this is not polarized . this diagram represents light that is not polarized . at some point , the field might be pointing this way , at some later point it 's this way ; it 's just random . you never know which way the electric field 's going to be pointing . whereas these over here , these are polarized . so how could you polarize this light ? let 's say you wanted light that was polarized . you were doing an experiment . you needed polarized light . well , that 's easy . you can use what 's called a polarizer . and this is a material that lets light through , but it only lets light through in one orientation , so you 're going to have a polarizer that , for instance , only lets through vertically polarized light . so this is a polarizer . these are cheap : thin , plastic , configured in a way so that it only lets light through that 's vertically polarized . any light coming in here that 's not vertically polarized gets blocked , or absorbed . so what that means is , if you used this polarizer and held it in between your eye and this light bulb , you would only get this light . all the rest of it would get blocked . or you could just rotate this thing and imagine a polarizer that only lets through horizontal light . now it would only let through light that was this way , and so you would only get this part of the light . or you could just orient it at any angle you want and block everything but the certain angle that this polarizer is defined as letting light through . so you can do this . and once you hold this up , you get polarized light , light that 's only got one orientation . so that 's what polarization means . but why do we care about polarization ? well , let me get rid of this for a minute . you 've heard of polarized sunglasses . so imagine you 're standing near water , or maybe you 're standing on ice or snow or something reflective . there 's a problem . say the sun 's out . it 's shining . it 's a beautiful day -- except there 's going to be glare . let 's say you 're looking down at something here on the ground . it 's going to get light reflecting off of it from just ... you know , light 's coming in from all direction . but it also gets this direct light from the sun . so it gets light from reflected off the clouds and whatever , whatever 's nearby , ambient light . and there 's also this direct sunlight . that 's harsh . if that reflects straight up to your eye , that hurts . you do n't like that . it blocks our vision . it 's hard to see , it 's glare . we do n't want this glare . so what can we do ? well , it just so happens that , when light reflects off of a surface , even though the light from the sun is not polarized , once it reflects , it does get polarized or at least partially polarized . so this surface here , once this light reflects , it 's coming in at all orientations . you got electric field ... you never know what electric field you 're going to get straight from the sun . and when it reflects , though , you mostly get , upon reflection , the direction of polarization defined by the plane of the surface that it hit . so because the floor is horizontal , when this light ray hits the ground and reflects , that reflected light gets partially polarized . this horizontal component of the electric field is going to be more present than the other components . maybe not completely . sometimes it could be . it could be completely polarized , but often it 's just partially polarized . but that 's pretty cool , because now you know what we can do . i know how to block this . we should get some sunglasses . we put some sunglasses on and we make our glasses so that these are polarized . and how do we want these polarized ? i want to get rid of the glare . so what i do is , i make sure my sunglasses only let through vertically polarized light . here 's some polarizers . that way , a lot of this glare gets blocked because it does not have a vertical orientation , it has a horizontal orientation . and then we can block it . so that 's one good thing that polarization does for us , and understanding it , we can get rid of glare . also , fishermen like it because , if you 're trying to look in the water at fish , you want to see in through the water , you want to see this light from the fish getting to you . you do n't want to see the glare off of the sun getting to you . so polarized sunglasses are useful . also , we can play a trick on our eye , if we really wanted to . you could take one of these , make one eye have a vertical orientation for the polarization , have the other eye with a horizontal ... and you 're thinking , `` this is stupid . `` why would you do this for ? '' `` this eye 's going to get a lot of glare . '' we would n't use these outside , when you 're , like , skiing or fishing , but you could play a trick on your eyes if you went to the movies and you went and watched a movie . well , the reason our eyes see 3d is because they 're spaced a little bit apart . they each get a different , slightly different image . that makes us see in 3d . we can play the same trick on our eye if we have the polarization like this . if light , if some of the light from the movie theater screen is coming in with one polarization , and the other light 's coming in with the other polarization , we can send two different images to our eyes at the same time . if you took these off , it 'd look like garbage because you 'd be getting both of these slightly different images , it 'd look all blurry . and it does . if you take off your 3d glasses and look at a 3d movie , looks terrible , because now both eyes are getting both images . but if you put your glasses back on , now this eye only gets the orientation that it 's supposed to get , and this eye only gets the orientation that it 's supposed to get , and you get a 3d image . so it 's useful in many ways . let me show you one more thing here . let 's come back here . this light was polarized vertically . so that 's called linear polarization . any time ... same with these . these are all linear polarization because , just up and down , one linear direction , just diagonal . this is also linear . all of these are linear . you can get circular polarized light . so if we come back to here , we 've got our electric field pointing up , like that . now let 's say we sent in another light ray , another light ray that also had a polarization , but not in this direction . let 's say our other light ray had polarization in this direction , so it looks like this , kind of like what our magnetic field would have looked like . but this is a completely different light ray with its own polarization and its own magnetic field . so we send this in . what would happen ? well , at this point , you 'd have a electric field that points this way . at this point , you 'd have a electric field that points that way . what would your eye see if you were over here ? let 's see . if i draw our axis here . all right , when this point right here gets to your eye , what am i going to see ? well , i 'm going to have a light ray that 's one part of a light ray . one component points up . that 's this electric field . one component points left . that 's this electric field . so the total , my total electric field , would point this way . i could to the pythagorean theorem if i wanted to figure out the size of it , but i just want to know the direction for now . and then it gets to here , and look at it : they both have zero . this light ray has zero electric field , this one has zero electric fields . so then it 'd just be at zero . now what happens over here ? well , i 've got light . this one points to the right at that point , this pink one , and then this red one would be pointing down . so what would i have at that point ? i 'd have light that went this way , and it would just be doing this over and over . it would just be ... i 'd just have diagonally polarized light . this is n't giving me anything new . you might think this is dumb . why do this ? why send in two different waves to just get diagonally polarized light ? i could have just sent in one wave that was diagonally polarized and got the same thing . the reason is , if you shift this purple wave , this pink wave , by 90 degrees of phase , by pi over two in phase , something magical happens . let me show you what happens here , if we move this to here . now we do n't just get diagonally linear polarized light . what we 're going to get is ... let me get rid of this . okay , so we start off with red , right ? the red electric field points up , and then this pink wave 's electric field is zero at that point . so this is all i have . my total electric field would just be up . i 'm going to draw it right here . the green 'll be the total . now i come over to here , and at this point , there 's some red electric field that points up , but there 's some of this other electric field that points this way . so i 'd have a total electric field that would point that way . and then i get over to here , and i 'd have all of the electric field from the pink one , none from the red one . it would point all left then . look what 's happening . the polarization of this light , if i shift this , if i 'm sitting here , looking with my eye , as my eye receives this light , i 'm going to see this light rotate its polarization . the polarization i 'm going to notice swings around in a circular pattern . and because of this , we call this circular polarization . so this is another type of polarization , where the actual angle of polarization rotates smoothly as this light ray enters your eye . and you know what ? er , drrr ... all right , actually , i sent you to receive this one first . that makes no sense . you 're going to receive the ones closes to you first in this light ray going this way . so you 'd actually receive this one first , then that one , then this one , then this one . because of that , you would n't see this going in a counterclockwise way , you 'd see this going in a clockwise circularly polarized way . sorry about that . you might think , `` okay , why ? `` why even bother with circular polarization ? '' well , i kind of lied earlier . turns out , in the movie theater example , they do n't actually do it like this , typically . oftentimes in the movie theaters , we do n't have just linearly polarized sunglasses . this would be a problem because , when you look at the movie theater screen , and if you were to tilt your head just a little bit ... think about it . this one 's not really going to get the right image anymore . it 's going to get some of both . and this one 's going to get some of both . it 's going to be blurry . your head would have to be perfectly level the whole time , which might be annoying . so what we do is , instead , we create circular polarized glasses , so that this one would only get one polarization , this one would get the other direction . this way , even if you tilt your head a little bit ... shoot , clockwise is clockwise , counterclockwise is counterclockwise . by using circular polarization for 3d movies , it can make it a little easier on you eyes to see a better 3d image , even if your head 's tilted a little bit .
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you were doing an experiment . you needed polarized light . well , that 's easy .
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is all glare polarized light ?
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- let 's talk about polarization of light . we know what light waves are ; they 're electromagnetic waves . so they 're made out of electric fields . and that 's not good enough . we know there 's not just electric fields . that could n't sustain itself . there 's got to be magnetic fields there , as well , that are changing . those are perpendicular , so you can kind of draw them . it 's hard , on something two-dimensional , but you can kind of imagine those looking something like this . and those magnetic fields would point at a right angle to the electric fields . but this gets really messy if i try to draw both the electric and magnetic fields at the same time . so we 're going to leave the magnetic fields out . it 's often good enough to just know the direction of the electric field when we focus on the electric field . so what does polarization mean ? polarization refers to the fact that , if this light ray was heading straight toward your eye , or a detector , over here , what would you see ? well , if i draw an axis over here , and this point here , in the middle , this is this line -- so imagine we 're looking straight down that line -- and then up and down is up and down , and then left and right , that direction i have the magnetic field , would be this way and that way . what would my eye see ? well , my eye 's only going to see electric fields that either point up or electric fields that point down . they might have different values , but i 'm only going to see electric fields that point up or down . because of that , this light ray is polarized . so polarized light is light where the electric field is only oscillating in one direction . up or down , that 's one direction -- vertically . or it could be polarized horizontally . or it could be polarized diagonally . but either way , you could have this wave polarized along any direction . i mean , a light ray like this , if we had it coming in diagonal , this light ray that 's oscillating like this , where the electric field oscillates like that , that also polarized . these are both polarized because there 's only one direction that the electric field is oscillating in . and you might thing , `` pff , how could you ever have `` a light ray that 's not polarized ? '' easy . most light that you get is not polarized . that is to say , light that 's coming from the sun , straight from the sun -- typically not polarized . light from a lightbulb , an old incandescent light bulb , this thing 's hot . you can get light polarized in any direction , all at once , all overlapping . so if we draw this case for a light bulb , just a random incandescent light bulb , you might get light , some of the light , hitting you eye , you can get some light that 's got that direction , you got light that 's got this direction , you got light in all these directions at any given moment . i mean , you 'd have to add these up to get the total , and they might not all be the same value . but what i 'm trying to say is , at any given moment , you do n't know what direction the electric field 's going to be hitting your eye at from a random source . it could be in any direction . so this is not polarized . this diagram represents light that is not polarized . at some point , the field might be pointing this way , at some later point it 's this way ; it 's just random . you never know which way the electric field 's going to be pointing . whereas these over here , these are polarized . so how could you polarize this light ? let 's say you wanted light that was polarized . you were doing an experiment . you needed polarized light . well , that 's easy . you can use what 's called a polarizer . and this is a material that lets light through , but it only lets light through in one orientation , so you 're going to have a polarizer that , for instance , only lets through vertically polarized light . so this is a polarizer . these are cheap : thin , plastic , configured in a way so that it only lets light through that 's vertically polarized . any light coming in here that 's not vertically polarized gets blocked , or absorbed . so what that means is , if you used this polarizer and held it in between your eye and this light bulb , you would only get this light . all the rest of it would get blocked . or you could just rotate this thing and imagine a polarizer that only lets through horizontal light . now it would only let through light that was this way , and so you would only get this part of the light . or you could just orient it at any angle you want and block everything but the certain angle that this polarizer is defined as letting light through . so you can do this . and once you hold this up , you get polarized light , light that 's only got one orientation . so that 's what polarization means . but why do we care about polarization ? well , let me get rid of this for a minute . you 've heard of polarized sunglasses . so imagine you 're standing near water , or maybe you 're standing on ice or snow or something reflective . there 's a problem . say the sun 's out . it 's shining . it 's a beautiful day -- except there 's going to be glare . let 's say you 're looking down at something here on the ground . it 's going to get light reflecting off of it from just ... you know , light 's coming in from all direction . but it also gets this direct light from the sun . so it gets light from reflected off the clouds and whatever , whatever 's nearby , ambient light . and there 's also this direct sunlight . that 's harsh . if that reflects straight up to your eye , that hurts . you do n't like that . it blocks our vision . it 's hard to see , it 's glare . we do n't want this glare . so what can we do ? well , it just so happens that , when light reflects off of a surface , even though the light from the sun is not polarized , once it reflects , it does get polarized or at least partially polarized . so this surface here , once this light reflects , it 's coming in at all orientations . you got electric field ... you never know what electric field you 're going to get straight from the sun . and when it reflects , though , you mostly get , upon reflection , the direction of polarization defined by the plane of the surface that it hit . so because the floor is horizontal , when this light ray hits the ground and reflects , that reflected light gets partially polarized . this horizontal component of the electric field is going to be more present than the other components . maybe not completely . sometimes it could be . it could be completely polarized , but often it 's just partially polarized . but that 's pretty cool , because now you know what we can do . i know how to block this . we should get some sunglasses . we put some sunglasses on and we make our glasses so that these are polarized . and how do we want these polarized ? i want to get rid of the glare . so what i do is , i make sure my sunglasses only let through vertically polarized light . here 's some polarizers . that way , a lot of this glare gets blocked because it does not have a vertical orientation , it has a horizontal orientation . and then we can block it . so that 's one good thing that polarization does for us , and understanding it , we can get rid of glare . also , fishermen like it because , if you 're trying to look in the water at fish , you want to see in through the water , you want to see this light from the fish getting to you . you do n't want to see the glare off of the sun getting to you . so polarized sunglasses are useful . also , we can play a trick on our eye , if we really wanted to . you could take one of these , make one eye have a vertical orientation for the polarization , have the other eye with a horizontal ... and you 're thinking , `` this is stupid . `` why would you do this for ? '' `` this eye 's going to get a lot of glare . '' we would n't use these outside , when you 're , like , skiing or fishing , but you could play a trick on your eyes if you went to the movies and you went and watched a movie . well , the reason our eyes see 3d is because they 're spaced a little bit apart . they each get a different , slightly different image . that makes us see in 3d . we can play the same trick on our eye if we have the polarization like this . if light , if some of the light from the movie theater screen is coming in with one polarization , and the other light 's coming in with the other polarization , we can send two different images to our eyes at the same time . if you took these off , it 'd look like garbage because you 'd be getting both of these slightly different images , it 'd look all blurry . and it does . if you take off your 3d glasses and look at a 3d movie , looks terrible , because now both eyes are getting both images . but if you put your glasses back on , now this eye only gets the orientation that it 's supposed to get , and this eye only gets the orientation that it 's supposed to get , and you get a 3d image . so it 's useful in many ways . let me show you one more thing here . let 's come back here . this light was polarized vertically . so that 's called linear polarization . any time ... same with these . these are all linear polarization because , just up and down , one linear direction , just diagonal . this is also linear . all of these are linear . you can get circular polarized light . so if we come back to here , we 've got our electric field pointing up , like that . now let 's say we sent in another light ray , another light ray that also had a polarization , but not in this direction . let 's say our other light ray had polarization in this direction , so it looks like this , kind of like what our magnetic field would have looked like . but this is a completely different light ray with its own polarization and its own magnetic field . so we send this in . what would happen ? well , at this point , you 'd have a electric field that points this way . at this point , you 'd have a electric field that points that way . what would your eye see if you were over here ? let 's see . if i draw our axis here . all right , when this point right here gets to your eye , what am i going to see ? well , i 'm going to have a light ray that 's one part of a light ray . one component points up . that 's this electric field . one component points left . that 's this electric field . so the total , my total electric field , would point this way . i could to the pythagorean theorem if i wanted to figure out the size of it , but i just want to know the direction for now . and then it gets to here , and look at it : they both have zero . this light ray has zero electric field , this one has zero electric fields . so then it 'd just be at zero . now what happens over here ? well , i 've got light . this one points to the right at that point , this pink one , and then this red one would be pointing down . so what would i have at that point ? i 'd have light that went this way , and it would just be doing this over and over . it would just be ... i 'd just have diagonally polarized light . this is n't giving me anything new . you might think this is dumb . why do this ? why send in two different waves to just get diagonally polarized light ? i could have just sent in one wave that was diagonally polarized and got the same thing . the reason is , if you shift this purple wave , this pink wave , by 90 degrees of phase , by pi over two in phase , something magical happens . let me show you what happens here , if we move this to here . now we do n't just get diagonally linear polarized light . what we 're going to get is ... let me get rid of this . okay , so we start off with red , right ? the red electric field points up , and then this pink wave 's electric field is zero at that point . so this is all i have . my total electric field would just be up . i 'm going to draw it right here . the green 'll be the total . now i come over to here , and at this point , there 's some red electric field that points up , but there 's some of this other electric field that points this way . so i 'd have a total electric field that would point that way . and then i get over to here , and i 'd have all of the electric field from the pink one , none from the red one . it would point all left then . look what 's happening . the polarization of this light , if i shift this , if i 'm sitting here , looking with my eye , as my eye receives this light , i 'm going to see this light rotate its polarization . the polarization i 'm going to notice swings around in a circular pattern . and because of this , we call this circular polarization . so this is another type of polarization , where the actual angle of polarization rotates smoothly as this light ray enters your eye . and you know what ? er , drrr ... all right , actually , i sent you to receive this one first . that makes no sense . you 're going to receive the ones closes to you first in this light ray going this way . so you 'd actually receive this one first , then that one , then this one , then this one . because of that , you would n't see this going in a counterclockwise way , you 'd see this going in a clockwise circularly polarized way . sorry about that . you might think , `` okay , why ? `` why even bother with circular polarization ? '' well , i kind of lied earlier . turns out , in the movie theater example , they do n't actually do it like this , typically . oftentimes in the movie theaters , we do n't have just linearly polarized sunglasses . this would be a problem because , when you look at the movie theater screen , and if you were to tilt your head just a little bit ... think about it . this one 's not really going to get the right image anymore . it 's going to get some of both . and this one 's going to get some of both . it 's going to be blurry . your head would have to be perfectly level the whole time , which might be annoying . so what we do is , instead , we create circular polarized glasses , so that this one would only get one polarization , this one would get the other direction . this way , even if you tilt your head a little bit ... shoot , clockwise is clockwise , counterclockwise is counterclockwise . by using circular polarization for 3d movies , it can make it a little easier on you eyes to see a better 3d image , even if your head 's tilted a little bit .
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so what we do is , instead , we create circular polarized glasses , so that this one would only get one polarization , this one would get the other direction . this way , even if you tilt your head a little bit ... shoot , clockwise is clockwise , counterclockwise is counterclockwise . by using circular polarization for 3d movies , it can make it a little easier on you eyes to see a better 3d image , even if your head 's tilted a little bit .
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please explain the 3d movie effect where the light moves in clockwise , fine but what about anti-clockwise and both simultaneously ?
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- let 's talk about polarization of light . we know what light waves are ; they 're electromagnetic waves . so they 're made out of electric fields . and that 's not good enough . we know there 's not just electric fields . that could n't sustain itself . there 's got to be magnetic fields there , as well , that are changing . those are perpendicular , so you can kind of draw them . it 's hard , on something two-dimensional , but you can kind of imagine those looking something like this . and those magnetic fields would point at a right angle to the electric fields . but this gets really messy if i try to draw both the electric and magnetic fields at the same time . so we 're going to leave the magnetic fields out . it 's often good enough to just know the direction of the electric field when we focus on the electric field . so what does polarization mean ? polarization refers to the fact that , if this light ray was heading straight toward your eye , or a detector , over here , what would you see ? well , if i draw an axis over here , and this point here , in the middle , this is this line -- so imagine we 're looking straight down that line -- and then up and down is up and down , and then left and right , that direction i have the magnetic field , would be this way and that way . what would my eye see ? well , my eye 's only going to see electric fields that either point up or electric fields that point down . they might have different values , but i 'm only going to see electric fields that point up or down . because of that , this light ray is polarized . so polarized light is light where the electric field is only oscillating in one direction . up or down , that 's one direction -- vertically . or it could be polarized horizontally . or it could be polarized diagonally . but either way , you could have this wave polarized along any direction . i mean , a light ray like this , if we had it coming in diagonal , this light ray that 's oscillating like this , where the electric field oscillates like that , that also polarized . these are both polarized because there 's only one direction that the electric field is oscillating in . and you might thing , `` pff , how could you ever have `` a light ray that 's not polarized ? '' easy . most light that you get is not polarized . that is to say , light that 's coming from the sun , straight from the sun -- typically not polarized . light from a lightbulb , an old incandescent light bulb , this thing 's hot . you can get light polarized in any direction , all at once , all overlapping . so if we draw this case for a light bulb , just a random incandescent light bulb , you might get light , some of the light , hitting you eye , you can get some light that 's got that direction , you got light that 's got this direction , you got light in all these directions at any given moment . i mean , you 'd have to add these up to get the total , and they might not all be the same value . but what i 'm trying to say is , at any given moment , you do n't know what direction the electric field 's going to be hitting your eye at from a random source . it could be in any direction . so this is not polarized . this diagram represents light that is not polarized . at some point , the field might be pointing this way , at some later point it 's this way ; it 's just random . you never know which way the electric field 's going to be pointing . whereas these over here , these are polarized . so how could you polarize this light ? let 's say you wanted light that was polarized . you were doing an experiment . you needed polarized light . well , that 's easy . you can use what 's called a polarizer . and this is a material that lets light through , but it only lets light through in one orientation , so you 're going to have a polarizer that , for instance , only lets through vertically polarized light . so this is a polarizer . these are cheap : thin , plastic , configured in a way so that it only lets light through that 's vertically polarized . any light coming in here that 's not vertically polarized gets blocked , or absorbed . so what that means is , if you used this polarizer and held it in between your eye and this light bulb , you would only get this light . all the rest of it would get blocked . or you could just rotate this thing and imagine a polarizer that only lets through horizontal light . now it would only let through light that was this way , and so you would only get this part of the light . or you could just orient it at any angle you want and block everything but the certain angle that this polarizer is defined as letting light through . so you can do this . and once you hold this up , you get polarized light , light that 's only got one orientation . so that 's what polarization means . but why do we care about polarization ? well , let me get rid of this for a minute . you 've heard of polarized sunglasses . so imagine you 're standing near water , or maybe you 're standing on ice or snow or something reflective . there 's a problem . say the sun 's out . it 's shining . it 's a beautiful day -- except there 's going to be glare . let 's say you 're looking down at something here on the ground . it 's going to get light reflecting off of it from just ... you know , light 's coming in from all direction . but it also gets this direct light from the sun . so it gets light from reflected off the clouds and whatever , whatever 's nearby , ambient light . and there 's also this direct sunlight . that 's harsh . if that reflects straight up to your eye , that hurts . you do n't like that . it blocks our vision . it 's hard to see , it 's glare . we do n't want this glare . so what can we do ? well , it just so happens that , when light reflects off of a surface , even though the light from the sun is not polarized , once it reflects , it does get polarized or at least partially polarized . so this surface here , once this light reflects , it 's coming in at all orientations . you got electric field ... you never know what electric field you 're going to get straight from the sun . and when it reflects , though , you mostly get , upon reflection , the direction of polarization defined by the plane of the surface that it hit . so because the floor is horizontal , when this light ray hits the ground and reflects , that reflected light gets partially polarized . this horizontal component of the electric field is going to be more present than the other components . maybe not completely . sometimes it could be . it could be completely polarized , but often it 's just partially polarized . but that 's pretty cool , because now you know what we can do . i know how to block this . we should get some sunglasses . we put some sunglasses on and we make our glasses so that these are polarized . and how do we want these polarized ? i want to get rid of the glare . so what i do is , i make sure my sunglasses only let through vertically polarized light . here 's some polarizers . that way , a lot of this glare gets blocked because it does not have a vertical orientation , it has a horizontal orientation . and then we can block it . so that 's one good thing that polarization does for us , and understanding it , we can get rid of glare . also , fishermen like it because , if you 're trying to look in the water at fish , you want to see in through the water , you want to see this light from the fish getting to you . you do n't want to see the glare off of the sun getting to you . so polarized sunglasses are useful . also , we can play a trick on our eye , if we really wanted to . you could take one of these , make one eye have a vertical orientation for the polarization , have the other eye with a horizontal ... and you 're thinking , `` this is stupid . `` why would you do this for ? '' `` this eye 's going to get a lot of glare . '' we would n't use these outside , when you 're , like , skiing or fishing , but you could play a trick on your eyes if you went to the movies and you went and watched a movie . well , the reason our eyes see 3d is because they 're spaced a little bit apart . they each get a different , slightly different image . that makes us see in 3d . we can play the same trick on our eye if we have the polarization like this . if light , if some of the light from the movie theater screen is coming in with one polarization , and the other light 's coming in with the other polarization , we can send two different images to our eyes at the same time . if you took these off , it 'd look like garbage because you 'd be getting both of these slightly different images , it 'd look all blurry . and it does . if you take off your 3d glasses and look at a 3d movie , looks terrible , because now both eyes are getting both images . but if you put your glasses back on , now this eye only gets the orientation that it 's supposed to get , and this eye only gets the orientation that it 's supposed to get , and you get a 3d image . so it 's useful in many ways . let me show you one more thing here . let 's come back here . this light was polarized vertically . so that 's called linear polarization . any time ... same with these . these are all linear polarization because , just up and down , one linear direction , just diagonal . this is also linear . all of these are linear . you can get circular polarized light . so if we come back to here , we 've got our electric field pointing up , like that . now let 's say we sent in another light ray , another light ray that also had a polarization , but not in this direction . let 's say our other light ray had polarization in this direction , so it looks like this , kind of like what our magnetic field would have looked like . but this is a completely different light ray with its own polarization and its own magnetic field . so we send this in . what would happen ? well , at this point , you 'd have a electric field that points this way . at this point , you 'd have a electric field that points that way . what would your eye see if you were over here ? let 's see . if i draw our axis here . all right , when this point right here gets to your eye , what am i going to see ? well , i 'm going to have a light ray that 's one part of a light ray . one component points up . that 's this electric field . one component points left . that 's this electric field . so the total , my total electric field , would point this way . i could to the pythagorean theorem if i wanted to figure out the size of it , but i just want to know the direction for now . and then it gets to here , and look at it : they both have zero . this light ray has zero electric field , this one has zero electric fields . so then it 'd just be at zero . now what happens over here ? well , i 've got light . this one points to the right at that point , this pink one , and then this red one would be pointing down . so what would i have at that point ? i 'd have light that went this way , and it would just be doing this over and over . it would just be ... i 'd just have diagonally polarized light . this is n't giving me anything new . you might think this is dumb . why do this ? why send in two different waves to just get diagonally polarized light ? i could have just sent in one wave that was diagonally polarized and got the same thing . the reason is , if you shift this purple wave , this pink wave , by 90 degrees of phase , by pi over two in phase , something magical happens . let me show you what happens here , if we move this to here . now we do n't just get diagonally linear polarized light . what we 're going to get is ... let me get rid of this . okay , so we start off with red , right ? the red electric field points up , and then this pink wave 's electric field is zero at that point . so this is all i have . my total electric field would just be up . i 'm going to draw it right here . the green 'll be the total . now i come over to here , and at this point , there 's some red electric field that points up , but there 's some of this other electric field that points this way . so i 'd have a total electric field that would point that way . and then i get over to here , and i 'd have all of the electric field from the pink one , none from the red one . it would point all left then . look what 's happening . the polarization of this light , if i shift this , if i 'm sitting here , looking with my eye , as my eye receives this light , i 'm going to see this light rotate its polarization . the polarization i 'm going to notice swings around in a circular pattern . and because of this , we call this circular polarization . so this is another type of polarization , where the actual angle of polarization rotates smoothly as this light ray enters your eye . and you know what ? er , drrr ... all right , actually , i sent you to receive this one first . that makes no sense . you 're going to receive the ones closes to you first in this light ray going this way . so you 'd actually receive this one first , then that one , then this one , then this one . because of that , you would n't see this going in a counterclockwise way , you 'd see this going in a clockwise circularly polarized way . sorry about that . you might think , `` okay , why ? `` why even bother with circular polarization ? '' well , i kind of lied earlier . turns out , in the movie theater example , they do n't actually do it like this , typically . oftentimes in the movie theaters , we do n't have just linearly polarized sunglasses . this would be a problem because , when you look at the movie theater screen , and if you were to tilt your head just a little bit ... think about it . this one 's not really going to get the right image anymore . it 's going to get some of both . and this one 's going to get some of both . it 's going to be blurry . your head would have to be perfectly level the whole time , which might be annoying . so what we do is , instead , we create circular polarized glasses , so that this one would only get one polarization , this one would get the other direction . this way , even if you tilt your head a little bit ... shoot , clockwise is clockwise , counterclockwise is counterclockwise . by using circular polarization for 3d movies , it can make it a little easier on you eyes to see a better 3d image , even if your head 's tilted a little bit .
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well , the reason our eyes see 3d is because they 're spaced a little bit apart . they each get a different , slightly different image . that makes us see in 3d .
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we use glasses with different polarization for different purposes..but i did n't get why even use them ( except the 3d movie example ) ?
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- let 's talk about polarization of light . we know what light waves are ; they 're electromagnetic waves . so they 're made out of electric fields . and that 's not good enough . we know there 's not just electric fields . that could n't sustain itself . there 's got to be magnetic fields there , as well , that are changing . those are perpendicular , so you can kind of draw them . it 's hard , on something two-dimensional , but you can kind of imagine those looking something like this . and those magnetic fields would point at a right angle to the electric fields . but this gets really messy if i try to draw both the electric and magnetic fields at the same time . so we 're going to leave the magnetic fields out . it 's often good enough to just know the direction of the electric field when we focus on the electric field . so what does polarization mean ? polarization refers to the fact that , if this light ray was heading straight toward your eye , or a detector , over here , what would you see ? well , if i draw an axis over here , and this point here , in the middle , this is this line -- so imagine we 're looking straight down that line -- and then up and down is up and down , and then left and right , that direction i have the magnetic field , would be this way and that way . what would my eye see ? well , my eye 's only going to see electric fields that either point up or electric fields that point down . they might have different values , but i 'm only going to see electric fields that point up or down . because of that , this light ray is polarized . so polarized light is light where the electric field is only oscillating in one direction . up or down , that 's one direction -- vertically . or it could be polarized horizontally . or it could be polarized diagonally . but either way , you could have this wave polarized along any direction . i mean , a light ray like this , if we had it coming in diagonal , this light ray that 's oscillating like this , where the electric field oscillates like that , that also polarized . these are both polarized because there 's only one direction that the electric field is oscillating in . and you might thing , `` pff , how could you ever have `` a light ray that 's not polarized ? '' easy . most light that you get is not polarized . that is to say , light that 's coming from the sun , straight from the sun -- typically not polarized . light from a lightbulb , an old incandescent light bulb , this thing 's hot . you can get light polarized in any direction , all at once , all overlapping . so if we draw this case for a light bulb , just a random incandescent light bulb , you might get light , some of the light , hitting you eye , you can get some light that 's got that direction , you got light that 's got this direction , you got light in all these directions at any given moment . i mean , you 'd have to add these up to get the total , and they might not all be the same value . but what i 'm trying to say is , at any given moment , you do n't know what direction the electric field 's going to be hitting your eye at from a random source . it could be in any direction . so this is not polarized . this diagram represents light that is not polarized . at some point , the field might be pointing this way , at some later point it 's this way ; it 's just random . you never know which way the electric field 's going to be pointing . whereas these over here , these are polarized . so how could you polarize this light ? let 's say you wanted light that was polarized . you were doing an experiment . you needed polarized light . well , that 's easy . you can use what 's called a polarizer . and this is a material that lets light through , but it only lets light through in one orientation , so you 're going to have a polarizer that , for instance , only lets through vertically polarized light . so this is a polarizer . these are cheap : thin , plastic , configured in a way so that it only lets light through that 's vertically polarized . any light coming in here that 's not vertically polarized gets blocked , or absorbed . so what that means is , if you used this polarizer and held it in between your eye and this light bulb , you would only get this light . all the rest of it would get blocked . or you could just rotate this thing and imagine a polarizer that only lets through horizontal light . now it would only let through light that was this way , and so you would only get this part of the light . or you could just orient it at any angle you want and block everything but the certain angle that this polarizer is defined as letting light through . so you can do this . and once you hold this up , you get polarized light , light that 's only got one orientation . so that 's what polarization means . but why do we care about polarization ? well , let me get rid of this for a minute . you 've heard of polarized sunglasses . so imagine you 're standing near water , or maybe you 're standing on ice or snow or something reflective . there 's a problem . say the sun 's out . it 's shining . it 's a beautiful day -- except there 's going to be glare . let 's say you 're looking down at something here on the ground . it 's going to get light reflecting off of it from just ... you know , light 's coming in from all direction . but it also gets this direct light from the sun . so it gets light from reflected off the clouds and whatever , whatever 's nearby , ambient light . and there 's also this direct sunlight . that 's harsh . if that reflects straight up to your eye , that hurts . you do n't like that . it blocks our vision . it 's hard to see , it 's glare . we do n't want this glare . so what can we do ? well , it just so happens that , when light reflects off of a surface , even though the light from the sun is not polarized , once it reflects , it does get polarized or at least partially polarized . so this surface here , once this light reflects , it 's coming in at all orientations . you got electric field ... you never know what electric field you 're going to get straight from the sun . and when it reflects , though , you mostly get , upon reflection , the direction of polarization defined by the plane of the surface that it hit . so because the floor is horizontal , when this light ray hits the ground and reflects , that reflected light gets partially polarized . this horizontal component of the electric field is going to be more present than the other components . maybe not completely . sometimes it could be . it could be completely polarized , but often it 's just partially polarized . but that 's pretty cool , because now you know what we can do . i know how to block this . we should get some sunglasses . we put some sunglasses on and we make our glasses so that these are polarized . and how do we want these polarized ? i want to get rid of the glare . so what i do is , i make sure my sunglasses only let through vertically polarized light . here 's some polarizers . that way , a lot of this glare gets blocked because it does not have a vertical orientation , it has a horizontal orientation . and then we can block it . so that 's one good thing that polarization does for us , and understanding it , we can get rid of glare . also , fishermen like it because , if you 're trying to look in the water at fish , you want to see in through the water , you want to see this light from the fish getting to you . you do n't want to see the glare off of the sun getting to you . so polarized sunglasses are useful . also , we can play a trick on our eye , if we really wanted to . you could take one of these , make one eye have a vertical orientation for the polarization , have the other eye with a horizontal ... and you 're thinking , `` this is stupid . `` why would you do this for ? '' `` this eye 's going to get a lot of glare . '' we would n't use these outside , when you 're , like , skiing or fishing , but you could play a trick on your eyes if you went to the movies and you went and watched a movie . well , the reason our eyes see 3d is because they 're spaced a little bit apart . they each get a different , slightly different image . that makes us see in 3d . we can play the same trick on our eye if we have the polarization like this . if light , if some of the light from the movie theater screen is coming in with one polarization , and the other light 's coming in with the other polarization , we can send two different images to our eyes at the same time . if you took these off , it 'd look like garbage because you 'd be getting both of these slightly different images , it 'd look all blurry . and it does . if you take off your 3d glasses and look at a 3d movie , looks terrible , because now both eyes are getting both images . but if you put your glasses back on , now this eye only gets the orientation that it 's supposed to get , and this eye only gets the orientation that it 's supposed to get , and you get a 3d image . so it 's useful in many ways . let me show you one more thing here . let 's come back here . this light was polarized vertically . so that 's called linear polarization . any time ... same with these . these are all linear polarization because , just up and down , one linear direction , just diagonal . this is also linear . all of these are linear . you can get circular polarized light . so if we come back to here , we 've got our electric field pointing up , like that . now let 's say we sent in another light ray , another light ray that also had a polarization , but not in this direction . let 's say our other light ray had polarization in this direction , so it looks like this , kind of like what our magnetic field would have looked like . but this is a completely different light ray with its own polarization and its own magnetic field . so we send this in . what would happen ? well , at this point , you 'd have a electric field that points this way . at this point , you 'd have a electric field that points that way . what would your eye see if you were over here ? let 's see . if i draw our axis here . all right , when this point right here gets to your eye , what am i going to see ? well , i 'm going to have a light ray that 's one part of a light ray . one component points up . that 's this electric field . one component points left . that 's this electric field . so the total , my total electric field , would point this way . i could to the pythagorean theorem if i wanted to figure out the size of it , but i just want to know the direction for now . and then it gets to here , and look at it : they both have zero . this light ray has zero electric field , this one has zero electric fields . so then it 'd just be at zero . now what happens over here ? well , i 've got light . this one points to the right at that point , this pink one , and then this red one would be pointing down . so what would i have at that point ? i 'd have light that went this way , and it would just be doing this over and over . it would just be ... i 'd just have diagonally polarized light . this is n't giving me anything new . you might think this is dumb . why do this ? why send in two different waves to just get diagonally polarized light ? i could have just sent in one wave that was diagonally polarized and got the same thing . the reason is , if you shift this purple wave , this pink wave , by 90 degrees of phase , by pi over two in phase , something magical happens . let me show you what happens here , if we move this to here . now we do n't just get diagonally linear polarized light . what we 're going to get is ... let me get rid of this . okay , so we start off with red , right ? the red electric field points up , and then this pink wave 's electric field is zero at that point . so this is all i have . my total electric field would just be up . i 'm going to draw it right here . the green 'll be the total . now i come over to here , and at this point , there 's some red electric field that points up , but there 's some of this other electric field that points this way . so i 'd have a total electric field that would point that way . and then i get over to here , and i 'd have all of the electric field from the pink one , none from the red one . it would point all left then . look what 's happening . the polarization of this light , if i shift this , if i 'm sitting here , looking with my eye , as my eye receives this light , i 'm going to see this light rotate its polarization . the polarization i 'm going to notice swings around in a circular pattern . and because of this , we call this circular polarization . so this is another type of polarization , where the actual angle of polarization rotates smoothly as this light ray enters your eye . and you know what ? er , drrr ... all right , actually , i sent you to receive this one first . that makes no sense . you 're going to receive the ones closes to you first in this light ray going this way . so you 'd actually receive this one first , then that one , then this one , then this one . because of that , you would n't see this going in a counterclockwise way , you 'd see this going in a clockwise circularly polarized way . sorry about that . you might think , `` okay , why ? `` why even bother with circular polarization ? '' well , i kind of lied earlier . turns out , in the movie theater example , they do n't actually do it like this , typically . oftentimes in the movie theaters , we do n't have just linearly polarized sunglasses . this would be a problem because , when you look at the movie theater screen , and if you were to tilt your head just a little bit ... think about it . this one 's not really going to get the right image anymore . it 's going to get some of both . and this one 's going to get some of both . it 's going to be blurry . your head would have to be perfectly level the whole time , which might be annoying . so what we do is , instead , we create circular polarized glasses , so that this one would only get one polarization , this one would get the other direction . this way , even if you tilt your head a little bit ... shoot , clockwise is clockwise , counterclockwise is counterclockwise . by using circular polarization for 3d movies , it can make it a little easier on you eyes to see a better 3d image , even if your head 's tilted a little bit .
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you were doing an experiment . you needed polarized light . well , that 's easy .
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velocity of wave is perpendicular to direction of electric field , so they must be always polarized ; i think i still have n't got the concept of polarization , and difference in properties of polarized an d non polarized light , can anyone help ?
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- let 's talk about polarization of light . we know what light waves are ; they 're electromagnetic waves . so they 're made out of electric fields . and that 's not good enough . we know there 's not just electric fields . that could n't sustain itself . there 's got to be magnetic fields there , as well , that are changing . those are perpendicular , so you can kind of draw them . it 's hard , on something two-dimensional , but you can kind of imagine those looking something like this . and those magnetic fields would point at a right angle to the electric fields . but this gets really messy if i try to draw both the electric and magnetic fields at the same time . so we 're going to leave the magnetic fields out . it 's often good enough to just know the direction of the electric field when we focus on the electric field . so what does polarization mean ? polarization refers to the fact that , if this light ray was heading straight toward your eye , or a detector , over here , what would you see ? well , if i draw an axis over here , and this point here , in the middle , this is this line -- so imagine we 're looking straight down that line -- and then up and down is up and down , and then left and right , that direction i have the magnetic field , would be this way and that way . what would my eye see ? well , my eye 's only going to see electric fields that either point up or electric fields that point down . they might have different values , but i 'm only going to see electric fields that point up or down . because of that , this light ray is polarized . so polarized light is light where the electric field is only oscillating in one direction . up or down , that 's one direction -- vertically . or it could be polarized horizontally . or it could be polarized diagonally . but either way , you could have this wave polarized along any direction . i mean , a light ray like this , if we had it coming in diagonal , this light ray that 's oscillating like this , where the electric field oscillates like that , that also polarized . these are both polarized because there 's only one direction that the electric field is oscillating in . and you might thing , `` pff , how could you ever have `` a light ray that 's not polarized ? '' easy . most light that you get is not polarized . that is to say , light that 's coming from the sun , straight from the sun -- typically not polarized . light from a lightbulb , an old incandescent light bulb , this thing 's hot . you can get light polarized in any direction , all at once , all overlapping . so if we draw this case for a light bulb , just a random incandescent light bulb , you might get light , some of the light , hitting you eye , you can get some light that 's got that direction , you got light that 's got this direction , you got light in all these directions at any given moment . i mean , you 'd have to add these up to get the total , and they might not all be the same value . but what i 'm trying to say is , at any given moment , you do n't know what direction the electric field 's going to be hitting your eye at from a random source . it could be in any direction . so this is not polarized . this diagram represents light that is not polarized . at some point , the field might be pointing this way , at some later point it 's this way ; it 's just random . you never know which way the electric field 's going to be pointing . whereas these over here , these are polarized . so how could you polarize this light ? let 's say you wanted light that was polarized . you were doing an experiment . you needed polarized light . well , that 's easy . you can use what 's called a polarizer . and this is a material that lets light through , but it only lets light through in one orientation , so you 're going to have a polarizer that , for instance , only lets through vertically polarized light . so this is a polarizer . these are cheap : thin , plastic , configured in a way so that it only lets light through that 's vertically polarized . any light coming in here that 's not vertically polarized gets blocked , or absorbed . so what that means is , if you used this polarizer and held it in between your eye and this light bulb , you would only get this light . all the rest of it would get blocked . or you could just rotate this thing and imagine a polarizer that only lets through horizontal light . now it would only let through light that was this way , and so you would only get this part of the light . or you could just orient it at any angle you want and block everything but the certain angle that this polarizer is defined as letting light through . so you can do this . and once you hold this up , you get polarized light , light that 's only got one orientation . so that 's what polarization means . but why do we care about polarization ? well , let me get rid of this for a minute . you 've heard of polarized sunglasses . so imagine you 're standing near water , or maybe you 're standing on ice or snow or something reflective . there 's a problem . say the sun 's out . it 's shining . it 's a beautiful day -- except there 's going to be glare . let 's say you 're looking down at something here on the ground . it 's going to get light reflecting off of it from just ... you know , light 's coming in from all direction . but it also gets this direct light from the sun . so it gets light from reflected off the clouds and whatever , whatever 's nearby , ambient light . and there 's also this direct sunlight . that 's harsh . if that reflects straight up to your eye , that hurts . you do n't like that . it blocks our vision . it 's hard to see , it 's glare . we do n't want this glare . so what can we do ? well , it just so happens that , when light reflects off of a surface , even though the light from the sun is not polarized , once it reflects , it does get polarized or at least partially polarized . so this surface here , once this light reflects , it 's coming in at all orientations . you got electric field ... you never know what electric field you 're going to get straight from the sun . and when it reflects , though , you mostly get , upon reflection , the direction of polarization defined by the plane of the surface that it hit . so because the floor is horizontal , when this light ray hits the ground and reflects , that reflected light gets partially polarized . this horizontal component of the electric field is going to be more present than the other components . maybe not completely . sometimes it could be . it could be completely polarized , but often it 's just partially polarized . but that 's pretty cool , because now you know what we can do . i know how to block this . we should get some sunglasses . we put some sunglasses on and we make our glasses so that these are polarized . and how do we want these polarized ? i want to get rid of the glare . so what i do is , i make sure my sunglasses only let through vertically polarized light . here 's some polarizers . that way , a lot of this glare gets blocked because it does not have a vertical orientation , it has a horizontal orientation . and then we can block it . so that 's one good thing that polarization does for us , and understanding it , we can get rid of glare . also , fishermen like it because , if you 're trying to look in the water at fish , you want to see in through the water , you want to see this light from the fish getting to you . you do n't want to see the glare off of the sun getting to you . so polarized sunglasses are useful . also , we can play a trick on our eye , if we really wanted to . you could take one of these , make one eye have a vertical orientation for the polarization , have the other eye with a horizontal ... and you 're thinking , `` this is stupid . `` why would you do this for ? '' `` this eye 's going to get a lot of glare . '' we would n't use these outside , when you 're , like , skiing or fishing , but you could play a trick on your eyes if you went to the movies and you went and watched a movie . well , the reason our eyes see 3d is because they 're spaced a little bit apart . they each get a different , slightly different image . that makes us see in 3d . we can play the same trick on our eye if we have the polarization like this . if light , if some of the light from the movie theater screen is coming in with one polarization , and the other light 's coming in with the other polarization , we can send two different images to our eyes at the same time . if you took these off , it 'd look like garbage because you 'd be getting both of these slightly different images , it 'd look all blurry . and it does . if you take off your 3d glasses and look at a 3d movie , looks terrible , because now both eyes are getting both images . but if you put your glasses back on , now this eye only gets the orientation that it 's supposed to get , and this eye only gets the orientation that it 's supposed to get , and you get a 3d image . so it 's useful in many ways . let me show you one more thing here . let 's come back here . this light was polarized vertically . so that 's called linear polarization . any time ... same with these . these are all linear polarization because , just up and down , one linear direction , just diagonal . this is also linear . all of these are linear . you can get circular polarized light . so if we come back to here , we 've got our electric field pointing up , like that . now let 's say we sent in another light ray , another light ray that also had a polarization , but not in this direction . let 's say our other light ray had polarization in this direction , so it looks like this , kind of like what our magnetic field would have looked like . but this is a completely different light ray with its own polarization and its own magnetic field . so we send this in . what would happen ? well , at this point , you 'd have a electric field that points this way . at this point , you 'd have a electric field that points that way . what would your eye see if you were over here ? let 's see . if i draw our axis here . all right , when this point right here gets to your eye , what am i going to see ? well , i 'm going to have a light ray that 's one part of a light ray . one component points up . that 's this electric field . one component points left . that 's this electric field . so the total , my total electric field , would point this way . i could to the pythagorean theorem if i wanted to figure out the size of it , but i just want to know the direction for now . and then it gets to here , and look at it : they both have zero . this light ray has zero electric field , this one has zero electric fields . so then it 'd just be at zero . now what happens over here ? well , i 've got light . this one points to the right at that point , this pink one , and then this red one would be pointing down . so what would i have at that point ? i 'd have light that went this way , and it would just be doing this over and over . it would just be ... i 'd just have diagonally polarized light . this is n't giving me anything new . you might think this is dumb . why do this ? why send in two different waves to just get diagonally polarized light ? i could have just sent in one wave that was diagonally polarized and got the same thing . the reason is , if you shift this purple wave , this pink wave , by 90 degrees of phase , by pi over two in phase , something magical happens . let me show you what happens here , if we move this to here . now we do n't just get diagonally linear polarized light . what we 're going to get is ... let me get rid of this . okay , so we start off with red , right ? the red electric field points up , and then this pink wave 's electric field is zero at that point . so this is all i have . my total electric field would just be up . i 'm going to draw it right here . the green 'll be the total . now i come over to here , and at this point , there 's some red electric field that points up , but there 's some of this other electric field that points this way . so i 'd have a total electric field that would point that way . and then i get over to here , and i 'd have all of the electric field from the pink one , none from the red one . it would point all left then . look what 's happening . the polarization of this light , if i shift this , if i 'm sitting here , looking with my eye , as my eye receives this light , i 'm going to see this light rotate its polarization . the polarization i 'm going to notice swings around in a circular pattern . and because of this , we call this circular polarization . so this is another type of polarization , where the actual angle of polarization rotates smoothly as this light ray enters your eye . and you know what ? er , drrr ... all right , actually , i sent you to receive this one first . that makes no sense . you 're going to receive the ones closes to you first in this light ray going this way . so you 'd actually receive this one first , then that one , then this one , then this one . because of that , you would n't see this going in a counterclockwise way , you 'd see this going in a clockwise circularly polarized way . sorry about that . you might think , `` okay , why ? `` why even bother with circular polarization ? '' well , i kind of lied earlier . turns out , in the movie theater example , they do n't actually do it like this , typically . oftentimes in the movie theaters , we do n't have just linearly polarized sunglasses . this would be a problem because , when you look at the movie theater screen , and if you were to tilt your head just a little bit ... think about it . this one 's not really going to get the right image anymore . it 's going to get some of both . and this one 's going to get some of both . it 's going to be blurry . your head would have to be perfectly level the whole time , which might be annoying . so what we do is , instead , we create circular polarized glasses , so that this one would only get one polarization , this one would get the other direction . this way , even if you tilt your head a little bit ... shoot , clockwise is clockwise , counterclockwise is counterclockwise . by using circular polarization for 3d movies , it can make it a little easier on you eyes to see a better 3d image , even if your head 's tilted a little bit .
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we know what light waves are ; they 're electromagnetic waves . so they 're made out of electric fields . and that 's not good enough .
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how is a movie made 3-d ?
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- let 's talk about polarization of light . we know what light waves are ; they 're electromagnetic waves . so they 're made out of electric fields . and that 's not good enough . we know there 's not just electric fields . that could n't sustain itself . there 's got to be magnetic fields there , as well , that are changing . those are perpendicular , so you can kind of draw them . it 's hard , on something two-dimensional , but you can kind of imagine those looking something like this . and those magnetic fields would point at a right angle to the electric fields . but this gets really messy if i try to draw both the electric and magnetic fields at the same time . so we 're going to leave the magnetic fields out . it 's often good enough to just know the direction of the electric field when we focus on the electric field . so what does polarization mean ? polarization refers to the fact that , if this light ray was heading straight toward your eye , or a detector , over here , what would you see ? well , if i draw an axis over here , and this point here , in the middle , this is this line -- so imagine we 're looking straight down that line -- and then up and down is up and down , and then left and right , that direction i have the magnetic field , would be this way and that way . what would my eye see ? well , my eye 's only going to see electric fields that either point up or electric fields that point down . they might have different values , but i 'm only going to see electric fields that point up or down . because of that , this light ray is polarized . so polarized light is light where the electric field is only oscillating in one direction . up or down , that 's one direction -- vertically . or it could be polarized horizontally . or it could be polarized diagonally . but either way , you could have this wave polarized along any direction . i mean , a light ray like this , if we had it coming in diagonal , this light ray that 's oscillating like this , where the electric field oscillates like that , that also polarized . these are both polarized because there 's only one direction that the electric field is oscillating in . and you might thing , `` pff , how could you ever have `` a light ray that 's not polarized ? '' easy . most light that you get is not polarized . that is to say , light that 's coming from the sun , straight from the sun -- typically not polarized . light from a lightbulb , an old incandescent light bulb , this thing 's hot . you can get light polarized in any direction , all at once , all overlapping . so if we draw this case for a light bulb , just a random incandescent light bulb , you might get light , some of the light , hitting you eye , you can get some light that 's got that direction , you got light that 's got this direction , you got light in all these directions at any given moment . i mean , you 'd have to add these up to get the total , and they might not all be the same value . but what i 'm trying to say is , at any given moment , you do n't know what direction the electric field 's going to be hitting your eye at from a random source . it could be in any direction . so this is not polarized . this diagram represents light that is not polarized . at some point , the field might be pointing this way , at some later point it 's this way ; it 's just random . you never know which way the electric field 's going to be pointing . whereas these over here , these are polarized . so how could you polarize this light ? let 's say you wanted light that was polarized . you were doing an experiment . you needed polarized light . well , that 's easy . you can use what 's called a polarizer . and this is a material that lets light through , but it only lets light through in one orientation , so you 're going to have a polarizer that , for instance , only lets through vertically polarized light . so this is a polarizer . these are cheap : thin , plastic , configured in a way so that it only lets light through that 's vertically polarized . any light coming in here that 's not vertically polarized gets blocked , or absorbed . so what that means is , if you used this polarizer and held it in between your eye and this light bulb , you would only get this light . all the rest of it would get blocked . or you could just rotate this thing and imagine a polarizer that only lets through horizontal light . now it would only let through light that was this way , and so you would only get this part of the light . or you could just orient it at any angle you want and block everything but the certain angle that this polarizer is defined as letting light through . so you can do this . and once you hold this up , you get polarized light , light that 's only got one orientation . so that 's what polarization means . but why do we care about polarization ? well , let me get rid of this for a minute . you 've heard of polarized sunglasses . so imagine you 're standing near water , or maybe you 're standing on ice or snow or something reflective . there 's a problem . say the sun 's out . it 's shining . it 's a beautiful day -- except there 's going to be glare . let 's say you 're looking down at something here on the ground . it 's going to get light reflecting off of it from just ... you know , light 's coming in from all direction . but it also gets this direct light from the sun . so it gets light from reflected off the clouds and whatever , whatever 's nearby , ambient light . and there 's also this direct sunlight . that 's harsh . if that reflects straight up to your eye , that hurts . you do n't like that . it blocks our vision . it 's hard to see , it 's glare . we do n't want this glare . so what can we do ? well , it just so happens that , when light reflects off of a surface , even though the light from the sun is not polarized , once it reflects , it does get polarized or at least partially polarized . so this surface here , once this light reflects , it 's coming in at all orientations . you got electric field ... you never know what electric field you 're going to get straight from the sun . and when it reflects , though , you mostly get , upon reflection , the direction of polarization defined by the plane of the surface that it hit . so because the floor is horizontal , when this light ray hits the ground and reflects , that reflected light gets partially polarized . this horizontal component of the electric field is going to be more present than the other components . maybe not completely . sometimes it could be . it could be completely polarized , but often it 's just partially polarized . but that 's pretty cool , because now you know what we can do . i know how to block this . we should get some sunglasses . we put some sunglasses on and we make our glasses so that these are polarized . and how do we want these polarized ? i want to get rid of the glare . so what i do is , i make sure my sunglasses only let through vertically polarized light . here 's some polarizers . that way , a lot of this glare gets blocked because it does not have a vertical orientation , it has a horizontal orientation . and then we can block it . so that 's one good thing that polarization does for us , and understanding it , we can get rid of glare . also , fishermen like it because , if you 're trying to look in the water at fish , you want to see in through the water , you want to see this light from the fish getting to you . you do n't want to see the glare off of the sun getting to you . so polarized sunglasses are useful . also , we can play a trick on our eye , if we really wanted to . you could take one of these , make one eye have a vertical orientation for the polarization , have the other eye with a horizontal ... and you 're thinking , `` this is stupid . `` why would you do this for ? '' `` this eye 's going to get a lot of glare . '' we would n't use these outside , when you 're , like , skiing or fishing , but you could play a trick on your eyes if you went to the movies and you went and watched a movie . well , the reason our eyes see 3d is because they 're spaced a little bit apart . they each get a different , slightly different image . that makes us see in 3d . we can play the same trick on our eye if we have the polarization like this . if light , if some of the light from the movie theater screen is coming in with one polarization , and the other light 's coming in with the other polarization , we can send two different images to our eyes at the same time . if you took these off , it 'd look like garbage because you 'd be getting both of these slightly different images , it 'd look all blurry . and it does . if you take off your 3d glasses and look at a 3d movie , looks terrible , because now both eyes are getting both images . but if you put your glasses back on , now this eye only gets the orientation that it 's supposed to get , and this eye only gets the orientation that it 's supposed to get , and you get a 3d image . so it 's useful in many ways . let me show you one more thing here . let 's come back here . this light was polarized vertically . so that 's called linear polarization . any time ... same with these . these are all linear polarization because , just up and down , one linear direction , just diagonal . this is also linear . all of these are linear . you can get circular polarized light . so if we come back to here , we 've got our electric field pointing up , like that . now let 's say we sent in another light ray , another light ray that also had a polarization , but not in this direction . let 's say our other light ray had polarization in this direction , so it looks like this , kind of like what our magnetic field would have looked like . but this is a completely different light ray with its own polarization and its own magnetic field . so we send this in . what would happen ? well , at this point , you 'd have a electric field that points this way . at this point , you 'd have a electric field that points that way . what would your eye see if you were over here ? let 's see . if i draw our axis here . all right , when this point right here gets to your eye , what am i going to see ? well , i 'm going to have a light ray that 's one part of a light ray . one component points up . that 's this electric field . one component points left . that 's this electric field . so the total , my total electric field , would point this way . i could to the pythagorean theorem if i wanted to figure out the size of it , but i just want to know the direction for now . and then it gets to here , and look at it : they both have zero . this light ray has zero electric field , this one has zero electric fields . so then it 'd just be at zero . now what happens over here ? well , i 've got light . this one points to the right at that point , this pink one , and then this red one would be pointing down . so what would i have at that point ? i 'd have light that went this way , and it would just be doing this over and over . it would just be ... i 'd just have diagonally polarized light . this is n't giving me anything new . you might think this is dumb . why do this ? why send in two different waves to just get diagonally polarized light ? i could have just sent in one wave that was diagonally polarized and got the same thing . the reason is , if you shift this purple wave , this pink wave , by 90 degrees of phase , by pi over two in phase , something magical happens . let me show you what happens here , if we move this to here . now we do n't just get diagonally linear polarized light . what we 're going to get is ... let me get rid of this . okay , so we start off with red , right ? the red electric field points up , and then this pink wave 's electric field is zero at that point . so this is all i have . my total electric field would just be up . i 'm going to draw it right here . the green 'll be the total . now i come over to here , and at this point , there 's some red electric field that points up , but there 's some of this other electric field that points this way . so i 'd have a total electric field that would point that way . and then i get over to here , and i 'd have all of the electric field from the pink one , none from the red one . it would point all left then . look what 's happening . the polarization of this light , if i shift this , if i 'm sitting here , looking with my eye , as my eye receives this light , i 'm going to see this light rotate its polarization . the polarization i 'm going to notice swings around in a circular pattern . and because of this , we call this circular polarization . so this is another type of polarization , where the actual angle of polarization rotates smoothly as this light ray enters your eye . and you know what ? er , drrr ... all right , actually , i sent you to receive this one first . that makes no sense . you 're going to receive the ones closes to you first in this light ray going this way . so you 'd actually receive this one first , then that one , then this one , then this one . because of that , you would n't see this going in a counterclockwise way , you 'd see this going in a clockwise circularly polarized way . sorry about that . you might think , `` okay , why ? `` why even bother with circular polarization ? '' well , i kind of lied earlier . turns out , in the movie theater example , they do n't actually do it like this , typically . oftentimes in the movie theaters , we do n't have just linearly polarized sunglasses . this would be a problem because , when you look at the movie theater screen , and if you were to tilt your head just a little bit ... think about it . this one 's not really going to get the right image anymore . it 's going to get some of both . and this one 's going to get some of both . it 's going to be blurry . your head would have to be perfectly level the whole time , which might be annoying . so what we do is , instead , we create circular polarized glasses , so that this one would only get one polarization , this one would get the other direction . this way , even if you tilt your head a little bit ... shoot , clockwise is clockwise , counterclockwise is counterclockwise . by using circular polarization for 3d movies , it can make it a little easier on you eyes to see a better 3d image , even if your head 's tilted a little bit .
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you 're going to receive the ones closes to you first in this light ray going this way . so you 'd actually receive this one first , then that one , then this one , then this one . because of that , you would n't see this going in a counterclockwise way , you 'd see this going in a clockwise circularly polarized way .
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do atoms in objects ( like an apple ) emit their own photon when hit by one of the sun 's photons ?
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- let 's talk about polarization of light . we know what light waves are ; they 're electromagnetic waves . so they 're made out of electric fields . and that 's not good enough . we know there 's not just electric fields . that could n't sustain itself . there 's got to be magnetic fields there , as well , that are changing . those are perpendicular , so you can kind of draw them . it 's hard , on something two-dimensional , but you can kind of imagine those looking something like this . and those magnetic fields would point at a right angle to the electric fields . but this gets really messy if i try to draw both the electric and magnetic fields at the same time . so we 're going to leave the magnetic fields out . it 's often good enough to just know the direction of the electric field when we focus on the electric field . so what does polarization mean ? polarization refers to the fact that , if this light ray was heading straight toward your eye , or a detector , over here , what would you see ? well , if i draw an axis over here , and this point here , in the middle , this is this line -- so imagine we 're looking straight down that line -- and then up and down is up and down , and then left and right , that direction i have the magnetic field , would be this way and that way . what would my eye see ? well , my eye 's only going to see electric fields that either point up or electric fields that point down . they might have different values , but i 'm only going to see electric fields that point up or down . because of that , this light ray is polarized . so polarized light is light where the electric field is only oscillating in one direction . up or down , that 's one direction -- vertically . or it could be polarized horizontally . or it could be polarized diagonally . but either way , you could have this wave polarized along any direction . i mean , a light ray like this , if we had it coming in diagonal , this light ray that 's oscillating like this , where the electric field oscillates like that , that also polarized . these are both polarized because there 's only one direction that the electric field is oscillating in . and you might thing , `` pff , how could you ever have `` a light ray that 's not polarized ? '' easy . most light that you get is not polarized . that is to say , light that 's coming from the sun , straight from the sun -- typically not polarized . light from a lightbulb , an old incandescent light bulb , this thing 's hot . you can get light polarized in any direction , all at once , all overlapping . so if we draw this case for a light bulb , just a random incandescent light bulb , you might get light , some of the light , hitting you eye , you can get some light that 's got that direction , you got light that 's got this direction , you got light in all these directions at any given moment . i mean , you 'd have to add these up to get the total , and they might not all be the same value . but what i 'm trying to say is , at any given moment , you do n't know what direction the electric field 's going to be hitting your eye at from a random source . it could be in any direction . so this is not polarized . this diagram represents light that is not polarized . at some point , the field might be pointing this way , at some later point it 's this way ; it 's just random . you never know which way the electric field 's going to be pointing . whereas these over here , these are polarized . so how could you polarize this light ? let 's say you wanted light that was polarized . you were doing an experiment . you needed polarized light . well , that 's easy . you can use what 's called a polarizer . and this is a material that lets light through , but it only lets light through in one orientation , so you 're going to have a polarizer that , for instance , only lets through vertically polarized light . so this is a polarizer . these are cheap : thin , plastic , configured in a way so that it only lets light through that 's vertically polarized . any light coming in here that 's not vertically polarized gets blocked , or absorbed . so what that means is , if you used this polarizer and held it in between your eye and this light bulb , you would only get this light . all the rest of it would get blocked . or you could just rotate this thing and imagine a polarizer that only lets through horizontal light . now it would only let through light that was this way , and so you would only get this part of the light . or you could just orient it at any angle you want and block everything but the certain angle that this polarizer is defined as letting light through . so you can do this . and once you hold this up , you get polarized light , light that 's only got one orientation . so that 's what polarization means . but why do we care about polarization ? well , let me get rid of this for a minute . you 've heard of polarized sunglasses . so imagine you 're standing near water , or maybe you 're standing on ice or snow or something reflective . there 's a problem . say the sun 's out . it 's shining . it 's a beautiful day -- except there 's going to be glare . let 's say you 're looking down at something here on the ground . it 's going to get light reflecting off of it from just ... you know , light 's coming in from all direction . but it also gets this direct light from the sun . so it gets light from reflected off the clouds and whatever , whatever 's nearby , ambient light . and there 's also this direct sunlight . that 's harsh . if that reflects straight up to your eye , that hurts . you do n't like that . it blocks our vision . it 's hard to see , it 's glare . we do n't want this glare . so what can we do ? well , it just so happens that , when light reflects off of a surface , even though the light from the sun is not polarized , once it reflects , it does get polarized or at least partially polarized . so this surface here , once this light reflects , it 's coming in at all orientations . you got electric field ... you never know what electric field you 're going to get straight from the sun . and when it reflects , though , you mostly get , upon reflection , the direction of polarization defined by the plane of the surface that it hit . so because the floor is horizontal , when this light ray hits the ground and reflects , that reflected light gets partially polarized . this horizontal component of the electric field is going to be more present than the other components . maybe not completely . sometimes it could be . it could be completely polarized , but often it 's just partially polarized . but that 's pretty cool , because now you know what we can do . i know how to block this . we should get some sunglasses . we put some sunglasses on and we make our glasses so that these are polarized . and how do we want these polarized ? i want to get rid of the glare . so what i do is , i make sure my sunglasses only let through vertically polarized light . here 's some polarizers . that way , a lot of this glare gets blocked because it does not have a vertical orientation , it has a horizontal orientation . and then we can block it . so that 's one good thing that polarization does for us , and understanding it , we can get rid of glare . also , fishermen like it because , if you 're trying to look in the water at fish , you want to see in through the water , you want to see this light from the fish getting to you . you do n't want to see the glare off of the sun getting to you . so polarized sunglasses are useful . also , we can play a trick on our eye , if we really wanted to . you could take one of these , make one eye have a vertical orientation for the polarization , have the other eye with a horizontal ... and you 're thinking , `` this is stupid . `` why would you do this for ? '' `` this eye 's going to get a lot of glare . '' we would n't use these outside , when you 're , like , skiing or fishing , but you could play a trick on your eyes if you went to the movies and you went and watched a movie . well , the reason our eyes see 3d is because they 're spaced a little bit apart . they each get a different , slightly different image . that makes us see in 3d . we can play the same trick on our eye if we have the polarization like this . if light , if some of the light from the movie theater screen is coming in with one polarization , and the other light 's coming in with the other polarization , we can send two different images to our eyes at the same time . if you took these off , it 'd look like garbage because you 'd be getting both of these slightly different images , it 'd look all blurry . and it does . if you take off your 3d glasses and look at a 3d movie , looks terrible , because now both eyes are getting both images . but if you put your glasses back on , now this eye only gets the orientation that it 's supposed to get , and this eye only gets the orientation that it 's supposed to get , and you get a 3d image . so it 's useful in many ways . let me show you one more thing here . let 's come back here . this light was polarized vertically . so that 's called linear polarization . any time ... same with these . these are all linear polarization because , just up and down , one linear direction , just diagonal . this is also linear . all of these are linear . you can get circular polarized light . so if we come back to here , we 've got our electric field pointing up , like that . now let 's say we sent in another light ray , another light ray that also had a polarization , but not in this direction . let 's say our other light ray had polarization in this direction , so it looks like this , kind of like what our magnetic field would have looked like . but this is a completely different light ray with its own polarization and its own magnetic field . so we send this in . what would happen ? well , at this point , you 'd have a electric field that points this way . at this point , you 'd have a electric field that points that way . what would your eye see if you were over here ? let 's see . if i draw our axis here . all right , when this point right here gets to your eye , what am i going to see ? well , i 'm going to have a light ray that 's one part of a light ray . one component points up . that 's this electric field . one component points left . that 's this electric field . so the total , my total electric field , would point this way . i could to the pythagorean theorem if i wanted to figure out the size of it , but i just want to know the direction for now . and then it gets to here , and look at it : they both have zero . this light ray has zero electric field , this one has zero electric fields . so then it 'd just be at zero . now what happens over here ? well , i 've got light . this one points to the right at that point , this pink one , and then this red one would be pointing down . so what would i have at that point ? i 'd have light that went this way , and it would just be doing this over and over . it would just be ... i 'd just have diagonally polarized light . this is n't giving me anything new . you might think this is dumb . why do this ? why send in two different waves to just get diagonally polarized light ? i could have just sent in one wave that was diagonally polarized and got the same thing . the reason is , if you shift this purple wave , this pink wave , by 90 degrees of phase , by pi over two in phase , something magical happens . let me show you what happens here , if we move this to here . now we do n't just get diagonally linear polarized light . what we 're going to get is ... let me get rid of this . okay , so we start off with red , right ? the red electric field points up , and then this pink wave 's electric field is zero at that point . so this is all i have . my total electric field would just be up . i 'm going to draw it right here . the green 'll be the total . now i come over to here , and at this point , there 's some red electric field that points up , but there 's some of this other electric field that points this way . so i 'd have a total electric field that would point that way . and then i get over to here , and i 'd have all of the electric field from the pink one , none from the red one . it would point all left then . look what 's happening . the polarization of this light , if i shift this , if i 'm sitting here , looking with my eye , as my eye receives this light , i 'm going to see this light rotate its polarization . the polarization i 'm going to notice swings around in a circular pattern . and because of this , we call this circular polarization . so this is another type of polarization , where the actual angle of polarization rotates smoothly as this light ray enters your eye . and you know what ? er , drrr ... all right , actually , i sent you to receive this one first . that makes no sense . you 're going to receive the ones closes to you first in this light ray going this way . so you 'd actually receive this one first , then that one , then this one , then this one . because of that , you would n't see this going in a counterclockwise way , you 'd see this going in a clockwise circularly polarized way . sorry about that . you might think , `` okay , why ? `` why even bother with circular polarization ? '' well , i kind of lied earlier . turns out , in the movie theater example , they do n't actually do it like this , typically . oftentimes in the movie theaters , we do n't have just linearly polarized sunglasses . this would be a problem because , when you look at the movie theater screen , and if you were to tilt your head just a little bit ... think about it . this one 's not really going to get the right image anymore . it 's going to get some of both . and this one 's going to get some of both . it 's going to be blurry . your head would have to be perfectly level the whole time , which might be annoying . so what we do is , instead , we create circular polarized glasses , so that this one would only get one polarization , this one would get the other direction . this way , even if you tilt your head a little bit ... shoot , clockwise is clockwise , counterclockwise is counterclockwise . by using circular polarization for 3d movies , it can make it a little easier on you eyes to see a better 3d image , even if your head 's tilted a little bit .
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so this surface here , once this light reflects , it 's coming in at all orientations . you got electric field ... you never know what electric field you 're going to get straight from the sun . and when it reflects , though , you mostly get , upon reflection , the direction of polarization defined by the plane of the surface that it hit .
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is it like only the things above can get affected by that electric field and the things below can not , or it is positive while it is pointing up ?
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- let 's talk about polarization of light . we know what light waves are ; they 're electromagnetic waves . so they 're made out of electric fields . and that 's not good enough . we know there 's not just electric fields . that could n't sustain itself . there 's got to be magnetic fields there , as well , that are changing . those are perpendicular , so you can kind of draw them . it 's hard , on something two-dimensional , but you can kind of imagine those looking something like this . and those magnetic fields would point at a right angle to the electric fields . but this gets really messy if i try to draw both the electric and magnetic fields at the same time . so we 're going to leave the magnetic fields out . it 's often good enough to just know the direction of the electric field when we focus on the electric field . so what does polarization mean ? polarization refers to the fact that , if this light ray was heading straight toward your eye , or a detector , over here , what would you see ? well , if i draw an axis over here , and this point here , in the middle , this is this line -- so imagine we 're looking straight down that line -- and then up and down is up and down , and then left and right , that direction i have the magnetic field , would be this way and that way . what would my eye see ? well , my eye 's only going to see electric fields that either point up or electric fields that point down . they might have different values , but i 'm only going to see electric fields that point up or down . because of that , this light ray is polarized . so polarized light is light where the electric field is only oscillating in one direction . up or down , that 's one direction -- vertically . or it could be polarized horizontally . or it could be polarized diagonally . but either way , you could have this wave polarized along any direction . i mean , a light ray like this , if we had it coming in diagonal , this light ray that 's oscillating like this , where the electric field oscillates like that , that also polarized . these are both polarized because there 's only one direction that the electric field is oscillating in . and you might thing , `` pff , how could you ever have `` a light ray that 's not polarized ? '' easy . most light that you get is not polarized . that is to say , light that 's coming from the sun , straight from the sun -- typically not polarized . light from a lightbulb , an old incandescent light bulb , this thing 's hot . you can get light polarized in any direction , all at once , all overlapping . so if we draw this case for a light bulb , just a random incandescent light bulb , you might get light , some of the light , hitting you eye , you can get some light that 's got that direction , you got light that 's got this direction , you got light in all these directions at any given moment . i mean , you 'd have to add these up to get the total , and they might not all be the same value . but what i 'm trying to say is , at any given moment , you do n't know what direction the electric field 's going to be hitting your eye at from a random source . it could be in any direction . so this is not polarized . this diagram represents light that is not polarized . at some point , the field might be pointing this way , at some later point it 's this way ; it 's just random . you never know which way the electric field 's going to be pointing . whereas these over here , these are polarized . so how could you polarize this light ? let 's say you wanted light that was polarized . you were doing an experiment . you needed polarized light . well , that 's easy . you can use what 's called a polarizer . and this is a material that lets light through , but it only lets light through in one orientation , so you 're going to have a polarizer that , for instance , only lets through vertically polarized light . so this is a polarizer . these are cheap : thin , plastic , configured in a way so that it only lets light through that 's vertically polarized . any light coming in here that 's not vertically polarized gets blocked , or absorbed . so what that means is , if you used this polarizer and held it in between your eye and this light bulb , you would only get this light . all the rest of it would get blocked . or you could just rotate this thing and imagine a polarizer that only lets through horizontal light . now it would only let through light that was this way , and so you would only get this part of the light . or you could just orient it at any angle you want and block everything but the certain angle that this polarizer is defined as letting light through . so you can do this . and once you hold this up , you get polarized light , light that 's only got one orientation . so that 's what polarization means . but why do we care about polarization ? well , let me get rid of this for a minute . you 've heard of polarized sunglasses . so imagine you 're standing near water , or maybe you 're standing on ice or snow or something reflective . there 's a problem . say the sun 's out . it 's shining . it 's a beautiful day -- except there 's going to be glare . let 's say you 're looking down at something here on the ground . it 's going to get light reflecting off of it from just ... you know , light 's coming in from all direction . but it also gets this direct light from the sun . so it gets light from reflected off the clouds and whatever , whatever 's nearby , ambient light . and there 's also this direct sunlight . that 's harsh . if that reflects straight up to your eye , that hurts . you do n't like that . it blocks our vision . it 's hard to see , it 's glare . we do n't want this glare . so what can we do ? well , it just so happens that , when light reflects off of a surface , even though the light from the sun is not polarized , once it reflects , it does get polarized or at least partially polarized . so this surface here , once this light reflects , it 's coming in at all orientations . you got electric field ... you never know what electric field you 're going to get straight from the sun . and when it reflects , though , you mostly get , upon reflection , the direction of polarization defined by the plane of the surface that it hit . so because the floor is horizontal , when this light ray hits the ground and reflects , that reflected light gets partially polarized . this horizontal component of the electric field is going to be more present than the other components . maybe not completely . sometimes it could be . it could be completely polarized , but often it 's just partially polarized . but that 's pretty cool , because now you know what we can do . i know how to block this . we should get some sunglasses . we put some sunglasses on and we make our glasses so that these are polarized . and how do we want these polarized ? i want to get rid of the glare . so what i do is , i make sure my sunglasses only let through vertically polarized light . here 's some polarizers . that way , a lot of this glare gets blocked because it does not have a vertical orientation , it has a horizontal orientation . and then we can block it . so that 's one good thing that polarization does for us , and understanding it , we can get rid of glare . also , fishermen like it because , if you 're trying to look in the water at fish , you want to see in through the water , you want to see this light from the fish getting to you . you do n't want to see the glare off of the sun getting to you . so polarized sunglasses are useful . also , we can play a trick on our eye , if we really wanted to . you could take one of these , make one eye have a vertical orientation for the polarization , have the other eye with a horizontal ... and you 're thinking , `` this is stupid . `` why would you do this for ? '' `` this eye 's going to get a lot of glare . '' we would n't use these outside , when you 're , like , skiing or fishing , but you could play a trick on your eyes if you went to the movies and you went and watched a movie . well , the reason our eyes see 3d is because they 're spaced a little bit apart . they each get a different , slightly different image . that makes us see in 3d . we can play the same trick on our eye if we have the polarization like this . if light , if some of the light from the movie theater screen is coming in with one polarization , and the other light 's coming in with the other polarization , we can send two different images to our eyes at the same time . if you took these off , it 'd look like garbage because you 'd be getting both of these slightly different images , it 'd look all blurry . and it does . if you take off your 3d glasses and look at a 3d movie , looks terrible , because now both eyes are getting both images . but if you put your glasses back on , now this eye only gets the orientation that it 's supposed to get , and this eye only gets the orientation that it 's supposed to get , and you get a 3d image . so it 's useful in many ways . let me show you one more thing here . let 's come back here . this light was polarized vertically . so that 's called linear polarization . any time ... same with these . these are all linear polarization because , just up and down , one linear direction , just diagonal . this is also linear . all of these are linear . you can get circular polarized light . so if we come back to here , we 've got our electric field pointing up , like that . now let 's say we sent in another light ray , another light ray that also had a polarization , but not in this direction . let 's say our other light ray had polarization in this direction , so it looks like this , kind of like what our magnetic field would have looked like . but this is a completely different light ray with its own polarization and its own magnetic field . so we send this in . what would happen ? well , at this point , you 'd have a electric field that points this way . at this point , you 'd have a electric field that points that way . what would your eye see if you were over here ? let 's see . if i draw our axis here . all right , when this point right here gets to your eye , what am i going to see ? well , i 'm going to have a light ray that 's one part of a light ray . one component points up . that 's this electric field . one component points left . that 's this electric field . so the total , my total electric field , would point this way . i could to the pythagorean theorem if i wanted to figure out the size of it , but i just want to know the direction for now . and then it gets to here , and look at it : they both have zero . this light ray has zero electric field , this one has zero electric fields . so then it 'd just be at zero . now what happens over here ? well , i 've got light . this one points to the right at that point , this pink one , and then this red one would be pointing down . so what would i have at that point ? i 'd have light that went this way , and it would just be doing this over and over . it would just be ... i 'd just have diagonally polarized light . this is n't giving me anything new . you might think this is dumb . why do this ? why send in two different waves to just get diagonally polarized light ? i could have just sent in one wave that was diagonally polarized and got the same thing . the reason is , if you shift this purple wave , this pink wave , by 90 degrees of phase , by pi over two in phase , something magical happens . let me show you what happens here , if we move this to here . now we do n't just get diagonally linear polarized light . what we 're going to get is ... let me get rid of this . okay , so we start off with red , right ? the red electric field points up , and then this pink wave 's electric field is zero at that point . so this is all i have . my total electric field would just be up . i 'm going to draw it right here . the green 'll be the total . now i come over to here , and at this point , there 's some red electric field that points up , but there 's some of this other electric field that points this way . so i 'd have a total electric field that would point that way . and then i get over to here , and i 'd have all of the electric field from the pink one , none from the red one . it would point all left then . look what 's happening . the polarization of this light , if i shift this , if i 'm sitting here , looking with my eye , as my eye receives this light , i 'm going to see this light rotate its polarization . the polarization i 'm going to notice swings around in a circular pattern . and because of this , we call this circular polarization . so this is another type of polarization , where the actual angle of polarization rotates smoothly as this light ray enters your eye . and you know what ? er , drrr ... all right , actually , i sent you to receive this one first . that makes no sense . you 're going to receive the ones closes to you first in this light ray going this way . so you 'd actually receive this one first , then that one , then this one , then this one . because of that , you would n't see this going in a counterclockwise way , you 'd see this going in a clockwise circularly polarized way . sorry about that . you might think , `` okay , why ? `` why even bother with circular polarization ? '' well , i kind of lied earlier . turns out , in the movie theater example , they do n't actually do it like this , typically . oftentimes in the movie theaters , we do n't have just linearly polarized sunglasses . this would be a problem because , when you look at the movie theater screen , and if you were to tilt your head just a little bit ... think about it . this one 's not really going to get the right image anymore . it 's going to get some of both . and this one 's going to get some of both . it 's going to be blurry . your head would have to be perfectly level the whole time , which might be annoying . so what we do is , instead , we create circular polarized glasses , so that this one would only get one polarization , this one would get the other direction . this way , even if you tilt your head a little bit ... shoot , clockwise is clockwise , counterclockwise is counterclockwise . by using circular polarization for 3d movies , it can make it a little easier on you eyes to see a better 3d image , even if your head 's tilted a little bit .
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because of that , this light ray is polarized . so polarized light is light where the electric field is only oscillating in one direction . up or down , that 's one direction -- vertically .
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is the graph representing a real model of light or it just represent the value of the electric field , the magnetic field , and the direction ?
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- let 's talk about polarization of light . we know what light waves are ; they 're electromagnetic waves . so they 're made out of electric fields . and that 's not good enough . we know there 's not just electric fields . that could n't sustain itself . there 's got to be magnetic fields there , as well , that are changing . those are perpendicular , so you can kind of draw them . it 's hard , on something two-dimensional , but you can kind of imagine those looking something like this . and those magnetic fields would point at a right angle to the electric fields . but this gets really messy if i try to draw both the electric and magnetic fields at the same time . so we 're going to leave the magnetic fields out . it 's often good enough to just know the direction of the electric field when we focus on the electric field . so what does polarization mean ? polarization refers to the fact that , if this light ray was heading straight toward your eye , or a detector , over here , what would you see ? well , if i draw an axis over here , and this point here , in the middle , this is this line -- so imagine we 're looking straight down that line -- and then up and down is up and down , and then left and right , that direction i have the magnetic field , would be this way and that way . what would my eye see ? well , my eye 's only going to see electric fields that either point up or electric fields that point down . they might have different values , but i 'm only going to see electric fields that point up or down . because of that , this light ray is polarized . so polarized light is light where the electric field is only oscillating in one direction . up or down , that 's one direction -- vertically . or it could be polarized horizontally . or it could be polarized diagonally . but either way , you could have this wave polarized along any direction . i mean , a light ray like this , if we had it coming in diagonal , this light ray that 's oscillating like this , where the electric field oscillates like that , that also polarized . these are both polarized because there 's only one direction that the electric field is oscillating in . and you might thing , `` pff , how could you ever have `` a light ray that 's not polarized ? '' easy . most light that you get is not polarized . that is to say , light that 's coming from the sun , straight from the sun -- typically not polarized . light from a lightbulb , an old incandescent light bulb , this thing 's hot . you can get light polarized in any direction , all at once , all overlapping . so if we draw this case for a light bulb , just a random incandescent light bulb , you might get light , some of the light , hitting you eye , you can get some light that 's got that direction , you got light that 's got this direction , you got light in all these directions at any given moment . i mean , you 'd have to add these up to get the total , and they might not all be the same value . but what i 'm trying to say is , at any given moment , you do n't know what direction the electric field 's going to be hitting your eye at from a random source . it could be in any direction . so this is not polarized . this diagram represents light that is not polarized . at some point , the field might be pointing this way , at some later point it 's this way ; it 's just random . you never know which way the electric field 's going to be pointing . whereas these over here , these are polarized . so how could you polarize this light ? let 's say you wanted light that was polarized . you were doing an experiment . you needed polarized light . well , that 's easy . you can use what 's called a polarizer . and this is a material that lets light through , but it only lets light through in one orientation , so you 're going to have a polarizer that , for instance , only lets through vertically polarized light . so this is a polarizer . these are cheap : thin , plastic , configured in a way so that it only lets light through that 's vertically polarized . any light coming in here that 's not vertically polarized gets blocked , or absorbed . so what that means is , if you used this polarizer and held it in between your eye and this light bulb , you would only get this light . all the rest of it would get blocked . or you could just rotate this thing and imagine a polarizer that only lets through horizontal light . now it would only let through light that was this way , and so you would only get this part of the light . or you could just orient it at any angle you want and block everything but the certain angle that this polarizer is defined as letting light through . so you can do this . and once you hold this up , you get polarized light , light that 's only got one orientation . so that 's what polarization means . but why do we care about polarization ? well , let me get rid of this for a minute . you 've heard of polarized sunglasses . so imagine you 're standing near water , or maybe you 're standing on ice or snow or something reflective . there 's a problem . say the sun 's out . it 's shining . it 's a beautiful day -- except there 's going to be glare . let 's say you 're looking down at something here on the ground . it 's going to get light reflecting off of it from just ... you know , light 's coming in from all direction . but it also gets this direct light from the sun . so it gets light from reflected off the clouds and whatever , whatever 's nearby , ambient light . and there 's also this direct sunlight . that 's harsh . if that reflects straight up to your eye , that hurts . you do n't like that . it blocks our vision . it 's hard to see , it 's glare . we do n't want this glare . so what can we do ? well , it just so happens that , when light reflects off of a surface , even though the light from the sun is not polarized , once it reflects , it does get polarized or at least partially polarized . so this surface here , once this light reflects , it 's coming in at all orientations . you got electric field ... you never know what electric field you 're going to get straight from the sun . and when it reflects , though , you mostly get , upon reflection , the direction of polarization defined by the plane of the surface that it hit . so because the floor is horizontal , when this light ray hits the ground and reflects , that reflected light gets partially polarized . this horizontal component of the electric field is going to be more present than the other components . maybe not completely . sometimes it could be . it could be completely polarized , but often it 's just partially polarized . but that 's pretty cool , because now you know what we can do . i know how to block this . we should get some sunglasses . we put some sunglasses on and we make our glasses so that these are polarized . and how do we want these polarized ? i want to get rid of the glare . so what i do is , i make sure my sunglasses only let through vertically polarized light . here 's some polarizers . that way , a lot of this glare gets blocked because it does not have a vertical orientation , it has a horizontal orientation . and then we can block it . so that 's one good thing that polarization does for us , and understanding it , we can get rid of glare . also , fishermen like it because , if you 're trying to look in the water at fish , you want to see in through the water , you want to see this light from the fish getting to you . you do n't want to see the glare off of the sun getting to you . so polarized sunglasses are useful . also , we can play a trick on our eye , if we really wanted to . you could take one of these , make one eye have a vertical orientation for the polarization , have the other eye with a horizontal ... and you 're thinking , `` this is stupid . `` why would you do this for ? '' `` this eye 's going to get a lot of glare . '' we would n't use these outside , when you 're , like , skiing or fishing , but you could play a trick on your eyes if you went to the movies and you went and watched a movie . well , the reason our eyes see 3d is because they 're spaced a little bit apart . they each get a different , slightly different image . that makes us see in 3d . we can play the same trick on our eye if we have the polarization like this . if light , if some of the light from the movie theater screen is coming in with one polarization , and the other light 's coming in with the other polarization , we can send two different images to our eyes at the same time . if you took these off , it 'd look like garbage because you 'd be getting both of these slightly different images , it 'd look all blurry . and it does . if you take off your 3d glasses and look at a 3d movie , looks terrible , because now both eyes are getting both images . but if you put your glasses back on , now this eye only gets the orientation that it 's supposed to get , and this eye only gets the orientation that it 's supposed to get , and you get a 3d image . so it 's useful in many ways . let me show you one more thing here . let 's come back here . this light was polarized vertically . so that 's called linear polarization . any time ... same with these . these are all linear polarization because , just up and down , one linear direction , just diagonal . this is also linear . all of these are linear . you can get circular polarized light . so if we come back to here , we 've got our electric field pointing up , like that . now let 's say we sent in another light ray , another light ray that also had a polarization , but not in this direction . let 's say our other light ray had polarization in this direction , so it looks like this , kind of like what our magnetic field would have looked like . but this is a completely different light ray with its own polarization and its own magnetic field . so we send this in . what would happen ? well , at this point , you 'd have a electric field that points this way . at this point , you 'd have a electric field that points that way . what would your eye see if you were over here ? let 's see . if i draw our axis here . all right , when this point right here gets to your eye , what am i going to see ? well , i 'm going to have a light ray that 's one part of a light ray . one component points up . that 's this electric field . one component points left . that 's this electric field . so the total , my total electric field , would point this way . i could to the pythagorean theorem if i wanted to figure out the size of it , but i just want to know the direction for now . and then it gets to here , and look at it : they both have zero . this light ray has zero electric field , this one has zero electric fields . so then it 'd just be at zero . now what happens over here ? well , i 've got light . this one points to the right at that point , this pink one , and then this red one would be pointing down . so what would i have at that point ? i 'd have light that went this way , and it would just be doing this over and over . it would just be ... i 'd just have diagonally polarized light . this is n't giving me anything new . you might think this is dumb . why do this ? why send in two different waves to just get diagonally polarized light ? i could have just sent in one wave that was diagonally polarized and got the same thing . the reason is , if you shift this purple wave , this pink wave , by 90 degrees of phase , by pi over two in phase , something magical happens . let me show you what happens here , if we move this to here . now we do n't just get diagonally linear polarized light . what we 're going to get is ... let me get rid of this . okay , so we start off with red , right ? the red electric field points up , and then this pink wave 's electric field is zero at that point . so this is all i have . my total electric field would just be up . i 'm going to draw it right here . the green 'll be the total . now i come over to here , and at this point , there 's some red electric field that points up , but there 's some of this other electric field that points this way . so i 'd have a total electric field that would point that way . and then i get over to here , and i 'd have all of the electric field from the pink one , none from the red one . it would point all left then . look what 's happening . the polarization of this light , if i shift this , if i 'm sitting here , looking with my eye , as my eye receives this light , i 'm going to see this light rotate its polarization . the polarization i 'm going to notice swings around in a circular pattern . and because of this , we call this circular polarization . so this is another type of polarization , where the actual angle of polarization rotates smoothly as this light ray enters your eye . and you know what ? er , drrr ... all right , actually , i sent you to receive this one first . that makes no sense . you 're going to receive the ones closes to you first in this light ray going this way . so you 'd actually receive this one first , then that one , then this one , then this one . because of that , you would n't see this going in a counterclockwise way , you 'd see this going in a clockwise circularly polarized way . sorry about that . you might think , `` okay , why ? `` why even bother with circular polarization ? '' well , i kind of lied earlier . turns out , in the movie theater example , they do n't actually do it like this , typically . oftentimes in the movie theaters , we do n't have just linearly polarized sunglasses . this would be a problem because , when you look at the movie theater screen , and if you were to tilt your head just a little bit ... think about it . this one 's not really going to get the right image anymore . it 's going to get some of both . and this one 's going to get some of both . it 's going to be blurry . your head would have to be perfectly level the whole time , which might be annoying . so what we do is , instead , we create circular polarized glasses , so that this one would only get one polarization , this one would get the other direction . this way , even if you tilt your head a little bit ... shoot , clockwise is clockwise , counterclockwise is counterclockwise . by using circular polarization for 3d movies , it can make it a little easier on you eyes to see a better 3d image , even if your head 's tilted a little bit .
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because of that , this light ray is polarized . so polarized light is light where the electric field is only oscillating in one direction . up or down , that 's one direction -- vertically .
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do charged particles interact with the electric and magnetic field components of light.if yes then is there any daily life experience related to it ?
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- let 's talk about polarization of light . we know what light waves are ; they 're electromagnetic waves . so they 're made out of electric fields . and that 's not good enough . we know there 's not just electric fields . that could n't sustain itself . there 's got to be magnetic fields there , as well , that are changing . those are perpendicular , so you can kind of draw them . it 's hard , on something two-dimensional , but you can kind of imagine those looking something like this . and those magnetic fields would point at a right angle to the electric fields . but this gets really messy if i try to draw both the electric and magnetic fields at the same time . so we 're going to leave the magnetic fields out . it 's often good enough to just know the direction of the electric field when we focus on the electric field . so what does polarization mean ? polarization refers to the fact that , if this light ray was heading straight toward your eye , or a detector , over here , what would you see ? well , if i draw an axis over here , and this point here , in the middle , this is this line -- so imagine we 're looking straight down that line -- and then up and down is up and down , and then left and right , that direction i have the magnetic field , would be this way and that way . what would my eye see ? well , my eye 's only going to see electric fields that either point up or electric fields that point down . they might have different values , but i 'm only going to see electric fields that point up or down . because of that , this light ray is polarized . so polarized light is light where the electric field is only oscillating in one direction . up or down , that 's one direction -- vertically . or it could be polarized horizontally . or it could be polarized diagonally . but either way , you could have this wave polarized along any direction . i mean , a light ray like this , if we had it coming in diagonal , this light ray that 's oscillating like this , where the electric field oscillates like that , that also polarized . these are both polarized because there 's only one direction that the electric field is oscillating in . and you might thing , `` pff , how could you ever have `` a light ray that 's not polarized ? '' easy . most light that you get is not polarized . that is to say , light that 's coming from the sun , straight from the sun -- typically not polarized . light from a lightbulb , an old incandescent light bulb , this thing 's hot . you can get light polarized in any direction , all at once , all overlapping . so if we draw this case for a light bulb , just a random incandescent light bulb , you might get light , some of the light , hitting you eye , you can get some light that 's got that direction , you got light that 's got this direction , you got light in all these directions at any given moment . i mean , you 'd have to add these up to get the total , and they might not all be the same value . but what i 'm trying to say is , at any given moment , you do n't know what direction the electric field 's going to be hitting your eye at from a random source . it could be in any direction . so this is not polarized . this diagram represents light that is not polarized . at some point , the field might be pointing this way , at some later point it 's this way ; it 's just random . you never know which way the electric field 's going to be pointing . whereas these over here , these are polarized . so how could you polarize this light ? let 's say you wanted light that was polarized . you were doing an experiment . you needed polarized light . well , that 's easy . you can use what 's called a polarizer . and this is a material that lets light through , but it only lets light through in one orientation , so you 're going to have a polarizer that , for instance , only lets through vertically polarized light . so this is a polarizer . these are cheap : thin , plastic , configured in a way so that it only lets light through that 's vertically polarized . any light coming in here that 's not vertically polarized gets blocked , or absorbed . so what that means is , if you used this polarizer and held it in between your eye and this light bulb , you would only get this light . all the rest of it would get blocked . or you could just rotate this thing and imagine a polarizer that only lets through horizontal light . now it would only let through light that was this way , and so you would only get this part of the light . or you could just orient it at any angle you want and block everything but the certain angle that this polarizer is defined as letting light through . so you can do this . and once you hold this up , you get polarized light , light that 's only got one orientation . so that 's what polarization means . but why do we care about polarization ? well , let me get rid of this for a minute . you 've heard of polarized sunglasses . so imagine you 're standing near water , or maybe you 're standing on ice or snow or something reflective . there 's a problem . say the sun 's out . it 's shining . it 's a beautiful day -- except there 's going to be glare . let 's say you 're looking down at something here on the ground . it 's going to get light reflecting off of it from just ... you know , light 's coming in from all direction . but it also gets this direct light from the sun . so it gets light from reflected off the clouds and whatever , whatever 's nearby , ambient light . and there 's also this direct sunlight . that 's harsh . if that reflects straight up to your eye , that hurts . you do n't like that . it blocks our vision . it 's hard to see , it 's glare . we do n't want this glare . so what can we do ? well , it just so happens that , when light reflects off of a surface , even though the light from the sun is not polarized , once it reflects , it does get polarized or at least partially polarized . so this surface here , once this light reflects , it 's coming in at all orientations . you got electric field ... you never know what electric field you 're going to get straight from the sun . and when it reflects , though , you mostly get , upon reflection , the direction of polarization defined by the plane of the surface that it hit . so because the floor is horizontal , when this light ray hits the ground and reflects , that reflected light gets partially polarized . this horizontal component of the electric field is going to be more present than the other components . maybe not completely . sometimes it could be . it could be completely polarized , but often it 's just partially polarized . but that 's pretty cool , because now you know what we can do . i know how to block this . we should get some sunglasses . we put some sunglasses on and we make our glasses so that these are polarized . and how do we want these polarized ? i want to get rid of the glare . so what i do is , i make sure my sunglasses only let through vertically polarized light . here 's some polarizers . that way , a lot of this glare gets blocked because it does not have a vertical orientation , it has a horizontal orientation . and then we can block it . so that 's one good thing that polarization does for us , and understanding it , we can get rid of glare . also , fishermen like it because , if you 're trying to look in the water at fish , you want to see in through the water , you want to see this light from the fish getting to you . you do n't want to see the glare off of the sun getting to you . so polarized sunglasses are useful . also , we can play a trick on our eye , if we really wanted to . you could take one of these , make one eye have a vertical orientation for the polarization , have the other eye with a horizontal ... and you 're thinking , `` this is stupid . `` why would you do this for ? '' `` this eye 's going to get a lot of glare . '' we would n't use these outside , when you 're , like , skiing or fishing , but you could play a trick on your eyes if you went to the movies and you went and watched a movie . well , the reason our eyes see 3d is because they 're spaced a little bit apart . they each get a different , slightly different image . that makes us see in 3d . we can play the same trick on our eye if we have the polarization like this . if light , if some of the light from the movie theater screen is coming in with one polarization , and the other light 's coming in with the other polarization , we can send two different images to our eyes at the same time . if you took these off , it 'd look like garbage because you 'd be getting both of these slightly different images , it 'd look all blurry . and it does . if you take off your 3d glasses and look at a 3d movie , looks terrible , because now both eyes are getting both images . but if you put your glasses back on , now this eye only gets the orientation that it 's supposed to get , and this eye only gets the orientation that it 's supposed to get , and you get a 3d image . so it 's useful in many ways . let me show you one more thing here . let 's come back here . this light was polarized vertically . so that 's called linear polarization . any time ... same with these . these are all linear polarization because , just up and down , one linear direction , just diagonal . this is also linear . all of these are linear . you can get circular polarized light . so if we come back to here , we 've got our electric field pointing up , like that . now let 's say we sent in another light ray , another light ray that also had a polarization , but not in this direction . let 's say our other light ray had polarization in this direction , so it looks like this , kind of like what our magnetic field would have looked like . but this is a completely different light ray with its own polarization and its own magnetic field . so we send this in . what would happen ? well , at this point , you 'd have a electric field that points this way . at this point , you 'd have a electric field that points that way . what would your eye see if you were over here ? let 's see . if i draw our axis here . all right , when this point right here gets to your eye , what am i going to see ? well , i 'm going to have a light ray that 's one part of a light ray . one component points up . that 's this electric field . one component points left . that 's this electric field . so the total , my total electric field , would point this way . i could to the pythagorean theorem if i wanted to figure out the size of it , but i just want to know the direction for now . and then it gets to here , and look at it : they both have zero . this light ray has zero electric field , this one has zero electric fields . so then it 'd just be at zero . now what happens over here ? well , i 've got light . this one points to the right at that point , this pink one , and then this red one would be pointing down . so what would i have at that point ? i 'd have light that went this way , and it would just be doing this over and over . it would just be ... i 'd just have diagonally polarized light . this is n't giving me anything new . you might think this is dumb . why do this ? why send in two different waves to just get diagonally polarized light ? i could have just sent in one wave that was diagonally polarized and got the same thing . the reason is , if you shift this purple wave , this pink wave , by 90 degrees of phase , by pi over two in phase , something magical happens . let me show you what happens here , if we move this to here . now we do n't just get diagonally linear polarized light . what we 're going to get is ... let me get rid of this . okay , so we start off with red , right ? the red electric field points up , and then this pink wave 's electric field is zero at that point . so this is all i have . my total electric field would just be up . i 'm going to draw it right here . the green 'll be the total . now i come over to here , and at this point , there 's some red electric field that points up , but there 's some of this other electric field that points this way . so i 'd have a total electric field that would point that way . and then i get over to here , and i 'd have all of the electric field from the pink one , none from the red one . it would point all left then . look what 's happening . the polarization of this light , if i shift this , if i 'm sitting here , looking with my eye , as my eye receives this light , i 'm going to see this light rotate its polarization . the polarization i 'm going to notice swings around in a circular pattern . and because of this , we call this circular polarization . so this is another type of polarization , where the actual angle of polarization rotates smoothly as this light ray enters your eye . and you know what ? er , drrr ... all right , actually , i sent you to receive this one first . that makes no sense . you 're going to receive the ones closes to you first in this light ray going this way . so you 'd actually receive this one first , then that one , then this one , then this one . because of that , you would n't see this going in a counterclockwise way , you 'd see this going in a clockwise circularly polarized way . sorry about that . you might think , `` okay , why ? `` why even bother with circular polarization ? '' well , i kind of lied earlier . turns out , in the movie theater example , they do n't actually do it like this , typically . oftentimes in the movie theaters , we do n't have just linearly polarized sunglasses . this would be a problem because , when you look at the movie theater screen , and if you were to tilt your head just a little bit ... think about it . this one 's not really going to get the right image anymore . it 's going to get some of both . and this one 's going to get some of both . it 's going to be blurry . your head would have to be perfectly level the whole time , which might be annoying . so what we do is , instead , we create circular polarized glasses , so that this one would only get one polarization , this one would get the other direction . this way , even if you tilt your head a little bit ... shoot , clockwise is clockwise , counterclockwise is counterclockwise . by using circular polarization for 3d movies , it can make it a little easier on you eyes to see a better 3d image , even if your head 's tilted a little bit .
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and it does . if you take off your 3d glasses and look at a 3d movie , looks terrible , because now both eyes are getting both images . but if you put your glasses back on , now this eye only gets the orientation that it 's supposed to get , and this eye only gets the orientation that it 's supposed to get , and you get a 3d image .
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are the two overlapping images of a 3d movie different drawn ?
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- let 's talk about polarization of light . we know what light waves are ; they 're electromagnetic waves . so they 're made out of electric fields . and that 's not good enough . we know there 's not just electric fields . that could n't sustain itself . there 's got to be magnetic fields there , as well , that are changing . those are perpendicular , so you can kind of draw them . it 's hard , on something two-dimensional , but you can kind of imagine those looking something like this . and those magnetic fields would point at a right angle to the electric fields . but this gets really messy if i try to draw both the electric and magnetic fields at the same time . so we 're going to leave the magnetic fields out . it 's often good enough to just know the direction of the electric field when we focus on the electric field . so what does polarization mean ? polarization refers to the fact that , if this light ray was heading straight toward your eye , or a detector , over here , what would you see ? well , if i draw an axis over here , and this point here , in the middle , this is this line -- so imagine we 're looking straight down that line -- and then up and down is up and down , and then left and right , that direction i have the magnetic field , would be this way and that way . what would my eye see ? well , my eye 's only going to see electric fields that either point up or electric fields that point down . they might have different values , but i 'm only going to see electric fields that point up or down . because of that , this light ray is polarized . so polarized light is light where the electric field is only oscillating in one direction . up or down , that 's one direction -- vertically . or it could be polarized horizontally . or it could be polarized diagonally . but either way , you could have this wave polarized along any direction . i mean , a light ray like this , if we had it coming in diagonal , this light ray that 's oscillating like this , where the electric field oscillates like that , that also polarized . these are both polarized because there 's only one direction that the electric field is oscillating in . and you might thing , `` pff , how could you ever have `` a light ray that 's not polarized ? '' easy . most light that you get is not polarized . that is to say , light that 's coming from the sun , straight from the sun -- typically not polarized . light from a lightbulb , an old incandescent light bulb , this thing 's hot . you can get light polarized in any direction , all at once , all overlapping . so if we draw this case for a light bulb , just a random incandescent light bulb , you might get light , some of the light , hitting you eye , you can get some light that 's got that direction , you got light that 's got this direction , you got light in all these directions at any given moment . i mean , you 'd have to add these up to get the total , and they might not all be the same value . but what i 'm trying to say is , at any given moment , you do n't know what direction the electric field 's going to be hitting your eye at from a random source . it could be in any direction . so this is not polarized . this diagram represents light that is not polarized . at some point , the field might be pointing this way , at some later point it 's this way ; it 's just random . you never know which way the electric field 's going to be pointing . whereas these over here , these are polarized . so how could you polarize this light ? let 's say you wanted light that was polarized . you were doing an experiment . you needed polarized light . well , that 's easy . you can use what 's called a polarizer . and this is a material that lets light through , but it only lets light through in one orientation , so you 're going to have a polarizer that , for instance , only lets through vertically polarized light . so this is a polarizer . these are cheap : thin , plastic , configured in a way so that it only lets light through that 's vertically polarized . any light coming in here that 's not vertically polarized gets blocked , or absorbed . so what that means is , if you used this polarizer and held it in between your eye and this light bulb , you would only get this light . all the rest of it would get blocked . or you could just rotate this thing and imagine a polarizer that only lets through horizontal light . now it would only let through light that was this way , and so you would only get this part of the light . or you could just orient it at any angle you want and block everything but the certain angle that this polarizer is defined as letting light through . so you can do this . and once you hold this up , you get polarized light , light that 's only got one orientation . so that 's what polarization means . but why do we care about polarization ? well , let me get rid of this for a minute . you 've heard of polarized sunglasses . so imagine you 're standing near water , or maybe you 're standing on ice or snow or something reflective . there 's a problem . say the sun 's out . it 's shining . it 's a beautiful day -- except there 's going to be glare . let 's say you 're looking down at something here on the ground . it 's going to get light reflecting off of it from just ... you know , light 's coming in from all direction . but it also gets this direct light from the sun . so it gets light from reflected off the clouds and whatever , whatever 's nearby , ambient light . and there 's also this direct sunlight . that 's harsh . if that reflects straight up to your eye , that hurts . you do n't like that . it blocks our vision . it 's hard to see , it 's glare . we do n't want this glare . so what can we do ? well , it just so happens that , when light reflects off of a surface , even though the light from the sun is not polarized , once it reflects , it does get polarized or at least partially polarized . so this surface here , once this light reflects , it 's coming in at all orientations . you got electric field ... you never know what electric field you 're going to get straight from the sun . and when it reflects , though , you mostly get , upon reflection , the direction of polarization defined by the plane of the surface that it hit . so because the floor is horizontal , when this light ray hits the ground and reflects , that reflected light gets partially polarized . this horizontal component of the electric field is going to be more present than the other components . maybe not completely . sometimes it could be . it could be completely polarized , but often it 's just partially polarized . but that 's pretty cool , because now you know what we can do . i know how to block this . we should get some sunglasses . we put some sunglasses on and we make our glasses so that these are polarized . and how do we want these polarized ? i want to get rid of the glare . so what i do is , i make sure my sunglasses only let through vertically polarized light . here 's some polarizers . that way , a lot of this glare gets blocked because it does not have a vertical orientation , it has a horizontal orientation . and then we can block it . so that 's one good thing that polarization does for us , and understanding it , we can get rid of glare . also , fishermen like it because , if you 're trying to look in the water at fish , you want to see in through the water , you want to see this light from the fish getting to you . you do n't want to see the glare off of the sun getting to you . so polarized sunglasses are useful . also , we can play a trick on our eye , if we really wanted to . you could take one of these , make one eye have a vertical orientation for the polarization , have the other eye with a horizontal ... and you 're thinking , `` this is stupid . `` why would you do this for ? '' `` this eye 's going to get a lot of glare . '' we would n't use these outside , when you 're , like , skiing or fishing , but you could play a trick on your eyes if you went to the movies and you went and watched a movie . well , the reason our eyes see 3d is because they 're spaced a little bit apart . they each get a different , slightly different image . that makes us see in 3d . we can play the same trick on our eye if we have the polarization like this . if light , if some of the light from the movie theater screen is coming in with one polarization , and the other light 's coming in with the other polarization , we can send two different images to our eyes at the same time . if you took these off , it 'd look like garbage because you 'd be getting both of these slightly different images , it 'd look all blurry . and it does . if you take off your 3d glasses and look at a 3d movie , looks terrible , because now both eyes are getting both images . but if you put your glasses back on , now this eye only gets the orientation that it 's supposed to get , and this eye only gets the orientation that it 's supposed to get , and you get a 3d image . so it 's useful in many ways . let me show you one more thing here . let 's come back here . this light was polarized vertically . so that 's called linear polarization . any time ... same with these . these are all linear polarization because , just up and down , one linear direction , just diagonal . this is also linear . all of these are linear . you can get circular polarized light . so if we come back to here , we 've got our electric field pointing up , like that . now let 's say we sent in another light ray , another light ray that also had a polarization , but not in this direction . let 's say our other light ray had polarization in this direction , so it looks like this , kind of like what our magnetic field would have looked like . but this is a completely different light ray with its own polarization and its own magnetic field . so we send this in . what would happen ? well , at this point , you 'd have a electric field that points this way . at this point , you 'd have a electric field that points that way . what would your eye see if you were over here ? let 's see . if i draw our axis here . all right , when this point right here gets to your eye , what am i going to see ? well , i 'm going to have a light ray that 's one part of a light ray . one component points up . that 's this electric field . one component points left . that 's this electric field . so the total , my total electric field , would point this way . i could to the pythagorean theorem if i wanted to figure out the size of it , but i just want to know the direction for now . and then it gets to here , and look at it : they both have zero . this light ray has zero electric field , this one has zero electric fields . so then it 'd just be at zero . now what happens over here ? well , i 've got light . this one points to the right at that point , this pink one , and then this red one would be pointing down . so what would i have at that point ? i 'd have light that went this way , and it would just be doing this over and over . it would just be ... i 'd just have diagonally polarized light . this is n't giving me anything new . you might think this is dumb . why do this ? why send in two different waves to just get diagonally polarized light ? i could have just sent in one wave that was diagonally polarized and got the same thing . the reason is , if you shift this purple wave , this pink wave , by 90 degrees of phase , by pi over two in phase , something magical happens . let me show you what happens here , if we move this to here . now we do n't just get diagonally linear polarized light . what we 're going to get is ... let me get rid of this . okay , so we start off with red , right ? the red electric field points up , and then this pink wave 's electric field is zero at that point . so this is all i have . my total electric field would just be up . i 'm going to draw it right here . the green 'll be the total . now i come over to here , and at this point , there 's some red electric field that points up , but there 's some of this other electric field that points this way . so i 'd have a total electric field that would point that way . and then i get over to here , and i 'd have all of the electric field from the pink one , none from the red one . it would point all left then . look what 's happening . the polarization of this light , if i shift this , if i 'm sitting here , looking with my eye , as my eye receives this light , i 'm going to see this light rotate its polarization . the polarization i 'm going to notice swings around in a circular pattern . and because of this , we call this circular polarization . so this is another type of polarization , where the actual angle of polarization rotates smoothly as this light ray enters your eye . and you know what ? er , drrr ... all right , actually , i sent you to receive this one first . that makes no sense . you 're going to receive the ones closes to you first in this light ray going this way . so you 'd actually receive this one first , then that one , then this one , then this one . because of that , you would n't see this going in a counterclockwise way , you 'd see this going in a clockwise circularly polarized way . sorry about that . you might think , `` okay , why ? `` why even bother with circular polarization ? '' well , i kind of lied earlier . turns out , in the movie theater example , they do n't actually do it like this , typically . oftentimes in the movie theaters , we do n't have just linearly polarized sunglasses . this would be a problem because , when you look at the movie theater screen , and if you were to tilt your head just a little bit ... think about it . this one 's not really going to get the right image anymore . it 's going to get some of both . and this one 's going to get some of both . it 's going to be blurry . your head would have to be perfectly level the whole time , which might be annoying . so what we do is , instead , we create circular polarized glasses , so that this one would only get one polarization , this one would get the other direction . this way , even if you tilt your head a little bit ... shoot , clockwise is clockwise , counterclockwise is counterclockwise . by using circular polarization for 3d movies , it can make it a little easier on you eyes to see a better 3d image , even if your head 's tilted a little bit .
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whereas these over here , these are polarized . so how could you polarize this light ? let 's say you wanted light that was polarized .
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does the ozone in our atmosphere polarize light ?
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- let 's talk about polarization of light . we know what light waves are ; they 're electromagnetic waves . so they 're made out of electric fields . and that 's not good enough . we know there 's not just electric fields . that could n't sustain itself . there 's got to be magnetic fields there , as well , that are changing . those are perpendicular , so you can kind of draw them . it 's hard , on something two-dimensional , but you can kind of imagine those looking something like this . and those magnetic fields would point at a right angle to the electric fields . but this gets really messy if i try to draw both the electric and magnetic fields at the same time . so we 're going to leave the magnetic fields out . it 's often good enough to just know the direction of the electric field when we focus on the electric field . so what does polarization mean ? polarization refers to the fact that , if this light ray was heading straight toward your eye , or a detector , over here , what would you see ? well , if i draw an axis over here , and this point here , in the middle , this is this line -- so imagine we 're looking straight down that line -- and then up and down is up and down , and then left and right , that direction i have the magnetic field , would be this way and that way . what would my eye see ? well , my eye 's only going to see electric fields that either point up or electric fields that point down . they might have different values , but i 'm only going to see electric fields that point up or down . because of that , this light ray is polarized . so polarized light is light where the electric field is only oscillating in one direction . up or down , that 's one direction -- vertically . or it could be polarized horizontally . or it could be polarized diagonally . but either way , you could have this wave polarized along any direction . i mean , a light ray like this , if we had it coming in diagonal , this light ray that 's oscillating like this , where the electric field oscillates like that , that also polarized . these are both polarized because there 's only one direction that the electric field is oscillating in . and you might thing , `` pff , how could you ever have `` a light ray that 's not polarized ? '' easy . most light that you get is not polarized . that is to say , light that 's coming from the sun , straight from the sun -- typically not polarized . light from a lightbulb , an old incandescent light bulb , this thing 's hot . you can get light polarized in any direction , all at once , all overlapping . so if we draw this case for a light bulb , just a random incandescent light bulb , you might get light , some of the light , hitting you eye , you can get some light that 's got that direction , you got light that 's got this direction , you got light in all these directions at any given moment . i mean , you 'd have to add these up to get the total , and they might not all be the same value . but what i 'm trying to say is , at any given moment , you do n't know what direction the electric field 's going to be hitting your eye at from a random source . it could be in any direction . so this is not polarized . this diagram represents light that is not polarized . at some point , the field might be pointing this way , at some later point it 's this way ; it 's just random . you never know which way the electric field 's going to be pointing . whereas these over here , these are polarized . so how could you polarize this light ? let 's say you wanted light that was polarized . you were doing an experiment . you needed polarized light . well , that 's easy . you can use what 's called a polarizer . and this is a material that lets light through , but it only lets light through in one orientation , so you 're going to have a polarizer that , for instance , only lets through vertically polarized light . so this is a polarizer . these are cheap : thin , plastic , configured in a way so that it only lets light through that 's vertically polarized . any light coming in here that 's not vertically polarized gets blocked , or absorbed . so what that means is , if you used this polarizer and held it in between your eye and this light bulb , you would only get this light . all the rest of it would get blocked . or you could just rotate this thing and imagine a polarizer that only lets through horizontal light . now it would only let through light that was this way , and so you would only get this part of the light . or you could just orient it at any angle you want and block everything but the certain angle that this polarizer is defined as letting light through . so you can do this . and once you hold this up , you get polarized light , light that 's only got one orientation . so that 's what polarization means . but why do we care about polarization ? well , let me get rid of this for a minute . you 've heard of polarized sunglasses . so imagine you 're standing near water , or maybe you 're standing on ice or snow or something reflective . there 's a problem . say the sun 's out . it 's shining . it 's a beautiful day -- except there 's going to be glare . let 's say you 're looking down at something here on the ground . it 's going to get light reflecting off of it from just ... you know , light 's coming in from all direction . but it also gets this direct light from the sun . so it gets light from reflected off the clouds and whatever , whatever 's nearby , ambient light . and there 's also this direct sunlight . that 's harsh . if that reflects straight up to your eye , that hurts . you do n't like that . it blocks our vision . it 's hard to see , it 's glare . we do n't want this glare . so what can we do ? well , it just so happens that , when light reflects off of a surface , even though the light from the sun is not polarized , once it reflects , it does get polarized or at least partially polarized . so this surface here , once this light reflects , it 's coming in at all orientations . you got electric field ... you never know what electric field you 're going to get straight from the sun . and when it reflects , though , you mostly get , upon reflection , the direction of polarization defined by the plane of the surface that it hit . so because the floor is horizontal , when this light ray hits the ground and reflects , that reflected light gets partially polarized . this horizontal component of the electric field is going to be more present than the other components . maybe not completely . sometimes it could be . it could be completely polarized , but often it 's just partially polarized . but that 's pretty cool , because now you know what we can do . i know how to block this . we should get some sunglasses . we put some sunglasses on and we make our glasses so that these are polarized . and how do we want these polarized ? i want to get rid of the glare . so what i do is , i make sure my sunglasses only let through vertically polarized light . here 's some polarizers . that way , a lot of this glare gets blocked because it does not have a vertical orientation , it has a horizontal orientation . and then we can block it . so that 's one good thing that polarization does for us , and understanding it , we can get rid of glare . also , fishermen like it because , if you 're trying to look in the water at fish , you want to see in through the water , you want to see this light from the fish getting to you . you do n't want to see the glare off of the sun getting to you . so polarized sunglasses are useful . also , we can play a trick on our eye , if we really wanted to . you could take one of these , make one eye have a vertical orientation for the polarization , have the other eye with a horizontal ... and you 're thinking , `` this is stupid . `` why would you do this for ? '' `` this eye 's going to get a lot of glare . '' we would n't use these outside , when you 're , like , skiing or fishing , but you could play a trick on your eyes if you went to the movies and you went and watched a movie . well , the reason our eyes see 3d is because they 're spaced a little bit apart . they each get a different , slightly different image . that makes us see in 3d . we can play the same trick on our eye if we have the polarization like this . if light , if some of the light from the movie theater screen is coming in with one polarization , and the other light 's coming in with the other polarization , we can send two different images to our eyes at the same time . if you took these off , it 'd look like garbage because you 'd be getting both of these slightly different images , it 'd look all blurry . and it does . if you take off your 3d glasses and look at a 3d movie , looks terrible , because now both eyes are getting both images . but if you put your glasses back on , now this eye only gets the orientation that it 's supposed to get , and this eye only gets the orientation that it 's supposed to get , and you get a 3d image . so it 's useful in many ways . let me show you one more thing here . let 's come back here . this light was polarized vertically . so that 's called linear polarization . any time ... same with these . these are all linear polarization because , just up and down , one linear direction , just diagonal . this is also linear . all of these are linear . you can get circular polarized light . so if we come back to here , we 've got our electric field pointing up , like that . now let 's say we sent in another light ray , another light ray that also had a polarization , but not in this direction . let 's say our other light ray had polarization in this direction , so it looks like this , kind of like what our magnetic field would have looked like . but this is a completely different light ray with its own polarization and its own magnetic field . so we send this in . what would happen ? well , at this point , you 'd have a electric field that points this way . at this point , you 'd have a electric field that points that way . what would your eye see if you were over here ? let 's see . if i draw our axis here . all right , when this point right here gets to your eye , what am i going to see ? well , i 'm going to have a light ray that 's one part of a light ray . one component points up . that 's this electric field . one component points left . that 's this electric field . so the total , my total electric field , would point this way . i could to the pythagorean theorem if i wanted to figure out the size of it , but i just want to know the direction for now . and then it gets to here , and look at it : they both have zero . this light ray has zero electric field , this one has zero electric fields . so then it 'd just be at zero . now what happens over here ? well , i 've got light . this one points to the right at that point , this pink one , and then this red one would be pointing down . so what would i have at that point ? i 'd have light that went this way , and it would just be doing this over and over . it would just be ... i 'd just have diagonally polarized light . this is n't giving me anything new . you might think this is dumb . why do this ? why send in two different waves to just get diagonally polarized light ? i could have just sent in one wave that was diagonally polarized and got the same thing . the reason is , if you shift this purple wave , this pink wave , by 90 degrees of phase , by pi over two in phase , something magical happens . let me show you what happens here , if we move this to here . now we do n't just get diagonally linear polarized light . what we 're going to get is ... let me get rid of this . okay , so we start off with red , right ? the red electric field points up , and then this pink wave 's electric field is zero at that point . so this is all i have . my total electric field would just be up . i 'm going to draw it right here . the green 'll be the total . now i come over to here , and at this point , there 's some red electric field that points up , but there 's some of this other electric field that points this way . so i 'd have a total electric field that would point that way . and then i get over to here , and i 'd have all of the electric field from the pink one , none from the red one . it would point all left then . look what 's happening . the polarization of this light , if i shift this , if i 'm sitting here , looking with my eye , as my eye receives this light , i 'm going to see this light rotate its polarization . the polarization i 'm going to notice swings around in a circular pattern . and because of this , we call this circular polarization . so this is another type of polarization , where the actual angle of polarization rotates smoothly as this light ray enters your eye . and you know what ? er , drrr ... all right , actually , i sent you to receive this one first . that makes no sense . you 're going to receive the ones closes to you first in this light ray going this way . so you 'd actually receive this one first , then that one , then this one , then this one . because of that , you would n't see this going in a counterclockwise way , you 'd see this going in a clockwise circularly polarized way . sorry about that . you might think , `` okay , why ? `` why even bother with circular polarization ? '' well , i kind of lied earlier . turns out , in the movie theater example , they do n't actually do it like this , typically . oftentimes in the movie theaters , we do n't have just linearly polarized sunglasses . this would be a problem because , when you look at the movie theater screen , and if you were to tilt your head just a little bit ... think about it . this one 's not really going to get the right image anymore . it 's going to get some of both . and this one 's going to get some of both . it 's going to be blurry . your head would have to be perfectly level the whole time , which might be annoying . so what we do is , instead , we create circular polarized glasses , so that this one would only get one polarization , this one would get the other direction . this way , even if you tilt your head a little bit ... shoot , clockwise is clockwise , counterclockwise is counterclockwise . by using circular polarization for 3d movies , it can make it a little easier on you eyes to see a better 3d image , even if your head 's tilted a little bit .
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so we 're going to leave the magnetic fields out . it 's often good enough to just know the direction of the electric field when we focus on the electric field . so what does polarization mean ? polarization refers to the fact that , if this light ray was heading straight toward your eye , or a detector , over here , what would you see ?
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when he refers to the direction of polarization as `` the direction the electromagnetic field is pointing , '' what does he mean ?
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- let 's talk about polarization of light . we know what light waves are ; they 're electromagnetic waves . so they 're made out of electric fields . and that 's not good enough . we know there 's not just electric fields . that could n't sustain itself . there 's got to be magnetic fields there , as well , that are changing . those are perpendicular , so you can kind of draw them . it 's hard , on something two-dimensional , but you can kind of imagine those looking something like this . and those magnetic fields would point at a right angle to the electric fields . but this gets really messy if i try to draw both the electric and magnetic fields at the same time . so we 're going to leave the magnetic fields out . it 's often good enough to just know the direction of the electric field when we focus on the electric field . so what does polarization mean ? polarization refers to the fact that , if this light ray was heading straight toward your eye , or a detector , over here , what would you see ? well , if i draw an axis over here , and this point here , in the middle , this is this line -- so imagine we 're looking straight down that line -- and then up and down is up and down , and then left and right , that direction i have the magnetic field , would be this way and that way . what would my eye see ? well , my eye 's only going to see electric fields that either point up or electric fields that point down . they might have different values , but i 'm only going to see electric fields that point up or down . because of that , this light ray is polarized . so polarized light is light where the electric field is only oscillating in one direction . up or down , that 's one direction -- vertically . or it could be polarized horizontally . or it could be polarized diagonally . but either way , you could have this wave polarized along any direction . i mean , a light ray like this , if we had it coming in diagonal , this light ray that 's oscillating like this , where the electric field oscillates like that , that also polarized . these are both polarized because there 's only one direction that the electric field is oscillating in . and you might thing , `` pff , how could you ever have `` a light ray that 's not polarized ? '' easy . most light that you get is not polarized . that is to say , light that 's coming from the sun , straight from the sun -- typically not polarized . light from a lightbulb , an old incandescent light bulb , this thing 's hot . you can get light polarized in any direction , all at once , all overlapping . so if we draw this case for a light bulb , just a random incandescent light bulb , you might get light , some of the light , hitting you eye , you can get some light that 's got that direction , you got light that 's got this direction , you got light in all these directions at any given moment . i mean , you 'd have to add these up to get the total , and they might not all be the same value . but what i 'm trying to say is , at any given moment , you do n't know what direction the electric field 's going to be hitting your eye at from a random source . it could be in any direction . so this is not polarized . this diagram represents light that is not polarized . at some point , the field might be pointing this way , at some later point it 's this way ; it 's just random . you never know which way the electric field 's going to be pointing . whereas these over here , these are polarized . so how could you polarize this light ? let 's say you wanted light that was polarized . you were doing an experiment . you needed polarized light . well , that 's easy . you can use what 's called a polarizer . and this is a material that lets light through , but it only lets light through in one orientation , so you 're going to have a polarizer that , for instance , only lets through vertically polarized light . so this is a polarizer . these are cheap : thin , plastic , configured in a way so that it only lets light through that 's vertically polarized . any light coming in here that 's not vertically polarized gets blocked , or absorbed . so what that means is , if you used this polarizer and held it in between your eye and this light bulb , you would only get this light . all the rest of it would get blocked . or you could just rotate this thing and imagine a polarizer that only lets through horizontal light . now it would only let through light that was this way , and so you would only get this part of the light . or you could just orient it at any angle you want and block everything but the certain angle that this polarizer is defined as letting light through . so you can do this . and once you hold this up , you get polarized light , light that 's only got one orientation . so that 's what polarization means . but why do we care about polarization ? well , let me get rid of this for a minute . you 've heard of polarized sunglasses . so imagine you 're standing near water , or maybe you 're standing on ice or snow or something reflective . there 's a problem . say the sun 's out . it 's shining . it 's a beautiful day -- except there 's going to be glare . let 's say you 're looking down at something here on the ground . it 's going to get light reflecting off of it from just ... you know , light 's coming in from all direction . but it also gets this direct light from the sun . so it gets light from reflected off the clouds and whatever , whatever 's nearby , ambient light . and there 's also this direct sunlight . that 's harsh . if that reflects straight up to your eye , that hurts . you do n't like that . it blocks our vision . it 's hard to see , it 's glare . we do n't want this glare . so what can we do ? well , it just so happens that , when light reflects off of a surface , even though the light from the sun is not polarized , once it reflects , it does get polarized or at least partially polarized . so this surface here , once this light reflects , it 's coming in at all orientations . you got electric field ... you never know what electric field you 're going to get straight from the sun . and when it reflects , though , you mostly get , upon reflection , the direction of polarization defined by the plane of the surface that it hit . so because the floor is horizontal , when this light ray hits the ground and reflects , that reflected light gets partially polarized . this horizontal component of the electric field is going to be more present than the other components . maybe not completely . sometimes it could be . it could be completely polarized , but often it 's just partially polarized . but that 's pretty cool , because now you know what we can do . i know how to block this . we should get some sunglasses . we put some sunglasses on and we make our glasses so that these are polarized . and how do we want these polarized ? i want to get rid of the glare . so what i do is , i make sure my sunglasses only let through vertically polarized light . here 's some polarizers . that way , a lot of this glare gets blocked because it does not have a vertical orientation , it has a horizontal orientation . and then we can block it . so that 's one good thing that polarization does for us , and understanding it , we can get rid of glare . also , fishermen like it because , if you 're trying to look in the water at fish , you want to see in through the water , you want to see this light from the fish getting to you . you do n't want to see the glare off of the sun getting to you . so polarized sunglasses are useful . also , we can play a trick on our eye , if we really wanted to . you could take one of these , make one eye have a vertical orientation for the polarization , have the other eye with a horizontal ... and you 're thinking , `` this is stupid . `` why would you do this for ? '' `` this eye 's going to get a lot of glare . '' we would n't use these outside , when you 're , like , skiing or fishing , but you could play a trick on your eyes if you went to the movies and you went and watched a movie . well , the reason our eyes see 3d is because they 're spaced a little bit apart . they each get a different , slightly different image . that makes us see in 3d . we can play the same trick on our eye if we have the polarization like this . if light , if some of the light from the movie theater screen is coming in with one polarization , and the other light 's coming in with the other polarization , we can send two different images to our eyes at the same time . if you took these off , it 'd look like garbage because you 'd be getting both of these slightly different images , it 'd look all blurry . and it does . if you take off your 3d glasses and look at a 3d movie , looks terrible , because now both eyes are getting both images . but if you put your glasses back on , now this eye only gets the orientation that it 's supposed to get , and this eye only gets the orientation that it 's supposed to get , and you get a 3d image . so it 's useful in many ways . let me show you one more thing here . let 's come back here . this light was polarized vertically . so that 's called linear polarization . any time ... same with these . these are all linear polarization because , just up and down , one linear direction , just diagonal . this is also linear . all of these are linear . you can get circular polarized light . so if we come back to here , we 've got our electric field pointing up , like that . now let 's say we sent in another light ray , another light ray that also had a polarization , but not in this direction . let 's say our other light ray had polarization in this direction , so it looks like this , kind of like what our magnetic field would have looked like . but this is a completely different light ray with its own polarization and its own magnetic field . so we send this in . what would happen ? well , at this point , you 'd have a electric field that points this way . at this point , you 'd have a electric field that points that way . what would your eye see if you were over here ? let 's see . if i draw our axis here . all right , when this point right here gets to your eye , what am i going to see ? well , i 'm going to have a light ray that 's one part of a light ray . one component points up . that 's this electric field . one component points left . that 's this electric field . so the total , my total electric field , would point this way . i could to the pythagorean theorem if i wanted to figure out the size of it , but i just want to know the direction for now . and then it gets to here , and look at it : they both have zero . this light ray has zero electric field , this one has zero electric fields . so then it 'd just be at zero . now what happens over here ? well , i 've got light . this one points to the right at that point , this pink one , and then this red one would be pointing down . so what would i have at that point ? i 'd have light that went this way , and it would just be doing this over and over . it would just be ... i 'd just have diagonally polarized light . this is n't giving me anything new . you might think this is dumb . why do this ? why send in two different waves to just get diagonally polarized light ? i could have just sent in one wave that was diagonally polarized and got the same thing . the reason is , if you shift this purple wave , this pink wave , by 90 degrees of phase , by pi over two in phase , something magical happens . let me show you what happens here , if we move this to here . now we do n't just get diagonally linear polarized light . what we 're going to get is ... let me get rid of this . okay , so we start off with red , right ? the red electric field points up , and then this pink wave 's electric field is zero at that point . so this is all i have . my total electric field would just be up . i 'm going to draw it right here . the green 'll be the total . now i come over to here , and at this point , there 's some red electric field that points up , but there 's some of this other electric field that points this way . so i 'd have a total electric field that would point that way . and then i get over to here , and i 'd have all of the electric field from the pink one , none from the red one . it would point all left then . look what 's happening . the polarization of this light , if i shift this , if i 'm sitting here , looking with my eye , as my eye receives this light , i 'm going to see this light rotate its polarization . the polarization i 'm going to notice swings around in a circular pattern . and because of this , we call this circular polarization . so this is another type of polarization , where the actual angle of polarization rotates smoothly as this light ray enters your eye . and you know what ? er , drrr ... all right , actually , i sent you to receive this one first . that makes no sense . you 're going to receive the ones closes to you first in this light ray going this way . so you 'd actually receive this one first , then that one , then this one , then this one . because of that , you would n't see this going in a counterclockwise way , you 'd see this going in a clockwise circularly polarized way . sorry about that . you might think , `` okay , why ? `` why even bother with circular polarization ? '' well , i kind of lied earlier . turns out , in the movie theater example , they do n't actually do it like this , typically . oftentimes in the movie theaters , we do n't have just linearly polarized sunglasses . this would be a problem because , when you look at the movie theater screen , and if you were to tilt your head just a little bit ... think about it . this one 's not really going to get the right image anymore . it 's going to get some of both . and this one 's going to get some of both . it 's going to be blurry . your head would have to be perfectly level the whole time , which might be annoying . so what we do is , instead , we create circular polarized glasses , so that this one would only get one polarization , this one would get the other direction . this way , even if you tilt your head a little bit ... shoot , clockwise is clockwise , counterclockwise is counterclockwise . by using circular polarization for 3d movies , it can make it a little easier on you eyes to see a better 3d image , even if your head 's tilted a little bit .
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you were doing an experiment . you needed polarized light . well , that 's easy .
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whice one is easy to see with open eyes , polarized light or unpolarized light ?
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- let 's talk about polarization of light . we know what light waves are ; they 're electromagnetic waves . so they 're made out of electric fields . and that 's not good enough . we know there 's not just electric fields . that could n't sustain itself . there 's got to be magnetic fields there , as well , that are changing . those are perpendicular , so you can kind of draw them . it 's hard , on something two-dimensional , but you can kind of imagine those looking something like this . and those magnetic fields would point at a right angle to the electric fields . but this gets really messy if i try to draw both the electric and magnetic fields at the same time . so we 're going to leave the magnetic fields out . it 's often good enough to just know the direction of the electric field when we focus on the electric field . so what does polarization mean ? polarization refers to the fact that , if this light ray was heading straight toward your eye , or a detector , over here , what would you see ? well , if i draw an axis over here , and this point here , in the middle , this is this line -- so imagine we 're looking straight down that line -- and then up and down is up and down , and then left and right , that direction i have the magnetic field , would be this way and that way . what would my eye see ? well , my eye 's only going to see electric fields that either point up or electric fields that point down . they might have different values , but i 'm only going to see electric fields that point up or down . because of that , this light ray is polarized . so polarized light is light where the electric field is only oscillating in one direction . up or down , that 's one direction -- vertically . or it could be polarized horizontally . or it could be polarized diagonally . but either way , you could have this wave polarized along any direction . i mean , a light ray like this , if we had it coming in diagonal , this light ray that 's oscillating like this , where the electric field oscillates like that , that also polarized . these are both polarized because there 's only one direction that the electric field is oscillating in . and you might thing , `` pff , how could you ever have `` a light ray that 's not polarized ? '' easy . most light that you get is not polarized . that is to say , light that 's coming from the sun , straight from the sun -- typically not polarized . light from a lightbulb , an old incandescent light bulb , this thing 's hot . you can get light polarized in any direction , all at once , all overlapping . so if we draw this case for a light bulb , just a random incandescent light bulb , you might get light , some of the light , hitting you eye , you can get some light that 's got that direction , you got light that 's got this direction , you got light in all these directions at any given moment . i mean , you 'd have to add these up to get the total , and they might not all be the same value . but what i 'm trying to say is , at any given moment , you do n't know what direction the electric field 's going to be hitting your eye at from a random source . it could be in any direction . so this is not polarized . this diagram represents light that is not polarized . at some point , the field might be pointing this way , at some later point it 's this way ; it 's just random . you never know which way the electric field 's going to be pointing . whereas these over here , these are polarized . so how could you polarize this light ? let 's say you wanted light that was polarized . you were doing an experiment . you needed polarized light . well , that 's easy . you can use what 's called a polarizer . and this is a material that lets light through , but it only lets light through in one orientation , so you 're going to have a polarizer that , for instance , only lets through vertically polarized light . so this is a polarizer . these are cheap : thin , plastic , configured in a way so that it only lets light through that 's vertically polarized . any light coming in here that 's not vertically polarized gets blocked , or absorbed . so what that means is , if you used this polarizer and held it in between your eye and this light bulb , you would only get this light . all the rest of it would get blocked . or you could just rotate this thing and imagine a polarizer that only lets through horizontal light . now it would only let through light that was this way , and so you would only get this part of the light . or you could just orient it at any angle you want and block everything but the certain angle that this polarizer is defined as letting light through . so you can do this . and once you hold this up , you get polarized light , light that 's only got one orientation . so that 's what polarization means . but why do we care about polarization ? well , let me get rid of this for a minute . you 've heard of polarized sunglasses . so imagine you 're standing near water , or maybe you 're standing on ice or snow or something reflective . there 's a problem . say the sun 's out . it 's shining . it 's a beautiful day -- except there 's going to be glare . let 's say you 're looking down at something here on the ground . it 's going to get light reflecting off of it from just ... you know , light 's coming in from all direction . but it also gets this direct light from the sun . so it gets light from reflected off the clouds and whatever , whatever 's nearby , ambient light . and there 's also this direct sunlight . that 's harsh . if that reflects straight up to your eye , that hurts . you do n't like that . it blocks our vision . it 's hard to see , it 's glare . we do n't want this glare . so what can we do ? well , it just so happens that , when light reflects off of a surface , even though the light from the sun is not polarized , once it reflects , it does get polarized or at least partially polarized . so this surface here , once this light reflects , it 's coming in at all orientations . you got electric field ... you never know what electric field you 're going to get straight from the sun . and when it reflects , though , you mostly get , upon reflection , the direction of polarization defined by the plane of the surface that it hit . so because the floor is horizontal , when this light ray hits the ground and reflects , that reflected light gets partially polarized . this horizontal component of the electric field is going to be more present than the other components . maybe not completely . sometimes it could be . it could be completely polarized , but often it 's just partially polarized . but that 's pretty cool , because now you know what we can do . i know how to block this . we should get some sunglasses . we put some sunglasses on and we make our glasses so that these are polarized . and how do we want these polarized ? i want to get rid of the glare . so what i do is , i make sure my sunglasses only let through vertically polarized light . here 's some polarizers . that way , a lot of this glare gets blocked because it does not have a vertical orientation , it has a horizontal orientation . and then we can block it . so that 's one good thing that polarization does for us , and understanding it , we can get rid of glare . also , fishermen like it because , if you 're trying to look in the water at fish , you want to see in through the water , you want to see this light from the fish getting to you . you do n't want to see the glare off of the sun getting to you . so polarized sunglasses are useful . also , we can play a trick on our eye , if we really wanted to . you could take one of these , make one eye have a vertical orientation for the polarization , have the other eye with a horizontal ... and you 're thinking , `` this is stupid . `` why would you do this for ? '' `` this eye 's going to get a lot of glare . '' we would n't use these outside , when you 're , like , skiing or fishing , but you could play a trick on your eyes if you went to the movies and you went and watched a movie . well , the reason our eyes see 3d is because they 're spaced a little bit apart . they each get a different , slightly different image . that makes us see in 3d . we can play the same trick on our eye if we have the polarization like this . if light , if some of the light from the movie theater screen is coming in with one polarization , and the other light 's coming in with the other polarization , we can send two different images to our eyes at the same time . if you took these off , it 'd look like garbage because you 'd be getting both of these slightly different images , it 'd look all blurry . and it does . if you take off your 3d glasses and look at a 3d movie , looks terrible , because now both eyes are getting both images . but if you put your glasses back on , now this eye only gets the orientation that it 's supposed to get , and this eye only gets the orientation that it 's supposed to get , and you get a 3d image . so it 's useful in many ways . let me show you one more thing here . let 's come back here . this light was polarized vertically . so that 's called linear polarization . any time ... same with these . these are all linear polarization because , just up and down , one linear direction , just diagonal . this is also linear . all of these are linear . you can get circular polarized light . so if we come back to here , we 've got our electric field pointing up , like that . now let 's say we sent in another light ray , another light ray that also had a polarization , but not in this direction . let 's say our other light ray had polarization in this direction , so it looks like this , kind of like what our magnetic field would have looked like . but this is a completely different light ray with its own polarization and its own magnetic field . so we send this in . what would happen ? well , at this point , you 'd have a electric field that points this way . at this point , you 'd have a electric field that points that way . what would your eye see if you were over here ? let 's see . if i draw our axis here . all right , when this point right here gets to your eye , what am i going to see ? well , i 'm going to have a light ray that 's one part of a light ray . one component points up . that 's this electric field . one component points left . that 's this electric field . so the total , my total electric field , would point this way . i could to the pythagorean theorem if i wanted to figure out the size of it , but i just want to know the direction for now . and then it gets to here , and look at it : they both have zero . this light ray has zero electric field , this one has zero electric fields . so then it 'd just be at zero . now what happens over here ? well , i 've got light . this one points to the right at that point , this pink one , and then this red one would be pointing down . so what would i have at that point ? i 'd have light that went this way , and it would just be doing this over and over . it would just be ... i 'd just have diagonally polarized light . this is n't giving me anything new . you might think this is dumb . why do this ? why send in two different waves to just get diagonally polarized light ? i could have just sent in one wave that was diagonally polarized and got the same thing . the reason is , if you shift this purple wave , this pink wave , by 90 degrees of phase , by pi over two in phase , something magical happens . let me show you what happens here , if we move this to here . now we do n't just get diagonally linear polarized light . what we 're going to get is ... let me get rid of this . okay , so we start off with red , right ? the red electric field points up , and then this pink wave 's electric field is zero at that point . so this is all i have . my total electric field would just be up . i 'm going to draw it right here . the green 'll be the total . now i come over to here , and at this point , there 's some red electric field that points up , but there 's some of this other electric field that points this way . so i 'd have a total electric field that would point that way . and then i get over to here , and i 'd have all of the electric field from the pink one , none from the red one . it would point all left then . look what 's happening . the polarization of this light , if i shift this , if i 'm sitting here , looking with my eye , as my eye receives this light , i 'm going to see this light rotate its polarization . the polarization i 'm going to notice swings around in a circular pattern . and because of this , we call this circular polarization . so this is another type of polarization , where the actual angle of polarization rotates smoothly as this light ray enters your eye . and you know what ? er , drrr ... all right , actually , i sent you to receive this one first . that makes no sense . you 're going to receive the ones closes to you first in this light ray going this way . so you 'd actually receive this one first , then that one , then this one , then this one . because of that , you would n't see this going in a counterclockwise way , you 'd see this going in a clockwise circularly polarized way . sorry about that . you might think , `` okay , why ? `` why even bother with circular polarization ? '' well , i kind of lied earlier . turns out , in the movie theater example , they do n't actually do it like this , typically . oftentimes in the movie theaters , we do n't have just linearly polarized sunglasses . this would be a problem because , when you look at the movie theater screen , and if you were to tilt your head just a little bit ... think about it . this one 's not really going to get the right image anymore . it 's going to get some of both . and this one 's going to get some of both . it 's going to be blurry . your head would have to be perfectly level the whole time , which might be annoying . so what we do is , instead , we create circular polarized glasses , so that this one would only get one polarization , this one would get the other direction . this way , even if you tilt your head a little bit ... shoot , clockwise is clockwise , counterclockwise is counterclockwise . by using circular polarization for 3d movies , it can make it a little easier on you eyes to see a better 3d image , even if your head 's tilted a little bit .
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- let 's talk about polarization of light . we know what light waves are ; they 're electromagnetic waves .
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what are the other use of polarization of light in our everyday life except sun-glass ?
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- let 's talk about polarization of light . we know what light waves are ; they 're electromagnetic waves . so they 're made out of electric fields . and that 's not good enough . we know there 's not just electric fields . that could n't sustain itself . there 's got to be magnetic fields there , as well , that are changing . those are perpendicular , so you can kind of draw them . it 's hard , on something two-dimensional , but you can kind of imagine those looking something like this . and those magnetic fields would point at a right angle to the electric fields . but this gets really messy if i try to draw both the electric and magnetic fields at the same time . so we 're going to leave the magnetic fields out . it 's often good enough to just know the direction of the electric field when we focus on the electric field . so what does polarization mean ? polarization refers to the fact that , if this light ray was heading straight toward your eye , or a detector , over here , what would you see ? well , if i draw an axis over here , and this point here , in the middle , this is this line -- so imagine we 're looking straight down that line -- and then up and down is up and down , and then left and right , that direction i have the magnetic field , would be this way and that way . what would my eye see ? well , my eye 's only going to see electric fields that either point up or electric fields that point down . they might have different values , but i 'm only going to see electric fields that point up or down . because of that , this light ray is polarized . so polarized light is light where the electric field is only oscillating in one direction . up or down , that 's one direction -- vertically . or it could be polarized horizontally . or it could be polarized diagonally . but either way , you could have this wave polarized along any direction . i mean , a light ray like this , if we had it coming in diagonal , this light ray that 's oscillating like this , where the electric field oscillates like that , that also polarized . these are both polarized because there 's only one direction that the electric field is oscillating in . and you might thing , `` pff , how could you ever have `` a light ray that 's not polarized ? '' easy . most light that you get is not polarized . that is to say , light that 's coming from the sun , straight from the sun -- typically not polarized . light from a lightbulb , an old incandescent light bulb , this thing 's hot . you can get light polarized in any direction , all at once , all overlapping . so if we draw this case for a light bulb , just a random incandescent light bulb , you might get light , some of the light , hitting you eye , you can get some light that 's got that direction , you got light that 's got this direction , you got light in all these directions at any given moment . i mean , you 'd have to add these up to get the total , and they might not all be the same value . but what i 'm trying to say is , at any given moment , you do n't know what direction the electric field 's going to be hitting your eye at from a random source . it could be in any direction . so this is not polarized . this diagram represents light that is not polarized . at some point , the field might be pointing this way , at some later point it 's this way ; it 's just random . you never know which way the electric field 's going to be pointing . whereas these over here , these are polarized . so how could you polarize this light ? let 's say you wanted light that was polarized . you were doing an experiment . you needed polarized light . well , that 's easy . you can use what 's called a polarizer . and this is a material that lets light through , but it only lets light through in one orientation , so you 're going to have a polarizer that , for instance , only lets through vertically polarized light . so this is a polarizer . these are cheap : thin , plastic , configured in a way so that it only lets light through that 's vertically polarized . any light coming in here that 's not vertically polarized gets blocked , or absorbed . so what that means is , if you used this polarizer and held it in between your eye and this light bulb , you would only get this light . all the rest of it would get blocked . or you could just rotate this thing and imagine a polarizer that only lets through horizontal light . now it would only let through light that was this way , and so you would only get this part of the light . or you could just orient it at any angle you want and block everything but the certain angle that this polarizer is defined as letting light through . so you can do this . and once you hold this up , you get polarized light , light that 's only got one orientation . so that 's what polarization means . but why do we care about polarization ? well , let me get rid of this for a minute . you 've heard of polarized sunglasses . so imagine you 're standing near water , or maybe you 're standing on ice or snow or something reflective . there 's a problem . say the sun 's out . it 's shining . it 's a beautiful day -- except there 's going to be glare . let 's say you 're looking down at something here on the ground . it 's going to get light reflecting off of it from just ... you know , light 's coming in from all direction . but it also gets this direct light from the sun . so it gets light from reflected off the clouds and whatever , whatever 's nearby , ambient light . and there 's also this direct sunlight . that 's harsh . if that reflects straight up to your eye , that hurts . you do n't like that . it blocks our vision . it 's hard to see , it 's glare . we do n't want this glare . so what can we do ? well , it just so happens that , when light reflects off of a surface , even though the light from the sun is not polarized , once it reflects , it does get polarized or at least partially polarized . so this surface here , once this light reflects , it 's coming in at all orientations . you got electric field ... you never know what electric field you 're going to get straight from the sun . and when it reflects , though , you mostly get , upon reflection , the direction of polarization defined by the plane of the surface that it hit . so because the floor is horizontal , when this light ray hits the ground and reflects , that reflected light gets partially polarized . this horizontal component of the electric field is going to be more present than the other components . maybe not completely . sometimes it could be . it could be completely polarized , but often it 's just partially polarized . but that 's pretty cool , because now you know what we can do . i know how to block this . we should get some sunglasses . we put some sunglasses on and we make our glasses so that these are polarized . and how do we want these polarized ? i want to get rid of the glare . so what i do is , i make sure my sunglasses only let through vertically polarized light . here 's some polarizers . that way , a lot of this glare gets blocked because it does not have a vertical orientation , it has a horizontal orientation . and then we can block it . so that 's one good thing that polarization does for us , and understanding it , we can get rid of glare . also , fishermen like it because , if you 're trying to look in the water at fish , you want to see in through the water , you want to see this light from the fish getting to you . you do n't want to see the glare off of the sun getting to you . so polarized sunglasses are useful . also , we can play a trick on our eye , if we really wanted to . you could take one of these , make one eye have a vertical orientation for the polarization , have the other eye with a horizontal ... and you 're thinking , `` this is stupid . `` why would you do this for ? '' `` this eye 's going to get a lot of glare . '' we would n't use these outside , when you 're , like , skiing or fishing , but you could play a trick on your eyes if you went to the movies and you went and watched a movie . well , the reason our eyes see 3d is because they 're spaced a little bit apart . they each get a different , slightly different image . that makes us see in 3d . we can play the same trick on our eye if we have the polarization like this . if light , if some of the light from the movie theater screen is coming in with one polarization , and the other light 's coming in with the other polarization , we can send two different images to our eyes at the same time . if you took these off , it 'd look like garbage because you 'd be getting both of these slightly different images , it 'd look all blurry . and it does . if you take off your 3d glasses and look at a 3d movie , looks terrible , because now both eyes are getting both images . but if you put your glasses back on , now this eye only gets the orientation that it 's supposed to get , and this eye only gets the orientation that it 's supposed to get , and you get a 3d image . so it 's useful in many ways . let me show you one more thing here . let 's come back here . this light was polarized vertically . so that 's called linear polarization . any time ... same with these . these are all linear polarization because , just up and down , one linear direction , just diagonal . this is also linear . all of these are linear . you can get circular polarized light . so if we come back to here , we 've got our electric field pointing up , like that . now let 's say we sent in another light ray , another light ray that also had a polarization , but not in this direction . let 's say our other light ray had polarization in this direction , so it looks like this , kind of like what our magnetic field would have looked like . but this is a completely different light ray with its own polarization and its own magnetic field . so we send this in . what would happen ? well , at this point , you 'd have a electric field that points this way . at this point , you 'd have a electric field that points that way . what would your eye see if you were over here ? let 's see . if i draw our axis here . all right , when this point right here gets to your eye , what am i going to see ? well , i 'm going to have a light ray that 's one part of a light ray . one component points up . that 's this electric field . one component points left . that 's this electric field . so the total , my total electric field , would point this way . i could to the pythagorean theorem if i wanted to figure out the size of it , but i just want to know the direction for now . and then it gets to here , and look at it : they both have zero . this light ray has zero electric field , this one has zero electric fields . so then it 'd just be at zero . now what happens over here ? well , i 've got light . this one points to the right at that point , this pink one , and then this red one would be pointing down . so what would i have at that point ? i 'd have light that went this way , and it would just be doing this over and over . it would just be ... i 'd just have diagonally polarized light . this is n't giving me anything new . you might think this is dumb . why do this ? why send in two different waves to just get diagonally polarized light ? i could have just sent in one wave that was diagonally polarized and got the same thing . the reason is , if you shift this purple wave , this pink wave , by 90 degrees of phase , by pi over two in phase , something magical happens . let me show you what happens here , if we move this to here . now we do n't just get diagonally linear polarized light . what we 're going to get is ... let me get rid of this . okay , so we start off with red , right ? the red electric field points up , and then this pink wave 's electric field is zero at that point . so this is all i have . my total electric field would just be up . i 'm going to draw it right here . the green 'll be the total . now i come over to here , and at this point , there 's some red electric field that points up , but there 's some of this other electric field that points this way . so i 'd have a total electric field that would point that way . and then i get over to here , and i 'd have all of the electric field from the pink one , none from the red one . it would point all left then . look what 's happening . the polarization of this light , if i shift this , if i 'm sitting here , looking with my eye , as my eye receives this light , i 'm going to see this light rotate its polarization . the polarization i 'm going to notice swings around in a circular pattern . and because of this , we call this circular polarization . so this is another type of polarization , where the actual angle of polarization rotates smoothly as this light ray enters your eye . and you know what ? er , drrr ... all right , actually , i sent you to receive this one first . that makes no sense . you 're going to receive the ones closes to you first in this light ray going this way . so you 'd actually receive this one first , then that one , then this one , then this one . because of that , you would n't see this going in a counterclockwise way , you 'd see this going in a clockwise circularly polarized way . sorry about that . you might think , `` okay , why ? `` why even bother with circular polarization ? '' well , i kind of lied earlier . turns out , in the movie theater example , they do n't actually do it like this , typically . oftentimes in the movie theaters , we do n't have just linearly polarized sunglasses . this would be a problem because , when you look at the movie theater screen , and if you were to tilt your head just a little bit ... think about it . this one 's not really going to get the right image anymore . it 's going to get some of both . and this one 's going to get some of both . it 's going to be blurry . your head would have to be perfectly level the whole time , which might be annoying . so what we do is , instead , we create circular polarized glasses , so that this one would only get one polarization , this one would get the other direction . this way , even if you tilt your head a little bit ... shoot , clockwise is clockwise , counterclockwise is counterclockwise . by using circular polarization for 3d movies , it can make it a little easier on you eyes to see a better 3d image , even if your head 's tilted a little bit .
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and when it reflects , though , you mostly get , upon reflection , the direction of polarization defined by the plane of the surface that it hit . so because the floor is horizontal , when this light ray hits the ground and reflects , that reflected light gets partially polarized . this horizontal component of the electric field is going to be more present than the other components .
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in the example with the sun and the sunglasses , once the light is reflected on the ground , why is is partially polarized and why does the light mostly move in the direction of the surface ( so horizontally ) ?
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- let 's talk about polarization of light . we know what light waves are ; they 're electromagnetic waves . so they 're made out of electric fields . and that 's not good enough . we know there 's not just electric fields . that could n't sustain itself . there 's got to be magnetic fields there , as well , that are changing . those are perpendicular , so you can kind of draw them . it 's hard , on something two-dimensional , but you can kind of imagine those looking something like this . and those magnetic fields would point at a right angle to the electric fields . but this gets really messy if i try to draw both the electric and magnetic fields at the same time . so we 're going to leave the magnetic fields out . it 's often good enough to just know the direction of the electric field when we focus on the electric field . so what does polarization mean ? polarization refers to the fact that , if this light ray was heading straight toward your eye , or a detector , over here , what would you see ? well , if i draw an axis over here , and this point here , in the middle , this is this line -- so imagine we 're looking straight down that line -- and then up and down is up and down , and then left and right , that direction i have the magnetic field , would be this way and that way . what would my eye see ? well , my eye 's only going to see electric fields that either point up or electric fields that point down . they might have different values , but i 'm only going to see electric fields that point up or down . because of that , this light ray is polarized . so polarized light is light where the electric field is only oscillating in one direction . up or down , that 's one direction -- vertically . or it could be polarized horizontally . or it could be polarized diagonally . but either way , you could have this wave polarized along any direction . i mean , a light ray like this , if we had it coming in diagonal , this light ray that 's oscillating like this , where the electric field oscillates like that , that also polarized . these are both polarized because there 's only one direction that the electric field is oscillating in . and you might thing , `` pff , how could you ever have `` a light ray that 's not polarized ? '' easy . most light that you get is not polarized . that is to say , light that 's coming from the sun , straight from the sun -- typically not polarized . light from a lightbulb , an old incandescent light bulb , this thing 's hot . you can get light polarized in any direction , all at once , all overlapping . so if we draw this case for a light bulb , just a random incandescent light bulb , you might get light , some of the light , hitting you eye , you can get some light that 's got that direction , you got light that 's got this direction , you got light in all these directions at any given moment . i mean , you 'd have to add these up to get the total , and they might not all be the same value . but what i 'm trying to say is , at any given moment , you do n't know what direction the electric field 's going to be hitting your eye at from a random source . it could be in any direction . so this is not polarized . this diagram represents light that is not polarized . at some point , the field might be pointing this way , at some later point it 's this way ; it 's just random . you never know which way the electric field 's going to be pointing . whereas these over here , these are polarized . so how could you polarize this light ? let 's say you wanted light that was polarized . you were doing an experiment . you needed polarized light . well , that 's easy . you can use what 's called a polarizer . and this is a material that lets light through , but it only lets light through in one orientation , so you 're going to have a polarizer that , for instance , only lets through vertically polarized light . so this is a polarizer . these are cheap : thin , plastic , configured in a way so that it only lets light through that 's vertically polarized . any light coming in here that 's not vertically polarized gets blocked , or absorbed . so what that means is , if you used this polarizer and held it in between your eye and this light bulb , you would only get this light . all the rest of it would get blocked . or you could just rotate this thing and imagine a polarizer that only lets through horizontal light . now it would only let through light that was this way , and so you would only get this part of the light . or you could just orient it at any angle you want and block everything but the certain angle that this polarizer is defined as letting light through . so you can do this . and once you hold this up , you get polarized light , light that 's only got one orientation . so that 's what polarization means . but why do we care about polarization ? well , let me get rid of this for a minute . you 've heard of polarized sunglasses . so imagine you 're standing near water , or maybe you 're standing on ice or snow or something reflective . there 's a problem . say the sun 's out . it 's shining . it 's a beautiful day -- except there 's going to be glare . let 's say you 're looking down at something here on the ground . it 's going to get light reflecting off of it from just ... you know , light 's coming in from all direction . but it also gets this direct light from the sun . so it gets light from reflected off the clouds and whatever , whatever 's nearby , ambient light . and there 's also this direct sunlight . that 's harsh . if that reflects straight up to your eye , that hurts . you do n't like that . it blocks our vision . it 's hard to see , it 's glare . we do n't want this glare . so what can we do ? well , it just so happens that , when light reflects off of a surface , even though the light from the sun is not polarized , once it reflects , it does get polarized or at least partially polarized . so this surface here , once this light reflects , it 's coming in at all orientations . you got electric field ... you never know what electric field you 're going to get straight from the sun . and when it reflects , though , you mostly get , upon reflection , the direction of polarization defined by the plane of the surface that it hit . so because the floor is horizontal , when this light ray hits the ground and reflects , that reflected light gets partially polarized . this horizontal component of the electric field is going to be more present than the other components . maybe not completely . sometimes it could be . it could be completely polarized , but often it 's just partially polarized . but that 's pretty cool , because now you know what we can do . i know how to block this . we should get some sunglasses . we put some sunglasses on and we make our glasses so that these are polarized . and how do we want these polarized ? i want to get rid of the glare . so what i do is , i make sure my sunglasses only let through vertically polarized light . here 's some polarizers . that way , a lot of this glare gets blocked because it does not have a vertical orientation , it has a horizontal orientation . and then we can block it . so that 's one good thing that polarization does for us , and understanding it , we can get rid of glare . also , fishermen like it because , if you 're trying to look in the water at fish , you want to see in through the water , you want to see this light from the fish getting to you . you do n't want to see the glare off of the sun getting to you . so polarized sunglasses are useful . also , we can play a trick on our eye , if we really wanted to . you could take one of these , make one eye have a vertical orientation for the polarization , have the other eye with a horizontal ... and you 're thinking , `` this is stupid . `` why would you do this for ? '' `` this eye 's going to get a lot of glare . '' we would n't use these outside , when you 're , like , skiing or fishing , but you could play a trick on your eyes if you went to the movies and you went and watched a movie . well , the reason our eyes see 3d is because they 're spaced a little bit apart . they each get a different , slightly different image . that makes us see in 3d . we can play the same trick on our eye if we have the polarization like this . if light , if some of the light from the movie theater screen is coming in with one polarization , and the other light 's coming in with the other polarization , we can send two different images to our eyes at the same time . if you took these off , it 'd look like garbage because you 'd be getting both of these slightly different images , it 'd look all blurry . and it does . if you take off your 3d glasses and look at a 3d movie , looks terrible , because now both eyes are getting both images . but if you put your glasses back on , now this eye only gets the orientation that it 's supposed to get , and this eye only gets the orientation that it 's supposed to get , and you get a 3d image . so it 's useful in many ways . let me show you one more thing here . let 's come back here . this light was polarized vertically . so that 's called linear polarization . any time ... same with these . these are all linear polarization because , just up and down , one linear direction , just diagonal . this is also linear . all of these are linear . you can get circular polarized light . so if we come back to here , we 've got our electric field pointing up , like that . now let 's say we sent in another light ray , another light ray that also had a polarization , but not in this direction . let 's say our other light ray had polarization in this direction , so it looks like this , kind of like what our magnetic field would have looked like . but this is a completely different light ray with its own polarization and its own magnetic field . so we send this in . what would happen ? well , at this point , you 'd have a electric field that points this way . at this point , you 'd have a electric field that points that way . what would your eye see if you were over here ? let 's see . if i draw our axis here . all right , when this point right here gets to your eye , what am i going to see ? well , i 'm going to have a light ray that 's one part of a light ray . one component points up . that 's this electric field . one component points left . that 's this electric field . so the total , my total electric field , would point this way . i could to the pythagorean theorem if i wanted to figure out the size of it , but i just want to know the direction for now . and then it gets to here , and look at it : they both have zero . this light ray has zero electric field , this one has zero electric fields . so then it 'd just be at zero . now what happens over here ? well , i 've got light . this one points to the right at that point , this pink one , and then this red one would be pointing down . so what would i have at that point ? i 'd have light that went this way , and it would just be doing this over and over . it would just be ... i 'd just have diagonally polarized light . this is n't giving me anything new . you might think this is dumb . why do this ? why send in two different waves to just get diagonally polarized light ? i could have just sent in one wave that was diagonally polarized and got the same thing . the reason is , if you shift this purple wave , this pink wave , by 90 degrees of phase , by pi over two in phase , something magical happens . let me show you what happens here , if we move this to here . now we do n't just get diagonally linear polarized light . what we 're going to get is ... let me get rid of this . okay , so we start off with red , right ? the red electric field points up , and then this pink wave 's electric field is zero at that point . so this is all i have . my total electric field would just be up . i 'm going to draw it right here . the green 'll be the total . now i come over to here , and at this point , there 's some red electric field that points up , but there 's some of this other electric field that points this way . so i 'd have a total electric field that would point that way . and then i get over to here , and i 'd have all of the electric field from the pink one , none from the red one . it would point all left then . look what 's happening . the polarization of this light , if i shift this , if i 'm sitting here , looking with my eye , as my eye receives this light , i 'm going to see this light rotate its polarization . the polarization i 'm going to notice swings around in a circular pattern . and because of this , we call this circular polarization . so this is another type of polarization , where the actual angle of polarization rotates smoothly as this light ray enters your eye . and you know what ? er , drrr ... all right , actually , i sent you to receive this one first . that makes no sense . you 're going to receive the ones closes to you first in this light ray going this way . so you 'd actually receive this one first , then that one , then this one , then this one . because of that , you would n't see this going in a counterclockwise way , you 'd see this going in a clockwise circularly polarized way . sorry about that . you might think , `` okay , why ? `` why even bother with circular polarization ? '' well , i kind of lied earlier . turns out , in the movie theater example , they do n't actually do it like this , typically . oftentimes in the movie theaters , we do n't have just linearly polarized sunglasses . this would be a problem because , when you look at the movie theater screen , and if you were to tilt your head just a little bit ... think about it . this one 's not really going to get the right image anymore . it 's going to get some of both . and this one 's going to get some of both . it 's going to be blurry . your head would have to be perfectly level the whole time , which might be annoying . so what we do is , instead , we create circular polarized glasses , so that this one would only get one polarization , this one would get the other direction . this way , even if you tilt your head a little bit ... shoot , clockwise is clockwise , counterclockwise is counterclockwise . by using circular polarization for 3d movies , it can make it a little easier on you eyes to see a better 3d image , even if your head 's tilted a little bit .
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because of that , this light ray is polarized . so polarized light is light where the electric field is only oscillating in one direction . up or down , that 's one direction -- vertically .
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do eyes only detect electric field and not the magnetic component of light ?
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- let 's talk about polarization of light . we know what light waves are ; they 're electromagnetic waves . so they 're made out of electric fields . and that 's not good enough . we know there 's not just electric fields . that could n't sustain itself . there 's got to be magnetic fields there , as well , that are changing . those are perpendicular , so you can kind of draw them . it 's hard , on something two-dimensional , but you can kind of imagine those looking something like this . and those magnetic fields would point at a right angle to the electric fields . but this gets really messy if i try to draw both the electric and magnetic fields at the same time . so we 're going to leave the magnetic fields out . it 's often good enough to just know the direction of the electric field when we focus on the electric field . so what does polarization mean ? polarization refers to the fact that , if this light ray was heading straight toward your eye , or a detector , over here , what would you see ? well , if i draw an axis over here , and this point here , in the middle , this is this line -- so imagine we 're looking straight down that line -- and then up and down is up and down , and then left and right , that direction i have the magnetic field , would be this way and that way . what would my eye see ? well , my eye 's only going to see electric fields that either point up or electric fields that point down . they might have different values , but i 'm only going to see electric fields that point up or down . because of that , this light ray is polarized . so polarized light is light where the electric field is only oscillating in one direction . up or down , that 's one direction -- vertically . or it could be polarized horizontally . or it could be polarized diagonally . but either way , you could have this wave polarized along any direction . i mean , a light ray like this , if we had it coming in diagonal , this light ray that 's oscillating like this , where the electric field oscillates like that , that also polarized . these are both polarized because there 's only one direction that the electric field is oscillating in . and you might thing , `` pff , how could you ever have `` a light ray that 's not polarized ? '' easy . most light that you get is not polarized . that is to say , light that 's coming from the sun , straight from the sun -- typically not polarized . light from a lightbulb , an old incandescent light bulb , this thing 's hot . you can get light polarized in any direction , all at once , all overlapping . so if we draw this case for a light bulb , just a random incandescent light bulb , you might get light , some of the light , hitting you eye , you can get some light that 's got that direction , you got light that 's got this direction , you got light in all these directions at any given moment . i mean , you 'd have to add these up to get the total , and they might not all be the same value . but what i 'm trying to say is , at any given moment , you do n't know what direction the electric field 's going to be hitting your eye at from a random source . it could be in any direction . so this is not polarized . this diagram represents light that is not polarized . at some point , the field might be pointing this way , at some later point it 's this way ; it 's just random . you never know which way the electric field 's going to be pointing . whereas these over here , these are polarized . so how could you polarize this light ? let 's say you wanted light that was polarized . you were doing an experiment . you needed polarized light . well , that 's easy . you can use what 's called a polarizer . and this is a material that lets light through , but it only lets light through in one orientation , so you 're going to have a polarizer that , for instance , only lets through vertically polarized light . so this is a polarizer . these are cheap : thin , plastic , configured in a way so that it only lets light through that 's vertically polarized . any light coming in here that 's not vertically polarized gets blocked , or absorbed . so what that means is , if you used this polarizer and held it in between your eye and this light bulb , you would only get this light . all the rest of it would get blocked . or you could just rotate this thing and imagine a polarizer that only lets through horizontal light . now it would only let through light that was this way , and so you would only get this part of the light . or you could just orient it at any angle you want and block everything but the certain angle that this polarizer is defined as letting light through . so you can do this . and once you hold this up , you get polarized light , light that 's only got one orientation . so that 's what polarization means . but why do we care about polarization ? well , let me get rid of this for a minute . you 've heard of polarized sunglasses . so imagine you 're standing near water , or maybe you 're standing on ice or snow or something reflective . there 's a problem . say the sun 's out . it 's shining . it 's a beautiful day -- except there 's going to be glare . let 's say you 're looking down at something here on the ground . it 's going to get light reflecting off of it from just ... you know , light 's coming in from all direction . but it also gets this direct light from the sun . so it gets light from reflected off the clouds and whatever , whatever 's nearby , ambient light . and there 's also this direct sunlight . that 's harsh . if that reflects straight up to your eye , that hurts . you do n't like that . it blocks our vision . it 's hard to see , it 's glare . we do n't want this glare . so what can we do ? well , it just so happens that , when light reflects off of a surface , even though the light from the sun is not polarized , once it reflects , it does get polarized or at least partially polarized . so this surface here , once this light reflects , it 's coming in at all orientations . you got electric field ... you never know what electric field you 're going to get straight from the sun . and when it reflects , though , you mostly get , upon reflection , the direction of polarization defined by the plane of the surface that it hit . so because the floor is horizontal , when this light ray hits the ground and reflects , that reflected light gets partially polarized . this horizontal component of the electric field is going to be more present than the other components . maybe not completely . sometimes it could be . it could be completely polarized , but often it 's just partially polarized . but that 's pretty cool , because now you know what we can do . i know how to block this . we should get some sunglasses . we put some sunglasses on and we make our glasses so that these are polarized . and how do we want these polarized ? i want to get rid of the glare . so what i do is , i make sure my sunglasses only let through vertically polarized light . here 's some polarizers . that way , a lot of this glare gets blocked because it does not have a vertical orientation , it has a horizontal orientation . and then we can block it . so that 's one good thing that polarization does for us , and understanding it , we can get rid of glare . also , fishermen like it because , if you 're trying to look in the water at fish , you want to see in through the water , you want to see this light from the fish getting to you . you do n't want to see the glare off of the sun getting to you . so polarized sunglasses are useful . also , we can play a trick on our eye , if we really wanted to . you could take one of these , make one eye have a vertical orientation for the polarization , have the other eye with a horizontal ... and you 're thinking , `` this is stupid . `` why would you do this for ? '' `` this eye 's going to get a lot of glare . '' we would n't use these outside , when you 're , like , skiing or fishing , but you could play a trick on your eyes if you went to the movies and you went and watched a movie . well , the reason our eyes see 3d is because they 're spaced a little bit apart . they each get a different , slightly different image . that makes us see in 3d . we can play the same trick on our eye if we have the polarization like this . if light , if some of the light from the movie theater screen is coming in with one polarization , and the other light 's coming in with the other polarization , we can send two different images to our eyes at the same time . if you took these off , it 'd look like garbage because you 'd be getting both of these slightly different images , it 'd look all blurry . and it does . if you take off your 3d glasses and look at a 3d movie , looks terrible , because now both eyes are getting both images . but if you put your glasses back on , now this eye only gets the orientation that it 's supposed to get , and this eye only gets the orientation that it 's supposed to get , and you get a 3d image . so it 's useful in many ways . let me show you one more thing here . let 's come back here . this light was polarized vertically . so that 's called linear polarization . any time ... same with these . these are all linear polarization because , just up and down , one linear direction , just diagonal . this is also linear . all of these are linear . you can get circular polarized light . so if we come back to here , we 've got our electric field pointing up , like that . now let 's say we sent in another light ray , another light ray that also had a polarization , but not in this direction . let 's say our other light ray had polarization in this direction , so it looks like this , kind of like what our magnetic field would have looked like . but this is a completely different light ray with its own polarization and its own magnetic field . so we send this in . what would happen ? well , at this point , you 'd have a electric field that points this way . at this point , you 'd have a electric field that points that way . what would your eye see if you were over here ? let 's see . if i draw our axis here . all right , when this point right here gets to your eye , what am i going to see ? well , i 'm going to have a light ray that 's one part of a light ray . one component points up . that 's this electric field . one component points left . that 's this electric field . so the total , my total electric field , would point this way . i could to the pythagorean theorem if i wanted to figure out the size of it , but i just want to know the direction for now . and then it gets to here , and look at it : they both have zero . this light ray has zero electric field , this one has zero electric fields . so then it 'd just be at zero . now what happens over here ? well , i 've got light . this one points to the right at that point , this pink one , and then this red one would be pointing down . so what would i have at that point ? i 'd have light that went this way , and it would just be doing this over and over . it would just be ... i 'd just have diagonally polarized light . this is n't giving me anything new . you might think this is dumb . why do this ? why send in two different waves to just get diagonally polarized light ? i could have just sent in one wave that was diagonally polarized and got the same thing . the reason is , if you shift this purple wave , this pink wave , by 90 degrees of phase , by pi over two in phase , something magical happens . let me show you what happens here , if we move this to here . now we do n't just get diagonally linear polarized light . what we 're going to get is ... let me get rid of this . okay , so we start off with red , right ? the red electric field points up , and then this pink wave 's electric field is zero at that point . so this is all i have . my total electric field would just be up . i 'm going to draw it right here . the green 'll be the total . now i come over to here , and at this point , there 's some red electric field that points up , but there 's some of this other electric field that points this way . so i 'd have a total electric field that would point that way . and then i get over to here , and i 'd have all of the electric field from the pink one , none from the red one . it would point all left then . look what 's happening . the polarization of this light , if i shift this , if i 'm sitting here , looking with my eye , as my eye receives this light , i 'm going to see this light rotate its polarization . the polarization i 'm going to notice swings around in a circular pattern . and because of this , we call this circular polarization . so this is another type of polarization , where the actual angle of polarization rotates smoothly as this light ray enters your eye . and you know what ? er , drrr ... all right , actually , i sent you to receive this one first . that makes no sense . you 're going to receive the ones closes to you first in this light ray going this way . so you 'd actually receive this one first , then that one , then this one , then this one . because of that , you would n't see this going in a counterclockwise way , you 'd see this going in a clockwise circularly polarized way . sorry about that . you might think , `` okay , why ? `` why even bother with circular polarization ? '' well , i kind of lied earlier . turns out , in the movie theater example , they do n't actually do it like this , typically . oftentimes in the movie theaters , we do n't have just linearly polarized sunglasses . this would be a problem because , when you look at the movie theater screen , and if you were to tilt your head just a little bit ... think about it . this one 's not really going to get the right image anymore . it 's going to get some of both . and this one 's going to get some of both . it 's going to be blurry . your head would have to be perfectly level the whole time , which might be annoying . so what we do is , instead , we create circular polarized glasses , so that this one would only get one polarization , this one would get the other direction . this way , even if you tilt your head a little bit ... shoot , clockwise is clockwise , counterclockwise is counterclockwise . by using circular polarization for 3d movies , it can make it a little easier on you eyes to see a better 3d image , even if your head 's tilted a little bit .
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you were doing an experiment . you needed polarized light . well , that 's easy .
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how is the light mostly horizontal ( thus a vertical polarized sun glasses blocking most of the glare ) ?
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- let 's talk about polarization of light . we know what light waves are ; they 're electromagnetic waves . so they 're made out of electric fields . and that 's not good enough . we know there 's not just electric fields . that could n't sustain itself . there 's got to be magnetic fields there , as well , that are changing . those are perpendicular , so you can kind of draw them . it 's hard , on something two-dimensional , but you can kind of imagine those looking something like this . and those magnetic fields would point at a right angle to the electric fields . but this gets really messy if i try to draw both the electric and magnetic fields at the same time . so we 're going to leave the magnetic fields out . it 's often good enough to just know the direction of the electric field when we focus on the electric field . so what does polarization mean ? polarization refers to the fact that , if this light ray was heading straight toward your eye , or a detector , over here , what would you see ? well , if i draw an axis over here , and this point here , in the middle , this is this line -- so imagine we 're looking straight down that line -- and then up and down is up and down , and then left and right , that direction i have the magnetic field , would be this way and that way . what would my eye see ? well , my eye 's only going to see electric fields that either point up or electric fields that point down . they might have different values , but i 'm only going to see electric fields that point up or down . because of that , this light ray is polarized . so polarized light is light where the electric field is only oscillating in one direction . up or down , that 's one direction -- vertically . or it could be polarized horizontally . or it could be polarized diagonally . but either way , you could have this wave polarized along any direction . i mean , a light ray like this , if we had it coming in diagonal , this light ray that 's oscillating like this , where the electric field oscillates like that , that also polarized . these are both polarized because there 's only one direction that the electric field is oscillating in . and you might thing , `` pff , how could you ever have `` a light ray that 's not polarized ? '' easy . most light that you get is not polarized . that is to say , light that 's coming from the sun , straight from the sun -- typically not polarized . light from a lightbulb , an old incandescent light bulb , this thing 's hot . you can get light polarized in any direction , all at once , all overlapping . so if we draw this case for a light bulb , just a random incandescent light bulb , you might get light , some of the light , hitting you eye , you can get some light that 's got that direction , you got light that 's got this direction , you got light in all these directions at any given moment . i mean , you 'd have to add these up to get the total , and they might not all be the same value . but what i 'm trying to say is , at any given moment , you do n't know what direction the electric field 's going to be hitting your eye at from a random source . it could be in any direction . so this is not polarized . this diagram represents light that is not polarized . at some point , the field might be pointing this way , at some later point it 's this way ; it 's just random . you never know which way the electric field 's going to be pointing . whereas these over here , these are polarized . so how could you polarize this light ? let 's say you wanted light that was polarized . you were doing an experiment . you needed polarized light . well , that 's easy . you can use what 's called a polarizer . and this is a material that lets light through , but it only lets light through in one orientation , so you 're going to have a polarizer that , for instance , only lets through vertically polarized light . so this is a polarizer . these are cheap : thin , plastic , configured in a way so that it only lets light through that 's vertically polarized . any light coming in here that 's not vertically polarized gets blocked , or absorbed . so what that means is , if you used this polarizer and held it in between your eye and this light bulb , you would only get this light . all the rest of it would get blocked . or you could just rotate this thing and imagine a polarizer that only lets through horizontal light . now it would only let through light that was this way , and so you would only get this part of the light . or you could just orient it at any angle you want and block everything but the certain angle that this polarizer is defined as letting light through . so you can do this . and once you hold this up , you get polarized light , light that 's only got one orientation . so that 's what polarization means . but why do we care about polarization ? well , let me get rid of this for a minute . you 've heard of polarized sunglasses . so imagine you 're standing near water , or maybe you 're standing on ice or snow or something reflective . there 's a problem . say the sun 's out . it 's shining . it 's a beautiful day -- except there 's going to be glare . let 's say you 're looking down at something here on the ground . it 's going to get light reflecting off of it from just ... you know , light 's coming in from all direction . but it also gets this direct light from the sun . so it gets light from reflected off the clouds and whatever , whatever 's nearby , ambient light . and there 's also this direct sunlight . that 's harsh . if that reflects straight up to your eye , that hurts . you do n't like that . it blocks our vision . it 's hard to see , it 's glare . we do n't want this glare . so what can we do ? well , it just so happens that , when light reflects off of a surface , even though the light from the sun is not polarized , once it reflects , it does get polarized or at least partially polarized . so this surface here , once this light reflects , it 's coming in at all orientations . you got electric field ... you never know what electric field you 're going to get straight from the sun . and when it reflects , though , you mostly get , upon reflection , the direction of polarization defined by the plane of the surface that it hit . so because the floor is horizontal , when this light ray hits the ground and reflects , that reflected light gets partially polarized . this horizontal component of the electric field is going to be more present than the other components . maybe not completely . sometimes it could be . it could be completely polarized , but often it 's just partially polarized . but that 's pretty cool , because now you know what we can do . i know how to block this . we should get some sunglasses . we put some sunglasses on and we make our glasses so that these are polarized . and how do we want these polarized ? i want to get rid of the glare . so what i do is , i make sure my sunglasses only let through vertically polarized light . here 's some polarizers . that way , a lot of this glare gets blocked because it does not have a vertical orientation , it has a horizontal orientation . and then we can block it . so that 's one good thing that polarization does for us , and understanding it , we can get rid of glare . also , fishermen like it because , if you 're trying to look in the water at fish , you want to see in through the water , you want to see this light from the fish getting to you . you do n't want to see the glare off of the sun getting to you . so polarized sunglasses are useful . also , we can play a trick on our eye , if we really wanted to . you could take one of these , make one eye have a vertical orientation for the polarization , have the other eye with a horizontal ... and you 're thinking , `` this is stupid . `` why would you do this for ? '' `` this eye 's going to get a lot of glare . '' we would n't use these outside , when you 're , like , skiing or fishing , but you could play a trick on your eyes if you went to the movies and you went and watched a movie . well , the reason our eyes see 3d is because they 're spaced a little bit apart . they each get a different , slightly different image . that makes us see in 3d . we can play the same trick on our eye if we have the polarization like this . if light , if some of the light from the movie theater screen is coming in with one polarization , and the other light 's coming in with the other polarization , we can send two different images to our eyes at the same time . if you took these off , it 'd look like garbage because you 'd be getting both of these slightly different images , it 'd look all blurry . and it does . if you take off your 3d glasses and look at a 3d movie , looks terrible , because now both eyes are getting both images . but if you put your glasses back on , now this eye only gets the orientation that it 's supposed to get , and this eye only gets the orientation that it 's supposed to get , and you get a 3d image . so it 's useful in many ways . let me show you one more thing here . let 's come back here . this light was polarized vertically . so that 's called linear polarization . any time ... same with these . these are all linear polarization because , just up and down , one linear direction , just diagonal . this is also linear . all of these are linear . you can get circular polarized light . so if we come back to here , we 've got our electric field pointing up , like that . now let 's say we sent in another light ray , another light ray that also had a polarization , but not in this direction . let 's say our other light ray had polarization in this direction , so it looks like this , kind of like what our magnetic field would have looked like . but this is a completely different light ray with its own polarization and its own magnetic field . so we send this in . what would happen ? well , at this point , you 'd have a electric field that points this way . at this point , you 'd have a electric field that points that way . what would your eye see if you were over here ? let 's see . if i draw our axis here . all right , when this point right here gets to your eye , what am i going to see ? well , i 'm going to have a light ray that 's one part of a light ray . one component points up . that 's this electric field . one component points left . that 's this electric field . so the total , my total electric field , would point this way . i could to the pythagorean theorem if i wanted to figure out the size of it , but i just want to know the direction for now . and then it gets to here , and look at it : they both have zero . this light ray has zero electric field , this one has zero electric fields . so then it 'd just be at zero . now what happens over here ? well , i 've got light . this one points to the right at that point , this pink one , and then this red one would be pointing down . so what would i have at that point ? i 'd have light that went this way , and it would just be doing this over and over . it would just be ... i 'd just have diagonally polarized light . this is n't giving me anything new . you might think this is dumb . why do this ? why send in two different waves to just get diagonally polarized light ? i could have just sent in one wave that was diagonally polarized and got the same thing . the reason is , if you shift this purple wave , this pink wave , by 90 degrees of phase , by pi over two in phase , something magical happens . let me show you what happens here , if we move this to here . now we do n't just get diagonally linear polarized light . what we 're going to get is ... let me get rid of this . okay , so we start off with red , right ? the red electric field points up , and then this pink wave 's electric field is zero at that point . so this is all i have . my total electric field would just be up . i 'm going to draw it right here . the green 'll be the total . now i come over to here , and at this point , there 's some red electric field that points up , but there 's some of this other electric field that points this way . so i 'd have a total electric field that would point that way . and then i get over to here , and i 'd have all of the electric field from the pink one , none from the red one . it would point all left then . look what 's happening . the polarization of this light , if i shift this , if i 'm sitting here , looking with my eye , as my eye receives this light , i 'm going to see this light rotate its polarization . the polarization i 'm going to notice swings around in a circular pattern . and because of this , we call this circular polarization . so this is another type of polarization , where the actual angle of polarization rotates smoothly as this light ray enters your eye . and you know what ? er , drrr ... all right , actually , i sent you to receive this one first . that makes no sense . you 're going to receive the ones closes to you first in this light ray going this way . so you 'd actually receive this one first , then that one , then this one , then this one . because of that , you would n't see this going in a counterclockwise way , you 'd see this going in a clockwise circularly polarized way . sorry about that . you might think , `` okay , why ? `` why even bother with circular polarization ? '' well , i kind of lied earlier . turns out , in the movie theater example , they do n't actually do it like this , typically . oftentimes in the movie theaters , we do n't have just linearly polarized sunglasses . this would be a problem because , when you look at the movie theater screen , and if you were to tilt your head just a little bit ... think about it . this one 's not really going to get the right image anymore . it 's going to get some of both . and this one 's going to get some of both . it 's going to be blurry . your head would have to be perfectly level the whole time , which might be annoying . so what we do is , instead , we create circular polarized glasses , so that this one would only get one polarization , this one would get the other direction . this way , even if you tilt your head a little bit ... shoot , clockwise is clockwise , counterclockwise is counterclockwise . by using circular polarization for 3d movies , it can make it a little easier on you eyes to see a better 3d image , even if your head 's tilted a little bit .
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so then it 'd just be at zero . now what happens over here ? well , i 've got light .
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in photoelectric effect what happens when only the work function is provided ?
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- let 's talk about polarization of light . we know what light waves are ; they 're electromagnetic waves . so they 're made out of electric fields . and that 's not good enough . we know there 's not just electric fields . that could n't sustain itself . there 's got to be magnetic fields there , as well , that are changing . those are perpendicular , so you can kind of draw them . it 's hard , on something two-dimensional , but you can kind of imagine those looking something like this . and those magnetic fields would point at a right angle to the electric fields . but this gets really messy if i try to draw both the electric and magnetic fields at the same time . so we 're going to leave the magnetic fields out . it 's often good enough to just know the direction of the electric field when we focus on the electric field . so what does polarization mean ? polarization refers to the fact that , if this light ray was heading straight toward your eye , or a detector , over here , what would you see ? well , if i draw an axis over here , and this point here , in the middle , this is this line -- so imagine we 're looking straight down that line -- and then up and down is up and down , and then left and right , that direction i have the magnetic field , would be this way and that way . what would my eye see ? well , my eye 's only going to see electric fields that either point up or electric fields that point down . they might have different values , but i 'm only going to see electric fields that point up or down . because of that , this light ray is polarized . so polarized light is light where the electric field is only oscillating in one direction . up or down , that 's one direction -- vertically . or it could be polarized horizontally . or it could be polarized diagonally . but either way , you could have this wave polarized along any direction . i mean , a light ray like this , if we had it coming in diagonal , this light ray that 's oscillating like this , where the electric field oscillates like that , that also polarized . these are both polarized because there 's only one direction that the electric field is oscillating in . and you might thing , `` pff , how could you ever have `` a light ray that 's not polarized ? '' easy . most light that you get is not polarized . that is to say , light that 's coming from the sun , straight from the sun -- typically not polarized . light from a lightbulb , an old incandescent light bulb , this thing 's hot . you can get light polarized in any direction , all at once , all overlapping . so if we draw this case for a light bulb , just a random incandescent light bulb , you might get light , some of the light , hitting you eye , you can get some light that 's got that direction , you got light that 's got this direction , you got light in all these directions at any given moment . i mean , you 'd have to add these up to get the total , and they might not all be the same value . but what i 'm trying to say is , at any given moment , you do n't know what direction the electric field 's going to be hitting your eye at from a random source . it could be in any direction . so this is not polarized . this diagram represents light that is not polarized . at some point , the field might be pointing this way , at some later point it 's this way ; it 's just random . you never know which way the electric field 's going to be pointing . whereas these over here , these are polarized . so how could you polarize this light ? let 's say you wanted light that was polarized . you were doing an experiment . you needed polarized light . well , that 's easy . you can use what 's called a polarizer . and this is a material that lets light through , but it only lets light through in one orientation , so you 're going to have a polarizer that , for instance , only lets through vertically polarized light . so this is a polarizer . these are cheap : thin , plastic , configured in a way so that it only lets light through that 's vertically polarized . any light coming in here that 's not vertically polarized gets blocked , or absorbed . so what that means is , if you used this polarizer and held it in between your eye and this light bulb , you would only get this light . all the rest of it would get blocked . or you could just rotate this thing and imagine a polarizer that only lets through horizontal light . now it would only let through light that was this way , and so you would only get this part of the light . or you could just orient it at any angle you want and block everything but the certain angle that this polarizer is defined as letting light through . so you can do this . and once you hold this up , you get polarized light , light that 's only got one orientation . so that 's what polarization means . but why do we care about polarization ? well , let me get rid of this for a minute . you 've heard of polarized sunglasses . so imagine you 're standing near water , or maybe you 're standing on ice or snow or something reflective . there 's a problem . say the sun 's out . it 's shining . it 's a beautiful day -- except there 's going to be glare . let 's say you 're looking down at something here on the ground . it 's going to get light reflecting off of it from just ... you know , light 's coming in from all direction . but it also gets this direct light from the sun . so it gets light from reflected off the clouds and whatever , whatever 's nearby , ambient light . and there 's also this direct sunlight . that 's harsh . if that reflects straight up to your eye , that hurts . you do n't like that . it blocks our vision . it 's hard to see , it 's glare . we do n't want this glare . so what can we do ? well , it just so happens that , when light reflects off of a surface , even though the light from the sun is not polarized , once it reflects , it does get polarized or at least partially polarized . so this surface here , once this light reflects , it 's coming in at all orientations . you got electric field ... you never know what electric field you 're going to get straight from the sun . and when it reflects , though , you mostly get , upon reflection , the direction of polarization defined by the plane of the surface that it hit . so because the floor is horizontal , when this light ray hits the ground and reflects , that reflected light gets partially polarized . this horizontal component of the electric field is going to be more present than the other components . maybe not completely . sometimes it could be . it could be completely polarized , but often it 's just partially polarized . but that 's pretty cool , because now you know what we can do . i know how to block this . we should get some sunglasses . we put some sunglasses on and we make our glasses so that these are polarized . and how do we want these polarized ? i want to get rid of the glare . so what i do is , i make sure my sunglasses only let through vertically polarized light . here 's some polarizers . that way , a lot of this glare gets blocked because it does not have a vertical orientation , it has a horizontal orientation . and then we can block it . so that 's one good thing that polarization does for us , and understanding it , we can get rid of glare . also , fishermen like it because , if you 're trying to look in the water at fish , you want to see in through the water , you want to see this light from the fish getting to you . you do n't want to see the glare off of the sun getting to you . so polarized sunglasses are useful . also , we can play a trick on our eye , if we really wanted to . you could take one of these , make one eye have a vertical orientation for the polarization , have the other eye with a horizontal ... and you 're thinking , `` this is stupid . `` why would you do this for ? '' `` this eye 's going to get a lot of glare . '' we would n't use these outside , when you 're , like , skiing or fishing , but you could play a trick on your eyes if you went to the movies and you went and watched a movie . well , the reason our eyes see 3d is because they 're spaced a little bit apart . they each get a different , slightly different image . that makes us see in 3d . we can play the same trick on our eye if we have the polarization like this . if light , if some of the light from the movie theater screen is coming in with one polarization , and the other light 's coming in with the other polarization , we can send two different images to our eyes at the same time . if you took these off , it 'd look like garbage because you 'd be getting both of these slightly different images , it 'd look all blurry . and it does . if you take off your 3d glasses and look at a 3d movie , looks terrible , because now both eyes are getting both images . but if you put your glasses back on , now this eye only gets the orientation that it 's supposed to get , and this eye only gets the orientation that it 's supposed to get , and you get a 3d image . so it 's useful in many ways . let me show you one more thing here . let 's come back here . this light was polarized vertically . so that 's called linear polarization . any time ... same with these . these are all linear polarization because , just up and down , one linear direction , just diagonal . this is also linear . all of these are linear . you can get circular polarized light . so if we come back to here , we 've got our electric field pointing up , like that . now let 's say we sent in another light ray , another light ray that also had a polarization , but not in this direction . let 's say our other light ray had polarization in this direction , so it looks like this , kind of like what our magnetic field would have looked like . but this is a completely different light ray with its own polarization and its own magnetic field . so we send this in . what would happen ? well , at this point , you 'd have a electric field that points this way . at this point , you 'd have a electric field that points that way . what would your eye see if you were over here ? let 's see . if i draw our axis here . all right , when this point right here gets to your eye , what am i going to see ? well , i 'm going to have a light ray that 's one part of a light ray . one component points up . that 's this electric field . one component points left . that 's this electric field . so the total , my total electric field , would point this way . i could to the pythagorean theorem if i wanted to figure out the size of it , but i just want to know the direction for now . and then it gets to here , and look at it : they both have zero . this light ray has zero electric field , this one has zero electric fields . so then it 'd just be at zero . now what happens over here ? well , i 've got light . this one points to the right at that point , this pink one , and then this red one would be pointing down . so what would i have at that point ? i 'd have light that went this way , and it would just be doing this over and over . it would just be ... i 'd just have diagonally polarized light . this is n't giving me anything new . you might think this is dumb . why do this ? why send in two different waves to just get diagonally polarized light ? i could have just sent in one wave that was diagonally polarized and got the same thing . the reason is , if you shift this purple wave , this pink wave , by 90 degrees of phase , by pi over two in phase , something magical happens . let me show you what happens here , if we move this to here . now we do n't just get diagonally linear polarized light . what we 're going to get is ... let me get rid of this . okay , so we start off with red , right ? the red electric field points up , and then this pink wave 's electric field is zero at that point . so this is all i have . my total electric field would just be up . i 'm going to draw it right here . the green 'll be the total . now i come over to here , and at this point , there 's some red electric field that points up , but there 's some of this other electric field that points this way . so i 'd have a total electric field that would point that way . and then i get over to here , and i 'd have all of the electric field from the pink one , none from the red one . it would point all left then . look what 's happening . the polarization of this light , if i shift this , if i 'm sitting here , looking with my eye , as my eye receives this light , i 'm going to see this light rotate its polarization . the polarization i 'm going to notice swings around in a circular pattern . and because of this , we call this circular polarization . so this is another type of polarization , where the actual angle of polarization rotates smoothly as this light ray enters your eye . and you know what ? er , drrr ... all right , actually , i sent you to receive this one first . that makes no sense . you 're going to receive the ones closes to you first in this light ray going this way . so you 'd actually receive this one first , then that one , then this one , then this one . because of that , you would n't see this going in a counterclockwise way , you 'd see this going in a clockwise circularly polarized way . sorry about that . you might think , `` okay , why ? `` why even bother with circular polarization ? '' well , i kind of lied earlier . turns out , in the movie theater example , they do n't actually do it like this , typically . oftentimes in the movie theaters , we do n't have just linearly polarized sunglasses . this would be a problem because , when you look at the movie theater screen , and if you were to tilt your head just a little bit ... think about it . this one 's not really going to get the right image anymore . it 's going to get some of both . and this one 's going to get some of both . it 's going to be blurry . your head would have to be perfectly level the whole time , which might be annoying . so what we do is , instead , we create circular polarized glasses , so that this one would only get one polarization , this one would get the other direction . this way , even if you tilt your head a little bit ... shoot , clockwise is clockwise , counterclockwise is counterclockwise . by using circular polarization for 3d movies , it can make it a little easier on you eyes to see a better 3d image , even if your head 's tilted a little bit .
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all right , when this point right here gets to your eye , what am i going to see ? well , i 'm going to have a light ray that 's one part of a light ray . one component points up .
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when i see a light ray entering my eyes , how do i differentiate between a horizontally and a vertically polarised light ray ?
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- let 's talk about polarization of light . we know what light waves are ; they 're electromagnetic waves . so they 're made out of electric fields . and that 's not good enough . we know there 's not just electric fields . that could n't sustain itself . there 's got to be magnetic fields there , as well , that are changing . those are perpendicular , so you can kind of draw them . it 's hard , on something two-dimensional , but you can kind of imagine those looking something like this . and those magnetic fields would point at a right angle to the electric fields . but this gets really messy if i try to draw both the electric and magnetic fields at the same time . so we 're going to leave the magnetic fields out . it 's often good enough to just know the direction of the electric field when we focus on the electric field . so what does polarization mean ? polarization refers to the fact that , if this light ray was heading straight toward your eye , or a detector , over here , what would you see ? well , if i draw an axis over here , and this point here , in the middle , this is this line -- so imagine we 're looking straight down that line -- and then up and down is up and down , and then left and right , that direction i have the magnetic field , would be this way and that way . what would my eye see ? well , my eye 's only going to see electric fields that either point up or electric fields that point down . they might have different values , but i 'm only going to see electric fields that point up or down . because of that , this light ray is polarized . so polarized light is light where the electric field is only oscillating in one direction . up or down , that 's one direction -- vertically . or it could be polarized horizontally . or it could be polarized diagonally . but either way , you could have this wave polarized along any direction . i mean , a light ray like this , if we had it coming in diagonal , this light ray that 's oscillating like this , where the electric field oscillates like that , that also polarized . these are both polarized because there 's only one direction that the electric field is oscillating in . and you might thing , `` pff , how could you ever have `` a light ray that 's not polarized ? '' easy . most light that you get is not polarized . that is to say , light that 's coming from the sun , straight from the sun -- typically not polarized . light from a lightbulb , an old incandescent light bulb , this thing 's hot . you can get light polarized in any direction , all at once , all overlapping . so if we draw this case for a light bulb , just a random incandescent light bulb , you might get light , some of the light , hitting you eye , you can get some light that 's got that direction , you got light that 's got this direction , you got light in all these directions at any given moment . i mean , you 'd have to add these up to get the total , and they might not all be the same value . but what i 'm trying to say is , at any given moment , you do n't know what direction the electric field 's going to be hitting your eye at from a random source . it could be in any direction . so this is not polarized . this diagram represents light that is not polarized . at some point , the field might be pointing this way , at some later point it 's this way ; it 's just random . you never know which way the electric field 's going to be pointing . whereas these over here , these are polarized . so how could you polarize this light ? let 's say you wanted light that was polarized . you were doing an experiment . you needed polarized light . well , that 's easy . you can use what 's called a polarizer . and this is a material that lets light through , but it only lets light through in one orientation , so you 're going to have a polarizer that , for instance , only lets through vertically polarized light . so this is a polarizer . these are cheap : thin , plastic , configured in a way so that it only lets light through that 's vertically polarized . any light coming in here that 's not vertically polarized gets blocked , or absorbed . so what that means is , if you used this polarizer and held it in between your eye and this light bulb , you would only get this light . all the rest of it would get blocked . or you could just rotate this thing and imagine a polarizer that only lets through horizontal light . now it would only let through light that was this way , and so you would only get this part of the light . or you could just orient it at any angle you want and block everything but the certain angle that this polarizer is defined as letting light through . so you can do this . and once you hold this up , you get polarized light , light that 's only got one orientation . so that 's what polarization means . but why do we care about polarization ? well , let me get rid of this for a minute . you 've heard of polarized sunglasses . so imagine you 're standing near water , or maybe you 're standing on ice or snow or something reflective . there 's a problem . say the sun 's out . it 's shining . it 's a beautiful day -- except there 's going to be glare . let 's say you 're looking down at something here on the ground . it 's going to get light reflecting off of it from just ... you know , light 's coming in from all direction . but it also gets this direct light from the sun . so it gets light from reflected off the clouds and whatever , whatever 's nearby , ambient light . and there 's also this direct sunlight . that 's harsh . if that reflects straight up to your eye , that hurts . you do n't like that . it blocks our vision . it 's hard to see , it 's glare . we do n't want this glare . so what can we do ? well , it just so happens that , when light reflects off of a surface , even though the light from the sun is not polarized , once it reflects , it does get polarized or at least partially polarized . so this surface here , once this light reflects , it 's coming in at all orientations . you got electric field ... you never know what electric field you 're going to get straight from the sun . and when it reflects , though , you mostly get , upon reflection , the direction of polarization defined by the plane of the surface that it hit . so because the floor is horizontal , when this light ray hits the ground and reflects , that reflected light gets partially polarized . this horizontal component of the electric field is going to be more present than the other components . maybe not completely . sometimes it could be . it could be completely polarized , but often it 's just partially polarized . but that 's pretty cool , because now you know what we can do . i know how to block this . we should get some sunglasses . we put some sunglasses on and we make our glasses so that these are polarized . and how do we want these polarized ? i want to get rid of the glare . so what i do is , i make sure my sunglasses only let through vertically polarized light . here 's some polarizers . that way , a lot of this glare gets blocked because it does not have a vertical orientation , it has a horizontal orientation . and then we can block it . so that 's one good thing that polarization does for us , and understanding it , we can get rid of glare . also , fishermen like it because , if you 're trying to look in the water at fish , you want to see in through the water , you want to see this light from the fish getting to you . you do n't want to see the glare off of the sun getting to you . so polarized sunglasses are useful . also , we can play a trick on our eye , if we really wanted to . you could take one of these , make one eye have a vertical orientation for the polarization , have the other eye with a horizontal ... and you 're thinking , `` this is stupid . `` why would you do this for ? '' `` this eye 's going to get a lot of glare . '' we would n't use these outside , when you 're , like , skiing or fishing , but you could play a trick on your eyes if you went to the movies and you went and watched a movie . well , the reason our eyes see 3d is because they 're spaced a little bit apart . they each get a different , slightly different image . that makes us see in 3d . we can play the same trick on our eye if we have the polarization like this . if light , if some of the light from the movie theater screen is coming in with one polarization , and the other light 's coming in with the other polarization , we can send two different images to our eyes at the same time . if you took these off , it 'd look like garbage because you 'd be getting both of these slightly different images , it 'd look all blurry . and it does . if you take off your 3d glasses and look at a 3d movie , looks terrible , because now both eyes are getting both images . but if you put your glasses back on , now this eye only gets the orientation that it 's supposed to get , and this eye only gets the orientation that it 's supposed to get , and you get a 3d image . so it 's useful in many ways . let me show you one more thing here . let 's come back here . this light was polarized vertically . so that 's called linear polarization . any time ... same with these . these are all linear polarization because , just up and down , one linear direction , just diagonal . this is also linear . all of these are linear . you can get circular polarized light . so if we come back to here , we 've got our electric field pointing up , like that . now let 's say we sent in another light ray , another light ray that also had a polarization , but not in this direction . let 's say our other light ray had polarization in this direction , so it looks like this , kind of like what our magnetic field would have looked like . but this is a completely different light ray with its own polarization and its own magnetic field . so we send this in . what would happen ? well , at this point , you 'd have a electric field that points this way . at this point , you 'd have a electric field that points that way . what would your eye see if you were over here ? let 's see . if i draw our axis here . all right , when this point right here gets to your eye , what am i going to see ? well , i 'm going to have a light ray that 's one part of a light ray . one component points up . that 's this electric field . one component points left . that 's this electric field . so the total , my total electric field , would point this way . i could to the pythagorean theorem if i wanted to figure out the size of it , but i just want to know the direction for now . and then it gets to here , and look at it : they both have zero . this light ray has zero electric field , this one has zero electric fields . so then it 'd just be at zero . now what happens over here ? well , i 've got light . this one points to the right at that point , this pink one , and then this red one would be pointing down . so what would i have at that point ? i 'd have light that went this way , and it would just be doing this over and over . it would just be ... i 'd just have diagonally polarized light . this is n't giving me anything new . you might think this is dumb . why do this ? why send in two different waves to just get diagonally polarized light ? i could have just sent in one wave that was diagonally polarized and got the same thing . the reason is , if you shift this purple wave , this pink wave , by 90 degrees of phase , by pi over two in phase , something magical happens . let me show you what happens here , if we move this to here . now we do n't just get diagonally linear polarized light . what we 're going to get is ... let me get rid of this . okay , so we start off with red , right ? the red electric field points up , and then this pink wave 's electric field is zero at that point . so this is all i have . my total electric field would just be up . i 'm going to draw it right here . the green 'll be the total . now i come over to here , and at this point , there 's some red electric field that points up , but there 's some of this other electric field that points this way . so i 'd have a total electric field that would point that way . and then i get over to here , and i 'd have all of the electric field from the pink one , none from the red one . it would point all left then . look what 's happening . the polarization of this light , if i shift this , if i 'm sitting here , looking with my eye , as my eye receives this light , i 'm going to see this light rotate its polarization . the polarization i 'm going to notice swings around in a circular pattern . and because of this , we call this circular polarization . so this is another type of polarization , where the actual angle of polarization rotates smoothly as this light ray enters your eye . and you know what ? er , drrr ... all right , actually , i sent you to receive this one first . that makes no sense . you 're going to receive the ones closes to you first in this light ray going this way . so you 'd actually receive this one first , then that one , then this one , then this one . because of that , you would n't see this going in a counterclockwise way , you 'd see this going in a clockwise circularly polarized way . sorry about that . you might think , `` okay , why ? `` why even bother with circular polarization ? '' well , i kind of lied earlier . turns out , in the movie theater example , they do n't actually do it like this , typically . oftentimes in the movie theaters , we do n't have just linearly polarized sunglasses . this would be a problem because , when you look at the movie theater screen , and if you were to tilt your head just a little bit ... think about it . this one 's not really going to get the right image anymore . it 's going to get some of both . and this one 's going to get some of both . it 's going to be blurry . your head would have to be perfectly level the whole time , which might be annoying . so what we do is , instead , we create circular polarized glasses , so that this one would only get one polarization , this one would get the other direction . this way , even if you tilt your head a little bit ... shoot , clockwise is clockwise , counterclockwise is counterclockwise . by using circular polarization for 3d movies , it can make it a little easier on you eyes to see a better 3d image , even if your head 's tilted a little bit .
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you can get light polarized in any direction , all at once , all overlapping . so if we draw this case for a light bulb , just a random incandescent light bulb , you might get light , some of the light , hitting you eye , you can get some light that 's got that direction , you got light that 's got this direction , you got light in all these directions at any given moment . i mean , you 'd have to add these up to get the total , and they might not all be the same value .
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if you take only a single light wave , will it be polarised ?
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- let 's talk about polarization of light . we know what light waves are ; they 're electromagnetic waves . so they 're made out of electric fields . and that 's not good enough . we know there 's not just electric fields . that could n't sustain itself . there 's got to be magnetic fields there , as well , that are changing . those are perpendicular , so you can kind of draw them . it 's hard , on something two-dimensional , but you can kind of imagine those looking something like this . and those magnetic fields would point at a right angle to the electric fields . but this gets really messy if i try to draw both the electric and magnetic fields at the same time . so we 're going to leave the magnetic fields out . it 's often good enough to just know the direction of the electric field when we focus on the electric field . so what does polarization mean ? polarization refers to the fact that , if this light ray was heading straight toward your eye , or a detector , over here , what would you see ? well , if i draw an axis over here , and this point here , in the middle , this is this line -- so imagine we 're looking straight down that line -- and then up and down is up and down , and then left and right , that direction i have the magnetic field , would be this way and that way . what would my eye see ? well , my eye 's only going to see electric fields that either point up or electric fields that point down . they might have different values , but i 'm only going to see electric fields that point up or down . because of that , this light ray is polarized . so polarized light is light where the electric field is only oscillating in one direction . up or down , that 's one direction -- vertically . or it could be polarized horizontally . or it could be polarized diagonally . but either way , you could have this wave polarized along any direction . i mean , a light ray like this , if we had it coming in diagonal , this light ray that 's oscillating like this , where the electric field oscillates like that , that also polarized . these are both polarized because there 's only one direction that the electric field is oscillating in . and you might thing , `` pff , how could you ever have `` a light ray that 's not polarized ? '' easy . most light that you get is not polarized . that is to say , light that 's coming from the sun , straight from the sun -- typically not polarized . light from a lightbulb , an old incandescent light bulb , this thing 's hot . you can get light polarized in any direction , all at once , all overlapping . so if we draw this case for a light bulb , just a random incandescent light bulb , you might get light , some of the light , hitting you eye , you can get some light that 's got that direction , you got light that 's got this direction , you got light in all these directions at any given moment . i mean , you 'd have to add these up to get the total , and they might not all be the same value . but what i 'm trying to say is , at any given moment , you do n't know what direction the electric field 's going to be hitting your eye at from a random source . it could be in any direction . so this is not polarized . this diagram represents light that is not polarized . at some point , the field might be pointing this way , at some later point it 's this way ; it 's just random . you never know which way the electric field 's going to be pointing . whereas these over here , these are polarized . so how could you polarize this light ? let 's say you wanted light that was polarized . you were doing an experiment . you needed polarized light . well , that 's easy . you can use what 's called a polarizer . and this is a material that lets light through , but it only lets light through in one orientation , so you 're going to have a polarizer that , for instance , only lets through vertically polarized light . so this is a polarizer . these are cheap : thin , plastic , configured in a way so that it only lets light through that 's vertically polarized . any light coming in here that 's not vertically polarized gets blocked , or absorbed . so what that means is , if you used this polarizer and held it in between your eye and this light bulb , you would only get this light . all the rest of it would get blocked . or you could just rotate this thing and imagine a polarizer that only lets through horizontal light . now it would only let through light that was this way , and so you would only get this part of the light . or you could just orient it at any angle you want and block everything but the certain angle that this polarizer is defined as letting light through . so you can do this . and once you hold this up , you get polarized light , light that 's only got one orientation . so that 's what polarization means . but why do we care about polarization ? well , let me get rid of this for a minute . you 've heard of polarized sunglasses . so imagine you 're standing near water , or maybe you 're standing on ice or snow or something reflective . there 's a problem . say the sun 's out . it 's shining . it 's a beautiful day -- except there 's going to be glare . let 's say you 're looking down at something here on the ground . it 's going to get light reflecting off of it from just ... you know , light 's coming in from all direction . but it also gets this direct light from the sun . so it gets light from reflected off the clouds and whatever , whatever 's nearby , ambient light . and there 's also this direct sunlight . that 's harsh . if that reflects straight up to your eye , that hurts . you do n't like that . it blocks our vision . it 's hard to see , it 's glare . we do n't want this glare . so what can we do ? well , it just so happens that , when light reflects off of a surface , even though the light from the sun is not polarized , once it reflects , it does get polarized or at least partially polarized . so this surface here , once this light reflects , it 's coming in at all orientations . you got electric field ... you never know what electric field you 're going to get straight from the sun . and when it reflects , though , you mostly get , upon reflection , the direction of polarization defined by the plane of the surface that it hit . so because the floor is horizontal , when this light ray hits the ground and reflects , that reflected light gets partially polarized . this horizontal component of the electric field is going to be more present than the other components . maybe not completely . sometimes it could be . it could be completely polarized , but often it 's just partially polarized . but that 's pretty cool , because now you know what we can do . i know how to block this . we should get some sunglasses . we put some sunglasses on and we make our glasses so that these are polarized . and how do we want these polarized ? i want to get rid of the glare . so what i do is , i make sure my sunglasses only let through vertically polarized light . here 's some polarizers . that way , a lot of this glare gets blocked because it does not have a vertical orientation , it has a horizontal orientation . and then we can block it . so that 's one good thing that polarization does for us , and understanding it , we can get rid of glare . also , fishermen like it because , if you 're trying to look in the water at fish , you want to see in through the water , you want to see this light from the fish getting to you . you do n't want to see the glare off of the sun getting to you . so polarized sunglasses are useful . also , we can play a trick on our eye , if we really wanted to . you could take one of these , make one eye have a vertical orientation for the polarization , have the other eye with a horizontal ... and you 're thinking , `` this is stupid . `` why would you do this for ? '' `` this eye 's going to get a lot of glare . '' we would n't use these outside , when you 're , like , skiing or fishing , but you could play a trick on your eyes if you went to the movies and you went and watched a movie . well , the reason our eyes see 3d is because they 're spaced a little bit apart . they each get a different , slightly different image . that makes us see in 3d . we can play the same trick on our eye if we have the polarization like this . if light , if some of the light from the movie theater screen is coming in with one polarization , and the other light 's coming in with the other polarization , we can send two different images to our eyes at the same time . if you took these off , it 'd look like garbage because you 'd be getting both of these slightly different images , it 'd look all blurry . and it does . if you take off your 3d glasses and look at a 3d movie , looks terrible , because now both eyes are getting both images . but if you put your glasses back on , now this eye only gets the orientation that it 's supposed to get , and this eye only gets the orientation that it 's supposed to get , and you get a 3d image . so it 's useful in many ways . let me show you one more thing here . let 's come back here . this light was polarized vertically . so that 's called linear polarization . any time ... same with these . these are all linear polarization because , just up and down , one linear direction , just diagonal . this is also linear . all of these are linear . you can get circular polarized light . so if we come back to here , we 've got our electric field pointing up , like that . now let 's say we sent in another light ray , another light ray that also had a polarization , but not in this direction . let 's say our other light ray had polarization in this direction , so it looks like this , kind of like what our magnetic field would have looked like . but this is a completely different light ray with its own polarization and its own magnetic field . so we send this in . what would happen ? well , at this point , you 'd have a electric field that points this way . at this point , you 'd have a electric field that points that way . what would your eye see if you were over here ? let 's see . if i draw our axis here . all right , when this point right here gets to your eye , what am i going to see ? well , i 'm going to have a light ray that 's one part of a light ray . one component points up . that 's this electric field . one component points left . that 's this electric field . so the total , my total electric field , would point this way . i could to the pythagorean theorem if i wanted to figure out the size of it , but i just want to know the direction for now . and then it gets to here , and look at it : they both have zero . this light ray has zero electric field , this one has zero electric fields . so then it 'd just be at zero . now what happens over here ? well , i 've got light . this one points to the right at that point , this pink one , and then this red one would be pointing down . so what would i have at that point ? i 'd have light that went this way , and it would just be doing this over and over . it would just be ... i 'd just have diagonally polarized light . this is n't giving me anything new . you might think this is dumb . why do this ? why send in two different waves to just get diagonally polarized light ? i could have just sent in one wave that was diagonally polarized and got the same thing . the reason is , if you shift this purple wave , this pink wave , by 90 degrees of phase , by pi over two in phase , something magical happens . let me show you what happens here , if we move this to here . now we do n't just get diagonally linear polarized light . what we 're going to get is ... let me get rid of this . okay , so we start off with red , right ? the red electric field points up , and then this pink wave 's electric field is zero at that point . so this is all i have . my total electric field would just be up . i 'm going to draw it right here . the green 'll be the total . now i come over to here , and at this point , there 's some red electric field that points up , but there 's some of this other electric field that points this way . so i 'd have a total electric field that would point that way . and then i get over to here , and i 'd have all of the electric field from the pink one , none from the red one . it would point all left then . look what 's happening . the polarization of this light , if i shift this , if i 'm sitting here , looking with my eye , as my eye receives this light , i 'm going to see this light rotate its polarization . the polarization i 'm going to notice swings around in a circular pattern . and because of this , we call this circular polarization . so this is another type of polarization , where the actual angle of polarization rotates smoothly as this light ray enters your eye . and you know what ? er , drrr ... all right , actually , i sent you to receive this one first . that makes no sense . you 're going to receive the ones closes to you first in this light ray going this way . so you 'd actually receive this one first , then that one , then this one , then this one . because of that , you would n't see this going in a counterclockwise way , you 'd see this going in a clockwise circularly polarized way . sorry about that . you might think , `` okay , why ? `` why even bother with circular polarization ? '' well , i kind of lied earlier . turns out , in the movie theater example , they do n't actually do it like this , typically . oftentimes in the movie theaters , we do n't have just linearly polarized sunglasses . this would be a problem because , when you look at the movie theater screen , and if you were to tilt your head just a little bit ... think about it . this one 's not really going to get the right image anymore . it 's going to get some of both . and this one 's going to get some of both . it 's going to be blurry . your head would have to be perfectly level the whole time , which might be annoying . so what we do is , instead , we create circular polarized glasses , so that this one would only get one polarization , this one would get the other direction . this way , even if you tilt your head a little bit ... shoot , clockwise is clockwise , counterclockwise is counterclockwise . by using circular polarization for 3d movies , it can make it a little easier on you eyes to see a better 3d image , even if your head 's tilted a little bit .
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it 's hard , on something two-dimensional , but you can kind of imagine those looking something like this . and those magnetic fields would point at a right angle to the electric fields . but this gets really messy if i try to draw both the electric and magnetic fields at the same time .
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why cant we see electric fields that move left to right ?
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- let 's talk about polarization of light . we know what light waves are ; they 're electromagnetic waves . so they 're made out of electric fields . and that 's not good enough . we know there 's not just electric fields . that could n't sustain itself . there 's got to be magnetic fields there , as well , that are changing . those are perpendicular , so you can kind of draw them . it 's hard , on something two-dimensional , but you can kind of imagine those looking something like this . and those magnetic fields would point at a right angle to the electric fields . but this gets really messy if i try to draw both the electric and magnetic fields at the same time . so we 're going to leave the magnetic fields out . it 's often good enough to just know the direction of the electric field when we focus on the electric field . so what does polarization mean ? polarization refers to the fact that , if this light ray was heading straight toward your eye , or a detector , over here , what would you see ? well , if i draw an axis over here , and this point here , in the middle , this is this line -- so imagine we 're looking straight down that line -- and then up and down is up and down , and then left and right , that direction i have the magnetic field , would be this way and that way . what would my eye see ? well , my eye 's only going to see electric fields that either point up or electric fields that point down . they might have different values , but i 'm only going to see electric fields that point up or down . because of that , this light ray is polarized . so polarized light is light where the electric field is only oscillating in one direction . up or down , that 's one direction -- vertically . or it could be polarized horizontally . or it could be polarized diagonally . but either way , you could have this wave polarized along any direction . i mean , a light ray like this , if we had it coming in diagonal , this light ray that 's oscillating like this , where the electric field oscillates like that , that also polarized . these are both polarized because there 's only one direction that the electric field is oscillating in . and you might thing , `` pff , how could you ever have `` a light ray that 's not polarized ? '' easy . most light that you get is not polarized . that is to say , light that 's coming from the sun , straight from the sun -- typically not polarized . light from a lightbulb , an old incandescent light bulb , this thing 's hot . you can get light polarized in any direction , all at once , all overlapping . so if we draw this case for a light bulb , just a random incandescent light bulb , you might get light , some of the light , hitting you eye , you can get some light that 's got that direction , you got light that 's got this direction , you got light in all these directions at any given moment . i mean , you 'd have to add these up to get the total , and they might not all be the same value . but what i 'm trying to say is , at any given moment , you do n't know what direction the electric field 's going to be hitting your eye at from a random source . it could be in any direction . so this is not polarized . this diagram represents light that is not polarized . at some point , the field might be pointing this way , at some later point it 's this way ; it 's just random . you never know which way the electric field 's going to be pointing . whereas these over here , these are polarized . so how could you polarize this light ? let 's say you wanted light that was polarized . you were doing an experiment . you needed polarized light . well , that 's easy . you can use what 's called a polarizer . and this is a material that lets light through , but it only lets light through in one orientation , so you 're going to have a polarizer that , for instance , only lets through vertically polarized light . so this is a polarizer . these are cheap : thin , plastic , configured in a way so that it only lets light through that 's vertically polarized . any light coming in here that 's not vertically polarized gets blocked , or absorbed . so what that means is , if you used this polarizer and held it in between your eye and this light bulb , you would only get this light . all the rest of it would get blocked . or you could just rotate this thing and imagine a polarizer that only lets through horizontal light . now it would only let through light that was this way , and so you would only get this part of the light . or you could just orient it at any angle you want and block everything but the certain angle that this polarizer is defined as letting light through . so you can do this . and once you hold this up , you get polarized light , light that 's only got one orientation . so that 's what polarization means . but why do we care about polarization ? well , let me get rid of this for a minute . you 've heard of polarized sunglasses . so imagine you 're standing near water , or maybe you 're standing on ice or snow or something reflective . there 's a problem . say the sun 's out . it 's shining . it 's a beautiful day -- except there 's going to be glare . let 's say you 're looking down at something here on the ground . it 's going to get light reflecting off of it from just ... you know , light 's coming in from all direction . but it also gets this direct light from the sun . so it gets light from reflected off the clouds and whatever , whatever 's nearby , ambient light . and there 's also this direct sunlight . that 's harsh . if that reflects straight up to your eye , that hurts . you do n't like that . it blocks our vision . it 's hard to see , it 's glare . we do n't want this glare . so what can we do ? well , it just so happens that , when light reflects off of a surface , even though the light from the sun is not polarized , once it reflects , it does get polarized or at least partially polarized . so this surface here , once this light reflects , it 's coming in at all orientations . you got electric field ... you never know what electric field you 're going to get straight from the sun . and when it reflects , though , you mostly get , upon reflection , the direction of polarization defined by the plane of the surface that it hit . so because the floor is horizontal , when this light ray hits the ground and reflects , that reflected light gets partially polarized . this horizontal component of the electric field is going to be more present than the other components . maybe not completely . sometimes it could be . it could be completely polarized , but often it 's just partially polarized . but that 's pretty cool , because now you know what we can do . i know how to block this . we should get some sunglasses . we put some sunglasses on and we make our glasses so that these are polarized . and how do we want these polarized ? i want to get rid of the glare . so what i do is , i make sure my sunglasses only let through vertically polarized light . here 's some polarizers . that way , a lot of this glare gets blocked because it does not have a vertical orientation , it has a horizontal orientation . and then we can block it . so that 's one good thing that polarization does for us , and understanding it , we can get rid of glare . also , fishermen like it because , if you 're trying to look in the water at fish , you want to see in through the water , you want to see this light from the fish getting to you . you do n't want to see the glare off of the sun getting to you . so polarized sunglasses are useful . also , we can play a trick on our eye , if we really wanted to . you could take one of these , make one eye have a vertical orientation for the polarization , have the other eye with a horizontal ... and you 're thinking , `` this is stupid . `` why would you do this for ? '' `` this eye 's going to get a lot of glare . '' we would n't use these outside , when you 're , like , skiing or fishing , but you could play a trick on your eyes if you went to the movies and you went and watched a movie . well , the reason our eyes see 3d is because they 're spaced a little bit apart . they each get a different , slightly different image . that makes us see in 3d . we can play the same trick on our eye if we have the polarization like this . if light , if some of the light from the movie theater screen is coming in with one polarization , and the other light 's coming in with the other polarization , we can send two different images to our eyes at the same time . if you took these off , it 'd look like garbage because you 'd be getting both of these slightly different images , it 'd look all blurry . and it does . if you take off your 3d glasses and look at a 3d movie , looks terrible , because now both eyes are getting both images . but if you put your glasses back on , now this eye only gets the orientation that it 's supposed to get , and this eye only gets the orientation that it 's supposed to get , and you get a 3d image . so it 's useful in many ways . let me show you one more thing here . let 's come back here . this light was polarized vertically . so that 's called linear polarization . any time ... same with these . these are all linear polarization because , just up and down , one linear direction , just diagonal . this is also linear . all of these are linear . you can get circular polarized light . so if we come back to here , we 've got our electric field pointing up , like that . now let 's say we sent in another light ray , another light ray that also had a polarization , but not in this direction . let 's say our other light ray had polarization in this direction , so it looks like this , kind of like what our magnetic field would have looked like . but this is a completely different light ray with its own polarization and its own magnetic field . so we send this in . what would happen ? well , at this point , you 'd have a electric field that points this way . at this point , you 'd have a electric field that points that way . what would your eye see if you were over here ? let 's see . if i draw our axis here . all right , when this point right here gets to your eye , what am i going to see ? well , i 'm going to have a light ray that 's one part of a light ray . one component points up . that 's this electric field . one component points left . that 's this electric field . so the total , my total electric field , would point this way . i could to the pythagorean theorem if i wanted to figure out the size of it , but i just want to know the direction for now . and then it gets to here , and look at it : they both have zero . this light ray has zero electric field , this one has zero electric fields . so then it 'd just be at zero . now what happens over here ? well , i 've got light . this one points to the right at that point , this pink one , and then this red one would be pointing down . so what would i have at that point ? i 'd have light that went this way , and it would just be doing this over and over . it would just be ... i 'd just have diagonally polarized light . this is n't giving me anything new . you might think this is dumb . why do this ? why send in two different waves to just get diagonally polarized light ? i could have just sent in one wave that was diagonally polarized and got the same thing . the reason is , if you shift this purple wave , this pink wave , by 90 degrees of phase , by pi over two in phase , something magical happens . let me show you what happens here , if we move this to here . now we do n't just get diagonally linear polarized light . what we 're going to get is ... let me get rid of this . okay , so we start off with red , right ? the red electric field points up , and then this pink wave 's electric field is zero at that point . so this is all i have . my total electric field would just be up . i 'm going to draw it right here . the green 'll be the total . now i come over to here , and at this point , there 's some red electric field that points up , but there 's some of this other electric field that points this way . so i 'd have a total electric field that would point that way . and then i get over to here , and i 'd have all of the electric field from the pink one , none from the red one . it would point all left then . look what 's happening . the polarization of this light , if i shift this , if i 'm sitting here , looking with my eye , as my eye receives this light , i 'm going to see this light rotate its polarization . the polarization i 'm going to notice swings around in a circular pattern . and because of this , we call this circular polarization . so this is another type of polarization , where the actual angle of polarization rotates smoothly as this light ray enters your eye . and you know what ? er , drrr ... all right , actually , i sent you to receive this one first . that makes no sense . you 're going to receive the ones closes to you first in this light ray going this way . so you 'd actually receive this one first , then that one , then this one , then this one . because of that , you would n't see this going in a counterclockwise way , you 'd see this going in a clockwise circularly polarized way . sorry about that . you might think , `` okay , why ? `` why even bother with circular polarization ? '' well , i kind of lied earlier . turns out , in the movie theater example , they do n't actually do it like this , typically . oftentimes in the movie theaters , we do n't have just linearly polarized sunglasses . this would be a problem because , when you look at the movie theater screen , and if you were to tilt your head just a little bit ... think about it . this one 's not really going to get the right image anymore . it 's going to get some of both . and this one 's going to get some of both . it 's going to be blurry . your head would have to be perfectly level the whole time , which might be annoying . so what we do is , instead , we create circular polarized glasses , so that this one would only get one polarization , this one would get the other direction . this way , even if you tilt your head a little bit ... shoot , clockwise is clockwise , counterclockwise is counterclockwise . by using circular polarization for 3d movies , it can make it a little easier on you eyes to see a better 3d image , even if your head 's tilted a little bit .
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we can play the same trick on our eye if we have the polarization like this . if light , if some of the light from the movie theater screen is coming in with one polarization , and the other light 's coming in with the other polarization , we can send two different images to our eyes at the same time . if you took these off , it 'd look like garbage because you 'd be getting both of these slightly different images , it 'd look all blurry .
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which factor is responsible for polarization of light coming from sky and how ?
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- let 's talk about polarization of light . we know what light waves are ; they 're electromagnetic waves . so they 're made out of electric fields . and that 's not good enough . we know there 's not just electric fields . that could n't sustain itself . there 's got to be magnetic fields there , as well , that are changing . those are perpendicular , so you can kind of draw them . it 's hard , on something two-dimensional , but you can kind of imagine those looking something like this . and those magnetic fields would point at a right angle to the electric fields . but this gets really messy if i try to draw both the electric and magnetic fields at the same time . so we 're going to leave the magnetic fields out . it 's often good enough to just know the direction of the electric field when we focus on the electric field . so what does polarization mean ? polarization refers to the fact that , if this light ray was heading straight toward your eye , or a detector , over here , what would you see ? well , if i draw an axis over here , and this point here , in the middle , this is this line -- so imagine we 're looking straight down that line -- and then up and down is up and down , and then left and right , that direction i have the magnetic field , would be this way and that way . what would my eye see ? well , my eye 's only going to see electric fields that either point up or electric fields that point down . they might have different values , but i 'm only going to see electric fields that point up or down . because of that , this light ray is polarized . so polarized light is light where the electric field is only oscillating in one direction . up or down , that 's one direction -- vertically . or it could be polarized horizontally . or it could be polarized diagonally . but either way , you could have this wave polarized along any direction . i mean , a light ray like this , if we had it coming in diagonal , this light ray that 's oscillating like this , where the electric field oscillates like that , that also polarized . these are both polarized because there 's only one direction that the electric field is oscillating in . and you might thing , `` pff , how could you ever have `` a light ray that 's not polarized ? '' easy . most light that you get is not polarized . that is to say , light that 's coming from the sun , straight from the sun -- typically not polarized . light from a lightbulb , an old incandescent light bulb , this thing 's hot . you can get light polarized in any direction , all at once , all overlapping . so if we draw this case for a light bulb , just a random incandescent light bulb , you might get light , some of the light , hitting you eye , you can get some light that 's got that direction , you got light that 's got this direction , you got light in all these directions at any given moment . i mean , you 'd have to add these up to get the total , and they might not all be the same value . but what i 'm trying to say is , at any given moment , you do n't know what direction the electric field 's going to be hitting your eye at from a random source . it could be in any direction . so this is not polarized . this diagram represents light that is not polarized . at some point , the field might be pointing this way , at some later point it 's this way ; it 's just random . you never know which way the electric field 's going to be pointing . whereas these over here , these are polarized . so how could you polarize this light ? let 's say you wanted light that was polarized . you were doing an experiment . you needed polarized light . well , that 's easy . you can use what 's called a polarizer . and this is a material that lets light through , but it only lets light through in one orientation , so you 're going to have a polarizer that , for instance , only lets through vertically polarized light . so this is a polarizer . these are cheap : thin , plastic , configured in a way so that it only lets light through that 's vertically polarized . any light coming in here that 's not vertically polarized gets blocked , or absorbed . so what that means is , if you used this polarizer and held it in between your eye and this light bulb , you would only get this light . all the rest of it would get blocked . or you could just rotate this thing and imagine a polarizer that only lets through horizontal light . now it would only let through light that was this way , and so you would only get this part of the light . or you could just orient it at any angle you want and block everything but the certain angle that this polarizer is defined as letting light through . so you can do this . and once you hold this up , you get polarized light , light that 's only got one orientation . so that 's what polarization means . but why do we care about polarization ? well , let me get rid of this for a minute . you 've heard of polarized sunglasses . so imagine you 're standing near water , or maybe you 're standing on ice or snow or something reflective . there 's a problem . say the sun 's out . it 's shining . it 's a beautiful day -- except there 's going to be glare . let 's say you 're looking down at something here on the ground . it 's going to get light reflecting off of it from just ... you know , light 's coming in from all direction . but it also gets this direct light from the sun . so it gets light from reflected off the clouds and whatever , whatever 's nearby , ambient light . and there 's also this direct sunlight . that 's harsh . if that reflects straight up to your eye , that hurts . you do n't like that . it blocks our vision . it 's hard to see , it 's glare . we do n't want this glare . so what can we do ? well , it just so happens that , when light reflects off of a surface , even though the light from the sun is not polarized , once it reflects , it does get polarized or at least partially polarized . so this surface here , once this light reflects , it 's coming in at all orientations . you got electric field ... you never know what electric field you 're going to get straight from the sun . and when it reflects , though , you mostly get , upon reflection , the direction of polarization defined by the plane of the surface that it hit . so because the floor is horizontal , when this light ray hits the ground and reflects , that reflected light gets partially polarized . this horizontal component of the electric field is going to be more present than the other components . maybe not completely . sometimes it could be . it could be completely polarized , but often it 's just partially polarized . but that 's pretty cool , because now you know what we can do . i know how to block this . we should get some sunglasses . we put some sunglasses on and we make our glasses so that these are polarized . and how do we want these polarized ? i want to get rid of the glare . so what i do is , i make sure my sunglasses only let through vertically polarized light . here 's some polarizers . that way , a lot of this glare gets blocked because it does not have a vertical orientation , it has a horizontal orientation . and then we can block it . so that 's one good thing that polarization does for us , and understanding it , we can get rid of glare . also , fishermen like it because , if you 're trying to look in the water at fish , you want to see in through the water , you want to see this light from the fish getting to you . you do n't want to see the glare off of the sun getting to you . so polarized sunglasses are useful . also , we can play a trick on our eye , if we really wanted to . you could take one of these , make one eye have a vertical orientation for the polarization , have the other eye with a horizontal ... and you 're thinking , `` this is stupid . `` why would you do this for ? '' `` this eye 's going to get a lot of glare . '' we would n't use these outside , when you 're , like , skiing or fishing , but you could play a trick on your eyes if you went to the movies and you went and watched a movie . well , the reason our eyes see 3d is because they 're spaced a little bit apart . they each get a different , slightly different image . that makes us see in 3d . we can play the same trick on our eye if we have the polarization like this . if light , if some of the light from the movie theater screen is coming in with one polarization , and the other light 's coming in with the other polarization , we can send two different images to our eyes at the same time . if you took these off , it 'd look like garbage because you 'd be getting both of these slightly different images , it 'd look all blurry . and it does . if you take off your 3d glasses and look at a 3d movie , looks terrible , because now both eyes are getting both images . but if you put your glasses back on , now this eye only gets the orientation that it 's supposed to get , and this eye only gets the orientation that it 's supposed to get , and you get a 3d image . so it 's useful in many ways . let me show you one more thing here . let 's come back here . this light was polarized vertically . so that 's called linear polarization . any time ... same with these . these are all linear polarization because , just up and down , one linear direction , just diagonal . this is also linear . all of these are linear . you can get circular polarized light . so if we come back to here , we 've got our electric field pointing up , like that . now let 's say we sent in another light ray , another light ray that also had a polarization , but not in this direction . let 's say our other light ray had polarization in this direction , so it looks like this , kind of like what our magnetic field would have looked like . but this is a completely different light ray with its own polarization and its own magnetic field . so we send this in . what would happen ? well , at this point , you 'd have a electric field that points this way . at this point , you 'd have a electric field that points that way . what would your eye see if you were over here ? let 's see . if i draw our axis here . all right , when this point right here gets to your eye , what am i going to see ? well , i 'm going to have a light ray that 's one part of a light ray . one component points up . that 's this electric field . one component points left . that 's this electric field . so the total , my total electric field , would point this way . i could to the pythagorean theorem if i wanted to figure out the size of it , but i just want to know the direction for now . and then it gets to here , and look at it : they both have zero . this light ray has zero electric field , this one has zero electric fields . so then it 'd just be at zero . now what happens over here ? well , i 've got light . this one points to the right at that point , this pink one , and then this red one would be pointing down . so what would i have at that point ? i 'd have light that went this way , and it would just be doing this over and over . it would just be ... i 'd just have diagonally polarized light . this is n't giving me anything new . you might think this is dumb . why do this ? why send in two different waves to just get diagonally polarized light ? i could have just sent in one wave that was diagonally polarized and got the same thing . the reason is , if you shift this purple wave , this pink wave , by 90 degrees of phase , by pi over two in phase , something magical happens . let me show you what happens here , if we move this to here . now we do n't just get diagonally linear polarized light . what we 're going to get is ... let me get rid of this . okay , so we start off with red , right ? the red electric field points up , and then this pink wave 's electric field is zero at that point . so this is all i have . my total electric field would just be up . i 'm going to draw it right here . the green 'll be the total . now i come over to here , and at this point , there 's some red electric field that points up , but there 's some of this other electric field that points this way . so i 'd have a total electric field that would point that way . and then i get over to here , and i 'd have all of the electric field from the pink one , none from the red one . it would point all left then . look what 's happening . the polarization of this light , if i shift this , if i 'm sitting here , looking with my eye , as my eye receives this light , i 'm going to see this light rotate its polarization . the polarization i 'm going to notice swings around in a circular pattern . and because of this , we call this circular polarization . so this is another type of polarization , where the actual angle of polarization rotates smoothly as this light ray enters your eye . and you know what ? er , drrr ... all right , actually , i sent you to receive this one first . that makes no sense . you 're going to receive the ones closes to you first in this light ray going this way . so you 'd actually receive this one first , then that one , then this one , then this one . because of that , you would n't see this going in a counterclockwise way , you 'd see this going in a clockwise circularly polarized way . sorry about that . you might think , `` okay , why ? `` why even bother with circular polarization ? '' well , i kind of lied earlier . turns out , in the movie theater example , they do n't actually do it like this , typically . oftentimes in the movie theaters , we do n't have just linearly polarized sunglasses . this would be a problem because , when you look at the movie theater screen , and if you were to tilt your head just a little bit ... think about it . this one 's not really going to get the right image anymore . it 's going to get some of both . and this one 's going to get some of both . it 's going to be blurry . your head would have to be perfectly level the whole time , which might be annoying . so what we do is , instead , we create circular polarized glasses , so that this one would only get one polarization , this one would get the other direction . this way , even if you tilt your head a little bit ... shoot , clockwise is clockwise , counterclockwise is counterclockwise . by using circular polarization for 3d movies , it can make it a little easier on you eyes to see a better 3d image , even if your head 's tilted a little bit .
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or it could be polarized diagonally . but either way , you could have this wave polarized along any direction . i mean , a light ray like this , if we had it coming in diagonal , this light ray that 's oscillating like this , where the electric field oscillates like that , that also polarized .
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how can a sound wave in solid medium can be polarized from the source of the sound wave ?
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- let 's talk about polarization of light . we know what light waves are ; they 're electromagnetic waves . so they 're made out of electric fields . and that 's not good enough . we know there 's not just electric fields . that could n't sustain itself . there 's got to be magnetic fields there , as well , that are changing . those are perpendicular , so you can kind of draw them . it 's hard , on something two-dimensional , but you can kind of imagine those looking something like this . and those magnetic fields would point at a right angle to the electric fields . but this gets really messy if i try to draw both the electric and magnetic fields at the same time . so we 're going to leave the magnetic fields out . it 's often good enough to just know the direction of the electric field when we focus on the electric field . so what does polarization mean ? polarization refers to the fact that , if this light ray was heading straight toward your eye , or a detector , over here , what would you see ? well , if i draw an axis over here , and this point here , in the middle , this is this line -- so imagine we 're looking straight down that line -- and then up and down is up and down , and then left and right , that direction i have the magnetic field , would be this way and that way . what would my eye see ? well , my eye 's only going to see electric fields that either point up or electric fields that point down . they might have different values , but i 'm only going to see electric fields that point up or down . because of that , this light ray is polarized . so polarized light is light where the electric field is only oscillating in one direction . up or down , that 's one direction -- vertically . or it could be polarized horizontally . or it could be polarized diagonally . but either way , you could have this wave polarized along any direction . i mean , a light ray like this , if we had it coming in diagonal , this light ray that 's oscillating like this , where the electric field oscillates like that , that also polarized . these are both polarized because there 's only one direction that the electric field is oscillating in . and you might thing , `` pff , how could you ever have `` a light ray that 's not polarized ? '' easy . most light that you get is not polarized . that is to say , light that 's coming from the sun , straight from the sun -- typically not polarized . light from a lightbulb , an old incandescent light bulb , this thing 's hot . you can get light polarized in any direction , all at once , all overlapping . so if we draw this case for a light bulb , just a random incandescent light bulb , you might get light , some of the light , hitting you eye , you can get some light that 's got that direction , you got light that 's got this direction , you got light in all these directions at any given moment . i mean , you 'd have to add these up to get the total , and they might not all be the same value . but what i 'm trying to say is , at any given moment , you do n't know what direction the electric field 's going to be hitting your eye at from a random source . it could be in any direction . so this is not polarized . this diagram represents light that is not polarized . at some point , the field might be pointing this way , at some later point it 's this way ; it 's just random . you never know which way the electric field 's going to be pointing . whereas these over here , these are polarized . so how could you polarize this light ? let 's say you wanted light that was polarized . you were doing an experiment . you needed polarized light . well , that 's easy . you can use what 's called a polarizer . and this is a material that lets light through , but it only lets light through in one orientation , so you 're going to have a polarizer that , for instance , only lets through vertically polarized light . so this is a polarizer . these are cheap : thin , plastic , configured in a way so that it only lets light through that 's vertically polarized . any light coming in here that 's not vertically polarized gets blocked , or absorbed . so what that means is , if you used this polarizer and held it in between your eye and this light bulb , you would only get this light . all the rest of it would get blocked . or you could just rotate this thing and imagine a polarizer that only lets through horizontal light . now it would only let through light that was this way , and so you would only get this part of the light . or you could just orient it at any angle you want and block everything but the certain angle that this polarizer is defined as letting light through . so you can do this . and once you hold this up , you get polarized light , light that 's only got one orientation . so that 's what polarization means . but why do we care about polarization ? well , let me get rid of this for a minute . you 've heard of polarized sunglasses . so imagine you 're standing near water , or maybe you 're standing on ice or snow or something reflective . there 's a problem . say the sun 's out . it 's shining . it 's a beautiful day -- except there 's going to be glare . let 's say you 're looking down at something here on the ground . it 's going to get light reflecting off of it from just ... you know , light 's coming in from all direction . but it also gets this direct light from the sun . so it gets light from reflected off the clouds and whatever , whatever 's nearby , ambient light . and there 's also this direct sunlight . that 's harsh . if that reflects straight up to your eye , that hurts . you do n't like that . it blocks our vision . it 's hard to see , it 's glare . we do n't want this glare . so what can we do ? well , it just so happens that , when light reflects off of a surface , even though the light from the sun is not polarized , once it reflects , it does get polarized or at least partially polarized . so this surface here , once this light reflects , it 's coming in at all orientations . you got electric field ... you never know what electric field you 're going to get straight from the sun . and when it reflects , though , you mostly get , upon reflection , the direction of polarization defined by the plane of the surface that it hit . so because the floor is horizontal , when this light ray hits the ground and reflects , that reflected light gets partially polarized . this horizontal component of the electric field is going to be more present than the other components . maybe not completely . sometimes it could be . it could be completely polarized , but often it 's just partially polarized . but that 's pretty cool , because now you know what we can do . i know how to block this . we should get some sunglasses . we put some sunglasses on and we make our glasses so that these are polarized . and how do we want these polarized ? i want to get rid of the glare . so what i do is , i make sure my sunglasses only let through vertically polarized light . here 's some polarizers . that way , a lot of this glare gets blocked because it does not have a vertical orientation , it has a horizontal orientation . and then we can block it . so that 's one good thing that polarization does for us , and understanding it , we can get rid of glare . also , fishermen like it because , if you 're trying to look in the water at fish , you want to see in through the water , you want to see this light from the fish getting to you . you do n't want to see the glare off of the sun getting to you . so polarized sunglasses are useful . also , we can play a trick on our eye , if we really wanted to . you could take one of these , make one eye have a vertical orientation for the polarization , have the other eye with a horizontal ... and you 're thinking , `` this is stupid . `` why would you do this for ? '' `` this eye 's going to get a lot of glare . '' we would n't use these outside , when you 're , like , skiing or fishing , but you could play a trick on your eyes if you went to the movies and you went and watched a movie . well , the reason our eyes see 3d is because they 're spaced a little bit apart . they each get a different , slightly different image . that makes us see in 3d . we can play the same trick on our eye if we have the polarization like this . if light , if some of the light from the movie theater screen is coming in with one polarization , and the other light 's coming in with the other polarization , we can send two different images to our eyes at the same time . if you took these off , it 'd look like garbage because you 'd be getting both of these slightly different images , it 'd look all blurry . and it does . if you take off your 3d glasses and look at a 3d movie , looks terrible , because now both eyes are getting both images . but if you put your glasses back on , now this eye only gets the orientation that it 's supposed to get , and this eye only gets the orientation that it 's supposed to get , and you get a 3d image . so it 's useful in many ways . let me show you one more thing here . let 's come back here . this light was polarized vertically . so that 's called linear polarization . any time ... same with these . these are all linear polarization because , just up and down , one linear direction , just diagonal . this is also linear . all of these are linear . you can get circular polarized light . so if we come back to here , we 've got our electric field pointing up , like that . now let 's say we sent in another light ray , another light ray that also had a polarization , but not in this direction . let 's say our other light ray had polarization in this direction , so it looks like this , kind of like what our magnetic field would have looked like . but this is a completely different light ray with its own polarization and its own magnetic field . so we send this in . what would happen ? well , at this point , you 'd have a electric field that points this way . at this point , you 'd have a electric field that points that way . what would your eye see if you were over here ? let 's see . if i draw our axis here . all right , when this point right here gets to your eye , what am i going to see ? well , i 'm going to have a light ray that 's one part of a light ray . one component points up . that 's this electric field . one component points left . that 's this electric field . so the total , my total electric field , would point this way . i could to the pythagorean theorem if i wanted to figure out the size of it , but i just want to know the direction for now . and then it gets to here , and look at it : they both have zero . this light ray has zero electric field , this one has zero electric fields . so then it 'd just be at zero . now what happens over here ? well , i 've got light . this one points to the right at that point , this pink one , and then this red one would be pointing down . so what would i have at that point ? i 'd have light that went this way , and it would just be doing this over and over . it would just be ... i 'd just have diagonally polarized light . this is n't giving me anything new . you might think this is dumb . why do this ? why send in two different waves to just get diagonally polarized light ? i could have just sent in one wave that was diagonally polarized and got the same thing . the reason is , if you shift this purple wave , this pink wave , by 90 degrees of phase , by pi over two in phase , something magical happens . let me show you what happens here , if we move this to here . now we do n't just get diagonally linear polarized light . what we 're going to get is ... let me get rid of this . okay , so we start off with red , right ? the red electric field points up , and then this pink wave 's electric field is zero at that point . so this is all i have . my total electric field would just be up . i 'm going to draw it right here . the green 'll be the total . now i come over to here , and at this point , there 's some red electric field that points up , but there 's some of this other electric field that points this way . so i 'd have a total electric field that would point that way . and then i get over to here , and i 'd have all of the electric field from the pink one , none from the red one . it would point all left then . look what 's happening . the polarization of this light , if i shift this , if i 'm sitting here , looking with my eye , as my eye receives this light , i 'm going to see this light rotate its polarization . the polarization i 'm going to notice swings around in a circular pattern . and because of this , we call this circular polarization . so this is another type of polarization , where the actual angle of polarization rotates smoothly as this light ray enters your eye . and you know what ? er , drrr ... all right , actually , i sent you to receive this one first . that makes no sense . you 're going to receive the ones closes to you first in this light ray going this way . so you 'd actually receive this one first , then that one , then this one , then this one . because of that , you would n't see this going in a counterclockwise way , you 'd see this going in a clockwise circularly polarized way . sorry about that . you might think , `` okay , why ? `` why even bother with circular polarization ? '' well , i kind of lied earlier . turns out , in the movie theater example , they do n't actually do it like this , typically . oftentimes in the movie theaters , we do n't have just linearly polarized sunglasses . this would be a problem because , when you look at the movie theater screen , and if you were to tilt your head just a little bit ... think about it . this one 's not really going to get the right image anymore . it 's going to get some of both . and this one 's going to get some of both . it 's going to be blurry . your head would have to be perfectly level the whole time , which might be annoying . so what we do is , instead , we create circular polarized glasses , so that this one would only get one polarization , this one would get the other direction . this way , even if you tilt your head a little bit ... shoot , clockwise is clockwise , counterclockwise is counterclockwise . by using circular polarization for 3d movies , it can make it a little easier on you eyes to see a better 3d image , even if your head 's tilted a little bit .
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so we send this in . what would happen ? well , at this point , you 'd have a electric field that points this way .
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what would happen if the circular polarization were to be done with three electrical fields ?
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- let 's talk about polarization of light . we know what light waves are ; they 're electromagnetic waves . so they 're made out of electric fields . and that 's not good enough . we know there 's not just electric fields . that could n't sustain itself . there 's got to be magnetic fields there , as well , that are changing . those are perpendicular , so you can kind of draw them . it 's hard , on something two-dimensional , but you can kind of imagine those looking something like this . and those magnetic fields would point at a right angle to the electric fields . but this gets really messy if i try to draw both the electric and magnetic fields at the same time . so we 're going to leave the magnetic fields out . it 's often good enough to just know the direction of the electric field when we focus on the electric field . so what does polarization mean ? polarization refers to the fact that , if this light ray was heading straight toward your eye , or a detector , over here , what would you see ? well , if i draw an axis over here , and this point here , in the middle , this is this line -- so imagine we 're looking straight down that line -- and then up and down is up and down , and then left and right , that direction i have the magnetic field , would be this way and that way . what would my eye see ? well , my eye 's only going to see electric fields that either point up or electric fields that point down . they might have different values , but i 'm only going to see electric fields that point up or down . because of that , this light ray is polarized . so polarized light is light where the electric field is only oscillating in one direction . up or down , that 's one direction -- vertically . or it could be polarized horizontally . or it could be polarized diagonally . but either way , you could have this wave polarized along any direction . i mean , a light ray like this , if we had it coming in diagonal , this light ray that 's oscillating like this , where the electric field oscillates like that , that also polarized . these are both polarized because there 's only one direction that the electric field is oscillating in . and you might thing , `` pff , how could you ever have `` a light ray that 's not polarized ? '' easy . most light that you get is not polarized . that is to say , light that 's coming from the sun , straight from the sun -- typically not polarized . light from a lightbulb , an old incandescent light bulb , this thing 's hot . you can get light polarized in any direction , all at once , all overlapping . so if we draw this case for a light bulb , just a random incandescent light bulb , you might get light , some of the light , hitting you eye , you can get some light that 's got that direction , you got light that 's got this direction , you got light in all these directions at any given moment . i mean , you 'd have to add these up to get the total , and they might not all be the same value . but what i 'm trying to say is , at any given moment , you do n't know what direction the electric field 's going to be hitting your eye at from a random source . it could be in any direction . so this is not polarized . this diagram represents light that is not polarized . at some point , the field might be pointing this way , at some later point it 's this way ; it 's just random . you never know which way the electric field 's going to be pointing . whereas these over here , these are polarized . so how could you polarize this light ? let 's say you wanted light that was polarized . you were doing an experiment . you needed polarized light . well , that 's easy . you can use what 's called a polarizer . and this is a material that lets light through , but it only lets light through in one orientation , so you 're going to have a polarizer that , for instance , only lets through vertically polarized light . so this is a polarizer . these are cheap : thin , plastic , configured in a way so that it only lets light through that 's vertically polarized . any light coming in here that 's not vertically polarized gets blocked , or absorbed . so what that means is , if you used this polarizer and held it in between your eye and this light bulb , you would only get this light . all the rest of it would get blocked . or you could just rotate this thing and imagine a polarizer that only lets through horizontal light . now it would only let through light that was this way , and so you would only get this part of the light . or you could just orient it at any angle you want and block everything but the certain angle that this polarizer is defined as letting light through . so you can do this . and once you hold this up , you get polarized light , light that 's only got one orientation . so that 's what polarization means . but why do we care about polarization ? well , let me get rid of this for a minute . you 've heard of polarized sunglasses . so imagine you 're standing near water , or maybe you 're standing on ice or snow or something reflective . there 's a problem . say the sun 's out . it 's shining . it 's a beautiful day -- except there 's going to be glare . let 's say you 're looking down at something here on the ground . it 's going to get light reflecting off of it from just ... you know , light 's coming in from all direction . but it also gets this direct light from the sun . so it gets light from reflected off the clouds and whatever , whatever 's nearby , ambient light . and there 's also this direct sunlight . that 's harsh . if that reflects straight up to your eye , that hurts . you do n't like that . it blocks our vision . it 's hard to see , it 's glare . we do n't want this glare . so what can we do ? well , it just so happens that , when light reflects off of a surface , even though the light from the sun is not polarized , once it reflects , it does get polarized or at least partially polarized . so this surface here , once this light reflects , it 's coming in at all orientations . you got electric field ... you never know what electric field you 're going to get straight from the sun . and when it reflects , though , you mostly get , upon reflection , the direction of polarization defined by the plane of the surface that it hit . so because the floor is horizontal , when this light ray hits the ground and reflects , that reflected light gets partially polarized . this horizontal component of the electric field is going to be more present than the other components . maybe not completely . sometimes it could be . it could be completely polarized , but often it 's just partially polarized . but that 's pretty cool , because now you know what we can do . i know how to block this . we should get some sunglasses . we put some sunglasses on and we make our glasses so that these are polarized . and how do we want these polarized ? i want to get rid of the glare . so what i do is , i make sure my sunglasses only let through vertically polarized light . here 's some polarizers . that way , a lot of this glare gets blocked because it does not have a vertical orientation , it has a horizontal orientation . and then we can block it . so that 's one good thing that polarization does for us , and understanding it , we can get rid of glare . also , fishermen like it because , if you 're trying to look in the water at fish , you want to see in through the water , you want to see this light from the fish getting to you . you do n't want to see the glare off of the sun getting to you . so polarized sunglasses are useful . also , we can play a trick on our eye , if we really wanted to . you could take one of these , make one eye have a vertical orientation for the polarization , have the other eye with a horizontal ... and you 're thinking , `` this is stupid . `` why would you do this for ? '' `` this eye 's going to get a lot of glare . '' we would n't use these outside , when you 're , like , skiing or fishing , but you could play a trick on your eyes if you went to the movies and you went and watched a movie . well , the reason our eyes see 3d is because they 're spaced a little bit apart . they each get a different , slightly different image . that makes us see in 3d . we can play the same trick on our eye if we have the polarization like this . if light , if some of the light from the movie theater screen is coming in with one polarization , and the other light 's coming in with the other polarization , we can send two different images to our eyes at the same time . if you took these off , it 'd look like garbage because you 'd be getting both of these slightly different images , it 'd look all blurry . and it does . if you take off your 3d glasses and look at a 3d movie , looks terrible , because now both eyes are getting both images . but if you put your glasses back on , now this eye only gets the orientation that it 's supposed to get , and this eye only gets the orientation that it 's supposed to get , and you get a 3d image . so it 's useful in many ways . let me show you one more thing here . let 's come back here . this light was polarized vertically . so that 's called linear polarization . any time ... same with these . these are all linear polarization because , just up and down , one linear direction , just diagonal . this is also linear . all of these are linear . you can get circular polarized light . so if we come back to here , we 've got our electric field pointing up , like that . now let 's say we sent in another light ray , another light ray that also had a polarization , but not in this direction . let 's say our other light ray had polarization in this direction , so it looks like this , kind of like what our magnetic field would have looked like . but this is a completely different light ray with its own polarization and its own magnetic field . so we send this in . what would happen ? well , at this point , you 'd have a electric field that points this way . at this point , you 'd have a electric field that points that way . what would your eye see if you were over here ? let 's see . if i draw our axis here . all right , when this point right here gets to your eye , what am i going to see ? well , i 'm going to have a light ray that 's one part of a light ray . one component points up . that 's this electric field . one component points left . that 's this electric field . so the total , my total electric field , would point this way . i could to the pythagorean theorem if i wanted to figure out the size of it , but i just want to know the direction for now . and then it gets to here , and look at it : they both have zero . this light ray has zero electric field , this one has zero electric fields . so then it 'd just be at zero . now what happens over here ? well , i 've got light . this one points to the right at that point , this pink one , and then this red one would be pointing down . so what would i have at that point ? i 'd have light that went this way , and it would just be doing this over and over . it would just be ... i 'd just have diagonally polarized light . this is n't giving me anything new . you might think this is dumb . why do this ? why send in two different waves to just get diagonally polarized light ? i could have just sent in one wave that was diagonally polarized and got the same thing . the reason is , if you shift this purple wave , this pink wave , by 90 degrees of phase , by pi over two in phase , something magical happens . let me show you what happens here , if we move this to here . now we do n't just get diagonally linear polarized light . what we 're going to get is ... let me get rid of this . okay , so we start off with red , right ? the red electric field points up , and then this pink wave 's electric field is zero at that point . so this is all i have . my total electric field would just be up . i 'm going to draw it right here . the green 'll be the total . now i come over to here , and at this point , there 's some red electric field that points up , but there 's some of this other electric field that points this way . so i 'd have a total electric field that would point that way . and then i get over to here , and i 'd have all of the electric field from the pink one , none from the red one . it would point all left then . look what 's happening . the polarization of this light , if i shift this , if i 'm sitting here , looking with my eye , as my eye receives this light , i 'm going to see this light rotate its polarization . the polarization i 'm going to notice swings around in a circular pattern . and because of this , we call this circular polarization . so this is another type of polarization , where the actual angle of polarization rotates smoothly as this light ray enters your eye . and you know what ? er , drrr ... all right , actually , i sent you to receive this one first . that makes no sense . you 're going to receive the ones closes to you first in this light ray going this way . so you 'd actually receive this one first , then that one , then this one , then this one . because of that , you would n't see this going in a counterclockwise way , you 'd see this going in a clockwise circularly polarized way . sorry about that . you might think , `` okay , why ? `` why even bother with circular polarization ? '' well , i kind of lied earlier . turns out , in the movie theater example , they do n't actually do it like this , typically . oftentimes in the movie theaters , we do n't have just linearly polarized sunglasses . this would be a problem because , when you look at the movie theater screen , and if you were to tilt your head just a little bit ... think about it . this one 's not really going to get the right image anymore . it 's going to get some of both . and this one 's going to get some of both . it 's going to be blurry . your head would have to be perfectly level the whole time , which might be annoying . so what we do is , instead , we create circular polarized glasses , so that this one would only get one polarization , this one would get the other direction . this way , even if you tilt your head a little bit ... shoot , clockwise is clockwise , counterclockwise is counterclockwise . by using circular polarization for 3d movies , it can make it a little easier on you eyes to see a better 3d image , even if your head 's tilted a little bit .
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so we send this in . what would happen ? well , at this point , you 'd have a electric field that points this way .
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or how would the phase shift take place ?
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- let 's talk about polarization of light . we know what light waves are ; they 're electromagnetic waves . so they 're made out of electric fields . and that 's not good enough . we know there 's not just electric fields . that could n't sustain itself . there 's got to be magnetic fields there , as well , that are changing . those are perpendicular , so you can kind of draw them . it 's hard , on something two-dimensional , but you can kind of imagine those looking something like this . and those magnetic fields would point at a right angle to the electric fields . but this gets really messy if i try to draw both the electric and magnetic fields at the same time . so we 're going to leave the magnetic fields out . it 's often good enough to just know the direction of the electric field when we focus on the electric field . so what does polarization mean ? polarization refers to the fact that , if this light ray was heading straight toward your eye , or a detector , over here , what would you see ? well , if i draw an axis over here , and this point here , in the middle , this is this line -- so imagine we 're looking straight down that line -- and then up and down is up and down , and then left and right , that direction i have the magnetic field , would be this way and that way . what would my eye see ? well , my eye 's only going to see electric fields that either point up or electric fields that point down . they might have different values , but i 'm only going to see electric fields that point up or down . because of that , this light ray is polarized . so polarized light is light where the electric field is only oscillating in one direction . up or down , that 's one direction -- vertically . or it could be polarized horizontally . or it could be polarized diagonally . but either way , you could have this wave polarized along any direction . i mean , a light ray like this , if we had it coming in diagonal , this light ray that 's oscillating like this , where the electric field oscillates like that , that also polarized . these are both polarized because there 's only one direction that the electric field is oscillating in . and you might thing , `` pff , how could you ever have `` a light ray that 's not polarized ? '' easy . most light that you get is not polarized . that is to say , light that 's coming from the sun , straight from the sun -- typically not polarized . light from a lightbulb , an old incandescent light bulb , this thing 's hot . you can get light polarized in any direction , all at once , all overlapping . so if we draw this case for a light bulb , just a random incandescent light bulb , you might get light , some of the light , hitting you eye , you can get some light that 's got that direction , you got light that 's got this direction , you got light in all these directions at any given moment . i mean , you 'd have to add these up to get the total , and they might not all be the same value . but what i 'm trying to say is , at any given moment , you do n't know what direction the electric field 's going to be hitting your eye at from a random source . it could be in any direction . so this is not polarized . this diagram represents light that is not polarized . at some point , the field might be pointing this way , at some later point it 's this way ; it 's just random . you never know which way the electric field 's going to be pointing . whereas these over here , these are polarized . so how could you polarize this light ? let 's say you wanted light that was polarized . you were doing an experiment . you needed polarized light . well , that 's easy . you can use what 's called a polarizer . and this is a material that lets light through , but it only lets light through in one orientation , so you 're going to have a polarizer that , for instance , only lets through vertically polarized light . so this is a polarizer . these are cheap : thin , plastic , configured in a way so that it only lets light through that 's vertically polarized . any light coming in here that 's not vertically polarized gets blocked , or absorbed . so what that means is , if you used this polarizer and held it in between your eye and this light bulb , you would only get this light . all the rest of it would get blocked . or you could just rotate this thing and imagine a polarizer that only lets through horizontal light . now it would only let through light that was this way , and so you would only get this part of the light . or you could just orient it at any angle you want and block everything but the certain angle that this polarizer is defined as letting light through . so you can do this . and once you hold this up , you get polarized light , light that 's only got one orientation . so that 's what polarization means . but why do we care about polarization ? well , let me get rid of this for a minute . you 've heard of polarized sunglasses . so imagine you 're standing near water , or maybe you 're standing on ice or snow or something reflective . there 's a problem . say the sun 's out . it 's shining . it 's a beautiful day -- except there 's going to be glare . let 's say you 're looking down at something here on the ground . it 's going to get light reflecting off of it from just ... you know , light 's coming in from all direction . but it also gets this direct light from the sun . so it gets light from reflected off the clouds and whatever , whatever 's nearby , ambient light . and there 's also this direct sunlight . that 's harsh . if that reflects straight up to your eye , that hurts . you do n't like that . it blocks our vision . it 's hard to see , it 's glare . we do n't want this glare . so what can we do ? well , it just so happens that , when light reflects off of a surface , even though the light from the sun is not polarized , once it reflects , it does get polarized or at least partially polarized . so this surface here , once this light reflects , it 's coming in at all orientations . you got electric field ... you never know what electric field you 're going to get straight from the sun . and when it reflects , though , you mostly get , upon reflection , the direction of polarization defined by the plane of the surface that it hit . so because the floor is horizontal , when this light ray hits the ground and reflects , that reflected light gets partially polarized . this horizontal component of the electric field is going to be more present than the other components . maybe not completely . sometimes it could be . it could be completely polarized , but often it 's just partially polarized . but that 's pretty cool , because now you know what we can do . i know how to block this . we should get some sunglasses . we put some sunglasses on and we make our glasses so that these are polarized . and how do we want these polarized ? i want to get rid of the glare . so what i do is , i make sure my sunglasses only let through vertically polarized light . here 's some polarizers . that way , a lot of this glare gets blocked because it does not have a vertical orientation , it has a horizontal orientation . and then we can block it . so that 's one good thing that polarization does for us , and understanding it , we can get rid of glare . also , fishermen like it because , if you 're trying to look in the water at fish , you want to see in through the water , you want to see this light from the fish getting to you . you do n't want to see the glare off of the sun getting to you . so polarized sunglasses are useful . also , we can play a trick on our eye , if we really wanted to . you could take one of these , make one eye have a vertical orientation for the polarization , have the other eye with a horizontal ... and you 're thinking , `` this is stupid . `` why would you do this for ? '' `` this eye 's going to get a lot of glare . '' we would n't use these outside , when you 're , like , skiing or fishing , but you could play a trick on your eyes if you went to the movies and you went and watched a movie . well , the reason our eyes see 3d is because they 're spaced a little bit apart . they each get a different , slightly different image . that makes us see in 3d . we can play the same trick on our eye if we have the polarization like this . if light , if some of the light from the movie theater screen is coming in with one polarization , and the other light 's coming in with the other polarization , we can send two different images to our eyes at the same time . if you took these off , it 'd look like garbage because you 'd be getting both of these slightly different images , it 'd look all blurry . and it does . if you take off your 3d glasses and look at a 3d movie , looks terrible , because now both eyes are getting both images . but if you put your glasses back on , now this eye only gets the orientation that it 's supposed to get , and this eye only gets the orientation that it 's supposed to get , and you get a 3d image . so it 's useful in many ways . let me show you one more thing here . let 's come back here . this light was polarized vertically . so that 's called linear polarization . any time ... same with these . these are all linear polarization because , just up and down , one linear direction , just diagonal . this is also linear . all of these are linear . you can get circular polarized light . so if we come back to here , we 've got our electric field pointing up , like that . now let 's say we sent in another light ray , another light ray that also had a polarization , but not in this direction . let 's say our other light ray had polarization in this direction , so it looks like this , kind of like what our magnetic field would have looked like . but this is a completely different light ray with its own polarization and its own magnetic field . so we send this in . what would happen ? well , at this point , you 'd have a electric field that points this way . at this point , you 'd have a electric field that points that way . what would your eye see if you were over here ? let 's see . if i draw our axis here . all right , when this point right here gets to your eye , what am i going to see ? well , i 'm going to have a light ray that 's one part of a light ray . one component points up . that 's this electric field . one component points left . that 's this electric field . so the total , my total electric field , would point this way . i could to the pythagorean theorem if i wanted to figure out the size of it , but i just want to know the direction for now . and then it gets to here , and look at it : they both have zero . this light ray has zero electric field , this one has zero electric fields . so then it 'd just be at zero . now what happens over here ? well , i 've got light . this one points to the right at that point , this pink one , and then this red one would be pointing down . so what would i have at that point ? i 'd have light that went this way , and it would just be doing this over and over . it would just be ... i 'd just have diagonally polarized light . this is n't giving me anything new . you might think this is dumb . why do this ? why send in two different waves to just get diagonally polarized light ? i could have just sent in one wave that was diagonally polarized and got the same thing . the reason is , if you shift this purple wave , this pink wave , by 90 degrees of phase , by pi over two in phase , something magical happens . let me show you what happens here , if we move this to here . now we do n't just get diagonally linear polarized light . what we 're going to get is ... let me get rid of this . okay , so we start off with red , right ? the red electric field points up , and then this pink wave 's electric field is zero at that point . so this is all i have . my total electric field would just be up . i 'm going to draw it right here . the green 'll be the total . now i come over to here , and at this point , there 's some red electric field that points up , but there 's some of this other electric field that points this way . so i 'd have a total electric field that would point that way . and then i get over to here , and i 'd have all of the electric field from the pink one , none from the red one . it would point all left then . look what 's happening . the polarization of this light , if i shift this , if i 'm sitting here , looking with my eye , as my eye receives this light , i 'm going to see this light rotate its polarization . the polarization i 'm going to notice swings around in a circular pattern . and because of this , we call this circular polarization . so this is another type of polarization , where the actual angle of polarization rotates smoothly as this light ray enters your eye . and you know what ? er , drrr ... all right , actually , i sent you to receive this one first . that makes no sense . you 're going to receive the ones closes to you first in this light ray going this way . so you 'd actually receive this one first , then that one , then this one , then this one . because of that , you would n't see this going in a counterclockwise way , you 'd see this going in a clockwise circularly polarized way . sorry about that . you might think , `` okay , why ? `` why even bother with circular polarization ? '' well , i kind of lied earlier . turns out , in the movie theater example , they do n't actually do it like this , typically . oftentimes in the movie theaters , we do n't have just linearly polarized sunglasses . this would be a problem because , when you look at the movie theater screen , and if you were to tilt your head just a little bit ... think about it . this one 's not really going to get the right image anymore . it 's going to get some of both . and this one 's going to get some of both . it 's going to be blurry . your head would have to be perfectly level the whole time , which might be annoying . so what we do is , instead , we create circular polarized glasses , so that this one would only get one polarization , this one would get the other direction . this way , even if you tilt your head a little bit ... shoot , clockwise is clockwise , counterclockwise is counterclockwise . by using circular polarization for 3d movies , it can make it a little easier on you eyes to see a better 3d image , even if your head 's tilted a little bit .
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you might think , `` okay , why ? `` why even bother with circular polarization ? '' well , i kind of lied earlier .
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how would they interact to produce a circular polarization ?
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- let 's talk about polarization of light . we know what light waves are ; they 're electromagnetic waves . so they 're made out of electric fields . and that 's not good enough . we know there 's not just electric fields . that could n't sustain itself . there 's got to be magnetic fields there , as well , that are changing . those are perpendicular , so you can kind of draw them . it 's hard , on something two-dimensional , but you can kind of imagine those looking something like this . and those magnetic fields would point at a right angle to the electric fields . but this gets really messy if i try to draw both the electric and magnetic fields at the same time . so we 're going to leave the magnetic fields out . it 's often good enough to just know the direction of the electric field when we focus on the electric field . so what does polarization mean ? polarization refers to the fact that , if this light ray was heading straight toward your eye , or a detector , over here , what would you see ? well , if i draw an axis over here , and this point here , in the middle , this is this line -- so imagine we 're looking straight down that line -- and then up and down is up and down , and then left and right , that direction i have the magnetic field , would be this way and that way . what would my eye see ? well , my eye 's only going to see electric fields that either point up or electric fields that point down . they might have different values , but i 'm only going to see electric fields that point up or down . because of that , this light ray is polarized . so polarized light is light where the electric field is only oscillating in one direction . up or down , that 's one direction -- vertically . or it could be polarized horizontally . or it could be polarized diagonally . but either way , you could have this wave polarized along any direction . i mean , a light ray like this , if we had it coming in diagonal , this light ray that 's oscillating like this , where the electric field oscillates like that , that also polarized . these are both polarized because there 's only one direction that the electric field is oscillating in . and you might thing , `` pff , how could you ever have `` a light ray that 's not polarized ? '' easy . most light that you get is not polarized . that is to say , light that 's coming from the sun , straight from the sun -- typically not polarized . light from a lightbulb , an old incandescent light bulb , this thing 's hot . you can get light polarized in any direction , all at once , all overlapping . so if we draw this case for a light bulb , just a random incandescent light bulb , you might get light , some of the light , hitting you eye , you can get some light that 's got that direction , you got light that 's got this direction , you got light in all these directions at any given moment . i mean , you 'd have to add these up to get the total , and they might not all be the same value . but what i 'm trying to say is , at any given moment , you do n't know what direction the electric field 's going to be hitting your eye at from a random source . it could be in any direction . so this is not polarized . this diagram represents light that is not polarized . at some point , the field might be pointing this way , at some later point it 's this way ; it 's just random . you never know which way the electric field 's going to be pointing . whereas these over here , these are polarized . so how could you polarize this light ? let 's say you wanted light that was polarized . you were doing an experiment . you needed polarized light . well , that 's easy . you can use what 's called a polarizer . and this is a material that lets light through , but it only lets light through in one orientation , so you 're going to have a polarizer that , for instance , only lets through vertically polarized light . so this is a polarizer . these are cheap : thin , plastic , configured in a way so that it only lets light through that 's vertically polarized . any light coming in here that 's not vertically polarized gets blocked , or absorbed . so what that means is , if you used this polarizer and held it in between your eye and this light bulb , you would only get this light . all the rest of it would get blocked . or you could just rotate this thing and imagine a polarizer that only lets through horizontal light . now it would only let through light that was this way , and so you would only get this part of the light . or you could just orient it at any angle you want and block everything but the certain angle that this polarizer is defined as letting light through . so you can do this . and once you hold this up , you get polarized light , light that 's only got one orientation . so that 's what polarization means . but why do we care about polarization ? well , let me get rid of this for a minute . you 've heard of polarized sunglasses . so imagine you 're standing near water , or maybe you 're standing on ice or snow or something reflective . there 's a problem . say the sun 's out . it 's shining . it 's a beautiful day -- except there 's going to be glare . let 's say you 're looking down at something here on the ground . it 's going to get light reflecting off of it from just ... you know , light 's coming in from all direction . but it also gets this direct light from the sun . so it gets light from reflected off the clouds and whatever , whatever 's nearby , ambient light . and there 's also this direct sunlight . that 's harsh . if that reflects straight up to your eye , that hurts . you do n't like that . it blocks our vision . it 's hard to see , it 's glare . we do n't want this glare . so what can we do ? well , it just so happens that , when light reflects off of a surface , even though the light from the sun is not polarized , once it reflects , it does get polarized or at least partially polarized . so this surface here , once this light reflects , it 's coming in at all orientations . you got electric field ... you never know what electric field you 're going to get straight from the sun . and when it reflects , though , you mostly get , upon reflection , the direction of polarization defined by the plane of the surface that it hit . so because the floor is horizontal , when this light ray hits the ground and reflects , that reflected light gets partially polarized . this horizontal component of the electric field is going to be more present than the other components . maybe not completely . sometimes it could be . it could be completely polarized , but often it 's just partially polarized . but that 's pretty cool , because now you know what we can do . i know how to block this . we should get some sunglasses . we put some sunglasses on and we make our glasses so that these are polarized . and how do we want these polarized ? i want to get rid of the glare . so what i do is , i make sure my sunglasses only let through vertically polarized light . here 's some polarizers . that way , a lot of this glare gets blocked because it does not have a vertical orientation , it has a horizontal orientation . and then we can block it . so that 's one good thing that polarization does for us , and understanding it , we can get rid of glare . also , fishermen like it because , if you 're trying to look in the water at fish , you want to see in through the water , you want to see this light from the fish getting to you . you do n't want to see the glare off of the sun getting to you . so polarized sunglasses are useful . also , we can play a trick on our eye , if we really wanted to . you could take one of these , make one eye have a vertical orientation for the polarization , have the other eye with a horizontal ... and you 're thinking , `` this is stupid . `` why would you do this for ? '' `` this eye 's going to get a lot of glare . '' we would n't use these outside , when you 're , like , skiing or fishing , but you could play a trick on your eyes if you went to the movies and you went and watched a movie . well , the reason our eyes see 3d is because they 're spaced a little bit apart . they each get a different , slightly different image . that makes us see in 3d . we can play the same trick on our eye if we have the polarization like this . if light , if some of the light from the movie theater screen is coming in with one polarization , and the other light 's coming in with the other polarization , we can send two different images to our eyes at the same time . if you took these off , it 'd look like garbage because you 'd be getting both of these slightly different images , it 'd look all blurry . and it does . if you take off your 3d glasses and look at a 3d movie , looks terrible , because now both eyes are getting both images . but if you put your glasses back on , now this eye only gets the orientation that it 's supposed to get , and this eye only gets the orientation that it 's supposed to get , and you get a 3d image . so it 's useful in many ways . let me show you one more thing here . let 's come back here . this light was polarized vertically . so that 's called linear polarization . any time ... same with these . these are all linear polarization because , just up and down , one linear direction , just diagonal . this is also linear . all of these are linear . you can get circular polarized light . so if we come back to here , we 've got our electric field pointing up , like that . now let 's say we sent in another light ray , another light ray that also had a polarization , but not in this direction . let 's say our other light ray had polarization in this direction , so it looks like this , kind of like what our magnetic field would have looked like . but this is a completely different light ray with its own polarization and its own magnetic field . so we send this in . what would happen ? well , at this point , you 'd have a electric field that points this way . at this point , you 'd have a electric field that points that way . what would your eye see if you were over here ? let 's see . if i draw our axis here . all right , when this point right here gets to your eye , what am i going to see ? well , i 'm going to have a light ray that 's one part of a light ray . one component points up . that 's this electric field . one component points left . that 's this electric field . so the total , my total electric field , would point this way . i could to the pythagorean theorem if i wanted to figure out the size of it , but i just want to know the direction for now . and then it gets to here , and look at it : they both have zero . this light ray has zero electric field , this one has zero electric fields . so then it 'd just be at zero . now what happens over here ? well , i 've got light . this one points to the right at that point , this pink one , and then this red one would be pointing down . so what would i have at that point ? i 'd have light that went this way , and it would just be doing this over and over . it would just be ... i 'd just have diagonally polarized light . this is n't giving me anything new . you might think this is dumb . why do this ? why send in two different waves to just get diagonally polarized light ? i could have just sent in one wave that was diagonally polarized and got the same thing . the reason is , if you shift this purple wave , this pink wave , by 90 degrees of phase , by pi over two in phase , something magical happens . let me show you what happens here , if we move this to here . now we do n't just get diagonally linear polarized light . what we 're going to get is ... let me get rid of this . okay , so we start off with red , right ? the red electric field points up , and then this pink wave 's electric field is zero at that point . so this is all i have . my total electric field would just be up . i 'm going to draw it right here . the green 'll be the total . now i come over to here , and at this point , there 's some red electric field that points up , but there 's some of this other electric field that points this way . so i 'd have a total electric field that would point that way . and then i get over to here , and i 'd have all of the electric field from the pink one , none from the red one . it would point all left then . look what 's happening . the polarization of this light , if i shift this , if i 'm sitting here , looking with my eye , as my eye receives this light , i 'm going to see this light rotate its polarization . the polarization i 'm going to notice swings around in a circular pattern . and because of this , we call this circular polarization . so this is another type of polarization , where the actual angle of polarization rotates smoothly as this light ray enters your eye . and you know what ? er , drrr ... all right , actually , i sent you to receive this one first . that makes no sense . you 're going to receive the ones closes to you first in this light ray going this way . so you 'd actually receive this one first , then that one , then this one , then this one . because of that , you would n't see this going in a counterclockwise way , you 'd see this going in a clockwise circularly polarized way . sorry about that . you might think , `` okay , why ? `` why even bother with circular polarization ? '' well , i kind of lied earlier . turns out , in the movie theater example , they do n't actually do it like this , typically . oftentimes in the movie theaters , we do n't have just linearly polarized sunglasses . this would be a problem because , when you look at the movie theater screen , and if you were to tilt your head just a little bit ... think about it . this one 's not really going to get the right image anymore . it 's going to get some of both . and this one 's going to get some of both . it 's going to be blurry . your head would have to be perfectly level the whole time , which might be annoying . so what we do is , instead , we create circular polarized glasses , so that this one would only get one polarization , this one would get the other direction . this way , even if you tilt your head a little bit ... shoot , clockwise is clockwise , counterclockwise is counterclockwise . by using circular polarization for 3d movies , it can make it a little easier on you eyes to see a better 3d image , even if your head 's tilted a little bit .
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you might think , `` okay , why ? `` why even bother with circular polarization ? '' well , i kind of lied earlier .
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the circular polarization is not exactly about the orientation , what you said in the video is the another wave moves forward , however the direction is not changing ?
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- let 's talk about polarization of light . we know what light waves are ; they 're electromagnetic waves . so they 're made out of electric fields . and that 's not good enough . we know there 's not just electric fields . that could n't sustain itself . there 's got to be magnetic fields there , as well , that are changing . those are perpendicular , so you can kind of draw them . it 's hard , on something two-dimensional , but you can kind of imagine those looking something like this . and those magnetic fields would point at a right angle to the electric fields . but this gets really messy if i try to draw both the electric and magnetic fields at the same time . so we 're going to leave the magnetic fields out . it 's often good enough to just know the direction of the electric field when we focus on the electric field . so what does polarization mean ? polarization refers to the fact that , if this light ray was heading straight toward your eye , or a detector , over here , what would you see ? well , if i draw an axis over here , and this point here , in the middle , this is this line -- so imagine we 're looking straight down that line -- and then up and down is up and down , and then left and right , that direction i have the magnetic field , would be this way and that way . what would my eye see ? well , my eye 's only going to see electric fields that either point up or electric fields that point down . they might have different values , but i 'm only going to see electric fields that point up or down . because of that , this light ray is polarized . so polarized light is light where the electric field is only oscillating in one direction . up or down , that 's one direction -- vertically . or it could be polarized horizontally . or it could be polarized diagonally . but either way , you could have this wave polarized along any direction . i mean , a light ray like this , if we had it coming in diagonal , this light ray that 's oscillating like this , where the electric field oscillates like that , that also polarized . these are both polarized because there 's only one direction that the electric field is oscillating in . and you might thing , `` pff , how could you ever have `` a light ray that 's not polarized ? '' easy . most light that you get is not polarized . that is to say , light that 's coming from the sun , straight from the sun -- typically not polarized . light from a lightbulb , an old incandescent light bulb , this thing 's hot . you can get light polarized in any direction , all at once , all overlapping . so if we draw this case for a light bulb , just a random incandescent light bulb , you might get light , some of the light , hitting you eye , you can get some light that 's got that direction , you got light that 's got this direction , you got light in all these directions at any given moment . i mean , you 'd have to add these up to get the total , and they might not all be the same value . but what i 'm trying to say is , at any given moment , you do n't know what direction the electric field 's going to be hitting your eye at from a random source . it could be in any direction . so this is not polarized . this diagram represents light that is not polarized . at some point , the field might be pointing this way , at some later point it 's this way ; it 's just random . you never know which way the electric field 's going to be pointing . whereas these over here , these are polarized . so how could you polarize this light ? let 's say you wanted light that was polarized . you were doing an experiment . you needed polarized light . well , that 's easy . you can use what 's called a polarizer . and this is a material that lets light through , but it only lets light through in one orientation , so you 're going to have a polarizer that , for instance , only lets through vertically polarized light . so this is a polarizer . these are cheap : thin , plastic , configured in a way so that it only lets light through that 's vertically polarized . any light coming in here that 's not vertically polarized gets blocked , or absorbed . so what that means is , if you used this polarizer and held it in between your eye and this light bulb , you would only get this light . all the rest of it would get blocked . or you could just rotate this thing and imagine a polarizer that only lets through horizontal light . now it would only let through light that was this way , and so you would only get this part of the light . or you could just orient it at any angle you want and block everything but the certain angle that this polarizer is defined as letting light through . so you can do this . and once you hold this up , you get polarized light , light that 's only got one orientation . so that 's what polarization means . but why do we care about polarization ? well , let me get rid of this for a minute . you 've heard of polarized sunglasses . so imagine you 're standing near water , or maybe you 're standing on ice or snow or something reflective . there 's a problem . say the sun 's out . it 's shining . it 's a beautiful day -- except there 's going to be glare . let 's say you 're looking down at something here on the ground . it 's going to get light reflecting off of it from just ... you know , light 's coming in from all direction . but it also gets this direct light from the sun . so it gets light from reflected off the clouds and whatever , whatever 's nearby , ambient light . and there 's also this direct sunlight . that 's harsh . if that reflects straight up to your eye , that hurts . you do n't like that . it blocks our vision . it 's hard to see , it 's glare . we do n't want this glare . so what can we do ? well , it just so happens that , when light reflects off of a surface , even though the light from the sun is not polarized , once it reflects , it does get polarized or at least partially polarized . so this surface here , once this light reflects , it 's coming in at all orientations . you got electric field ... you never know what electric field you 're going to get straight from the sun . and when it reflects , though , you mostly get , upon reflection , the direction of polarization defined by the plane of the surface that it hit . so because the floor is horizontal , when this light ray hits the ground and reflects , that reflected light gets partially polarized . this horizontal component of the electric field is going to be more present than the other components . maybe not completely . sometimes it could be . it could be completely polarized , but often it 's just partially polarized . but that 's pretty cool , because now you know what we can do . i know how to block this . we should get some sunglasses . we put some sunglasses on and we make our glasses so that these are polarized . and how do we want these polarized ? i want to get rid of the glare . so what i do is , i make sure my sunglasses only let through vertically polarized light . here 's some polarizers . that way , a lot of this glare gets blocked because it does not have a vertical orientation , it has a horizontal orientation . and then we can block it . so that 's one good thing that polarization does for us , and understanding it , we can get rid of glare . also , fishermen like it because , if you 're trying to look in the water at fish , you want to see in through the water , you want to see this light from the fish getting to you . you do n't want to see the glare off of the sun getting to you . so polarized sunglasses are useful . also , we can play a trick on our eye , if we really wanted to . you could take one of these , make one eye have a vertical orientation for the polarization , have the other eye with a horizontal ... and you 're thinking , `` this is stupid . `` why would you do this for ? '' `` this eye 's going to get a lot of glare . '' we would n't use these outside , when you 're , like , skiing or fishing , but you could play a trick on your eyes if you went to the movies and you went and watched a movie . well , the reason our eyes see 3d is because they 're spaced a little bit apart . they each get a different , slightly different image . that makes us see in 3d . we can play the same trick on our eye if we have the polarization like this . if light , if some of the light from the movie theater screen is coming in with one polarization , and the other light 's coming in with the other polarization , we can send two different images to our eyes at the same time . if you took these off , it 'd look like garbage because you 'd be getting both of these slightly different images , it 'd look all blurry . and it does . if you take off your 3d glasses and look at a 3d movie , looks terrible , because now both eyes are getting both images . but if you put your glasses back on , now this eye only gets the orientation that it 's supposed to get , and this eye only gets the orientation that it 's supposed to get , and you get a 3d image . so it 's useful in many ways . let me show you one more thing here . let 's come back here . this light was polarized vertically . so that 's called linear polarization . any time ... same with these . these are all linear polarization because , just up and down , one linear direction , just diagonal . this is also linear . all of these are linear . you can get circular polarized light . so if we come back to here , we 've got our electric field pointing up , like that . now let 's say we sent in another light ray , another light ray that also had a polarization , but not in this direction . let 's say our other light ray had polarization in this direction , so it looks like this , kind of like what our magnetic field would have looked like . but this is a completely different light ray with its own polarization and its own magnetic field . so we send this in . what would happen ? well , at this point , you 'd have a electric field that points this way . at this point , you 'd have a electric field that points that way . what would your eye see if you were over here ? let 's see . if i draw our axis here . all right , when this point right here gets to your eye , what am i going to see ? well , i 'm going to have a light ray that 's one part of a light ray . one component points up . that 's this electric field . one component points left . that 's this electric field . so the total , my total electric field , would point this way . i could to the pythagorean theorem if i wanted to figure out the size of it , but i just want to know the direction for now . and then it gets to here , and look at it : they both have zero . this light ray has zero electric field , this one has zero electric fields . so then it 'd just be at zero . now what happens over here ? well , i 've got light . this one points to the right at that point , this pink one , and then this red one would be pointing down . so what would i have at that point ? i 'd have light that went this way , and it would just be doing this over and over . it would just be ... i 'd just have diagonally polarized light . this is n't giving me anything new . you might think this is dumb . why do this ? why send in two different waves to just get diagonally polarized light ? i could have just sent in one wave that was diagonally polarized and got the same thing . the reason is , if you shift this purple wave , this pink wave , by 90 degrees of phase , by pi over two in phase , something magical happens . let me show you what happens here , if we move this to here . now we do n't just get diagonally linear polarized light . what we 're going to get is ... let me get rid of this . okay , so we start off with red , right ? the red electric field points up , and then this pink wave 's electric field is zero at that point . so this is all i have . my total electric field would just be up . i 'm going to draw it right here . the green 'll be the total . now i come over to here , and at this point , there 's some red electric field that points up , but there 's some of this other electric field that points this way . so i 'd have a total electric field that would point that way . and then i get over to here , and i 'd have all of the electric field from the pink one , none from the red one . it would point all left then . look what 's happening . the polarization of this light , if i shift this , if i 'm sitting here , looking with my eye , as my eye receives this light , i 'm going to see this light rotate its polarization . the polarization i 'm going to notice swings around in a circular pattern . and because of this , we call this circular polarization . so this is another type of polarization , where the actual angle of polarization rotates smoothly as this light ray enters your eye . and you know what ? er , drrr ... all right , actually , i sent you to receive this one first . that makes no sense . you 're going to receive the ones closes to you first in this light ray going this way . so you 'd actually receive this one first , then that one , then this one , then this one . because of that , you would n't see this going in a counterclockwise way , you 'd see this going in a clockwise circularly polarized way . sorry about that . you might think , `` okay , why ? `` why even bother with circular polarization ? '' well , i kind of lied earlier . turns out , in the movie theater example , they do n't actually do it like this , typically . oftentimes in the movie theaters , we do n't have just linearly polarized sunglasses . this would be a problem because , when you look at the movie theater screen , and if you were to tilt your head just a little bit ... think about it . this one 's not really going to get the right image anymore . it 's going to get some of both . and this one 's going to get some of both . it 's going to be blurry . your head would have to be perfectly level the whole time , which might be annoying . so what we do is , instead , we create circular polarized glasses , so that this one would only get one polarization , this one would get the other direction . this way , even if you tilt your head a little bit ... shoot , clockwise is clockwise , counterclockwise is counterclockwise . by using circular polarization for 3d movies , it can make it a little easier on you eyes to see a better 3d image , even if your head 's tilted a little bit .
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you were doing an experiment . you needed polarized light . well , that 's easy .
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so the view screen on the enterprise is circularly polarized ?
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- let 's talk about polarization of light . we know what light waves are ; they 're electromagnetic waves . so they 're made out of electric fields . and that 's not good enough . we know there 's not just electric fields . that could n't sustain itself . there 's got to be magnetic fields there , as well , that are changing . those are perpendicular , so you can kind of draw them . it 's hard , on something two-dimensional , but you can kind of imagine those looking something like this . and those magnetic fields would point at a right angle to the electric fields . but this gets really messy if i try to draw both the electric and magnetic fields at the same time . so we 're going to leave the magnetic fields out . it 's often good enough to just know the direction of the electric field when we focus on the electric field . so what does polarization mean ? polarization refers to the fact that , if this light ray was heading straight toward your eye , or a detector , over here , what would you see ? well , if i draw an axis over here , and this point here , in the middle , this is this line -- so imagine we 're looking straight down that line -- and then up and down is up and down , and then left and right , that direction i have the magnetic field , would be this way and that way . what would my eye see ? well , my eye 's only going to see electric fields that either point up or electric fields that point down . they might have different values , but i 'm only going to see electric fields that point up or down . because of that , this light ray is polarized . so polarized light is light where the electric field is only oscillating in one direction . up or down , that 's one direction -- vertically . or it could be polarized horizontally . or it could be polarized diagonally . but either way , you could have this wave polarized along any direction . i mean , a light ray like this , if we had it coming in diagonal , this light ray that 's oscillating like this , where the electric field oscillates like that , that also polarized . these are both polarized because there 's only one direction that the electric field is oscillating in . and you might thing , `` pff , how could you ever have `` a light ray that 's not polarized ? '' easy . most light that you get is not polarized . that is to say , light that 's coming from the sun , straight from the sun -- typically not polarized . light from a lightbulb , an old incandescent light bulb , this thing 's hot . you can get light polarized in any direction , all at once , all overlapping . so if we draw this case for a light bulb , just a random incandescent light bulb , you might get light , some of the light , hitting you eye , you can get some light that 's got that direction , you got light that 's got this direction , you got light in all these directions at any given moment . i mean , you 'd have to add these up to get the total , and they might not all be the same value . but what i 'm trying to say is , at any given moment , you do n't know what direction the electric field 's going to be hitting your eye at from a random source . it could be in any direction . so this is not polarized . this diagram represents light that is not polarized . at some point , the field might be pointing this way , at some later point it 's this way ; it 's just random . you never know which way the electric field 's going to be pointing . whereas these over here , these are polarized . so how could you polarize this light ? let 's say you wanted light that was polarized . you were doing an experiment . you needed polarized light . well , that 's easy . you can use what 's called a polarizer . and this is a material that lets light through , but it only lets light through in one orientation , so you 're going to have a polarizer that , for instance , only lets through vertically polarized light . so this is a polarizer . these are cheap : thin , plastic , configured in a way so that it only lets light through that 's vertically polarized . any light coming in here that 's not vertically polarized gets blocked , or absorbed . so what that means is , if you used this polarizer and held it in between your eye and this light bulb , you would only get this light . all the rest of it would get blocked . or you could just rotate this thing and imagine a polarizer that only lets through horizontal light . now it would only let through light that was this way , and so you would only get this part of the light . or you could just orient it at any angle you want and block everything but the certain angle that this polarizer is defined as letting light through . so you can do this . and once you hold this up , you get polarized light , light that 's only got one orientation . so that 's what polarization means . but why do we care about polarization ? well , let me get rid of this for a minute . you 've heard of polarized sunglasses . so imagine you 're standing near water , or maybe you 're standing on ice or snow or something reflective . there 's a problem . say the sun 's out . it 's shining . it 's a beautiful day -- except there 's going to be glare . let 's say you 're looking down at something here on the ground . it 's going to get light reflecting off of it from just ... you know , light 's coming in from all direction . but it also gets this direct light from the sun . so it gets light from reflected off the clouds and whatever , whatever 's nearby , ambient light . and there 's also this direct sunlight . that 's harsh . if that reflects straight up to your eye , that hurts . you do n't like that . it blocks our vision . it 's hard to see , it 's glare . we do n't want this glare . so what can we do ? well , it just so happens that , when light reflects off of a surface , even though the light from the sun is not polarized , once it reflects , it does get polarized or at least partially polarized . so this surface here , once this light reflects , it 's coming in at all orientations . you got electric field ... you never know what electric field you 're going to get straight from the sun . and when it reflects , though , you mostly get , upon reflection , the direction of polarization defined by the plane of the surface that it hit . so because the floor is horizontal , when this light ray hits the ground and reflects , that reflected light gets partially polarized . this horizontal component of the electric field is going to be more present than the other components . maybe not completely . sometimes it could be . it could be completely polarized , but often it 's just partially polarized . but that 's pretty cool , because now you know what we can do . i know how to block this . we should get some sunglasses . we put some sunglasses on and we make our glasses so that these are polarized . and how do we want these polarized ? i want to get rid of the glare . so what i do is , i make sure my sunglasses only let through vertically polarized light . here 's some polarizers . that way , a lot of this glare gets blocked because it does not have a vertical orientation , it has a horizontal orientation . and then we can block it . so that 's one good thing that polarization does for us , and understanding it , we can get rid of glare . also , fishermen like it because , if you 're trying to look in the water at fish , you want to see in through the water , you want to see this light from the fish getting to you . you do n't want to see the glare off of the sun getting to you . so polarized sunglasses are useful . also , we can play a trick on our eye , if we really wanted to . you could take one of these , make one eye have a vertical orientation for the polarization , have the other eye with a horizontal ... and you 're thinking , `` this is stupid . `` why would you do this for ? '' `` this eye 's going to get a lot of glare . '' we would n't use these outside , when you 're , like , skiing or fishing , but you could play a trick on your eyes if you went to the movies and you went and watched a movie . well , the reason our eyes see 3d is because they 're spaced a little bit apart . they each get a different , slightly different image . that makes us see in 3d . we can play the same trick on our eye if we have the polarization like this . if light , if some of the light from the movie theater screen is coming in with one polarization , and the other light 's coming in with the other polarization , we can send two different images to our eyes at the same time . if you took these off , it 'd look like garbage because you 'd be getting both of these slightly different images , it 'd look all blurry . and it does . if you take off your 3d glasses and look at a 3d movie , looks terrible , because now both eyes are getting both images . but if you put your glasses back on , now this eye only gets the orientation that it 's supposed to get , and this eye only gets the orientation that it 's supposed to get , and you get a 3d image . so it 's useful in many ways . let me show you one more thing here . let 's come back here . this light was polarized vertically . so that 's called linear polarization . any time ... same with these . these are all linear polarization because , just up and down , one linear direction , just diagonal . this is also linear . all of these are linear . you can get circular polarized light . so if we come back to here , we 've got our electric field pointing up , like that . now let 's say we sent in another light ray , another light ray that also had a polarization , but not in this direction . let 's say our other light ray had polarization in this direction , so it looks like this , kind of like what our magnetic field would have looked like . but this is a completely different light ray with its own polarization and its own magnetic field . so we send this in . what would happen ? well , at this point , you 'd have a electric field that points this way . at this point , you 'd have a electric field that points that way . what would your eye see if you were over here ? let 's see . if i draw our axis here . all right , when this point right here gets to your eye , what am i going to see ? well , i 'm going to have a light ray that 's one part of a light ray . one component points up . that 's this electric field . one component points left . that 's this electric field . so the total , my total electric field , would point this way . i could to the pythagorean theorem if i wanted to figure out the size of it , but i just want to know the direction for now . and then it gets to here , and look at it : they both have zero . this light ray has zero electric field , this one has zero electric fields . so then it 'd just be at zero . now what happens over here ? well , i 've got light . this one points to the right at that point , this pink one , and then this red one would be pointing down . so what would i have at that point ? i 'd have light that went this way , and it would just be doing this over and over . it would just be ... i 'd just have diagonally polarized light . this is n't giving me anything new . you might think this is dumb . why do this ? why send in two different waves to just get diagonally polarized light ? i could have just sent in one wave that was diagonally polarized and got the same thing . the reason is , if you shift this purple wave , this pink wave , by 90 degrees of phase , by pi over two in phase , something magical happens . let me show you what happens here , if we move this to here . now we do n't just get diagonally linear polarized light . what we 're going to get is ... let me get rid of this . okay , so we start off with red , right ? the red electric field points up , and then this pink wave 's electric field is zero at that point . so this is all i have . my total electric field would just be up . i 'm going to draw it right here . the green 'll be the total . now i come over to here , and at this point , there 's some red electric field that points up , but there 's some of this other electric field that points this way . so i 'd have a total electric field that would point that way . and then i get over to here , and i 'd have all of the electric field from the pink one , none from the red one . it would point all left then . look what 's happening . the polarization of this light , if i shift this , if i 'm sitting here , looking with my eye , as my eye receives this light , i 'm going to see this light rotate its polarization . the polarization i 'm going to notice swings around in a circular pattern . and because of this , we call this circular polarization . so this is another type of polarization , where the actual angle of polarization rotates smoothly as this light ray enters your eye . and you know what ? er , drrr ... all right , actually , i sent you to receive this one first . that makes no sense . you 're going to receive the ones closes to you first in this light ray going this way . so you 'd actually receive this one first , then that one , then this one , then this one . because of that , you would n't see this going in a counterclockwise way , you 'd see this going in a clockwise circularly polarized way . sorry about that . you might think , `` okay , why ? `` why even bother with circular polarization ? '' well , i kind of lied earlier . turns out , in the movie theater example , they do n't actually do it like this , typically . oftentimes in the movie theaters , we do n't have just linearly polarized sunglasses . this would be a problem because , when you look at the movie theater screen , and if you were to tilt your head just a little bit ... think about it . this one 's not really going to get the right image anymore . it 's going to get some of both . and this one 's going to get some of both . it 's going to be blurry . your head would have to be perfectly level the whole time , which might be annoying . so what we do is , instead , we create circular polarized glasses , so that this one would only get one polarization , this one would get the other direction . this way , even if you tilt your head a little bit ... shoot , clockwise is clockwise , counterclockwise is counterclockwise . by using circular polarization for 3d movies , it can make it a little easier on you eyes to see a better 3d image , even if your head 's tilted a little bit .
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or it could be polarized diagonally . but either way , you could have this wave polarized along any direction . i mean , a light ray like this , if we had it coming in diagonal , this light ray that 's oscillating like this , where the electric field oscillates like that , that also polarized . these are both polarized because there 's only one direction that the electric field is oscillating in .
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what will the ray look like for a wave that only goes up ?
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- let 's talk about polarization of light . we know what light waves are ; they 're electromagnetic waves . so they 're made out of electric fields . and that 's not good enough . we know there 's not just electric fields . that could n't sustain itself . there 's got to be magnetic fields there , as well , that are changing . those are perpendicular , so you can kind of draw them . it 's hard , on something two-dimensional , but you can kind of imagine those looking something like this . and those magnetic fields would point at a right angle to the electric fields . but this gets really messy if i try to draw both the electric and magnetic fields at the same time . so we 're going to leave the magnetic fields out . it 's often good enough to just know the direction of the electric field when we focus on the electric field . so what does polarization mean ? polarization refers to the fact that , if this light ray was heading straight toward your eye , or a detector , over here , what would you see ? well , if i draw an axis over here , and this point here , in the middle , this is this line -- so imagine we 're looking straight down that line -- and then up and down is up and down , and then left and right , that direction i have the magnetic field , would be this way and that way . what would my eye see ? well , my eye 's only going to see electric fields that either point up or electric fields that point down . they might have different values , but i 'm only going to see electric fields that point up or down . because of that , this light ray is polarized . so polarized light is light where the electric field is only oscillating in one direction . up or down , that 's one direction -- vertically . or it could be polarized horizontally . or it could be polarized diagonally . but either way , you could have this wave polarized along any direction . i mean , a light ray like this , if we had it coming in diagonal , this light ray that 's oscillating like this , where the electric field oscillates like that , that also polarized . these are both polarized because there 's only one direction that the electric field is oscillating in . and you might thing , `` pff , how could you ever have `` a light ray that 's not polarized ? '' easy . most light that you get is not polarized . that is to say , light that 's coming from the sun , straight from the sun -- typically not polarized . light from a lightbulb , an old incandescent light bulb , this thing 's hot . you can get light polarized in any direction , all at once , all overlapping . so if we draw this case for a light bulb , just a random incandescent light bulb , you might get light , some of the light , hitting you eye , you can get some light that 's got that direction , you got light that 's got this direction , you got light in all these directions at any given moment . i mean , you 'd have to add these up to get the total , and they might not all be the same value . but what i 'm trying to say is , at any given moment , you do n't know what direction the electric field 's going to be hitting your eye at from a random source . it could be in any direction . so this is not polarized . this diagram represents light that is not polarized . at some point , the field might be pointing this way , at some later point it 's this way ; it 's just random . you never know which way the electric field 's going to be pointing . whereas these over here , these are polarized . so how could you polarize this light ? let 's say you wanted light that was polarized . you were doing an experiment . you needed polarized light . well , that 's easy . you can use what 's called a polarizer . and this is a material that lets light through , but it only lets light through in one orientation , so you 're going to have a polarizer that , for instance , only lets through vertically polarized light . so this is a polarizer . these are cheap : thin , plastic , configured in a way so that it only lets light through that 's vertically polarized . any light coming in here that 's not vertically polarized gets blocked , or absorbed . so what that means is , if you used this polarizer and held it in between your eye and this light bulb , you would only get this light . all the rest of it would get blocked . or you could just rotate this thing and imagine a polarizer that only lets through horizontal light . now it would only let through light that was this way , and so you would only get this part of the light . or you could just orient it at any angle you want and block everything but the certain angle that this polarizer is defined as letting light through . so you can do this . and once you hold this up , you get polarized light , light that 's only got one orientation . so that 's what polarization means . but why do we care about polarization ? well , let me get rid of this for a minute . you 've heard of polarized sunglasses . so imagine you 're standing near water , or maybe you 're standing on ice or snow or something reflective . there 's a problem . say the sun 's out . it 's shining . it 's a beautiful day -- except there 's going to be glare . let 's say you 're looking down at something here on the ground . it 's going to get light reflecting off of it from just ... you know , light 's coming in from all direction . but it also gets this direct light from the sun . so it gets light from reflected off the clouds and whatever , whatever 's nearby , ambient light . and there 's also this direct sunlight . that 's harsh . if that reflects straight up to your eye , that hurts . you do n't like that . it blocks our vision . it 's hard to see , it 's glare . we do n't want this glare . so what can we do ? well , it just so happens that , when light reflects off of a surface , even though the light from the sun is not polarized , once it reflects , it does get polarized or at least partially polarized . so this surface here , once this light reflects , it 's coming in at all orientations . you got electric field ... you never know what electric field you 're going to get straight from the sun . and when it reflects , though , you mostly get , upon reflection , the direction of polarization defined by the plane of the surface that it hit . so because the floor is horizontal , when this light ray hits the ground and reflects , that reflected light gets partially polarized . this horizontal component of the electric field is going to be more present than the other components . maybe not completely . sometimes it could be . it could be completely polarized , but often it 's just partially polarized . but that 's pretty cool , because now you know what we can do . i know how to block this . we should get some sunglasses . we put some sunglasses on and we make our glasses so that these are polarized . and how do we want these polarized ? i want to get rid of the glare . so what i do is , i make sure my sunglasses only let through vertically polarized light . here 's some polarizers . that way , a lot of this glare gets blocked because it does not have a vertical orientation , it has a horizontal orientation . and then we can block it . so that 's one good thing that polarization does for us , and understanding it , we can get rid of glare . also , fishermen like it because , if you 're trying to look in the water at fish , you want to see in through the water , you want to see this light from the fish getting to you . you do n't want to see the glare off of the sun getting to you . so polarized sunglasses are useful . also , we can play a trick on our eye , if we really wanted to . you could take one of these , make one eye have a vertical orientation for the polarization , have the other eye with a horizontal ... and you 're thinking , `` this is stupid . `` why would you do this for ? '' `` this eye 's going to get a lot of glare . '' we would n't use these outside , when you 're , like , skiing or fishing , but you could play a trick on your eyes if you went to the movies and you went and watched a movie . well , the reason our eyes see 3d is because they 're spaced a little bit apart . they each get a different , slightly different image . that makes us see in 3d . we can play the same trick on our eye if we have the polarization like this . if light , if some of the light from the movie theater screen is coming in with one polarization , and the other light 's coming in with the other polarization , we can send two different images to our eyes at the same time . if you took these off , it 'd look like garbage because you 'd be getting both of these slightly different images , it 'd look all blurry . and it does . if you take off your 3d glasses and look at a 3d movie , looks terrible , because now both eyes are getting both images . but if you put your glasses back on , now this eye only gets the orientation that it 's supposed to get , and this eye only gets the orientation that it 's supposed to get , and you get a 3d image . so it 's useful in many ways . let me show you one more thing here . let 's come back here . this light was polarized vertically . so that 's called linear polarization . any time ... same with these . these are all linear polarization because , just up and down , one linear direction , just diagonal . this is also linear . all of these are linear . you can get circular polarized light . so if we come back to here , we 've got our electric field pointing up , like that . now let 's say we sent in another light ray , another light ray that also had a polarization , but not in this direction . let 's say our other light ray had polarization in this direction , so it looks like this , kind of like what our magnetic field would have looked like . but this is a completely different light ray with its own polarization and its own magnetic field . so we send this in . what would happen ? well , at this point , you 'd have a electric field that points this way . at this point , you 'd have a electric field that points that way . what would your eye see if you were over here ? let 's see . if i draw our axis here . all right , when this point right here gets to your eye , what am i going to see ? well , i 'm going to have a light ray that 's one part of a light ray . one component points up . that 's this electric field . one component points left . that 's this electric field . so the total , my total electric field , would point this way . i could to the pythagorean theorem if i wanted to figure out the size of it , but i just want to know the direction for now . and then it gets to here , and look at it : they both have zero . this light ray has zero electric field , this one has zero electric fields . so then it 'd just be at zero . now what happens over here ? well , i 've got light . this one points to the right at that point , this pink one , and then this red one would be pointing down . so what would i have at that point ? i 'd have light that went this way , and it would just be doing this over and over . it would just be ... i 'd just have diagonally polarized light . this is n't giving me anything new . you might think this is dumb . why do this ? why send in two different waves to just get diagonally polarized light ? i could have just sent in one wave that was diagonally polarized and got the same thing . the reason is , if you shift this purple wave , this pink wave , by 90 degrees of phase , by pi over two in phase , something magical happens . let me show you what happens here , if we move this to here . now we do n't just get diagonally linear polarized light . what we 're going to get is ... let me get rid of this . okay , so we start off with red , right ? the red electric field points up , and then this pink wave 's electric field is zero at that point . so this is all i have . my total electric field would just be up . i 'm going to draw it right here . the green 'll be the total . now i come over to here , and at this point , there 's some red electric field that points up , but there 's some of this other electric field that points this way . so i 'd have a total electric field that would point that way . and then i get over to here , and i 'd have all of the electric field from the pink one , none from the red one . it would point all left then . look what 's happening . the polarization of this light , if i shift this , if i 'm sitting here , looking with my eye , as my eye receives this light , i 'm going to see this light rotate its polarization . the polarization i 'm going to notice swings around in a circular pattern . and because of this , we call this circular polarization . so this is another type of polarization , where the actual angle of polarization rotates smoothly as this light ray enters your eye . and you know what ? er , drrr ... all right , actually , i sent you to receive this one first . that makes no sense . you 're going to receive the ones closes to you first in this light ray going this way . so you 'd actually receive this one first , then that one , then this one , then this one . because of that , you would n't see this going in a counterclockwise way , you 'd see this going in a clockwise circularly polarized way . sorry about that . you might think , `` okay , why ? `` why even bother with circular polarization ? '' well , i kind of lied earlier . turns out , in the movie theater example , they do n't actually do it like this , typically . oftentimes in the movie theaters , we do n't have just linearly polarized sunglasses . this would be a problem because , when you look at the movie theater screen , and if you were to tilt your head just a little bit ... think about it . this one 's not really going to get the right image anymore . it 's going to get some of both . and this one 's going to get some of both . it 's going to be blurry . your head would have to be perfectly level the whole time , which might be annoying . so what we do is , instead , we create circular polarized glasses , so that this one would only get one polarization , this one would get the other direction . this way , even if you tilt your head a little bit ... shoot , clockwise is clockwise , counterclockwise is counterclockwise . by using circular polarization for 3d movies , it can make it a little easier on you eyes to see a better 3d image , even if your head 's tilted a little bit .
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and it does . if you take off your 3d glasses and look at a 3d movie , looks terrible , because now both eyes are getting both images . but if you put your glasses back on , now this eye only gets the orientation that it 's supposed to get , and this eye only gets the orientation that it 's supposed to get , and you get a 3d image .
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for the 3d glasses and the sunglasses question , is that why 3d glasses look like sunglasses ?
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- let 's talk about polarization of light . we know what light waves are ; they 're electromagnetic waves . so they 're made out of electric fields . and that 's not good enough . we know there 's not just electric fields . that could n't sustain itself . there 's got to be magnetic fields there , as well , that are changing . those are perpendicular , so you can kind of draw them . it 's hard , on something two-dimensional , but you can kind of imagine those looking something like this . and those magnetic fields would point at a right angle to the electric fields . but this gets really messy if i try to draw both the electric and magnetic fields at the same time . so we 're going to leave the magnetic fields out . it 's often good enough to just know the direction of the electric field when we focus on the electric field . so what does polarization mean ? polarization refers to the fact that , if this light ray was heading straight toward your eye , or a detector , over here , what would you see ? well , if i draw an axis over here , and this point here , in the middle , this is this line -- so imagine we 're looking straight down that line -- and then up and down is up and down , and then left and right , that direction i have the magnetic field , would be this way and that way . what would my eye see ? well , my eye 's only going to see electric fields that either point up or electric fields that point down . they might have different values , but i 'm only going to see electric fields that point up or down . because of that , this light ray is polarized . so polarized light is light where the electric field is only oscillating in one direction . up or down , that 's one direction -- vertically . or it could be polarized horizontally . or it could be polarized diagonally . but either way , you could have this wave polarized along any direction . i mean , a light ray like this , if we had it coming in diagonal , this light ray that 's oscillating like this , where the electric field oscillates like that , that also polarized . these are both polarized because there 's only one direction that the electric field is oscillating in . and you might thing , `` pff , how could you ever have `` a light ray that 's not polarized ? '' easy . most light that you get is not polarized . that is to say , light that 's coming from the sun , straight from the sun -- typically not polarized . light from a lightbulb , an old incandescent light bulb , this thing 's hot . you can get light polarized in any direction , all at once , all overlapping . so if we draw this case for a light bulb , just a random incandescent light bulb , you might get light , some of the light , hitting you eye , you can get some light that 's got that direction , you got light that 's got this direction , you got light in all these directions at any given moment . i mean , you 'd have to add these up to get the total , and they might not all be the same value . but what i 'm trying to say is , at any given moment , you do n't know what direction the electric field 's going to be hitting your eye at from a random source . it could be in any direction . so this is not polarized . this diagram represents light that is not polarized . at some point , the field might be pointing this way , at some later point it 's this way ; it 's just random . you never know which way the electric field 's going to be pointing . whereas these over here , these are polarized . so how could you polarize this light ? let 's say you wanted light that was polarized . you were doing an experiment . you needed polarized light . well , that 's easy . you can use what 's called a polarizer . and this is a material that lets light through , but it only lets light through in one orientation , so you 're going to have a polarizer that , for instance , only lets through vertically polarized light . so this is a polarizer . these are cheap : thin , plastic , configured in a way so that it only lets light through that 's vertically polarized . any light coming in here that 's not vertically polarized gets blocked , or absorbed . so what that means is , if you used this polarizer and held it in between your eye and this light bulb , you would only get this light . all the rest of it would get blocked . or you could just rotate this thing and imagine a polarizer that only lets through horizontal light . now it would only let through light that was this way , and so you would only get this part of the light . or you could just orient it at any angle you want and block everything but the certain angle that this polarizer is defined as letting light through . so you can do this . and once you hold this up , you get polarized light , light that 's only got one orientation . so that 's what polarization means . but why do we care about polarization ? well , let me get rid of this for a minute . you 've heard of polarized sunglasses . so imagine you 're standing near water , or maybe you 're standing on ice or snow or something reflective . there 's a problem . say the sun 's out . it 's shining . it 's a beautiful day -- except there 's going to be glare . let 's say you 're looking down at something here on the ground . it 's going to get light reflecting off of it from just ... you know , light 's coming in from all direction . but it also gets this direct light from the sun . so it gets light from reflected off the clouds and whatever , whatever 's nearby , ambient light . and there 's also this direct sunlight . that 's harsh . if that reflects straight up to your eye , that hurts . you do n't like that . it blocks our vision . it 's hard to see , it 's glare . we do n't want this glare . so what can we do ? well , it just so happens that , when light reflects off of a surface , even though the light from the sun is not polarized , once it reflects , it does get polarized or at least partially polarized . so this surface here , once this light reflects , it 's coming in at all orientations . you got electric field ... you never know what electric field you 're going to get straight from the sun . and when it reflects , though , you mostly get , upon reflection , the direction of polarization defined by the plane of the surface that it hit . so because the floor is horizontal , when this light ray hits the ground and reflects , that reflected light gets partially polarized . this horizontal component of the electric field is going to be more present than the other components . maybe not completely . sometimes it could be . it could be completely polarized , but often it 's just partially polarized . but that 's pretty cool , because now you know what we can do . i know how to block this . we should get some sunglasses . we put some sunglasses on and we make our glasses so that these are polarized . and how do we want these polarized ? i want to get rid of the glare . so what i do is , i make sure my sunglasses only let through vertically polarized light . here 's some polarizers . that way , a lot of this glare gets blocked because it does not have a vertical orientation , it has a horizontal orientation . and then we can block it . so that 's one good thing that polarization does for us , and understanding it , we can get rid of glare . also , fishermen like it because , if you 're trying to look in the water at fish , you want to see in through the water , you want to see this light from the fish getting to you . you do n't want to see the glare off of the sun getting to you . so polarized sunglasses are useful . also , we can play a trick on our eye , if we really wanted to . you could take one of these , make one eye have a vertical orientation for the polarization , have the other eye with a horizontal ... and you 're thinking , `` this is stupid . `` why would you do this for ? '' `` this eye 's going to get a lot of glare . '' we would n't use these outside , when you 're , like , skiing or fishing , but you could play a trick on your eyes if you went to the movies and you went and watched a movie . well , the reason our eyes see 3d is because they 're spaced a little bit apart . they each get a different , slightly different image . that makes us see in 3d . we can play the same trick on our eye if we have the polarization like this . if light , if some of the light from the movie theater screen is coming in with one polarization , and the other light 's coming in with the other polarization , we can send two different images to our eyes at the same time . if you took these off , it 'd look like garbage because you 'd be getting both of these slightly different images , it 'd look all blurry . and it does . if you take off your 3d glasses and look at a 3d movie , looks terrible , because now both eyes are getting both images . but if you put your glasses back on , now this eye only gets the orientation that it 's supposed to get , and this eye only gets the orientation that it 's supposed to get , and you get a 3d image . so it 's useful in many ways . let me show you one more thing here . let 's come back here . this light was polarized vertically . so that 's called linear polarization . any time ... same with these . these are all linear polarization because , just up and down , one linear direction , just diagonal . this is also linear . all of these are linear . you can get circular polarized light . so if we come back to here , we 've got our electric field pointing up , like that . now let 's say we sent in another light ray , another light ray that also had a polarization , but not in this direction . let 's say our other light ray had polarization in this direction , so it looks like this , kind of like what our magnetic field would have looked like . but this is a completely different light ray with its own polarization and its own magnetic field . so we send this in . what would happen ? well , at this point , you 'd have a electric field that points this way . at this point , you 'd have a electric field that points that way . what would your eye see if you were over here ? let 's see . if i draw our axis here . all right , when this point right here gets to your eye , what am i going to see ? well , i 'm going to have a light ray that 's one part of a light ray . one component points up . that 's this electric field . one component points left . that 's this electric field . so the total , my total electric field , would point this way . i could to the pythagorean theorem if i wanted to figure out the size of it , but i just want to know the direction for now . and then it gets to here , and look at it : they both have zero . this light ray has zero electric field , this one has zero electric fields . so then it 'd just be at zero . now what happens over here ? well , i 've got light . this one points to the right at that point , this pink one , and then this red one would be pointing down . so what would i have at that point ? i 'd have light that went this way , and it would just be doing this over and over . it would just be ... i 'd just have diagonally polarized light . this is n't giving me anything new . you might think this is dumb . why do this ? why send in two different waves to just get diagonally polarized light ? i could have just sent in one wave that was diagonally polarized and got the same thing . the reason is , if you shift this purple wave , this pink wave , by 90 degrees of phase , by pi over two in phase , something magical happens . let me show you what happens here , if we move this to here . now we do n't just get diagonally linear polarized light . what we 're going to get is ... let me get rid of this . okay , so we start off with red , right ? the red electric field points up , and then this pink wave 's electric field is zero at that point . so this is all i have . my total electric field would just be up . i 'm going to draw it right here . the green 'll be the total . now i come over to here , and at this point , there 's some red electric field that points up , but there 's some of this other electric field that points this way . so i 'd have a total electric field that would point that way . and then i get over to here , and i 'd have all of the electric field from the pink one , none from the red one . it would point all left then . look what 's happening . the polarization of this light , if i shift this , if i 'm sitting here , looking with my eye , as my eye receives this light , i 'm going to see this light rotate its polarization . the polarization i 'm going to notice swings around in a circular pattern . and because of this , we call this circular polarization . so this is another type of polarization , where the actual angle of polarization rotates smoothly as this light ray enters your eye . and you know what ? er , drrr ... all right , actually , i sent you to receive this one first . that makes no sense . you 're going to receive the ones closes to you first in this light ray going this way . so you 'd actually receive this one first , then that one , then this one , then this one . because of that , you would n't see this going in a counterclockwise way , you 'd see this going in a clockwise circularly polarized way . sorry about that . you might think , `` okay , why ? `` why even bother with circular polarization ? '' well , i kind of lied earlier . turns out , in the movie theater example , they do n't actually do it like this , typically . oftentimes in the movie theaters , we do n't have just linearly polarized sunglasses . this would be a problem because , when you look at the movie theater screen , and if you were to tilt your head just a little bit ... think about it . this one 's not really going to get the right image anymore . it 's going to get some of both . and this one 's going to get some of both . it 's going to be blurry . your head would have to be perfectly level the whole time , which might be annoying . so what we do is , instead , we create circular polarized glasses , so that this one would only get one polarization , this one would get the other direction . this way , even if you tilt your head a little bit ... shoot , clockwise is clockwise , counterclockwise is counterclockwise . by using circular polarization for 3d movies , it can make it a little easier on you eyes to see a better 3d image , even if your head 's tilted a little bit .
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it 's hard , on something two-dimensional , but you can kind of imagine those looking something like this . and those magnetic fields would point at a right angle to the electric fields . but this gets really messy if i try to draw both the electric and magnetic fields at the same time .
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if electric fields ( of `` point '' charges ) are spherical like gravity fields , and em waves are periodic perturbations of those fields propagated at the speed of light , how does it happen that em waves occur not as radiating wave fronts in space , but along and perpendicular to linear axes ?
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- let 's talk about polarization of light . we know what light waves are ; they 're electromagnetic waves . so they 're made out of electric fields . and that 's not good enough . we know there 's not just electric fields . that could n't sustain itself . there 's got to be magnetic fields there , as well , that are changing . those are perpendicular , so you can kind of draw them . it 's hard , on something two-dimensional , but you can kind of imagine those looking something like this . and those magnetic fields would point at a right angle to the electric fields . but this gets really messy if i try to draw both the electric and magnetic fields at the same time . so we 're going to leave the magnetic fields out . it 's often good enough to just know the direction of the electric field when we focus on the electric field . so what does polarization mean ? polarization refers to the fact that , if this light ray was heading straight toward your eye , or a detector , over here , what would you see ? well , if i draw an axis over here , and this point here , in the middle , this is this line -- so imagine we 're looking straight down that line -- and then up and down is up and down , and then left and right , that direction i have the magnetic field , would be this way and that way . what would my eye see ? well , my eye 's only going to see electric fields that either point up or electric fields that point down . they might have different values , but i 'm only going to see electric fields that point up or down . because of that , this light ray is polarized . so polarized light is light where the electric field is only oscillating in one direction . up or down , that 's one direction -- vertically . or it could be polarized horizontally . or it could be polarized diagonally . but either way , you could have this wave polarized along any direction . i mean , a light ray like this , if we had it coming in diagonal , this light ray that 's oscillating like this , where the electric field oscillates like that , that also polarized . these are both polarized because there 's only one direction that the electric field is oscillating in . and you might thing , `` pff , how could you ever have `` a light ray that 's not polarized ? '' easy . most light that you get is not polarized . that is to say , light that 's coming from the sun , straight from the sun -- typically not polarized . light from a lightbulb , an old incandescent light bulb , this thing 's hot . you can get light polarized in any direction , all at once , all overlapping . so if we draw this case for a light bulb , just a random incandescent light bulb , you might get light , some of the light , hitting you eye , you can get some light that 's got that direction , you got light that 's got this direction , you got light in all these directions at any given moment . i mean , you 'd have to add these up to get the total , and they might not all be the same value . but what i 'm trying to say is , at any given moment , you do n't know what direction the electric field 's going to be hitting your eye at from a random source . it could be in any direction . so this is not polarized . this diagram represents light that is not polarized . at some point , the field might be pointing this way , at some later point it 's this way ; it 's just random . you never know which way the electric field 's going to be pointing . whereas these over here , these are polarized . so how could you polarize this light ? let 's say you wanted light that was polarized . you were doing an experiment . you needed polarized light . well , that 's easy . you can use what 's called a polarizer . and this is a material that lets light through , but it only lets light through in one orientation , so you 're going to have a polarizer that , for instance , only lets through vertically polarized light . so this is a polarizer . these are cheap : thin , plastic , configured in a way so that it only lets light through that 's vertically polarized . any light coming in here that 's not vertically polarized gets blocked , or absorbed . so what that means is , if you used this polarizer and held it in between your eye and this light bulb , you would only get this light . all the rest of it would get blocked . or you could just rotate this thing and imagine a polarizer that only lets through horizontal light . now it would only let through light that was this way , and so you would only get this part of the light . or you could just orient it at any angle you want and block everything but the certain angle that this polarizer is defined as letting light through . so you can do this . and once you hold this up , you get polarized light , light that 's only got one orientation . so that 's what polarization means . but why do we care about polarization ? well , let me get rid of this for a minute . you 've heard of polarized sunglasses . so imagine you 're standing near water , or maybe you 're standing on ice or snow or something reflective . there 's a problem . say the sun 's out . it 's shining . it 's a beautiful day -- except there 's going to be glare . let 's say you 're looking down at something here on the ground . it 's going to get light reflecting off of it from just ... you know , light 's coming in from all direction . but it also gets this direct light from the sun . so it gets light from reflected off the clouds and whatever , whatever 's nearby , ambient light . and there 's also this direct sunlight . that 's harsh . if that reflects straight up to your eye , that hurts . you do n't like that . it blocks our vision . it 's hard to see , it 's glare . we do n't want this glare . so what can we do ? well , it just so happens that , when light reflects off of a surface , even though the light from the sun is not polarized , once it reflects , it does get polarized or at least partially polarized . so this surface here , once this light reflects , it 's coming in at all orientations . you got electric field ... you never know what electric field you 're going to get straight from the sun . and when it reflects , though , you mostly get , upon reflection , the direction of polarization defined by the plane of the surface that it hit . so because the floor is horizontal , when this light ray hits the ground and reflects , that reflected light gets partially polarized . this horizontal component of the electric field is going to be more present than the other components . maybe not completely . sometimes it could be . it could be completely polarized , but often it 's just partially polarized . but that 's pretty cool , because now you know what we can do . i know how to block this . we should get some sunglasses . we put some sunglasses on and we make our glasses so that these are polarized . and how do we want these polarized ? i want to get rid of the glare . so what i do is , i make sure my sunglasses only let through vertically polarized light . here 's some polarizers . that way , a lot of this glare gets blocked because it does not have a vertical orientation , it has a horizontal orientation . and then we can block it . so that 's one good thing that polarization does for us , and understanding it , we can get rid of glare . also , fishermen like it because , if you 're trying to look in the water at fish , you want to see in through the water , you want to see this light from the fish getting to you . you do n't want to see the glare off of the sun getting to you . so polarized sunglasses are useful . also , we can play a trick on our eye , if we really wanted to . you could take one of these , make one eye have a vertical orientation for the polarization , have the other eye with a horizontal ... and you 're thinking , `` this is stupid . `` why would you do this for ? '' `` this eye 's going to get a lot of glare . '' we would n't use these outside , when you 're , like , skiing or fishing , but you could play a trick on your eyes if you went to the movies and you went and watched a movie . well , the reason our eyes see 3d is because they 're spaced a little bit apart . they each get a different , slightly different image . that makes us see in 3d . we can play the same trick on our eye if we have the polarization like this . if light , if some of the light from the movie theater screen is coming in with one polarization , and the other light 's coming in with the other polarization , we can send two different images to our eyes at the same time . if you took these off , it 'd look like garbage because you 'd be getting both of these slightly different images , it 'd look all blurry . and it does . if you take off your 3d glasses and look at a 3d movie , looks terrible , because now both eyes are getting both images . but if you put your glasses back on , now this eye only gets the orientation that it 's supposed to get , and this eye only gets the orientation that it 's supposed to get , and you get a 3d image . so it 's useful in many ways . let me show you one more thing here . let 's come back here . this light was polarized vertically . so that 's called linear polarization . any time ... same with these . these are all linear polarization because , just up and down , one linear direction , just diagonal . this is also linear . all of these are linear . you can get circular polarized light . so if we come back to here , we 've got our electric field pointing up , like that . now let 's say we sent in another light ray , another light ray that also had a polarization , but not in this direction . let 's say our other light ray had polarization in this direction , so it looks like this , kind of like what our magnetic field would have looked like . but this is a completely different light ray with its own polarization and its own magnetic field . so we send this in . what would happen ? well , at this point , you 'd have a electric field that points this way . at this point , you 'd have a electric field that points that way . what would your eye see if you were over here ? let 's see . if i draw our axis here . all right , when this point right here gets to your eye , what am i going to see ? well , i 'm going to have a light ray that 's one part of a light ray . one component points up . that 's this electric field . one component points left . that 's this electric field . so the total , my total electric field , would point this way . i could to the pythagorean theorem if i wanted to figure out the size of it , but i just want to know the direction for now . and then it gets to here , and look at it : they both have zero . this light ray has zero electric field , this one has zero electric fields . so then it 'd just be at zero . now what happens over here ? well , i 've got light . this one points to the right at that point , this pink one , and then this red one would be pointing down . so what would i have at that point ? i 'd have light that went this way , and it would just be doing this over and over . it would just be ... i 'd just have diagonally polarized light . this is n't giving me anything new . you might think this is dumb . why do this ? why send in two different waves to just get diagonally polarized light ? i could have just sent in one wave that was diagonally polarized and got the same thing . the reason is , if you shift this purple wave , this pink wave , by 90 degrees of phase , by pi over two in phase , something magical happens . let me show you what happens here , if we move this to here . now we do n't just get diagonally linear polarized light . what we 're going to get is ... let me get rid of this . okay , so we start off with red , right ? the red electric field points up , and then this pink wave 's electric field is zero at that point . so this is all i have . my total electric field would just be up . i 'm going to draw it right here . the green 'll be the total . now i come over to here , and at this point , there 's some red electric field that points up , but there 's some of this other electric field that points this way . so i 'd have a total electric field that would point that way . and then i get over to here , and i 'd have all of the electric field from the pink one , none from the red one . it would point all left then . look what 's happening . the polarization of this light , if i shift this , if i 'm sitting here , looking with my eye , as my eye receives this light , i 'm going to see this light rotate its polarization . the polarization i 'm going to notice swings around in a circular pattern . and because of this , we call this circular polarization . so this is another type of polarization , where the actual angle of polarization rotates smoothly as this light ray enters your eye . and you know what ? er , drrr ... all right , actually , i sent you to receive this one first . that makes no sense . you 're going to receive the ones closes to you first in this light ray going this way . so you 'd actually receive this one first , then that one , then this one , then this one . because of that , you would n't see this going in a counterclockwise way , you 'd see this going in a clockwise circularly polarized way . sorry about that . you might think , `` okay , why ? `` why even bother with circular polarization ? '' well , i kind of lied earlier . turns out , in the movie theater example , they do n't actually do it like this , typically . oftentimes in the movie theaters , we do n't have just linearly polarized sunglasses . this would be a problem because , when you look at the movie theater screen , and if you were to tilt your head just a little bit ... think about it . this one 's not really going to get the right image anymore . it 's going to get some of both . and this one 's going to get some of both . it 's going to be blurry . your head would have to be perfectly level the whole time , which might be annoying . so what we do is , instead , we create circular polarized glasses , so that this one would only get one polarization , this one would get the other direction . this way , even if you tilt your head a little bit ... shoot , clockwise is clockwise , counterclockwise is counterclockwise . by using circular polarization for 3d movies , it can make it a little easier on you eyes to see a better 3d image , even if your head 's tilted a little bit .
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- let 's talk about polarization of light . we know what light waves are ; they 're electromagnetic waves .
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why is the position of hydrogen not with the halogens but with the alkali metals ?
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- let 's talk about polarization of light . we know what light waves are ; they 're electromagnetic waves . so they 're made out of electric fields . and that 's not good enough . we know there 's not just electric fields . that could n't sustain itself . there 's got to be magnetic fields there , as well , that are changing . those are perpendicular , so you can kind of draw them . it 's hard , on something two-dimensional , but you can kind of imagine those looking something like this . and those magnetic fields would point at a right angle to the electric fields . but this gets really messy if i try to draw both the electric and magnetic fields at the same time . so we 're going to leave the magnetic fields out . it 's often good enough to just know the direction of the electric field when we focus on the electric field . so what does polarization mean ? polarization refers to the fact that , if this light ray was heading straight toward your eye , or a detector , over here , what would you see ? well , if i draw an axis over here , and this point here , in the middle , this is this line -- so imagine we 're looking straight down that line -- and then up and down is up and down , and then left and right , that direction i have the magnetic field , would be this way and that way . what would my eye see ? well , my eye 's only going to see electric fields that either point up or electric fields that point down . they might have different values , but i 'm only going to see electric fields that point up or down . because of that , this light ray is polarized . so polarized light is light where the electric field is only oscillating in one direction . up or down , that 's one direction -- vertically . or it could be polarized horizontally . or it could be polarized diagonally . but either way , you could have this wave polarized along any direction . i mean , a light ray like this , if we had it coming in diagonal , this light ray that 's oscillating like this , where the electric field oscillates like that , that also polarized . these are both polarized because there 's only one direction that the electric field is oscillating in . and you might thing , `` pff , how could you ever have `` a light ray that 's not polarized ? '' easy . most light that you get is not polarized . that is to say , light that 's coming from the sun , straight from the sun -- typically not polarized . light from a lightbulb , an old incandescent light bulb , this thing 's hot . you can get light polarized in any direction , all at once , all overlapping . so if we draw this case for a light bulb , just a random incandescent light bulb , you might get light , some of the light , hitting you eye , you can get some light that 's got that direction , you got light that 's got this direction , you got light in all these directions at any given moment . i mean , you 'd have to add these up to get the total , and they might not all be the same value . but what i 'm trying to say is , at any given moment , you do n't know what direction the electric field 's going to be hitting your eye at from a random source . it could be in any direction . so this is not polarized . this diagram represents light that is not polarized . at some point , the field might be pointing this way , at some later point it 's this way ; it 's just random . you never know which way the electric field 's going to be pointing . whereas these over here , these are polarized . so how could you polarize this light ? let 's say you wanted light that was polarized . you were doing an experiment . you needed polarized light . well , that 's easy . you can use what 's called a polarizer . and this is a material that lets light through , but it only lets light through in one orientation , so you 're going to have a polarizer that , for instance , only lets through vertically polarized light . so this is a polarizer . these are cheap : thin , plastic , configured in a way so that it only lets light through that 's vertically polarized . any light coming in here that 's not vertically polarized gets blocked , or absorbed . so what that means is , if you used this polarizer and held it in between your eye and this light bulb , you would only get this light . all the rest of it would get blocked . or you could just rotate this thing and imagine a polarizer that only lets through horizontal light . now it would only let through light that was this way , and so you would only get this part of the light . or you could just orient it at any angle you want and block everything but the certain angle that this polarizer is defined as letting light through . so you can do this . and once you hold this up , you get polarized light , light that 's only got one orientation . so that 's what polarization means . but why do we care about polarization ? well , let me get rid of this for a minute . you 've heard of polarized sunglasses . so imagine you 're standing near water , or maybe you 're standing on ice or snow or something reflective . there 's a problem . say the sun 's out . it 's shining . it 's a beautiful day -- except there 's going to be glare . let 's say you 're looking down at something here on the ground . it 's going to get light reflecting off of it from just ... you know , light 's coming in from all direction . but it also gets this direct light from the sun . so it gets light from reflected off the clouds and whatever , whatever 's nearby , ambient light . and there 's also this direct sunlight . that 's harsh . if that reflects straight up to your eye , that hurts . you do n't like that . it blocks our vision . it 's hard to see , it 's glare . we do n't want this glare . so what can we do ? well , it just so happens that , when light reflects off of a surface , even though the light from the sun is not polarized , once it reflects , it does get polarized or at least partially polarized . so this surface here , once this light reflects , it 's coming in at all orientations . you got electric field ... you never know what electric field you 're going to get straight from the sun . and when it reflects , though , you mostly get , upon reflection , the direction of polarization defined by the plane of the surface that it hit . so because the floor is horizontal , when this light ray hits the ground and reflects , that reflected light gets partially polarized . this horizontal component of the electric field is going to be more present than the other components . maybe not completely . sometimes it could be . it could be completely polarized , but often it 's just partially polarized . but that 's pretty cool , because now you know what we can do . i know how to block this . we should get some sunglasses . we put some sunglasses on and we make our glasses so that these are polarized . and how do we want these polarized ? i want to get rid of the glare . so what i do is , i make sure my sunglasses only let through vertically polarized light . here 's some polarizers . that way , a lot of this glare gets blocked because it does not have a vertical orientation , it has a horizontal orientation . and then we can block it . so that 's one good thing that polarization does for us , and understanding it , we can get rid of glare . also , fishermen like it because , if you 're trying to look in the water at fish , you want to see in through the water , you want to see this light from the fish getting to you . you do n't want to see the glare off of the sun getting to you . so polarized sunglasses are useful . also , we can play a trick on our eye , if we really wanted to . you could take one of these , make one eye have a vertical orientation for the polarization , have the other eye with a horizontal ... and you 're thinking , `` this is stupid . `` why would you do this for ? '' `` this eye 's going to get a lot of glare . '' we would n't use these outside , when you 're , like , skiing or fishing , but you could play a trick on your eyes if you went to the movies and you went and watched a movie . well , the reason our eyes see 3d is because they 're spaced a little bit apart . they each get a different , slightly different image . that makes us see in 3d . we can play the same trick on our eye if we have the polarization like this . if light , if some of the light from the movie theater screen is coming in with one polarization , and the other light 's coming in with the other polarization , we can send two different images to our eyes at the same time . if you took these off , it 'd look like garbage because you 'd be getting both of these slightly different images , it 'd look all blurry . and it does . if you take off your 3d glasses and look at a 3d movie , looks terrible , because now both eyes are getting both images . but if you put your glasses back on , now this eye only gets the orientation that it 's supposed to get , and this eye only gets the orientation that it 's supposed to get , and you get a 3d image . so it 's useful in many ways . let me show you one more thing here . let 's come back here . this light was polarized vertically . so that 's called linear polarization . any time ... same with these . these are all linear polarization because , just up and down , one linear direction , just diagonal . this is also linear . all of these are linear . you can get circular polarized light . so if we come back to here , we 've got our electric field pointing up , like that . now let 's say we sent in another light ray , another light ray that also had a polarization , but not in this direction . let 's say our other light ray had polarization in this direction , so it looks like this , kind of like what our magnetic field would have looked like . but this is a completely different light ray with its own polarization and its own magnetic field . so we send this in . what would happen ? well , at this point , you 'd have a electric field that points this way . at this point , you 'd have a electric field that points that way . what would your eye see if you were over here ? let 's see . if i draw our axis here . all right , when this point right here gets to your eye , what am i going to see ? well , i 'm going to have a light ray that 's one part of a light ray . one component points up . that 's this electric field . one component points left . that 's this electric field . so the total , my total electric field , would point this way . i could to the pythagorean theorem if i wanted to figure out the size of it , but i just want to know the direction for now . and then it gets to here , and look at it : they both have zero . this light ray has zero electric field , this one has zero electric fields . so then it 'd just be at zero . now what happens over here ? well , i 've got light . this one points to the right at that point , this pink one , and then this red one would be pointing down . so what would i have at that point ? i 'd have light that went this way , and it would just be doing this over and over . it would just be ... i 'd just have diagonally polarized light . this is n't giving me anything new . you might think this is dumb . why do this ? why send in two different waves to just get diagonally polarized light ? i could have just sent in one wave that was diagonally polarized and got the same thing . the reason is , if you shift this purple wave , this pink wave , by 90 degrees of phase , by pi over two in phase , something magical happens . let me show you what happens here , if we move this to here . now we do n't just get diagonally linear polarized light . what we 're going to get is ... let me get rid of this . okay , so we start off with red , right ? the red electric field points up , and then this pink wave 's electric field is zero at that point . so this is all i have . my total electric field would just be up . i 'm going to draw it right here . the green 'll be the total . now i come over to here , and at this point , there 's some red electric field that points up , but there 's some of this other electric field that points this way . so i 'd have a total electric field that would point that way . and then i get over to here , and i 'd have all of the electric field from the pink one , none from the red one . it would point all left then . look what 's happening . the polarization of this light , if i shift this , if i 'm sitting here , looking with my eye , as my eye receives this light , i 'm going to see this light rotate its polarization . the polarization i 'm going to notice swings around in a circular pattern . and because of this , we call this circular polarization . so this is another type of polarization , where the actual angle of polarization rotates smoothly as this light ray enters your eye . and you know what ? er , drrr ... all right , actually , i sent you to receive this one first . that makes no sense . you 're going to receive the ones closes to you first in this light ray going this way . so you 'd actually receive this one first , then that one , then this one , then this one . because of that , you would n't see this going in a counterclockwise way , you 'd see this going in a clockwise circularly polarized way . sorry about that . you might think , `` okay , why ? `` why even bother with circular polarization ? '' well , i kind of lied earlier . turns out , in the movie theater example , they do n't actually do it like this , typically . oftentimes in the movie theaters , we do n't have just linearly polarized sunglasses . this would be a problem because , when you look at the movie theater screen , and if you were to tilt your head just a little bit ... think about it . this one 's not really going to get the right image anymore . it 's going to get some of both . and this one 's going to get some of both . it 's going to be blurry . your head would have to be perfectly level the whole time , which might be annoying . so what we do is , instead , we create circular polarized glasses , so that this one would only get one polarization , this one would get the other direction . this way , even if you tilt your head a little bit ... shoot , clockwise is clockwise , counterclockwise is counterclockwise . by using circular polarization for 3d movies , it can make it a little easier on you eyes to see a better 3d image , even if your head 's tilted a little bit .
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you can get light polarized in any direction , all at once , all overlapping . so if we draw this case for a light bulb , just a random incandescent light bulb , you might get light , some of the light , hitting you eye , you can get some light that 's got that direction , you got light that 's got this direction , you got light in all these directions at any given moment . i mean , you 'd have to add these up to get the total , and they might not all be the same value .
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but how do you make a circular polarised sheet knowing we need another light source which is out of phase w.r.t to incident light wave by ninety degrees ... the plastic polarised sheet is no source for such light ?
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- let 's talk about polarization of light . we know what light waves are ; they 're electromagnetic waves . so they 're made out of electric fields . and that 's not good enough . we know there 's not just electric fields . that could n't sustain itself . there 's got to be magnetic fields there , as well , that are changing . those are perpendicular , so you can kind of draw them . it 's hard , on something two-dimensional , but you can kind of imagine those looking something like this . and those magnetic fields would point at a right angle to the electric fields . but this gets really messy if i try to draw both the electric and magnetic fields at the same time . so we 're going to leave the magnetic fields out . it 's often good enough to just know the direction of the electric field when we focus on the electric field . so what does polarization mean ? polarization refers to the fact that , if this light ray was heading straight toward your eye , or a detector , over here , what would you see ? well , if i draw an axis over here , and this point here , in the middle , this is this line -- so imagine we 're looking straight down that line -- and then up and down is up and down , and then left and right , that direction i have the magnetic field , would be this way and that way . what would my eye see ? well , my eye 's only going to see electric fields that either point up or electric fields that point down . they might have different values , but i 'm only going to see electric fields that point up or down . because of that , this light ray is polarized . so polarized light is light where the electric field is only oscillating in one direction . up or down , that 's one direction -- vertically . or it could be polarized horizontally . or it could be polarized diagonally . but either way , you could have this wave polarized along any direction . i mean , a light ray like this , if we had it coming in diagonal , this light ray that 's oscillating like this , where the electric field oscillates like that , that also polarized . these are both polarized because there 's only one direction that the electric field is oscillating in . and you might thing , `` pff , how could you ever have `` a light ray that 's not polarized ? '' easy . most light that you get is not polarized . that is to say , light that 's coming from the sun , straight from the sun -- typically not polarized . light from a lightbulb , an old incandescent light bulb , this thing 's hot . you can get light polarized in any direction , all at once , all overlapping . so if we draw this case for a light bulb , just a random incandescent light bulb , you might get light , some of the light , hitting you eye , you can get some light that 's got that direction , you got light that 's got this direction , you got light in all these directions at any given moment . i mean , you 'd have to add these up to get the total , and they might not all be the same value . but what i 'm trying to say is , at any given moment , you do n't know what direction the electric field 's going to be hitting your eye at from a random source . it could be in any direction . so this is not polarized . this diagram represents light that is not polarized . at some point , the field might be pointing this way , at some later point it 's this way ; it 's just random . you never know which way the electric field 's going to be pointing . whereas these over here , these are polarized . so how could you polarize this light ? let 's say you wanted light that was polarized . you were doing an experiment . you needed polarized light . well , that 's easy . you can use what 's called a polarizer . and this is a material that lets light through , but it only lets light through in one orientation , so you 're going to have a polarizer that , for instance , only lets through vertically polarized light . so this is a polarizer . these are cheap : thin , plastic , configured in a way so that it only lets light through that 's vertically polarized . any light coming in here that 's not vertically polarized gets blocked , or absorbed . so what that means is , if you used this polarizer and held it in between your eye and this light bulb , you would only get this light . all the rest of it would get blocked . or you could just rotate this thing and imagine a polarizer that only lets through horizontal light . now it would only let through light that was this way , and so you would only get this part of the light . or you could just orient it at any angle you want and block everything but the certain angle that this polarizer is defined as letting light through . so you can do this . and once you hold this up , you get polarized light , light that 's only got one orientation . so that 's what polarization means . but why do we care about polarization ? well , let me get rid of this for a minute . you 've heard of polarized sunglasses . so imagine you 're standing near water , or maybe you 're standing on ice or snow or something reflective . there 's a problem . say the sun 's out . it 's shining . it 's a beautiful day -- except there 's going to be glare . let 's say you 're looking down at something here on the ground . it 's going to get light reflecting off of it from just ... you know , light 's coming in from all direction . but it also gets this direct light from the sun . so it gets light from reflected off the clouds and whatever , whatever 's nearby , ambient light . and there 's also this direct sunlight . that 's harsh . if that reflects straight up to your eye , that hurts . you do n't like that . it blocks our vision . it 's hard to see , it 's glare . we do n't want this glare . so what can we do ? well , it just so happens that , when light reflects off of a surface , even though the light from the sun is not polarized , once it reflects , it does get polarized or at least partially polarized . so this surface here , once this light reflects , it 's coming in at all orientations . you got electric field ... you never know what electric field you 're going to get straight from the sun . and when it reflects , though , you mostly get , upon reflection , the direction of polarization defined by the plane of the surface that it hit . so because the floor is horizontal , when this light ray hits the ground and reflects , that reflected light gets partially polarized . this horizontal component of the electric field is going to be more present than the other components . maybe not completely . sometimes it could be . it could be completely polarized , but often it 's just partially polarized . but that 's pretty cool , because now you know what we can do . i know how to block this . we should get some sunglasses . we put some sunglasses on and we make our glasses so that these are polarized . and how do we want these polarized ? i want to get rid of the glare . so what i do is , i make sure my sunglasses only let through vertically polarized light . here 's some polarizers . that way , a lot of this glare gets blocked because it does not have a vertical orientation , it has a horizontal orientation . and then we can block it . so that 's one good thing that polarization does for us , and understanding it , we can get rid of glare . also , fishermen like it because , if you 're trying to look in the water at fish , you want to see in through the water , you want to see this light from the fish getting to you . you do n't want to see the glare off of the sun getting to you . so polarized sunglasses are useful . also , we can play a trick on our eye , if we really wanted to . you could take one of these , make one eye have a vertical orientation for the polarization , have the other eye with a horizontal ... and you 're thinking , `` this is stupid . `` why would you do this for ? '' `` this eye 's going to get a lot of glare . '' we would n't use these outside , when you 're , like , skiing or fishing , but you could play a trick on your eyes if you went to the movies and you went and watched a movie . well , the reason our eyes see 3d is because they 're spaced a little bit apart . they each get a different , slightly different image . that makes us see in 3d . we can play the same trick on our eye if we have the polarization like this . if light , if some of the light from the movie theater screen is coming in with one polarization , and the other light 's coming in with the other polarization , we can send two different images to our eyes at the same time . if you took these off , it 'd look like garbage because you 'd be getting both of these slightly different images , it 'd look all blurry . and it does . if you take off your 3d glasses and look at a 3d movie , looks terrible , because now both eyes are getting both images . but if you put your glasses back on , now this eye only gets the orientation that it 's supposed to get , and this eye only gets the orientation that it 's supposed to get , and you get a 3d image . so it 's useful in many ways . let me show you one more thing here . let 's come back here . this light was polarized vertically . so that 's called linear polarization . any time ... same with these . these are all linear polarization because , just up and down , one linear direction , just diagonal . this is also linear . all of these are linear . you can get circular polarized light . so if we come back to here , we 've got our electric field pointing up , like that . now let 's say we sent in another light ray , another light ray that also had a polarization , but not in this direction . let 's say our other light ray had polarization in this direction , so it looks like this , kind of like what our magnetic field would have looked like . but this is a completely different light ray with its own polarization and its own magnetic field . so we send this in . what would happen ? well , at this point , you 'd have a electric field that points this way . at this point , you 'd have a electric field that points that way . what would your eye see if you were over here ? let 's see . if i draw our axis here . all right , when this point right here gets to your eye , what am i going to see ? well , i 'm going to have a light ray that 's one part of a light ray . one component points up . that 's this electric field . one component points left . that 's this electric field . so the total , my total electric field , would point this way . i could to the pythagorean theorem if i wanted to figure out the size of it , but i just want to know the direction for now . and then it gets to here , and look at it : they both have zero . this light ray has zero electric field , this one has zero electric fields . so then it 'd just be at zero . now what happens over here ? well , i 've got light . this one points to the right at that point , this pink one , and then this red one would be pointing down . so what would i have at that point ? i 'd have light that went this way , and it would just be doing this over and over . it would just be ... i 'd just have diagonally polarized light . this is n't giving me anything new . you might think this is dumb . why do this ? why send in two different waves to just get diagonally polarized light ? i could have just sent in one wave that was diagonally polarized and got the same thing . the reason is , if you shift this purple wave , this pink wave , by 90 degrees of phase , by pi over two in phase , something magical happens . let me show you what happens here , if we move this to here . now we do n't just get diagonally linear polarized light . what we 're going to get is ... let me get rid of this . okay , so we start off with red , right ? the red electric field points up , and then this pink wave 's electric field is zero at that point . so this is all i have . my total electric field would just be up . i 'm going to draw it right here . the green 'll be the total . now i come over to here , and at this point , there 's some red electric field that points up , but there 's some of this other electric field that points this way . so i 'd have a total electric field that would point that way . and then i get over to here , and i 'd have all of the electric field from the pink one , none from the red one . it would point all left then . look what 's happening . the polarization of this light , if i shift this , if i 'm sitting here , looking with my eye , as my eye receives this light , i 'm going to see this light rotate its polarization . the polarization i 'm going to notice swings around in a circular pattern . and because of this , we call this circular polarization . so this is another type of polarization , where the actual angle of polarization rotates smoothly as this light ray enters your eye . and you know what ? er , drrr ... all right , actually , i sent you to receive this one first . that makes no sense . you 're going to receive the ones closes to you first in this light ray going this way . so you 'd actually receive this one first , then that one , then this one , then this one . because of that , you would n't see this going in a counterclockwise way , you 'd see this going in a clockwise circularly polarized way . sorry about that . you might think , `` okay , why ? `` why even bother with circular polarization ? '' well , i kind of lied earlier . turns out , in the movie theater example , they do n't actually do it like this , typically . oftentimes in the movie theaters , we do n't have just linearly polarized sunglasses . this would be a problem because , when you look at the movie theater screen , and if you were to tilt your head just a little bit ... think about it . this one 's not really going to get the right image anymore . it 's going to get some of both . and this one 's going to get some of both . it 's going to be blurry . your head would have to be perfectly level the whole time , which might be annoying . so what we do is , instead , we create circular polarized glasses , so that this one would only get one polarization , this one would get the other direction . this way , even if you tilt your head a little bit ... shoot , clockwise is clockwise , counterclockwise is counterclockwise . by using circular polarization for 3d movies , it can make it a little easier on you eyes to see a better 3d image , even if your head 's tilted a little bit .
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you might think , `` okay , why ? `` why even bother with circular polarization ? '' well , i kind of lied earlier .
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how does one can change the orientation of the circular polarization ?
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- let 's talk about polarization of light . we know what light waves are ; they 're electromagnetic waves . so they 're made out of electric fields . and that 's not good enough . we know there 's not just electric fields . that could n't sustain itself . there 's got to be magnetic fields there , as well , that are changing . those are perpendicular , so you can kind of draw them . it 's hard , on something two-dimensional , but you can kind of imagine those looking something like this . and those magnetic fields would point at a right angle to the electric fields . but this gets really messy if i try to draw both the electric and magnetic fields at the same time . so we 're going to leave the magnetic fields out . it 's often good enough to just know the direction of the electric field when we focus on the electric field . so what does polarization mean ? polarization refers to the fact that , if this light ray was heading straight toward your eye , or a detector , over here , what would you see ? well , if i draw an axis over here , and this point here , in the middle , this is this line -- so imagine we 're looking straight down that line -- and then up and down is up and down , and then left and right , that direction i have the magnetic field , would be this way and that way . what would my eye see ? well , my eye 's only going to see electric fields that either point up or electric fields that point down . they might have different values , but i 'm only going to see electric fields that point up or down . because of that , this light ray is polarized . so polarized light is light where the electric field is only oscillating in one direction . up or down , that 's one direction -- vertically . or it could be polarized horizontally . or it could be polarized diagonally . but either way , you could have this wave polarized along any direction . i mean , a light ray like this , if we had it coming in diagonal , this light ray that 's oscillating like this , where the electric field oscillates like that , that also polarized . these are both polarized because there 's only one direction that the electric field is oscillating in . and you might thing , `` pff , how could you ever have `` a light ray that 's not polarized ? '' easy . most light that you get is not polarized . that is to say , light that 's coming from the sun , straight from the sun -- typically not polarized . light from a lightbulb , an old incandescent light bulb , this thing 's hot . you can get light polarized in any direction , all at once , all overlapping . so if we draw this case for a light bulb , just a random incandescent light bulb , you might get light , some of the light , hitting you eye , you can get some light that 's got that direction , you got light that 's got this direction , you got light in all these directions at any given moment . i mean , you 'd have to add these up to get the total , and they might not all be the same value . but what i 'm trying to say is , at any given moment , you do n't know what direction the electric field 's going to be hitting your eye at from a random source . it could be in any direction . so this is not polarized . this diagram represents light that is not polarized . at some point , the field might be pointing this way , at some later point it 's this way ; it 's just random . you never know which way the electric field 's going to be pointing . whereas these over here , these are polarized . so how could you polarize this light ? let 's say you wanted light that was polarized . you were doing an experiment . you needed polarized light . well , that 's easy . you can use what 's called a polarizer . and this is a material that lets light through , but it only lets light through in one orientation , so you 're going to have a polarizer that , for instance , only lets through vertically polarized light . so this is a polarizer . these are cheap : thin , plastic , configured in a way so that it only lets light through that 's vertically polarized . any light coming in here that 's not vertically polarized gets blocked , or absorbed . so what that means is , if you used this polarizer and held it in between your eye and this light bulb , you would only get this light . all the rest of it would get blocked . or you could just rotate this thing and imagine a polarizer that only lets through horizontal light . now it would only let through light that was this way , and so you would only get this part of the light . or you could just orient it at any angle you want and block everything but the certain angle that this polarizer is defined as letting light through . so you can do this . and once you hold this up , you get polarized light , light that 's only got one orientation . so that 's what polarization means . but why do we care about polarization ? well , let me get rid of this for a minute . you 've heard of polarized sunglasses . so imagine you 're standing near water , or maybe you 're standing on ice or snow or something reflective . there 's a problem . say the sun 's out . it 's shining . it 's a beautiful day -- except there 's going to be glare . let 's say you 're looking down at something here on the ground . it 's going to get light reflecting off of it from just ... you know , light 's coming in from all direction . but it also gets this direct light from the sun . so it gets light from reflected off the clouds and whatever , whatever 's nearby , ambient light . and there 's also this direct sunlight . that 's harsh . if that reflects straight up to your eye , that hurts . you do n't like that . it blocks our vision . it 's hard to see , it 's glare . we do n't want this glare . so what can we do ? well , it just so happens that , when light reflects off of a surface , even though the light from the sun is not polarized , once it reflects , it does get polarized or at least partially polarized . so this surface here , once this light reflects , it 's coming in at all orientations . you got electric field ... you never know what electric field you 're going to get straight from the sun . and when it reflects , though , you mostly get , upon reflection , the direction of polarization defined by the plane of the surface that it hit . so because the floor is horizontal , when this light ray hits the ground and reflects , that reflected light gets partially polarized . this horizontal component of the electric field is going to be more present than the other components . maybe not completely . sometimes it could be . it could be completely polarized , but often it 's just partially polarized . but that 's pretty cool , because now you know what we can do . i know how to block this . we should get some sunglasses . we put some sunglasses on and we make our glasses so that these are polarized . and how do we want these polarized ? i want to get rid of the glare . so what i do is , i make sure my sunglasses only let through vertically polarized light . here 's some polarizers . that way , a lot of this glare gets blocked because it does not have a vertical orientation , it has a horizontal orientation . and then we can block it . so that 's one good thing that polarization does for us , and understanding it , we can get rid of glare . also , fishermen like it because , if you 're trying to look in the water at fish , you want to see in through the water , you want to see this light from the fish getting to you . you do n't want to see the glare off of the sun getting to you . so polarized sunglasses are useful . also , we can play a trick on our eye , if we really wanted to . you could take one of these , make one eye have a vertical orientation for the polarization , have the other eye with a horizontal ... and you 're thinking , `` this is stupid . `` why would you do this for ? '' `` this eye 's going to get a lot of glare . '' we would n't use these outside , when you 're , like , skiing or fishing , but you could play a trick on your eyes if you went to the movies and you went and watched a movie . well , the reason our eyes see 3d is because they 're spaced a little bit apart . they each get a different , slightly different image . that makes us see in 3d . we can play the same trick on our eye if we have the polarization like this . if light , if some of the light from the movie theater screen is coming in with one polarization , and the other light 's coming in with the other polarization , we can send two different images to our eyes at the same time . if you took these off , it 'd look like garbage because you 'd be getting both of these slightly different images , it 'd look all blurry . and it does . if you take off your 3d glasses and look at a 3d movie , looks terrible , because now both eyes are getting both images . but if you put your glasses back on , now this eye only gets the orientation that it 's supposed to get , and this eye only gets the orientation that it 's supposed to get , and you get a 3d image . so it 's useful in many ways . let me show you one more thing here . let 's come back here . this light was polarized vertically . so that 's called linear polarization . any time ... same with these . these are all linear polarization because , just up and down , one linear direction , just diagonal . this is also linear . all of these are linear . you can get circular polarized light . so if we come back to here , we 've got our electric field pointing up , like that . now let 's say we sent in another light ray , another light ray that also had a polarization , but not in this direction . let 's say our other light ray had polarization in this direction , so it looks like this , kind of like what our magnetic field would have looked like . but this is a completely different light ray with its own polarization and its own magnetic field . so we send this in . what would happen ? well , at this point , you 'd have a electric field that points this way . at this point , you 'd have a electric field that points that way . what would your eye see if you were over here ? let 's see . if i draw our axis here . all right , when this point right here gets to your eye , what am i going to see ? well , i 'm going to have a light ray that 's one part of a light ray . one component points up . that 's this electric field . one component points left . that 's this electric field . so the total , my total electric field , would point this way . i could to the pythagorean theorem if i wanted to figure out the size of it , but i just want to know the direction for now . and then it gets to here , and look at it : they both have zero . this light ray has zero electric field , this one has zero electric fields . so then it 'd just be at zero . now what happens over here ? well , i 've got light . this one points to the right at that point , this pink one , and then this red one would be pointing down . so what would i have at that point ? i 'd have light that went this way , and it would just be doing this over and over . it would just be ... i 'd just have diagonally polarized light . this is n't giving me anything new . you might think this is dumb . why do this ? why send in two different waves to just get diagonally polarized light ? i could have just sent in one wave that was diagonally polarized and got the same thing . the reason is , if you shift this purple wave , this pink wave , by 90 degrees of phase , by pi over two in phase , something magical happens . let me show you what happens here , if we move this to here . now we do n't just get diagonally linear polarized light . what we 're going to get is ... let me get rid of this . okay , so we start off with red , right ? the red electric field points up , and then this pink wave 's electric field is zero at that point . so this is all i have . my total electric field would just be up . i 'm going to draw it right here . the green 'll be the total . now i come over to here , and at this point , there 's some red electric field that points up , but there 's some of this other electric field that points this way . so i 'd have a total electric field that would point that way . and then i get over to here , and i 'd have all of the electric field from the pink one , none from the red one . it would point all left then . look what 's happening . the polarization of this light , if i shift this , if i 'm sitting here , looking with my eye , as my eye receives this light , i 'm going to see this light rotate its polarization . the polarization i 'm going to notice swings around in a circular pattern . and because of this , we call this circular polarization . so this is another type of polarization , where the actual angle of polarization rotates smoothly as this light ray enters your eye . and you know what ? er , drrr ... all right , actually , i sent you to receive this one first . that makes no sense . you 're going to receive the ones closes to you first in this light ray going this way . so you 'd actually receive this one first , then that one , then this one , then this one . because of that , you would n't see this going in a counterclockwise way , you 'd see this going in a clockwise circularly polarized way . sorry about that . you might think , `` okay , why ? `` why even bother with circular polarization ? '' well , i kind of lied earlier . turns out , in the movie theater example , they do n't actually do it like this , typically . oftentimes in the movie theaters , we do n't have just linearly polarized sunglasses . this would be a problem because , when you look at the movie theater screen , and if you were to tilt your head just a little bit ... think about it . this one 's not really going to get the right image anymore . it 's going to get some of both . and this one 's going to get some of both . it 's going to be blurry . your head would have to be perfectly level the whole time , which might be annoying . so what we do is , instead , we create circular polarized glasses , so that this one would only get one polarization , this one would get the other direction . this way , even if you tilt your head a little bit ... shoot , clockwise is clockwise , counterclockwise is counterclockwise . by using circular polarization for 3d movies , it can make it a little easier on you eyes to see a better 3d image , even if your head 's tilted a little bit .
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this light was polarized vertically . so that 's called linear polarization . any time ...
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if we were asked to define linear/circular polarization , what would the answer be ?
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- let 's talk about polarization of light . we know what light waves are ; they 're electromagnetic waves . so they 're made out of electric fields . and that 's not good enough . we know there 's not just electric fields . that could n't sustain itself . there 's got to be magnetic fields there , as well , that are changing . those are perpendicular , so you can kind of draw them . it 's hard , on something two-dimensional , but you can kind of imagine those looking something like this . and those magnetic fields would point at a right angle to the electric fields . but this gets really messy if i try to draw both the electric and magnetic fields at the same time . so we 're going to leave the magnetic fields out . it 's often good enough to just know the direction of the electric field when we focus on the electric field . so what does polarization mean ? polarization refers to the fact that , if this light ray was heading straight toward your eye , or a detector , over here , what would you see ? well , if i draw an axis over here , and this point here , in the middle , this is this line -- so imagine we 're looking straight down that line -- and then up and down is up and down , and then left and right , that direction i have the magnetic field , would be this way and that way . what would my eye see ? well , my eye 's only going to see electric fields that either point up or electric fields that point down . they might have different values , but i 'm only going to see electric fields that point up or down . because of that , this light ray is polarized . so polarized light is light where the electric field is only oscillating in one direction . up or down , that 's one direction -- vertically . or it could be polarized horizontally . or it could be polarized diagonally . but either way , you could have this wave polarized along any direction . i mean , a light ray like this , if we had it coming in diagonal , this light ray that 's oscillating like this , where the electric field oscillates like that , that also polarized . these are both polarized because there 's only one direction that the electric field is oscillating in . and you might thing , `` pff , how could you ever have `` a light ray that 's not polarized ? '' easy . most light that you get is not polarized . that is to say , light that 's coming from the sun , straight from the sun -- typically not polarized . light from a lightbulb , an old incandescent light bulb , this thing 's hot . you can get light polarized in any direction , all at once , all overlapping . so if we draw this case for a light bulb , just a random incandescent light bulb , you might get light , some of the light , hitting you eye , you can get some light that 's got that direction , you got light that 's got this direction , you got light in all these directions at any given moment . i mean , you 'd have to add these up to get the total , and they might not all be the same value . but what i 'm trying to say is , at any given moment , you do n't know what direction the electric field 's going to be hitting your eye at from a random source . it could be in any direction . so this is not polarized . this diagram represents light that is not polarized . at some point , the field might be pointing this way , at some later point it 's this way ; it 's just random . you never know which way the electric field 's going to be pointing . whereas these over here , these are polarized . so how could you polarize this light ? let 's say you wanted light that was polarized . you were doing an experiment . you needed polarized light . well , that 's easy . you can use what 's called a polarizer . and this is a material that lets light through , but it only lets light through in one orientation , so you 're going to have a polarizer that , for instance , only lets through vertically polarized light . so this is a polarizer . these are cheap : thin , plastic , configured in a way so that it only lets light through that 's vertically polarized . any light coming in here that 's not vertically polarized gets blocked , or absorbed . so what that means is , if you used this polarizer and held it in between your eye and this light bulb , you would only get this light . all the rest of it would get blocked . or you could just rotate this thing and imagine a polarizer that only lets through horizontal light . now it would only let through light that was this way , and so you would only get this part of the light . or you could just orient it at any angle you want and block everything but the certain angle that this polarizer is defined as letting light through . so you can do this . and once you hold this up , you get polarized light , light that 's only got one orientation . so that 's what polarization means . but why do we care about polarization ? well , let me get rid of this for a minute . you 've heard of polarized sunglasses . so imagine you 're standing near water , or maybe you 're standing on ice or snow or something reflective . there 's a problem . say the sun 's out . it 's shining . it 's a beautiful day -- except there 's going to be glare . let 's say you 're looking down at something here on the ground . it 's going to get light reflecting off of it from just ... you know , light 's coming in from all direction . but it also gets this direct light from the sun . so it gets light from reflected off the clouds and whatever , whatever 's nearby , ambient light . and there 's also this direct sunlight . that 's harsh . if that reflects straight up to your eye , that hurts . you do n't like that . it blocks our vision . it 's hard to see , it 's glare . we do n't want this glare . so what can we do ? well , it just so happens that , when light reflects off of a surface , even though the light from the sun is not polarized , once it reflects , it does get polarized or at least partially polarized . so this surface here , once this light reflects , it 's coming in at all orientations . you got electric field ... you never know what electric field you 're going to get straight from the sun . and when it reflects , though , you mostly get , upon reflection , the direction of polarization defined by the plane of the surface that it hit . so because the floor is horizontal , when this light ray hits the ground and reflects , that reflected light gets partially polarized . this horizontal component of the electric field is going to be more present than the other components . maybe not completely . sometimes it could be . it could be completely polarized , but often it 's just partially polarized . but that 's pretty cool , because now you know what we can do . i know how to block this . we should get some sunglasses . we put some sunglasses on and we make our glasses so that these are polarized . and how do we want these polarized ? i want to get rid of the glare . so what i do is , i make sure my sunglasses only let through vertically polarized light . here 's some polarizers . that way , a lot of this glare gets blocked because it does not have a vertical orientation , it has a horizontal orientation . and then we can block it . so that 's one good thing that polarization does for us , and understanding it , we can get rid of glare . also , fishermen like it because , if you 're trying to look in the water at fish , you want to see in through the water , you want to see this light from the fish getting to you . you do n't want to see the glare off of the sun getting to you . so polarized sunglasses are useful . also , we can play a trick on our eye , if we really wanted to . you could take one of these , make one eye have a vertical orientation for the polarization , have the other eye with a horizontal ... and you 're thinking , `` this is stupid . `` why would you do this for ? '' `` this eye 's going to get a lot of glare . '' we would n't use these outside , when you 're , like , skiing or fishing , but you could play a trick on your eyes if you went to the movies and you went and watched a movie . well , the reason our eyes see 3d is because they 're spaced a little bit apart . they each get a different , slightly different image . that makes us see in 3d . we can play the same trick on our eye if we have the polarization like this . if light , if some of the light from the movie theater screen is coming in with one polarization , and the other light 's coming in with the other polarization , we can send two different images to our eyes at the same time . if you took these off , it 'd look like garbage because you 'd be getting both of these slightly different images , it 'd look all blurry . and it does . if you take off your 3d glasses and look at a 3d movie , looks terrible , because now both eyes are getting both images . but if you put your glasses back on , now this eye only gets the orientation that it 's supposed to get , and this eye only gets the orientation that it 's supposed to get , and you get a 3d image . so it 's useful in many ways . let me show you one more thing here . let 's come back here . this light was polarized vertically . so that 's called linear polarization . any time ... same with these . these are all linear polarization because , just up and down , one linear direction , just diagonal . this is also linear . all of these are linear . you can get circular polarized light . so if we come back to here , we 've got our electric field pointing up , like that . now let 's say we sent in another light ray , another light ray that also had a polarization , but not in this direction . let 's say our other light ray had polarization in this direction , so it looks like this , kind of like what our magnetic field would have looked like . but this is a completely different light ray with its own polarization and its own magnetic field . so we send this in . what would happen ? well , at this point , you 'd have a electric field that points this way . at this point , you 'd have a electric field that points that way . what would your eye see if you were over here ? let 's see . if i draw our axis here . all right , when this point right here gets to your eye , what am i going to see ? well , i 'm going to have a light ray that 's one part of a light ray . one component points up . that 's this electric field . one component points left . that 's this electric field . so the total , my total electric field , would point this way . i could to the pythagorean theorem if i wanted to figure out the size of it , but i just want to know the direction for now . and then it gets to here , and look at it : they both have zero . this light ray has zero electric field , this one has zero electric fields . so then it 'd just be at zero . now what happens over here ? well , i 've got light . this one points to the right at that point , this pink one , and then this red one would be pointing down . so what would i have at that point ? i 'd have light that went this way , and it would just be doing this over and over . it would just be ... i 'd just have diagonally polarized light . this is n't giving me anything new . you might think this is dumb . why do this ? why send in two different waves to just get diagonally polarized light ? i could have just sent in one wave that was diagonally polarized and got the same thing . the reason is , if you shift this purple wave , this pink wave , by 90 degrees of phase , by pi over two in phase , something magical happens . let me show you what happens here , if we move this to here . now we do n't just get diagonally linear polarized light . what we 're going to get is ... let me get rid of this . okay , so we start off with red , right ? the red electric field points up , and then this pink wave 's electric field is zero at that point . so this is all i have . my total electric field would just be up . i 'm going to draw it right here . the green 'll be the total . now i come over to here , and at this point , there 's some red electric field that points up , but there 's some of this other electric field that points this way . so i 'd have a total electric field that would point that way . and then i get over to here , and i 'd have all of the electric field from the pink one , none from the red one . it would point all left then . look what 's happening . the polarization of this light , if i shift this , if i 'm sitting here , looking with my eye , as my eye receives this light , i 'm going to see this light rotate its polarization . the polarization i 'm going to notice swings around in a circular pattern . and because of this , we call this circular polarization . so this is another type of polarization , where the actual angle of polarization rotates smoothly as this light ray enters your eye . and you know what ? er , drrr ... all right , actually , i sent you to receive this one first . that makes no sense . you 're going to receive the ones closes to you first in this light ray going this way . so you 'd actually receive this one first , then that one , then this one , then this one . because of that , you would n't see this going in a counterclockwise way , you 'd see this going in a clockwise circularly polarized way . sorry about that . you might think , `` okay , why ? `` why even bother with circular polarization ? '' well , i kind of lied earlier . turns out , in the movie theater example , they do n't actually do it like this , typically . oftentimes in the movie theaters , we do n't have just linearly polarized sunglasses . this would be a problem because , when you look at the movie theater screen , and if you were to tilt your head just a little bit ... think about it . this one 's not really going to get the right image anymore . it 's going to get some of both . and this one 's going to get some of both . it 's going to be blurry . your head would have to be perfectly level the whole time , which might be annoying . so what we do is , instead , we create circular polarized glasses , so that this one would only get one polarization , this one would get the other direction . this way , even if you tilt your head a little bit ... shoot , clockwise is clockwise , counterclockwise is counterclockwise . by using circular polarization for 3d movies , it can make it a little easier on you eyes to see a better 3d image , even if your head 's tilted a little bit .
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and it does . if you take off your 3d glasses and look at a 3d movie , looks terrible , because now both eyes are getting both images . but if you put your glasses back on , now this eye only gets the orientation that it 's supposed to get , and this eye only gets the orientation that it 's supposed to get , and you get a 3d image . so it 's useful in many ways .
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wait , do n't 3d glasses work because blue\red color gets blocked ?
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- let 's talk about polarization of light . we know what light waves are ; they 're electromagnetic waves . so they 're made out of electric fields . and that 's not good enough . we know there 's not just electric fields . that could n't sustain itself . there 's got to be magnetic fields there , as well , that are changing . those are perpendicular , so you can kind of draw them . it 's hard , on something two-dimensional , but you can kind of imagine those looking something like this . and those magnetic fields would point at a right angle to the electric fields . but this gets really messy if i try to draw both the electric and magnetic fields at the same time . so we 're going to leave the magnetic fields out . it 's often good enough to just know the direction of the electric field when we focus on the electric field . so what does polarization mean ? polarization refers to the fact that , if this light ray was heading straight toward your eye , or a detector , over here , what would you see ? well , if i draw an axis over here , and this point here , in the middle , this is this line -- so imagine we 're looking straight down that line -- and then up and down is up and down , and then left and right , that direction i have the magnetic field , would be this way and that way . what would my eye see ? well , my eye 's only going to see electric fields that either point up or electric fields that point down . they might have different values , but i 'm only going to see electric fields that point up or down . because of that , this light ray is polarized . so polarized light is light where the electric field is only oscillating in one direction . up or down , that 's one direction -- vertically . or it could be polarized horizontally . or it could be polarized diagonally . but either way , you could have this wave polarized along any direction . i mean , a light ray like this , if we had it coming in diagonal , this light ray that 's oscillating like this , where the electric field oscillates like that , that also polarized . these are both polarized because there 's only one direction that the electric field is oscillating in . and you might thing , `` pff , how could you ever have `` a light ray that 's not polarized ? '' easy . most light that you get is not polarized . that is to say , light that 's coming from the sun , straight from the sun -- typically not polarized . light from a lightbulb , an old incandescent light bulb , this thing 's hot . you can get light polarized in any direction , all at once , all overlapping . so if we draw this case for a light bulb , just a random incandescent light bulb , you might get light , some of the light , hitting you eye , you can get some light that 's got that direction , you got light that 's got this direction , you got light in all these directions at any given moment . i mean , you 'd have to add these up to get the total , and they might not all be the same value . but what i 'm trying to say is , at any given moment , you do n't know what direction the electric field 's going to be hitting your eye at from a random source . it could be in any direction . so this is not polarized . this diagram represents light that is not polarized . at some point , the field might be pointing this way , at some later point it 's this way ; it 's just random . you never know which way the electric field 's going to be pointing . whereas these over here , these are polarized . so how could you polarize this light ? let 's say you wanted light that was polarized . you were doing an experiment . you needed polarized light . well , that 's easy . you can use what 's called a polarizer . and this is a material that lets light through , but it only lets light through in one orientation , so you 're going to have a polarizer that , for instance , only lets through vertically polarized light . so this is a polarizer . these are cheap : thin , plastic , configured in a way so that it only lets light through that 's vertically polarized . any light coming in here that 's not vertically polarized gets blocked , or absorbed . so what that means is , if you used this polarizer and held it in between your eye and this light bulb , you would only get this light . all the rest of it would get blocked . or you could just rotate this thing and imagine a polarizer that only lets through horizontal light . now it would only let through light that was this way , and so you would only get this part of the light . or you could just orient it at any angle you want and block everything but the certain angle that this polarizer is defined as letting light through . so you can do this . and once you hold this up , you get polarized light , light that 's only got one orientation . so that 's what polarization means . but why do we care about polarization ? well , let me get rid of this for a minute . you 've heard of polarized sunglasses . so imagine you 're standing near water , or maybe you 're standing on ice or snow or something reflective . there 's a problem . say the sun 's out . it 's shining . it 's a beautiful day -- except there 's going to be glare . let 's say you 're looking down at something here on the ground . it 's going to get light reflecting off of it from just ... you know , light 's coming in from all direction . but it also gets this direct light from the sun . so it gets light from reflected off the clouds and whatever , whatever 's nearby , ambient light . and there 's also this direct sunlight . that 's harsh . if that reflects straight up to your eye , that hurts . you do n't like that . it blocks our vision . it 's hard to see , it 's glare . we do n't want this glare . so what can we do ? well , it just so happens that , when light reflects off of a surface , even though the light from the sun is not polarized , once it reflects , it does get polarized or at least partially polarized . so this surface here , once this light reflects , it 's coming in at all orientations . you got electric field ... you never know what electric field you 're going to get straight from the sun . and when it reflects , though , you mostly get , upon reflection , the direction of polarization defined by the plane of the surface that it hit . so because the floor is horizontal , when this light ray hits the ground and reflects , that reflected light gets partially polarized . this horizontal component of the electric field is going to be more present than the other components . maybe not completely . sometimes it could be . it could be completely polarized , but often it 's just partially polarized . but that 's pretty cool , because now you know what we can do . i know how to block this . we should get some sunglasses . we put some sunglasses on and we make our glasses so that these are polarized . and how do we want these polarized ? i want to get rid of the glare . so what i do is , i make sure my sunglasses only let through vertically polarized light . here 's some polarizers . that way , a lot of this glare gets blocked because it does not have a vertical orientation , it has a horizontal orientation . and then we can block it . so that 's one good thing that polarization does for us , and understanding it , we can get rid of glare . also , fishermen like it because , if you 're trying to look in the water at fish , you want to see in through the water , you want to see this light from the fish getting to you . you do n't want to see the glare off of the sun getting to you . so polarized sunglasses are useful . also , we can play a trick on our eye , if we really wanted to . you could take one of these , make one eye have a vertical orientation for the polarization , have the other eye with a horizontal ... and you 're thinking , `` this is stupid . `` why would you do this for ? '' `` this eye 's going to get a lot of glare . '' we would n't use these outside , when you 're , like , skiing or fishing , but you could play a trick on your eyes if you went to the movies and you went and watched a movie . well , the reason our eyes see 3d is because they 're spaced a little bit apart . they each get a different , slightly different image . that makes us see in 3d . we can play the same trick on our eye if we have the polarization like this . if light , if some of the light from the movie theater screen is coming in with one polarization , and the other light 's coming in with the other polarization , we can send two different images to our eyes at the same time . if you took these off , it 'd look like garbage because you 'd be getting both of these slightly different images , it 'd look all blurry . and it does . if you take off your 3d glasses and look at a 3d movie , looks terrible , because now both eyes are getting both images . but if you put your glasses back on , now this eye only gets the orientation that it 's supposed to get , and this eye only gets the orientation that it 's supposed to get , and you get a 3d image . so it 's useful in many ways . let me show you one more thing here . let 's come back here . this light was polarized vertically . so that 's called linear polarization . any time ... same with these . these are all linear polarization because , just up and down , one linear direction , just diagonal . this is also linear . all of these are linear . you can get circular polarized light . so if we come back to here , we 've got our electric field pointing up , like that . now let 's say we sent in another light ray , another light ray that also had a polarization , but not in this direction . let 's say our other light ray had polarization in this direction , so it looks like this , kind of like what our magnetic field would have looked like . but this is a completely different light ray with its own polarization and its own magnetic field . so we send this in . what would happen ? well , at this point , you 'd have a electric field that points this way . at this point , you 'd have a electric field that points that way . what would your eye see if you were over here ? let 's see . if i draw our axis here . all right , when this point right here gets to your eye , what am i going to see ? well , i 'm going to have a light ray that 's one part of a light ray . one component points up . that 's this electric field . one component points left . that 's this electric field . so the total , my total electric field , would point this way . i could to the pythagorean theorem if i wanted to figure out the size of it , but i just want to know the direction for now . and then it gets to here , and look at it : they both have zero . this light ray has zero electric field , this one has zero electric fields . so then it 'd just be at zero . now what happens over here ? well , i 've got light . this one points to the right at that point , this pink one , and then this red one would be pointing down . so what would i have at that point ? i 'd have light that went this way , and it would just be doing this over and over . it would just be ... i 'd just have diagonally polarized light . this is n't giving me anything new . you might think this is dumb . why do this ? why send in two different waves to just get diagonally polarized light ? i could have just sent in one wave that was diagonally polarized and got the same thing . the reason is , if you shift this purple wave , this pink wave , by 90 degrees of phase , by pi over two in phase , something magical happens . let me show you what happens here , if we move this to here . now we do n't just get diagonally linear polarized light . what we 're going to get is ... let me get rid of this . okay , so we start off with red , right ? the red electric field points up , and then this pink wave 's electric field is zero at that point . so this is all i have . my total electric field would just be up . i 'm going to draw it right here . the green 'll be the total . now i come over to here , and at this point , there 's some red electric field that points up , but there 's some of this other electric field that points this way . so i 'd have a total electric field that would point that way . and then i get over to here , and i 'd have all of the electric field from the pink one , none from the red one . it would point all left then . look what 's happening . the polarization of this light , if i shift this , if i 'm sitting here , looking with my eye , as my eye receives this light , i 'm going to see this light rotate its polarization . the polarization i 'm going to notice swings around in a circular pattern . and because of this , we call this circular polarization . so this is another type of polarization , where the actual angle of polarization rotates smoothly as this light ray enters your eye . and you know what ? er , drrr ... all right , actually , i sent you to receive this one first . that makes no sense . you 're going to receive the ones closes to you first in this light ray going this way . so you 'd actually receive this one first , then that one , then this one , then this one . because of that , you would n't see this going in a counterclockwise way , you 'd see this going in a clockwise circularly polarized way . sorry about that . you might think , `` okay , why ? `` why even bother with circular polarization ? '' well , i kind of lied earlier . turns out , in the movie theater example , they do n't actually do it like this , typically . oftentimes in the movie theaters , we do n't have just linearly polarized sunglasses . this would be a problem because , when you look at the movie theater screen , and if you were to tilt your head just a little bit ... think about it . this one 's not really going to get the right image anymore . it 's going to get some of both . and this one 's going to get some of both . it 's going to be blurry . your head would have to be perfectly level the whole time , which might be annoying . so what we do is , instead , we create circular polarized glasses , so that this one would only get one polarization , this one would get the other direction . this way , even if you tilt your head a little bit ... shoot , clockwise is clockwise , counterclockwise is counterclockwise . by using circular polarization for 3d movies , it can make it a little easier on you eyes to see a better 3d image , even if your head 's tilted a little bit .
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now let 's say we sent in another light ray , another light ray that also had a polarization , but not in this direction . let 's say our other light ray had polarization in this direction , so it looks like this , kind of like what our magnetic field would have looked like . but this is a completely different light ray with its own polarization and its own magnetic field .
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like , with one eye you see only blue-shaded image , and with other you see only red-shaded image , and since those images are placed the way it looks like the red or the blue ( it works both ways ) image is closer , your brain combines those two images into one that looks just like irl ?
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- let 's talk about polarization of light . we know what light waves are ; they 're electromagnetic waves . so they 're made out of electric fields . and that 's not good enough . we know there 's not just electric fields . that could n't sustain itself . there 's got to be magnetic fields there , as well , that are changing . those are perpendicular , so you can kind of draw them . it 's hard , on something two-dimensional , but you can kind of imagine those looking something like this . and those magnetic fields would point at a right angle to the electric fields . but this gets really messy if i try to draw both the electric and magnetic fields at the same time . so we 're going to leave the magnetic fields out . it 's often good enough to just know the direction of the electric field when we focus on the electric field . so what does polarization mean ? polarization refers to the fact that , if this light ray was heading straight toward your eye , or a detector , over here , what would you see ? well , if i draw an axis over here , and this point here , in the middle , this is this line -- so imagine we 're looking straight down that line -- and then up and down is up and down , and then left and right , that direction i have the magnetic field , would be this way and that way . what would my eye see ? well , my eye 's only going to see electric fields that either point up or electric fields that point down . they might have different values , but i 'm only going to see electric fields that point up or down . because of that , this light ray is polarized . so polarized light is light where the electric field is only oscillating in one direction . up or down , that 's one direction -- vertically . or it could be polarized horizontally . or it could be polarized diagonally . but either way , you could have this wave polarized along any direction . i mean , a light ray like this , if we had it coming in diagonal , this light ray that 's oscillating like this , where the electric field oscillates like that , that also polarized . these are both polarized because there 's only one direction that the electric field is oscillating in . and you might thing , `` pff , how could you ever have `` a light ray that 's not polarized ? '' easy . most light that you get is not polarized . that is to say , light that 's coming from the sun , straight from the sun -- typically not polarized . light from a lightbulb , an old incandescent light bulb , this thing 's hot . you can get light polarized in any direction , all at once , all overlapping . so if we draw this case for a light bulb , just a random incandescent light bulb , you might get light , some of the light , hitting you eye , you can get some light that 's got that direction , you got light that 's got this direction , you got light in all these directions at any given moment . i mean , you 'd have to add these up to get the total , and they might not all be the same value . but what i 'm trying to say is , at any given moment , you do n't know what direction the electric field 's going to be hitting your eye at from a random source . it could be in any direction . so this is not polarized . this diagram represents light that is not polarized . at some point , the field might be pointing this way , at some later point it 's this way ; it 's just random . you never know which way the electric field 's going to be pointing . whereas these over here , these are polarized . so how could you polarize this light ? let 's say you wanted light that was polarized . you were doing an experiment . you needed polarized light . well , that 's easy . you can use what 's called a polarizer . and this is a material that lets light through , but it only lets light through in one orientation , so you 're going to have a polarizer that , for instance , only lets through vertically polarized light . so this is a polarizer . these are cheap : thin , plastic , configured in a way so that it only lets light through that 's vertically polarized . any light coming in here that 's not vertically polarized gets blocked , or absorbed . so what that means is , if you used this polarizer and held it in between your eye and this light bulb , you would only get this light . all the rest of it would get blocked . or you could just rotate this thing and imagine a polarizer that only lets through horizontal light . now it would only let through light that was this way , and so you would only get this part of the light . or you could just orient it at any angle you want and block everything but the certain angle that this polarizer is defined as letting light through . so you can do this . and once you hold this up , you get polarized light , light that 's only got one orientation . so that 's what polarization means . but why do we care about polarization ? well , let me get rid of this for a minute . you 've heard of polarized sunglasses . so imagine you 're standing near water , or maybe you 're standing on ice or snow or something reflective . there 's a problem . say the sun 's out . it 's shining . it 's a beautiful day -- except there 's going to be glare . let 's say you 're looking down at something here on the ground . it 's going to get light reflecting off of it from just ... you know , light 's coming in from all direction . but it also gets this direct light from the sun . so it gets light from reflected off the clouds and whatever , whatever 's nearby , ambient light . and there 's also this direct sunlight . that 's harsh . if that reflects straight up to your eye , that hurts . you do n't like that . it blocks our vision . it 's hard to see , it 's glare . we do n't want this glare . so what can we do ? well , it just so happens that , when light reflects off of a surface , even though the light from the sun is not polarized , once it reflects , it does get polarized or at least partially polarized . so this surface here , once this light reflects , it 's coming in at all orientations . you got electric field ... you never know what electric field you 're going to get straight from the sun . and when it reflects , though , you mostly get , upon reflection , the direction of polarization defined by the plane of the surface that it hit . so because the floor is horizontal , when this light ray hits the ground and reflects , that reflected light gets partially polarized . this horizontal component of the electric field is going to be more present than the other components . maybe not completely . sometimes it could be . it could be completely polarized , but often it 's just partially polarized . but that 's pretty cool , because now you know what we can do . i know how to block this . we should get some sunglasses . we put some sunglasses on and we make our glasses so that these are polarized . and how do we want these polarized ? i want to get rid of the glare . so what i do is , i make sure my sunglasses only let through vertically polarized light . here 's some polarizers . that way , a lot of this glare gets blocked because it does not have a vertical orientation , it has a horizontal orientation . and then we can block it . so that 's one good thing that polarization does for us , and understanding it , we can get rid of glare . also , fishermen like it because , if you 're trying to look in the water at fish , you want to see in through the water , you want to see this light from the fish getting to you . you do n't want to see the glare off of the sun getting to you . so polarized sunglasses are useful . also , we can play a trick on our eye , if we really wanted to . you could take one of these , make one eye have a vertical orientation for the polarization , have the other eye with a horizontal ... and you 're thinking , `` this is stupid . `` why would you do this for ? '' `` this eye 's going to get a lot of glare . '' we would n't use these outside , when you 're , like , skiing or fishing , but you could play a trick on your eyes if you went to the movies and you went and watched a movie . well , the reason our eyes see 3d is because they 're spaced a little bit apart . they each get a different , slightly different image . that makes us see in 3d . we can play the same trick on our eye if we have the polarization like this . if light , if some of the light from the movie theater screen is coming in with one polarization , and the other light 's coming in with the other polarization , we can send two different images to our eyes at the same time . if you took these off , it 'd look like garbage because you 'd be getting both of these slightly different images , it 'd look all blurry . and it does . if you take off your 3d glasses and look at a 3d movie , looks terrible , because now both eyes are getting both images . but if you put your glasses back on , now this eye only gets the orientation that it 's supposed to get , and this eye only gets the orientation that it 's supposed to get , and you get a 3d image . so it 's useful in many ways . let me show you one more thing here . let 's come back here . this light was polarized vertically . so that 's called linear polarization . any time ... same with these . these are all linear polarization because , just up and down , one linear direction , just diagonal . this is also linear . all of these are linear . you can get circular polarized light . so if we come back to here , we 've got our electric field pointing up , like that . now let 's say we sent in another light ray , another light ray that also had a polarization , but not in this direction . let 's say our other light ray had polarization in this direction , so it looks like this , kind of like what our magnetic field would have looked like . but this is a completely different light ray with its own polarization and its own magnetic field . so we send this in . what would happen ? well , at this point , you 'd have a electric field that points this way . at this point , you 'd have a electric field that points that way . what would your eye see if you were over here ? let 's see . if i draw our axis here . all right , when this point right here gets to your eye , what am i going to see ? well , i 'm going to have a light ray that 's one part of a light ray . one component points up . that 's this electric field . one component points left . that 's this electric field . so the total , my total electric field , would point this way . i could to the pythagorean theorem if i wanted to figure out the size of it , but i just want to know the direction for now . and then it gets to here , and look at it : they both have zero . this light ray has zero electric field , this one has zero electric fields . so then it 'd just be at zero . now what happens over here ? well , i 've got light . this one points to the right at that point , this pink one , and then this red one would be pointing down . so what would i have at that point ? i 'd have light that went this way , and it would just be doing this over and over . it would just be ... i 'd just have diagonally polarized light . this is n't giving me anything new . you might think this is dumb . why do this ? why send in two different waves to just get diagonally polarized light ? i could have just sent in one wave that was diagonally polarized and got the same thing . the reason is , if you shift this purple wave , this pink wave , by 90 degrees of phase , by pi over two in phase , something magical happens . let me show you what happens here , if we move this to here . now we do n't just get diagonally linear polarized light . what we 're going to get is ... let me get rid of this . okay , so we start off with red , right ? the red electric field points up , and then this pink wave 's electric field is zero at that point . so this is all i have . my total electric field would just be up . i 'm going to draw it right here . the green 'll be the total . now i come over to here , and at this point , there 's some red electric field that points up , but there 's some of this other electric field that points this way . so i 'd have a total electric field that would point that way . and then i get over to here , and i 'd have all of the electric field from the pink one , none from the red one . it would point all left then . look what 's happening . the polarization of this light , if i shift this , if i 'm sitting here , looking with my eye , as my eye receives this light , i 'm going to see this light rotate its polarization . the polarization i 'm going to notice swings around in a circular pattern . and because of this , we call this circular polarization . so this is another type of polarization , where the actual angle of polarization rotates smoothly as this light ray enters your eye . and you know what ? er , drrr ... all right , actually , i sent you to receive this one first . that makes no sense . you 're going to receive the ones closes to you first in this light ray going this way . so you 'd actually receive this one first , then that one , then this one , then this one . because of that , you would n't see this going in a counterclockwise way , you 'd see this going in a clockwise circularly polarized way . sorry about that . you might think , `` okay , why ? `` why even bother with circular polarization ? '' well , i kind of lied earlier . turns out , in the movie theater example , they do n't actually do it like this , typically . oftentimes in the movie theaters , we do n't have just linearly polarized sunglasses . this would be a problem because , when you look at the movie theater screen , and if you were to tilt your head just a little bit ... think about it . this one 's not really going to get the right image anymore . it 's going to get some of both . and this one 's going to get some of both . it 's going to be blurry . your head would have to be perfectly level the whole time , which might be annoying . so what we do is , instead , we create circular polarized glasses , so that this one would only get one polarization , this one would get the other direction . this way , even if you tilt your head a little bit ... shoot , clockwise is clockwise , counterclockwise is counterclockwise . by using circular polarization for 3d movies , it can make it a little easier on you eyes to see a better 3d image , even if your head 's tilted a little bit .
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they might have different values , but i 'm only going to see electric fields that point up or down . because of that , this light ray is polarized . so polarized light is light where the electric field is only oscillating in one direction .
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if you take a specific photon in an unpolarized light ray , is n't the photon itself polarized ?
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- let 's talk about polarization of light . we know what light waves are ; they 're electromagnetic waves . so they 're made out of electric fields . and that 's not good enough . we know there 's not just electric fields . that could n't sustain itself . there 's got to be magnetic fields there , as well , that are changing . those are perpendicular , so you can kind of draw them . it 's hard , on something two-dimensional , but you can kind of imagine those looking something like this . and those magnetic fields would point at a right angle to the electric fields . but this gets really messy if i try to draw both the electric and magnetic fields at the same time . so we 're going to leave the magnetic fields out . it 's often good enough to just know the direction of the electric field when we focus on the electric field . so what does polarization mean ? polarization refers to the fact that , if this light ray was heading straight toward your eye , or a detector , over here , what would you see ? well , if i draw an axis over here , and this point here , in the middle , this is this line -- so imagine we 're looking straight down that line -- and then up and down is up and down , and then left and right , that direction i have the magnetic field , would be this way and that way . what would my eye see ? well , my eye 's only going to see electric fields that either point up or electric fields that point down . they might have different values , but i 'm only going to see electric fields that point up or down . because of that , this light ray is polarized . so polarized light is light where the electric field is only oscillating in one direction . up or down , that 's one direction -- vertically . or it could be polarized horizontally . or it could be polarized diagonally . but either way , you could have this wave polarized along any direction . i mean , a light ray like this , if we had it coming in diagonal , this light ray that 's oscillating like this , where the electric field oscillates like that , that also polarized . these are both polarized because there 's only one direction that the electric field is oscillating in . and you might thing , `` pff , how could you ever have `` a light ray that 's not polarized ? '' easy . most light that you get is not polarized . that is to say , light that 's coming from the sun , straight from the sun -- typically not polarized . light from a lightbulb , an old incandescent light bulb , this thing 's hot . you can get light polarized in any direction , all at once , all overlapping . so if we draw this case for a light bulb , just a random incandescent light bulb , you might get light , some of the light , hitting you eye , you can get some light that 's got that direction , you got light that 's got this direction , you got light in all these directions at any given moment . i mean , you 'd have to add these up to get the total , and they might not all be the same value . but what i 'm trying to say is , at any given moment , you do n't know what direction the electric field 's going to be hitting your eye at from a random source . it could be in any direction . so this is not polarized . this diagram represents light that is not polarized . at some point , the field might be pointing this way , at some later point it 's this way ; it 's just random . you never know which way the electric field 's going to be pointing . whereas these over here , these are polarized . so how could you polarize this light ? let 's say you wanted light that was polarized . you were doing an experiment . you needed polarized light . well , that 's easy . you can use what 's called a polarizer . and this is a material that lets light through , but it only lets light through in one orientation , so you 're going to have a polarizer that , for instance , only lets through vertically polarized light . so this is a polarizer . these are cheap : thin , plastic , configured in a way so that it only lets light through that 's vertically polarized . any light coming in here that 's not vertically polarized gets blocked , or absorbed . so what that means is , if you used this polarizer and held it in between your eye and this light bulb , you would only get this light . all the rest of it would get blocked . or you could just rotate this thing and imagine a polarizer that only lets through horizontal light . now it would only let through light that was this way , and so you would only get this part of the light . or you could just orient it at any angle you want and block everything but the certain angle that this polarizer is defined as letting light through . so you can do this . and once you hold this up , you get polarized light , light that 's only got one orientation . so that 's what polarization means . but why do we care about polarization ? well , let me get rid of this for a minute . you 've heard of polarized sunglasses . so imagine you 're standing near water , or maybe you 're standing on ice or snow or something reflective . there 's a problem . say the sun 's out . it 's shining . it 's a beautiful day -- except there 's going to be glare . let 's say you 're looking down at something here on the ground . it 's going to get light reflecting off of it from just ... you know , light 's coming in from all direction . but it also gets this direct light from the sun . so it gets light from reflected off the clouds and whatever , whatever 's nearby , ambient light . and there 's also this direct sunlight . that 's harsh . if that reflects straight up to your eye , that hurts . you do n't like that . it blocks our vision . it 's hard to see , it 's glare . we do n't want this glare . so what can we do ? well , it just so happens that , when light reflects off of a surface , even though the light from the sun is not polarized , once it reflects , it does get polarized or at least partially polarized . so this surface here , once this light reflects , it 's coming in at all orientations . you got electric field ... you never know what electric field you 're going to get straight from the sun . and when it reflects , though , you mostly get , upon reflection , the direction of polarization defined by the plane of the surface that it hit . so because the floor is horizontal , when this light ray hits the ground and reflects , that reflected light gets partially polarized . this horizontal component of the electric field is going to be more present than the other components . maybe not completely . sometimes it could be . it could be completely polarized , but often it 's just partially polarized . but that 's pretty cool , because now you know what we can do . i know how to block this . we should get some sunglasses . we put some sunglasses on and we make our glasses so that these are polarized . and how do we want these polarized ? i want to get rid of the glare . so what i do is , i make sure my sunglasses only let through vertically polarized light . here 's some polarizers . that way , a lot of this glare gets blocked because it does not have a vertical orientation , it has a horizontal orientation . and then we can block it . so that 's one good thing that polarization does for us , and understanding it , we can get rid of glare . also , fishermen like it because , if you 're trying to look in the water at fish , you want to see in through the water , you want to see this light from the fish getting to you . you do n't want to see the glare off of the sun getting to you . so polarized sunglasses are useful . also , we can play a trick on our eye , if we really wanted to . you could take one of these , make one eye have a vertical orientation for the polarization , have the other eye with a horizontal ... and you 're thinking , `` this is stupid . `` why would you do this for ? '' `` this eye 's going to get a lot of glare . '' we would n't use these outside , when you 're , like , skiing or fishing , but you could play a trick on your eyes if you went to the movies and you went and watched a movie . well , the reason our eyes see 3d is because they 're spaced a little bit apart . they each get a different , slightly different image . that makes us see in 3d . we can play the same trick on our eye if we have the polarization like this . if light , if some of the light from the movie theater screen is coming in with one polarization , and the other light 's coming in with the other polarization , we can send two different images to our eyes at the same time . if you took these off , it 'd look like garbage because you 'd be getting both of these slightly different images , it 'd look all blurry . and it does . if you take off your 3d glasses and look at a 3d movie , looks terrible , because now both eyes are getting both images . but if you put your glasses back on , now this eye only gets the orientation that it 's supposed to get , and this eye only gets the orientation that it 's supposed to get , and you get a 3d image . so it 's useful in many ways . let me show you one more thing here . let 's come back here . this light was polarized vertically . so that 's called linear polarization . any time ... same with these . these are all linear polarization because , just up and down , one linear direction , just diagonal . this is also linear . all of these are linear . you can get circular polarized light . so if we come back to here , we 've got our electric field pointing up , like that . now let 's say we sent in another light ray , another light ray that also had a polarization , but not in this direction . let 's say our other light ray had polarization in this direction , so it looks like this , kind of like what our magnetic field would have looked like . but this is a completely different light ray with its own polarization and its own magnetic field . so we send this in . what would happen ? well , at this point , you 'd have a electric field that points this way . at this point , you 'd have a electric field that points that way . what would your eye see if you were over here ? let 's see . if i draw our axis here . all right , when this point right here gets to your eye , what am i going to see ? well , i 'm going to have a light ray that 's one part of a light ray . one component points up . that 's this electric field . one component points left . that 's this electric field . so the total , my total electric field , would point this way . i could to the pythagorean theorem if i wanted to figure out the size of it , but i just want to know the direction for now . and then it gets to here , and look at it : they both have zero . this light ray has zero electric field , this one has zero electric fields . so then it 'd just be at zero . now what happens over here ? well , i 've got light . this one points to the right at that point , this pink one , and then this red one would be pointing down . so what would i have at that point ? i 'd have light that went this way , and it would just be doing this over and over . it would just be ... i 'd just have diagonally polarized light . this is n't giving me anything new . you might think this is dumb . why do this ? why send in two different waves to just get diagonally polarized light ? i could have just sent in one wave that was diagonally polarized and got the same thing . the reason is , if you shift this purple wave , this pink wave , by 90 degrees of phase , by pi over two in phase , something magical happens . let me show you what happens here , if we move this to here . now we do n't just get diagonally linear polarized light . what we 're going to get is ... let me get rid of this . okay , so we start off with red , right ? the red electric field points up , and then this pink wave 's electric field is zero at that point . so this is all i have . my total electric field would just be up . i 'm going to draw it right here . the green 'll be the total . now i come over to here , and at this point , there 's some red electric field that points up , but there 's some of this other electric field that points this way . so i 'd have a total electric field that would point that way . and then i get over to here , and i 'd have all of the electric field from the pink one , none from the red one . it would point all left then . look what 's happening . the polarization of this light , if i shift this , if i 'm sitting here , looking with my eye , as my eye receives this light , i 'm going to see this light rotate its polarization . the polarization i 'm going to notice swings around in a circular pattern . and because of this , we call this circular polarization . so this is another type of polarization , where the actual angle of polarization rotates smoothly as this light ray enters your eye . and you know what ? er , drrr ... all right , actually , i sent you to receive this one first . that makes no sense . you 're going to receive the ones closes to you first in this light ray going this way . so you 'd actually receive this one first , then that one , then this one , then this one . because of that , you would n't see this going in a counterclockwise way , you 'd see this going in a clockwise circularly polarized way . sorry about that . you might think , `` okay , why ? `` why even bother with circular polarization ? '' well , i kind of lied earlier . turns out , in the movie theater example , they do n't actually do it like this , typically . oftentimes in the movie theaters , we do n't have just linearly polarized sunglasses . this would be a problem because , when you look at the movie theater screen , and if you were to tilt your head just a little bit ... think about it . this one 's not really going to get the right image anymore . it 's going to get some of both . and this one 's going to get some of both . it 's going to be blurry . your head would have to be perfectly level the whole time , which might be annoying . so what we do is , instead , we create circular polarized glasses , so that this one would only get one polarization , this one would get the other direction . this way , even if you tilt your head a little bit ... shoot , clockwise is clockwise , counterclockwise is counterclockwise . by using circular polarization for 3d movies , it can make it a little easier on you eyes to see a better 3d image , even if your head 's tilted a little bit .
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maybe not completely . sometimes it could be . it could be completely polarized , but often it 's just partially polarized .
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why is that our sky appears white sometimes when we view it in certain directions on hot days ?
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- let 's talk about polarization of light . we know what light waves are ; they 're electromagnetic waves . so they 're made out of electric fields . and that 's not good enough . we know there 's not just electric fields . that could n't sustain itself . there 's got to be magnetic fields there , as well , that are changing . those are perpendicular , so you can kind of draw them . it 's hard , on something two-dimensional , but you can kind of imagine those looking something like this . and those magnetic fields would point at a right angle to the electric fields . but this gets really messy if i try to draw both the electric and magnetic fields at the same time . so we 're going to leave the magnetic fields out . it 's often good enough to just know the direction of the electric field when we focus on the electric field . so what does polarization mean ? polarization refers to the fact that , if this light ray was heading straight toward your eye , or a detector , over here , what would you see ? well , if i draw an axis over here , and this point here , in the middle , this is this line -- so imagine we 're looking straight down that line -- and then up and down is up and down , and then left and right , that direction i have the magnetic field , would be this way and that way . what would my eye see ? well , my eye 's only going to see electric fields that either point up or electric fields that point down . they might have different values , but i 'm only going to see electric fields that point up or down . because of that , this light ray is polarized . so polarized light is light where the electric field is only oscillating in one direction . up or down , that 's one direction -- vertically . or it could be polarized horizontally . or it could be polarized diagonally . but either way , you could have this wave polarized along any direction . i mean , a light ray like this , if we had it coming in diagonal , this light ray that 's oscillating like this , where the electric field oscillates like that , that also polarized . these are both polarized because there 's only one direction that the electric field is oscillating in . and you might thing , `` pff , how could you ever have `` a light ray that 's not polarized ? '' easy . most light that you get is not polarized . that is to say , light that 's coming from the sun , straight from the sun -- typically not polarized . light from a lightbulb , an old incandescent light bulb , this thing 's hot . you can get light polarized in any direction , all at once , all overlapping . so if we draw this case for a light bulb , just a random incandescent light bulb , you might get light , some of the light , hitting you eye , you can get some light that 's got that direction , you got light that 's got this direction , you got light in all these directions at any given moment . i mean , you 'd have to add these up to get the total , and they might not all be the same value . but what i 'm trying to say is , at any given moment , you do n't know what direction the electric field 's going to be hitting your eye at from a random source . it could be in any direction . so this is not polarized . this diagram represents light that is not polarized . at some point , the field might be pointing this way , at some later point it 's this way ; it 's just random . you never know which way the electric field 's going to be pointing . whereas these over here , these are polarized . so how could you polarize this light ? let 's say you wanted light that was polarized . you were doing an experiment . you needed polarized light . well , that 's easy . you can use what 's called a polarizer . and this is a material that lets light through , but it only lets light through in one orientation , so you 're going to have a polarizer that , for instance , only lets through vertically polarized light . so this is a polarizer . these are cheap : thin , plastic , configured in a way so that it only lets light through that 's vertically polarized . any light coming in here that 's not vertically polarized gets blocked , or absorbed . so what that means is , if you used this polarizer and held it in between your eye and this light bulb , you would only get this light . all the rest of it would get blocked . or you could just rotate this thing and imagine a polarizer that only lets through horizontal light . now it would only let through light that was this way , and so you would only get this part of the light . or you could just orient it at any angle you want and block everything but the certain angle that this polarizer is defined as letting light through . so you can do this . and once you hold this up , you get polarized light , light that 's only got one orientation . so that 's what polarization means . but why do we care about polarization ? well , let me get rid of this for a minute . you 've heard of polarized sunglasses . so imagine you 're standing near water , or maybe you 're standing on ice or snow or something reflective . there 's a problem . say the sun 's out . it 's shining . it 's a beautiful day -- except there 's going to be glare . let 's say you 're looking down at something here on the ground . it 's going to get light reflecting off of it from just ... you know , light 's coming in from all direction . but it also gets this direct light from the sun . so it gets light from reflected off the clouds and whatever , whatever 's nearby , ambient light . and there 's also this direct sunlight . that 's harsh . if that reflects straight up to your eye , that hurts . you do n't like that . it blocks our vision . it 's hard to see , it 's glare . we do n't want this glare . so what can we do ? well , it just so happens that , when light reflects off of a surface , even though the light from the sun is not polarized , once it reflects , it does get polarized or at least partially polarized . so this surface here , once this light reflects , it 's coming in at all orientations . you got electric field ... you never know what electric field you 're going to get straight from the sun . and when it reflects , though , you mostly get , upon reflection , the direction of polarization defined by the plane of the surface that it hit . so because the floor is horizontal , when this light ray hits the ground and reflects , that reflected light gets partially polarized . this horizontal component of the electric field is going to be more present than the other components . maybe not completely . sometimes it could be . it could be completely polarized , but often it 's just partially polarized . but that 's pretty cool , because now you know what we can do . i know how to block this . we should get some sunglasses . we put some sunglasses on and we make our glasses so that these are polarized . and how do we want these polarized ? i want to get rid of the glare . so what i do is , i make sure my sunglasses only let through vertically polarized light . here 's some polarizers . that way , a lot of this glare gets blocked because it does not have a vertical orientation , it has a horizontal orientation . and then we can block it . so that 's one good thing that polarization does for us , and understanding it , we can get rid of glare . also , fishermen like it because , if you 're trying to look in the water at fish , you want to see in through the water , you want to see this light from the fish getting to you . you do n't want to see the glare off of the sun getting to you . so polarized sunglasses are useful . also , we can play a trick on our eye , if we really wanted to . you could take one of these , make one eye have a vertical orientation for the polarization , have the other eye with a horizontal ... and you 're thinking , `` this is stupid . `` why would you do this for ? '' `` this eye 's going to get a lot of glare . '' we would n't use these outside , when you 're , like , skiing or fishing , but you could play a trick on your eyes if you went to the movies and you went and watched a movie . well , the reason our eyes see 3d is because they 're spaced a little bit apart . they each get a different , slightly different image . that makes us see in 3d . we can play the same trick on our eye if we have the polarization like this . if light , if some of the light from the movie theater screen is coming in with one polarization , and the other light 's coming in with the other polarization , we can send two different images to our eyes at the same time . if you took these off , it 'd look like garbage because you 'd be getting both of these slightly different images , it 'd look all blurry . and it does . if you take off your 3d glasses and look at a 3d movie , looks terrible , because now both eyes are getting both images . but if you put your glasses back on , now this eye only gets the orientation that it 's supposed to get , and this eye only gets the orientation that it 's supposed to get , and you get a 3d image . so it 's useful in many ways . let me show you one more thing here . let 's come back here . this light was polarized vertically . so that 's called linear polarization . any time ... same with these . these are all linear polarization because , just up and down , one linear direction , just diagonal . this is also linear . all of these are linear . you can get circular polarized light . so if we come back to here , we 've got our electric field pointing up , like that . now let 's say we sent in another light ray , another light ray that also had a polarization , but not in this direction . let 's say our other light ray had polarization in this direction , so it looks like this , kind of like what our magnetic field would have looked like . but this is a completely different light ray with its own polarization and its own magnetic field . so we send this in . what would happen ? well , at this point , you 'd have a electric field that points this way . at this point , you 'd have a electric field that points that way . what would your eye see if you were over here ? let 's see . if i draw our axis here . all right , when this point right here gets to your eye , what am i going to see ? well , i 'm going to have a light ray that 's one part of a light ray . one component points up . that 's this electric field . one component points left . that 's this electric field . so the total , my total electric field , would point this way . i could to the pythagorean theorem if i wanted to figure out the size of it , but i just want to know the direction for now . and then it gets to here , and look at it : they both have zero . this light ray has zero electric field , this one has zero electric fields . so then it 'd just be at zero . now what happens over here ? well , i 've got light . this one points to the right at that point , this pink one , and then this red one would be pointing down . so what would i have at that point ? i 'd have light that went this way , and it would just be doing this over and over . it would just be ... i 'd just have diagonally polarized light . this is n't giving me anything new . you might think this is dumb . why do this ? why send in two different waves to just get diagonally polarized light ? i could have just sent in one wave that was diagonally polarized and got the same thing . the reason is , if you shift this purple wave , this pink wave , by 90 degrees of phase , by pi over two in phase , something magical happens . let me show you what happens here , if we move this to here . now we do n't just get diagonally linear polarized light . what we 're going to get is ... let me get rid of this . okay , so we start off with red , right ? the red electric field points up , and then this pink wave 's electric field is zero at that point . so this is all i have . my total electric field would just be up . i 'm going to draw it right here . the green 'll be the total . now i come over to here , and at this point , there 's some red electric field that points up , but there 's some of this other electric field that points this way . so i 'd have a total electric field that would point that way . and then i get over to here , and i 'd have all of the electric field from the pink one , none from the red one . it would point all left then . look what 's happening . the polarization of this light , if i shift this , if i 'm sitting here , looking with my eye , as my eye receives this light , i 'm going to see this light rotate its polarization . the polarization i 'm going to notice swings around in a circular pattern . and because of this , we call this circular polarization . so this is another type of polarization , where the actual angle of polarization rotates smoothly as this light ray enters your eye . and you know what ? er , drrr ... all right , actually , i sent you to receive this one first . that makes no sense . you 're going to receive the ones closes to you first in this light ray going this way . so you 'd actually receive this one first , then that one , then this one , then this one . because of that , you would n't see this going in a counterclockwise way , you 'd see this going in a clockwise circularly polarized way . sorry about that . you might think , `` okay , why ? `` why even bother with circular polarization ? '' well , i kind of lied earlier . turns out , in the movie theater example , they do n't actually do it like this , typically . oftentimes in the movie theaters , we do n't have just linearly polarized sunglasses . this would be a problem because , when you look at the movie theater screen , and if you were to tilt your head just a little bit ... think about it . this one 's not really going to get the right image anymore . it 's going to get some of both . and this one 's going to get some of both . it 's going to be blurry . your head would have to be perfectly level the whole time , which might be annoying . so what we do is , instead , we create circular polarized glasses , so that this one would only get one polarization , this one would get the other direction . this way , even if you tilt your head a little bit ... shoot , clockwise is clockwise , counterclockwise is counterclockwise . by using circular polarization for 3d movies , it can make it a little easier on you eyes to see a better 3d image , even if your head 's tilted a little bit .
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- let 's talk about polarization of light . we know what light waves are ; they 're electromagnetic waves . so they 're made out of electric fields .
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in un-polarised light , do the electric and magnetic waves which are in the same plane undergo constructive superposition ?
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- let 's talk about polarization of light . we know what light waves are ; they 're electromagnetic waves . so they 're made out of electric fields . and that 's not good enough . we know there 's not just electric fields . that could n't sustain itself . there 's got to be magnetic fields there , as well , that are changing . those are perpendicular , so you can kind of draw them . it 's hard , on something two-dimensional , but you can kind of imagine those looking something like this . and those magnetic fields would point at a right angle to the electric fields . but this gets really messy if i try to draw both the electric and magnetic fields at the same time . so we 're going to leave the magnetic fields out . it 's often good enough to just know the direction of the electric field when we focus on the electric field . so what does polarization mean ? polarization refers to the fact that , if this light ray was heading straight toward your eye , or a detector , over here , what would you see ? well , if i draw an axis over here , and this point here , in the middle , this is this line -- so imagine we 're looking straight down that line -- and then up and down is up and down , and then left and right , that direction i have the magnetic field , would be this way and that way . what would my eye see ? well , my eye 's only going to see electric fields that either point up or electric fields that point down . they might have different values , but i 'm only going to see electric fields that point up or down . because of that , this light ray is polarized . so polarized light is light where the electric field is only oscillating in one direction . up or down , that 's one direction -- vertically . or it could be polarized horizontally . or it could be polarized diagonally . but either way , you could have this wave polarized along any direction . i mean , a light ray like this , if we had it coming in diagonal , this light ray that 's oscillating like this , where the electric field oscillates like that , that also polarized . these are both polarized because there 's only one direction that the electric field is oscillating in . and you might thing , `` pff , how could you ever have `` a light ray that 's not polarized ? '' easy . most light that you get is not polarized . that is to say , light that 's coming from the sun , straight from the sun -- typically not polarized . light from a lightbulb , an old incandescent light bulb , this thing 's hot . you can get light polarized in any direction , all at once , all overlapping . so if we draw this case for a light bulb , just a random incandescent light bulb , you might get light , some of the light , hitting you eye , you can get some light that 's got that direction , you got light that 's got this direction , you got light in all these directions at any given moment . i mean , you 'd have to add these up to get the total , and they might not all be the same value . but what i 'm trying to say is , at any given moment , you do n't know what direction the electric field 's going to be hitting your eye at from a random source . it could be in any direction . so this is not polarized . this diagram represents light that is not polarized . at some point , the field might be pointing this way , at some later point it 's this way ; it 's just random . you never know which way the electric field 's going to be pointing . whereas these over here , these are polarized . so how could you polarize this light ? let 's say you wanted light that was polarized . you were doing an experiment . you needed polarized light . well , that 's easy . you can use what 's called a polarizer . and this is a material that lets light through , but it only lets light through in one orientation , so you 're going to have a polarizer that , for instance , only lets through vertically polarized light . so this is a polarizer . these are cheap : thin , plastic , configured in a way so that it only lets light through that 's vertically polarized . any light coming in here that 's not vertically polarized gets blocked , or absorbed . so what that means is , if you used this polarizer and held it in between your eye and this light bulb , you would only get this light . all the rest of it would get blocked . or you could just rotate this thing and imagine a polarizer that only lets through horizontal light . now it would only let through light that was this way , and so you would only get this part of the light . or you could just orient it at any angle you want and block everything but the certain angle that this polarizer is defined as letting light through . so you can do this . and once you hold this up , you get polarized light , light that 's only got one orientation . so that 's what polarization means . but why do we care about polarization ? well , let me get rid of this for a minute . you 've heard of polarized sunglasses . so imagine you 're standing near water , or maybe you 're standing on ice or snow or something reflective . there 's a problem . say the sun 's out . it 's shining . it 's a beautiful day -- except there 's going to be glare . let 's say you 're looking down at something here on the ground . it 's going to get light reflecting off of it from just ... you know , light 's coming in from all direction . but it also gets this direct light from the sun . so it gets light from reflected off the clouds and whatever , whatever 's nearby , ambient light . and there 's also this direct sunlight . that 's harsh . if that reflects straight up to your eye , that hurts . you do n't like that . it blocks our vision . it 's hard to see , it 's glare . we do n't want this glare . so what can we do ? well , it just so happens that , when light reflects off of a surface , even though the light from the sun is not polarized , once it reflects , it does get polarized or at least partially polarized . so this surface here , once this light reflects , it 's coming in at all orientations . you got electric field ... you never know what electric field you 're going to get straight from the sun . and when it reflects , though , you mostly get , upon reflection , the direction of polarization defined by the plane of the surface that it hit . so because the floor is horizontal , when this light ray hits the ground and reflects , that reflected light gets partially polarized . this horizontal component of the electric field is going to be more present than the other components . maybe not completely . sometimes it could be . it could be completely polarized , but often it 's just partially polarized . but that 's pretty cool , because now you know what we can do . i know how to block this . we should get some sunglasses . we put some sunglasses on and we make our glasses so that these are polarized . and how do we want these polarized ? i want to get rid of the glare . so what i do is , i make sure my sunglasses only let through vertically polarized light . here 's some polarizers . that way , a lot of this glare gets blocked because it does not have a vertical orientation , it has a horizontal orientation . and then we can block it . so that 's one good thing that polarization does for us , and understanding it , we can get rid of glare . also , fishermen like it because , if you 're trying to look in the water at fish , you want to see in through the water , you want to see this light from the fish getting to you . you do n't want to see the glare off of the sun getting to you . so polarized sunglasses are useful . also , we can play a trick on our eye , if we really wanted to . you could take one of these , make one eye have a vertical orientation for the polarization , have the other eye with a horizontal ... and you 're thinking , `` this is stupid . `` why would you do this for ? '' `` this eye 's going to get a lot of glare . '' we would n't use these outside , when you 're , like , skiing or fishing , but you could play a trick on your eyes if you went to the movies and you went and watched a movie . well , the reason our eyes see 3d is because they 're spaced a little bit apart . they each get a different , slightly different image . that makes us see in 3d . we can play the same trick on our eye if we have the polarization like this . if light , if some of the light from the movie theater screen is coming in with one polarization , and the other light 's coming in with the other polarization , we can send two different images to our eyes at the same time . if you took these off , it 'd look like garbage because you 'd be getting both of these slightly different images , it 'd look all blurry . and it does . if you take off your 3d glasses and look at a 3d movie , looks terrible , because now both eyes are getting both images . but if you put your glasses back on , now this eye only gets the orientation that it 's supposed to get , and this eye only gets the orientation that it 's supposed to get , and you get a 3d image . so it 's useful in many ways . let me show you one more thing here . let 's come back here . this light was polarized vertically . so that 's called linear polarization . any time ... same with these . these are all linear polarization because , just up and down , one linear direction , just diagonal . this is also linear . all of these are linear . you can get circular polarized light . so if we come back to here , we 've got our electric field pointing up , like that . now let 's say we sent in another light ray , another light ray that also had a polarization , but not in this direction . let 's say our other light ray had polarization in this direction , so it looks like this , kind of like what our magnetic field would have looked like . but this is a completely different light ray with its own polarization and its own magnetic field . so we send this in . what would happen ? well , at this point , you 'd have a electric field that points this way . at this point , you 'd have a electric field that points that way . what would your eye see if you were over here ? let 's see . if i draw our axis here . all right , when this point right here gets to your eye , what am i going to see ? well , i 'm going to have a light ray that 's one part of a light ray . one component points up . that 's this electric field . one component points left . that 's this electric field . so the total , my total electric field , would point this way . i could to the pythagorean theorem if i wanted to figure out the size of it , but i just want to know the direction for now . and then it gets to here , and look at it : they both have zero . this light ray has zero electric field , this one has zero electric fields . so then it 'd just be at zero . now what happens over here ? well , i 've got light . this one points to the right at that point , this pink one , and then this red one would be pointing down . so what would i have at that point ? i 'd have light that went this way , and it would just be doing this over and over . it would just be ... i 'd just have diagonally polarized light . this is n't giving me anything new . you might think this is dumb . why do this ? why send in two different waves to just get diagonally polarized light ? i could have just sent in one wave that was diagonally polarized and got the same thing . the reason is , if you shift this purple wave , this pink wave , by 90 degrees of phase , by pi over two in phase , something magical happens . let me show you what happens here , if we move this to here . now we do n't just get diagonally linear polarized light . what we 're going to get is ... let me get rid of this . okay , so we start off with red , right ? the red electric field points up , and then this pink wave 's electric field is zero at that point . so this is all i have . my total electric field would just be up . i 'm going to draw it right here . the green 'll be the total . now i come over to here , and at this point , there 's some red electric field that points up , but there 's some of this other electric field that points this way . so i 'd have a total electric field that would point that way . and then i get over to here , and i 'd have all of the electric field from the pink one , none from the red one . it would point all left then . look what 's happening . the polarization of this light , if i shift this , if i 'm sitting here , looking with my eye , as my eye receives this light , i 'm going to see this light rotate its polarization . the polarization i 'm going to notice swings around in a circular pattern . and because of this , we call this circular polarization . so this is another type of polarization , where the actual angle of polarization rotates smoothly as this light ray enters your eye . and you know what ? er , drrr ... all right , actually , i sent you to receive this one first . that makes no sense . you 're going to receive the ones closes to you first in this light ray going this way . so you 'd actually receive this one first , then that one , then this one , then this one . because of that , you would n't see this going in a counterclockwise way , you 'd see this going in a clockwise circularly polarized way . sorry about that . you might think , `` okay , why ? `` why even bother with circular polarization ? '' well , i kind of lied earlier . turns out , in the movie theater example , they do n't actually do it like this , typically . oftentimes in the movie theaters , we do n't have just linearly polarized sunglasses . this would be a problem because , when you look at the movie theater screen , and if you were to tilt your head just a little bit ... think about it . this one 's not really going to get the right image anymore . it 's going to get some of both . and this one 's going to get some of both . it 's going to be blurry . your head would have to be perfectly level the whole time , which might be annoying . so what we do is , instead , we create circular polarized glasses , so that this one would only get one polarization , this one would get the other direction . this way , even if you tilt your head a little bit ... shoot , clockwise is clockwise , counterclockwise is counterclockwise . by using circular polarization for 3d movies , it can make it a little easier on you eyes to see a better 3d image , even if your head 's tilted a little bit .
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so this is a polarizer . these are cheap : thin , plastic , configured in a way so that it only lets light through that 's vertically polarized . any light coming in here that 's not vertically polarized gets blocked , or absorbed .
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how does the plastic limit it 's polarity ?
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- let 's talk about polarization of light . we know what light waves are ; they 're electromagnetic waves . so they 're made out of electric fields . and that 's not good enough . we know there 's not just electric fields . that could n't sustain itself . there 's got to be magnetic fields there , as well , that are changing . those are perpendicular , so you can kind of draw them . it 's hard , on something two-dimensional , but you can kind of imagine those looking something like this . and those magnetic fields would point at a right angle to the electric fields . but this gets really messy if i try to draw both the electric and magnetic fields at the same time . so we 're going to leave the magnetic fields out . it 's often good enough to just know the direction of the electric field when we focus on the electric field . so what does polarization mean ? polarization refers to the fact that , if this light ray was heading straight toward your eye , or a detector , over here , what would you see ? well , if i draw an axis over here , and this point here , in the middle , this is this line -- so imagine we 're looking straight down that line -- and then up and down is up and down , and then left and right , that direction i have the magnetic field , would be this way and that way . what would my eye see ? well , my eye 's only going to see electric fields that either point up or electric fields that point down . they might have different values , but i 'm only going to see electric fields that point up or down . because of that , this light ray is polarized . so polarized light is light where the electric field is only oscillating in one direction . up or down , that 's one direction -- vertically . or it could be polarized horizontally . or it could be polarized diagonally . but either way , you could have this wave polarized along any direction . i mean , a light ray like this , if we had it coming in diagonal , this light ray that 's oscillating like this , where the electric field oscillates like that , that also polarized . these are both polarized because there 's only one direction that the electric field is oscillating in . and you might thing , `` pff , how could you ever have `` a light ray that 's not polarized ? '' easy . most light that you get is not polarized . that is to say , light that 's coming from the sun , straight from the sun -- typically not polarized . light from a lightbulb , an old incandescent light bulb , this thing 's hot . you can get light polarized in any direction , all at once , all overlapping . so if we draw this case for a light bulb , just a random incandescent light bulb , you might get light , some of the light , hitting you eye , you can get some light that 's got that direction , you got light that 's got this direction , you got light in all these directions at any given moment . i mean , you 'd have to add these up to get the total , and they might not all be the same value . but what i 'm trying to say is , at any given moment , you do n't know what direction the electric field 's going to be hitting your eye at from a random source . it could be in any direction . so this is not polarized . this diagram represents light that is not polarized . at some point , the field might be pointing this way , at some later point it 's this way ; it 's just random . you never know which way the electric field 's going to be pointing . whereas these over here , these are polarized . so how could you polarize this light ? let 's say you wanted light that was polarized . you were doing an experiment . you needed polarized light . well , that 's easy . you can use what 's called a polarizer . and this is a material that lets light through , but it only lets light through in one orientation , so you 're going to have a polarizer that , for instance , only lets through vertically polarized light . so this is a polarizer . these are cheap : thin , plastic , configured in a way so that it only lets light through that 's vertically polarized . any light coming in here that 's not vertically polarized gets blocked , or absorbed . so what that means is , if you used this polarizer and held it in between your eye and this light bulb , you would only get this light . all the rest of it would get blocked . or you could just rotate this thing and imagine a polarizer that only lets through horizontal light . now it would only let through light that was this way , and so you would only get this part of the light . or you could just orient it at any angle you want and block everything but the certain angle that this polarizer is defined as letting light through . so you can do this . and once you hold this up , you get polarized light , light that 's only got one orientation . so that 's what polarization means . but why do we care about polarization ? well , let me get rid of this for a minute . you 've heard of polarized sunglasses . so imagine you 're standing near water , or maybe you 're standing on ice or snow or something reflective . there 's a problem . say the sun 's out . it 's shining . it 's a beautiful day -- except there 's going to be glare . let 's say you 're looking down at something here on the ground . it 's going to get light reflecting off of it from just ... you know , light 's coming in from all direction . but it also gets this direct light from the sun . so it gets light from reflected off the clouds and whatever , whatever 's nearby , ambient light . and there 's also this direct sunlight . that 's harsh . if that reflects straight up to your eye , that hurts . you do n't like that . it blocks our vision . it 's hard to see , it 's glare . we do n't want this glare . so what can we do ? well , it just so happens that , when light reflects off of a surface , even though the light from the sun is not polarized , once it reflects , it does get polarized or at least partially polarized . so this surface here , once this light reflects , it 's coming in at all orientations . you got electric field ... you never know what electric field you 're going to get straight from the sun . and when it reflects , though , you mostly get , upon reflection , the direction of polarization defined by the plane of the surface that it hit . so because the floor is horizontal , when this light ray hits the ground and reflects , that reflected light gets partially polarized . this horizontal component of the electric field is going to be more present than the other components . maybe not completely . sometimes it could be . it could be completely polarized , but often it 's just partially polarized . but that 's pretty cool , because now you know what we can do . i know how to block this . we should get some sunglasses . we put some sunglasses on and we make our glasses so that these are polarized . and how do we want these polarized ? i want to get rid of the glare . so what i do is , i make sure my sunglasses only let through vertically polarized light . here 's some polarizers . that way , a lot of this glare gets blocked because it does not have a vertical orientation , it has a horizontal orientation . and then we can block it . so that 's one good thing that polarization does for us , and understanding it , we can get rid of glare . also , fishermen like it because , if you 're trying to look in the water at fish , you want to see in through the water , you want to see this light from the fish getting to you . you do n't want to see the glare off of the sun getting to you . so polarized sunglasses are useful . also , we can play a trick on our eye , if we really wanted to . you could take one of these , make one eye have a vertical orientation for the polarization , have the other eye with a horizontal ... and you 're thinking , `` this is stupid . `` why would you do this for ? '' `` this eye 's going to get a lot of glare . '' we would n't use these outside , when you 're , like , skiing or fishing , but you could play a trick on your eyes if you went to the movies and you went and watched a movie . well , the reason our eyes see 3d is because they 're spaced a little bit apart . they each get a different , slightly different image . that makes us see in 3d . we can play the same trick on our eye if we have the polarization like this . if light , if some of the light from the movie theater screen is coming in with one polarization , and the other light 's coming in with the other polarization , we can send two different images to our eyes at the same time . if you took these off , it 'd look like garbage because you 'd be getting both of these slightly different images , it 'd look all blurry . and it does . if you take off your 3d glasses and look at a 3d movie , looks terrible , because now both eyes are getting both images . but if you put your glasses back on , now this eye only gets the orientation that it 's supposed to get , and this eye only gets the orientation that it 's supposed to get , and you get a 3d image . so it 's useful in many ways . let me show you one more thing here . let 's come back here . this light was polarized vertically . so that 's called linear polarization . any time ... same with these . these are all linear polarization because , just up and down , one linear direction , just diagonal . this is also linear . all of these are linear . you can get circular polarized light . so if we come back to here , we 've got our electric field pointing up , like that . now let 's say we sent in another light ray , another light ray that also had a polarization , but not in this direction . let 's say our other light ray had polarization in this direction , so it looks like this , kind of like what our magnetic field would have looked like . but this is a completely different light ray with its own polarization and its own magnetic field . so we send this in . what would happen ? well , at this point , you 'd have a electric field that points this way . at this point , you 'd have a electric field that points that way . what would your eye see if you were over here ? let 's see . if i draw our axis here . all right , when this point right here gets to your eye , what am i going to see ? well , i 'm going to have a light ray that 's one part of a light ray . one component points up . that 's this electric field . one component points left . that 's this electric field . so the total , my total electric field , would point this way . i could to the pythagorean theorem if i wanted to figure out the size of it , but i just want to know the direction for now . and then it gets to here , and look at it : they both have zero . this light ray has zero electric field , this one has zero electric fields . so then it 'd just be at zero . now what happens over here ? well , i 've got light . this one points to the right at that point , this pink one , and then this red one would be pointing down . so what would i have at that point ? i 'd have light that went this way , and it would just be doing this over and over . it would just be ... i 'd just have diagonally polarized light . this is n't giving me anything new . you might think this is dumb . why do this ? why send in two different waves to just get diagonally polarized light ? i could have just sent in one wave that was diagonally polarized and got the same thing . the reason is , if you shift this purple wave , this pink wave , by 90 degrees of phase , by pi over two in phase , something magical happens . let me show you what happens here , if we move this to here . now we do n't just get diagonally linear polarized light . what we 're going to get is ... let me get rid of this . okay , so we start off with red , right ? the red electric field points up , and then this pink wave 's electric field is zero at that point . so this is all i have . my total electric field would just be up . i 'm going to draw it right here . the green 'll be the total . now i come over to here , and at this point , there 's some red electric field that points up , but there 's some of this other electric field that points this way . so i 'd have a total electric field that would point that way . and then i get over to here , and i 'd have all of the electric field from the pink one , none from the red one . it would point all left then . look what 's happening . the polarization of this light , if i shift this , if i 'm sitting here , looking with my eye , as my eye receives this light , i 'm going to see this light rotate its polarization . the polarization i 'm going to notice swings around in a circular pattern . and because of this , we call this circular polarization . so this is another type of polarization , where the actual angle of polarization rotates smoothly as this light ray enters your eye . and you know what ? er , drrr ... all right , actually , i sent you to receive this one first . that makes no sense . you 're going to receive the ones closes to you first in this light ray going this way . so you 'd actually receive this one first , then that one , then this one , then this one . because of that , you would n't see this going in a counterclockwise way , you 'd see this going in a clockwise circularly polarized way . sorry about that . you might think , `` okay , why ? `` why even bother with circular polarization ? '' well , i kind of lied earlier . turns out , in the movie theater example , they do n't actually do it like this , typically . oftentimes in the movie theaters , we do n't have just linearly polarized sunglasses . this would be a problem because , when you look at the movie theater screen , and if you were to tilt your head just a little bit ... think about it . this one 's not really going to get the right image anymore . it 's going to get some of both . and this one 's going to get some of both . it 's going to be blurry . your head would have to be perfectly level the whole time , which might be annoying . so what we do is , instead , we create circular polarized glasses , so that this one would only get one polarization , this one would get the other direction . this way , even if you tilt your head a little bit ... shoot , clockwise is clockwise , counterclockwise is counterclockwise . by using circular polarization for 3d movies , it can make it a little easier on you eyes to see a better 3d image , even if your head 's tilted a little bit .
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why do this ? why send in two different waves to just get diagonally polarized light ? i could have just sent in one wave that was diagonally polarized and got the same thing .
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in the last concept , if i send two differently polarized light with phase difference of pi/2 what will i see ?
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- let 's talk about polarization of light . we know what light waves are ; they 're electromagnetic waves . so they 're made out of electric fields . and that 's not good enough . we know there 's not just electric fields . that could n't sustain itself . there 's got to be magnetic fields there , as well , that are changing . those are perpendicular , so you can kind of draw them . it 's hard , on something two-dimensional , but you can kind of imagine those looking something like this . and those magnetic fields would point at a right angle to the electric fields . but this gets really messy if i try to draw both the electric and magnetic fields at the same time . so we 're going to leave the magnetic fields out . it 's often good enough to just know the direction of the electric field when we focus on the electric field . so what does polarization mean ? polarization refers to the fact that , if this light ray was heading straight toward your eye , or a detector , over here , what would you see ? well , if i draw an axis over here , and this point here , in the middle , this is this line -- so imagine we 're looking straight down that line -- and then up and down is up and down , and then left and right , that direction i have the magnetic field , would be this way and that way . what would my eye see ? well , my eye 's only going to see electric fields that either point up or electric fields that point down . they might have different values , but i 'm only going to see electric fields that point up or down . because of that , this light ray is polarized . so polarized light is light where the electric field is only oscillating in one direction . up or down , that 's one direction -- vertically . or it could be polarized horizontally . or it could be polarized diagonally . but either way , you could have this wave polarized along any direction . i mean , a light ray like this , if we had it coming in diagonal , this light ray that 's oscillating like this , where the electric field oscillates like that , that also polarized . these are both polarized because there 's only one direction that the electric field is oscillating in . and you might thing , `` pff , how could you ever have `` a light ray that 's not polarized ? '' easy . most light that you get is not polarized . that is to say , light that 's coming from the sun , straight from the sun -- typically not polarized . light from a lightbulb , an old incandescent light bulb , this thing 's hot . you can get light polarized in any direction , all at once , all overlapping . so if we draw this case for a light bulb , just a random incandescent light bulb , you might get light , some of the light , hitting you eye , you can get some light that 's got that direction , you got light that 's got this direction , you got light in all these directions at any given moment . i mean , you 'd have to add these up to get the total , and they might not all be the same value . but what i 'm trying to say is , at any given moment , you do n't know what direction the electric field 's going to be hitting your eye at from a random source . it could be in any direction . so this is not polarized . this diagram represents light that is not polarized . at some point , the field might be pointing this way , at some later point it 's this way ; it 's just random . you never know which way the electric field 's going to be pointing . whereas these over here , these are polarized . so how could you polarize this light ? let 's say you wanted light that was polarized . you were doing an experiment . you needed polarized light . well , that 's easy . you can use what 's called a polarizer . and this is a material that lets light through , but it only lets light through in one orientation , so you 're going to have a polarizer that , for instance , only lets through vertically polarized light . so this is a polarizer . these are cheap : thin , plastic , configured in a way so that it only lets light through that 's vertically polarized . any light coming in here that 's not vertically polarized gets blocked , or absorbed . so what that means is , if you used this polarizer and held it in between your eye and this light bulb , you would only get this light . all the rest of it would get blocked . or you could just rotate this thing and imagine a polarizer that only lets through horizontal light . now it would only let through light that was this way , and so you would only get this part of the light . or you could just orient it at any angle you want and block everything but the certain angle that this polarizer is defined as letting light through . so you can do this . and once you hold this up , you get polarized light , light that 's only got one orientation . so that 's what polarization means . but why do we care about polarization ? well , let me get rid of this for a minute . you 've heard of polarized sunglasses . so imagine you 're standing near water , or maybe you 're standing on ice or snow or something reflective . there 's a problem . say the sun 's out . it 's shining . it 's a beautiful day -- except there 's going to be glare . let 's say you 're looking down at something here on the ground . it 's going to get light reflecting off of it from just ... you know , light 's coming in from all direction . but it also gets this direct light from the sun . so it gets light from reflected off the clouds and whatever , whatever 's nearby , ambient light . and there 's also this direct sunlight . that 's harsh . if that reflects straight up to your eye , that hurts . you do n't like that . it blocks our vision . it 's hard to see , it 's glare . we do n't want this glare . so what can we do ? well , it just so happens that , when light reflects off of a surface , even though the light from the sun is not polarized , once it reflects , it does get polarized or at least partially polarized . so this surface here , once this light reflects , it 's coming in at all orientations . you got electric field ... you never know what electric field you 're going to get straight from the sun . and when it reflects , though , you mostly get , upon reflection , the direction of polarization defined by the plane of the surface that it hit . so because the floor is horizontal , when this light ray hits the ground and reflects , that reflected light gets partially polarized . this horizontal component of the electric field is going to be more present than the other components . maybe not completely . sometimes it could be . it could be completely polarized , but often it 's just partially polarized . but that 's pretty cool , because now you know what we can do . i know how to block this . we should get some sunglasses . we put some sunglasses on and we make our glasses so that these are polarized . and how do we want these polarized ? i want to get rid of the glare . so what i do is , i make sure my sunglasses only let through vertically polarized light . here 's some polarizers . that way , a lot of this glare gets blocked because it does not have a vertical orientation , it has a horizontal orientation . and then we can block it . so that 's one good thing that polarization does for us , and understanding it , we can get rid of glare . also , fishermen like it because , if you 're trying to look in the water at fish , you want to see in through the water , you want to see this light from the fish getting to you . you do n't want to see the glare off of the sun getting to you . so polarized sunglasses are useful . also , we can play a trick on our eye , if we really wanted to . you could take one of these , make one eye have a vertical orientation for the polarization , have the other eye with a horizontal ... and you 're thinking , `` this is stupid . `` why would you do this for ? '' `` this eye 's going to get a lot of glare . '' we would n't use these outside , when you 're , like , skiing or fishing , but you could play a trick on your eyes if you went to the movies and you went and watched a movie . well , the reason our eyes see 3d is because they 're spaced a little bit apart . they each get a different , slightly different image . that makes us see in 3d . we can play the same trick on our eye if we have the polarization like this . if light , if some of the light from the movie theater screen is coming in with one polarization , and the other light 's coming in with the other polarization , we can send two different images to our eyes at the same time . if you took these off , it 'd look like garbage because you 'd be getting both of these slightly different images , it 'd look all blurry . and it does . if you take off your 3d glasses and look at a 3d movie , looks terrible , because now both eyes are getting both images . but if you put your glasses back on , now this eye only gets the orientation that it 's supposed to get , and this eye only gets the orientation that it 's supposed to get , and you get a 3d image . so it 's useful in many ways . let me show you one more thing here . let 's come back here . this light was polarized vertically . so that 's called linear polarization . any time ... same with these . these are all linear polarization because , just up and down , one linear direction , just diagonal . this is also linear . all of these are linear . you can get circular polarized light . so if we come back to here , we 've got our electric field pointing up , like that . now let 's say we sent in another light ray , another light ray that also had a polarization , but not in this direction . let 's say our other light ray had polarization in this direction , so it looks like this , kind of like what our magnetic field would have looked like . but this is a completely different light ray with its own polarization and its own magnetic field . so we send this in . what would happen ? well , at this point , you 'd have a electric field that points this way . at this point , you 'd have a electric field that points that way . what would your eye see if you were over here ? let 's see . if i draw our axis here . all right , when this point right here gets to your eye , what am i going to see ? well , i 'm going to have a light ray that 's one part of a light ray . one component points up . that 's this electric field . one component points left . that 's this electric field . so the total , my total electric field , would point this way . i could to the pythagorean theorem if i wanted to figure out the size of it , but i just want to know the direction for now . and then it gets to here , and look at it : they both have zero . this light ray has zero electric field , this one has zero electric fields . so then it 'd just be at zero . now what happens over here ? well , i 've got light . this one points to the right at that point , this pink one , and then this red one would be pointing down . so what would i have at that point ? i 'd have light that went this way , and it would just be doing this over and over . it would just be ... i 'd just have diagonally polarized light . this is n't giving me anything new . you might think this is dumb . why do this ? why send in two different waves to just get diagonally polarized light ? i could have just sent in one wave that was diagonally polarized and got the same thing . the reason is , if you shift this purple wave , this pink wave , by 90 degrees of phase , by pi over two in phase , something magical happens . let me show you what happens here , if we move this to here . now we do n't just get diagonally linear polarized light . what we 're going to get is ... let me get rid of this . okay , so we start off with red , right ? the red electric field points up , and then this pink wave 's electric field is zero at that point . so this is all i have . my total electric field would just be up . i 'm going to draw it right here . the green 'll be the total . now i come over to here , and at this point , there 's some red electric field that points up , but there 's some of this other electric field that points this way . so i 'd have a total electric field that would point that way . and then i get over to here , and i 'd have all of the electric field from the pink one , none from the red one . it would point all left then . look what 's happening . the polarization of this light , if i shift this , if i 'm sitting here , looking with my eye , as my eye receives this light , i 'm going to see this light rotate its polarization . the polarization i 'm going to notice swings around in a circular pattern . and because of this , we call this circular polarization . so this is another type of polarization , where the actual angle of polarization rotates smoothly as this light ray enters your eye . and you know what ? er , drrr ... all right , actually , i sent you to receive this one first . that makes no sense . you 're going to receive the ones closes to you first in this light ray going this way . so you 'd actually receive this one first , then that one , then this one , then this one . because of that , you would n't see this going in a counterclockwise way , you 'd see this going in a clockwise circularly polarized way . sorry about that . you might think , `` okay , why ? `` why even bother with circular polarization ? '' well , i kind of lied earlier . turns out , in the movie theater example , they do n't actually do it like this , typically . oftentimes in the movie theaters , we do n't have just linearly polarized sunglasses . this would be a problem because , when you look at the movie theater screen , and if you were to tilt your head just a little bit ... think about it . this one 's not really going to get the right image anymore . it 's going to get some of both . and this one 's going to get some of both . it 's going to be blurry . your head would have to be perfectly level the whole time , which might be annoying . so what we do is , instead , we create circular polarized glasses , so that this one would only get one polarization , this one would get the other direction . this way , even if you tilt your head a little bit ... shoot , clockwise is clockwise , counterclockwise is counterclockwise . by using circular polarization for 3d movies , it can make it a little easier on you eyes to see a better 3d image , even if your head 's tilted a little bit .
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you do n't want to see the glare off of the sun getting to you . so polarized sunglasses are useful . also , we can play a trick on our eye , if we really wanted to .
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what 's the difference between polarized sunglasses and regular sunglasses ?
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- let 's talk about polarization of light . we know what light waves are ; they 're electromagnetic waves . so they 're made out of electric fields . and that 's not good enough . we know there 's not just electric fields . that could n't sustain itself . there 's got to be magnetic fields there , as well , that are changing . those are perpendicular , so you can kind of draw them . it 's hard , on something two-dimensional , but you can kind of imagine those looking something like this . and those magnetic fields would point at a right angle to the electric fields . but this gets really messy if i try to draw both the electric and magnetic fields at the same time . so we 're going to leave the magnetic fields out . it 's often good enough to just know the direction of the electric field when we focus on the electric field . so what does polarization mean ? polarization refers to the fact that , if this light ray was heading straight toward your eye , or a detector , over here , what would you see ? well , if i draw an axis over here , and this point here , in the middle , this is this line -- so imagine we 're looking straight down that line -- and then up and down is up and down , and then left and right , that direction i have the magnetic field , would be this way and that way . what would my eye see ? well , my eye 's only going to see electric fields that either point up or electric fields that point down . they might have different values , but i 'm only going to see electric fields that point up or down . because of that , this light ray is polarized . so polarized light is light where the electric field is only oscillating in one direction . up or down , that 's one direction -- vertically . or it could be polarized horizontally . or it could be polarized diagonally . but either way , you could have this wave polarized along any direction . i mean , a light ray like this , if we had it coming in diagonal , this light ray that 's oscillating like this , where the electric field oscillates like that , that also polarized . these are both polarized because there 's only one direction that the electric field is oscillating in . and you might thing , `` pff , how could you ever have `` a light ray that 's not polarized ? '' easy . most light that you get is not polarized . that is to say , light that 's coming from the sun , straight from the sun -- typically not polarized . light from a lightbulb , an old incandescent light bulb , this thing 's hot . you can get light polarized in any direction , all at once , all overlapping . so if we draw this case for a light bulb , just a random incandescent light bulb , you might get light , some of the light , hitting you eye , you can get some light that 's got that direction , you got light that 's got this direction , you got light in all these directions at any given moment . i mean , you 'd have to add these up to get the total , and they might not all be the same value . but what i 'm trying to say is , at any given moment , you do n't know what direction the electric field 's going to be hitting your eye at from a random source . it could be in any direction . so this is not polarized . this diagram represents light that is not polarized . at some point , the field might be pointing this way , at some later point it 's this way ; it 's just random . you never know which way the electric field 's going to be pointing . whereas these over here , these are polarized . so how could you polarize this light ? let 's say you wanted light that was polarized . you were doing an experiment . you needed polarized light . well , that 's easy . you can use what 's called a polarizer . and this is a material that lets light through , but it only lets light through in one orientation , so you 're going to have a polarizer that , for instance , only lets through vertically polarized light . so this is a polarizer . these are cheap : thin , plastic , configured in a way so that it only lets light through that 's vertically polarized . any light coming in here that 's not vertically polarized gets blocked , or absorbed . so what that means is , if you used this polarizer and held it in between your eye and this light bulb , you would only get this light . all the rest of it would get blocked . or you could just rotate this thing and imagine a polarizer that only lets through horizontal light . now it would only let through light that was this way , and so you would only get this part of the light . or you could just orient it at any angle you want and block everything but the certain angle that this polarizer is defined as letting light through . so you can do this . and once you hold this up , you get polarized light , light that 's only got one orientation . so that 's what polarization means . but why do we care about polarization ? well , let me get rid of this for a minute . you 've heard of polarized sunglasses . so imagine you 're standing near water , or maybe you 're standing on ice or snow or something reflective . there 's a problem . say the sun 's out . it 's shining . it 's a beautiful day -- except there 's going to be glare . let 's say you 're looking down at something here on the ground . it 's going to get light reflecting off of it from just ... you know , light 's coming in from all direction . but it also gets this direct light from the sun . so it gets light from reflected off the clouds and whatever , whatever 's nearby , ambient light . and there 's also this direct sunlight . that 's harsh . if that reflects straight up to your eye , that hurts . you do n't like that . it blocks our vision . it 's hard to see , it 's glare . we do n't want this glare . so what can we do ? well , it just so happens that , when light reflects off of a surface , even though the light from the sun is not polarized , once it reflects , it does get polarized or at least partially polarized . so this surface here , once this light reflects , it 's coming in at all orientations . you got electric field ... you never know what electric field you 're going to get straight from the sun . and when it reflects , though , you mostly get , upon reflection , the direction of polarization defined by the plane of the surface that it hit . so because the floor is horizontal , when this light ray hits the ground and reflects , that reflected light gets partially polarized . this horizontal component of the electric field is going to be more present than the other components . maybe not completely . sometimes it could be . it could be completely polarized , but often it 's just partially polarized . but that 's pretty cool , because now you know what we can do . i know how to block this . we should get some sunglasses . we put some sunglasses on and we make our glasses so that these are polarized . and how do we want these polarized ? i want to get rid of the glare . so what i do is , i make sure my sunglasses only let through vertically polarized light . here 's some polarizers . that way , a lot of this glare gets blocked because it does not have a vertical orientation , it has a horizontal orientation . and then we can block it . so that 's one good thing that polarization does for us , and understanding it , we can get rid of glare . also , fishermen like it because , if you 're trying to look in the water at fish , you want to see in through the water , you want to see this light from the fish getting to you . you do n't want to see the glare off of the sun getting to you . so polarized sunglasses are useful . also , we can play a trick on our eye , if we really wanted to . you could take one of these , make one eye have a vertical orientation for the polarization , have the other eye with a horizontal ... and you 're thinking , `` this is stupid . `` why would you do this for ? '' `` this eye 's going to get a lot of glare . '' we would n't use these outside , when you 're , like , skiing or fishing , but you could play a trick on your eyes if you went to the movies and you went and watched a movie . well , the reason our eyes see 3d is because they 're spaced a little bit apart . they each get a different , slightly different image . that makes us see in 3d . we can play the same trick on our eye if we have the polarization like this . if light , if some of the light from the movie theater screen is coming in with one polarization , and the other light 's coming in with the other polarization , we can send two different images to our eyes at the same time . if you took these off , it 'd look like garbage because you 'd be getting both of these slightly different images , it 'd look all blurry . and it does . if you take off your 3d glasses and look at a 3d movie , looks terrible , because now both eyes are getting both images . but if you put your glasses back on , now this eye only gets the orientation that it 's supposed to get , and this eye only gets the orientation that it 's supposed to get , and you get a 3d image . so it 's useful in many ways . let me show you one more thing here . let 's come back here . this light was polarized vertically . so that 's called linear polarization . any time ... same with these . these are all linear polarization because , just up and down , one linear direction , just diagonal . this is also linear . all of these are linear . you can get circular polarized light . so if we come back to here , we 've got our electric field pointing up , like that . now let 's say we sent in another light ray , another light ray that also had a polarization , but not in this direction . let 's say our other light ray had polarization in this direction , so it looks like this , kind of like what our magnetic field would have looked like . but this is a completely different light ray with its own polarization and its own magnetic field . so we send this in . what would happen ? well , at this point , you 'd have a electric field that points this way . at this point , you 'd have a electric field that points that way . what would your eye see if you were over here ? let 's see . if i draw our axis here . all right , when this point right here gets to your eye , what am i going to see ? well , i 'm going to have a light ray that 's one part of a light ray . one component points up . that 's this electric field . one component points left . that 's this electric field . so the total , my total electric field , would point this way . i could to the pythagorean theorem if i wanted to figure out the size of it , but i just want to know the direction for now . and then it gets to here , and look at it : they both have zero . this light ray has zero electric field , this one has zero electric fields . so then it 'd just be at zero . now what happens over here ? well , i 've got light . this one points to the right at that point , this pink one , and then this red one would be pointing down . so what would i have at that point ? i 'd have light that went this way , and it would just be doing this over and over . it would just be ... i 'd just have diagonally polarized light . this is n't giving me anything new . you might think this is dumb . why do this ? why send in two different waves to just get diagonally polarized light ? i could have just sent in one wave that was diagonally polarized and got the same thing . the reason is , if you shift this purple wave , this pink wave , by 90 degrees of phase , by pi over two in phase , something magical happens . let me show you what happens here , if we move this to here . now we do n't just get diagonally linear polarized light . what we 're going to get is ... let me get rid of this . okay , so we start off with red , right ? the red electric field points up , and then this pink wave 's electric field is zero at that point . so this is all i have . my total electric field would just be up . i 'm going to draw it right here . the green 'll be the total . now i come over to here , and at this point , there 's some red electric field that points up , but there 's some of this other electric field that points this way . so i 'd have a total electric field that would point that way . and then i get over to here , and i 'd have all of the electric field from the pink one , none from the red one . it would point all left then . look what 's happening . the polarization of this light , if i shift this , if i 'm sitting here , looking with my eye , as my eye receives this light , i 'm going to see this light rotate its polarization . the polarization i 'm going to notice swings around in a circular pattern . and because of this , we call this circular polarization . so this is another type of polarization , where the actual angle of polarization rotates smoothly as this light ray enters your eye . and you know what ? er , drrr ... all right , actually , i sent you to receive this one first . that makes no sense . you 're going to receive the ones closes to you first in this light ray going this way . so you 'd actually receive this one first , then that one , then this one , then this one . because of that , you would n't see this going in a counterclockwise way , you 'd see this going in a clockwise circularly polarized way . sorry about that . you might think , `` okay , why ? `` why even bother with circular polarization ? '' well , i kind of lied earlier . turns out , in the movie theater example , they do n't actually do it like this , typically . oftentimes in the movie theaters , we do n't have just linearly polarized sunglasses . this would be a problem because , when you look at the movie theater screen , and if you were to tilt your head just a little bit ... think about it . this one 's not really going to get the right image anymore . it 's going to get some of both . and this one 's going to get some of both . it 's going to be blurry . your head would have to be perfectly level the whole time , which might be annoying . so what we do is , instead , we create circular polarized glasses , so that this one would only get one polarization , this one would get the other direction . this way , even if you tilt your head a little bit ... shoot , clockwise is clockwise , counterclockwise is counterclockwise . by using circular polarization for 3d movies , it can make it a little easier on you eyes to see a better 3d image , even if your head 's tilted a little bit .
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here 's some polarizers . that way , a lot of this glare gets blocked because it does not have a vertical orientation , it has a horizontal orientation . and then we can block it .
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why is it vertical but not horizontal ?
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- let 's talk about polarization of light . we know what light waves are ; they 're electromagnetic waves . so they 're made out of electric fields . and that 's not good enough . we know there 's not just electric fields . that could n't sustain itself . there 's got to be magnetic fields there , as well , that are changing . those are perpendicular , so you can kind of draw them . it 's hard , on something two-dimensional , but you can kind of imagine those looking something like this . and those magnetic fields would point at a right angle to the electric fields . but this gets really messy if i try to draw both the electric and magnetic fields at the same time . so we 're going to leave the magnetic fields out . it 's often good enough to just know the direction of the electric field when we focus on the electric field . so what does polarization mean ? polarization refers to the fact that , if this light ray was heading straight toward your eye , or a detector , over here , what would you see ? well , if i draw an axis over here , and this point here , in the middle , this is this line -- so imagine we 're looking straight down that line -- and then up and down is up and down , and then left and right , that direction i have the magnetic field , would be this way and that way . what would my eye see ? well , my eye 's only going to see electric fields that either point up or electric fields that point down . they might have different values , but i 'm only going to see electric fields that point up or down . because of that , this light ray is polarized . so polarized light is light where the electric field is only oscillating in one direction . up or down , that 's one direction -- vertically . or it could be polarized horizontally . or it could be polarized diagonally . but either way , you could have this wave polarized along any direction . i mean , a light ray like this , if we had it coming in diagonal , this light ray that 's oscillating like this , where the electric field oscillates like that , that also polarized . these are both polarized because there 's only one direction that the electric field is oscillating in . and you might thing , `` pff , how could you ever have `` a light ray that 's not polarized ? '' easy . most light that you get is not polarized . that is to say , light that 's coming from the sun , straight from the sun -- typically not polarized . light from a lightbulb , an old incandescent light bulb , this thing 's hot . you can get light polarized in any direction , all at once , all overlapping . so if we draw this case for a light bulb , just a random incandescent light bulb , you might get light , some of the light , hitting you eye , you can get some light that 's got that direction , you got light that 's got this direction , you got light in all these directions at any given moment . i mean , you 'd have to add these up to get the total , and they might not all be the same value . but what i 'm trying to say is , at any given moment , you do n't know what direction the electric field 's going to be hitting your eye at from a random source . it could be in any direction . so this is not polarized . this diagram represents light that is not polarized . at some point , the field might be pointing this way , at some later point it 's this way ; it 's just random . you never know which way the electric field 's going to be pointing . whereas these over here , these are polarized . so how could you polarize this light ? let 's say you wanted light that was polarized . you were doing an experiment . you needed polarized light . well , that 's easy . you can use what 's called a polarizer . and this is a material that lets light through , but it only lets light through in one orientation , so you 're going to have a polarizer that , for instance , only lets through vertically polarized light . so this is a polarizer . these are cheap : thin , plastic , configured in a way so that it only lets light through that 's vertically polarized . any light coming in here that 's not vertically polarized gets blocked , or absorbed . so what that means is , if you used this polarizer and held it in between your eye and this light bulb , you would only get this light . all the rest of it would get blocked . or you could just rotate this thing and imagine a polarizer that only lets through horizontal light . now it would only let through light that was this way , and so you would only get this part of the light . or you could just orient it at any angle you want and block everything but the certain angle that this polarizer is defined as letting light through . so you can do this . and once you hold this up , you get polarized light , light that 's only got one orientation . so that 's what polarization means . but why do we care about polarization ? well , let me get rid of this for a minute . you 've heard of polarized sunglasses . so imagine you 're standing near water , or maybe you 're standing on ice or snow or something reflective . there 's a problem . say the sun 's out . it 's shining . it 's a beautiful day -- except there 's going to be glare . let 's say you 're looking down at something here on the ground . it 's going to get light reflecting off of it from just ... you know , light 's coming in from all direction . but it also gets this direct light from the sun . so it gets light from reflected off the clouds and whatever , whatever 's nearby , ambient light . and there 's also this direct sunlight . that 's harsh . if that reflects straight up to your eye , that hurts . you do n't like that . it blocks our vision . it 's hard to see , it 's glare . we do n't want this glare . so what can we do ? well , it just so happens that , when light reflects off of a surface , even though the light from the sun is not polarized , once it reflects , it does get polarized or at least partially polarized . so this surface here , once this light reflects , it 's coming in at all orientations . you got electric field ... you never know what electric field you 're going to get straight from the sun . and when it reflects , though , you mostly get , upon reflection , the direction of polarization defined by the plane of the surface that it hit . so because the floor is horizontal , when this light ray hits the ground and reflects , that reflected light gets partially polarized . this horizontal component of the electric field is going to be more present than the other components . maybe not completely . sometimes it could be . it could be completely polarized , but often it 's just partially polarized . but that 's pretty cool , because now you know what we can do . i know how to block this . we should get some sunglasses . we put some sunglasses on and we make our glasses so that these are polarized . and how do we want these polarized ? i want to get rid of the glare . so what i do is , i make sure my sunglasses only let through vertically polarized light . here 's some polarizers . that way , a lot of this glare gets blocked because it does not have a vertical orientation , it has a horizontal orientation . and then we can block it . so that 's one good thing that polarization does for us , and understanding it , we can get rid of glare . also , fishermen like it because , if you 're trying to look in the water at fish , you want to see in through the water , you want to see this light from the fish getting to you . you do n't want to see the glare off of the sun getting to you . so polarized sunglasses are useful . also , we can play a trick on our eye , if we really wanted to . you could take one of these , make one eye have a vertical orientation for the polarization , have the other eye with a horizontal ... and you 're thinking , `` this is stupid . `` why would you do this for ? '' `` this eye 's going to get a lot of glare . '' we would n't use these outside , when you 're , like , skiing or fishing , but you could play a trick on your eyes if you went to the movies and you went and watched a movie . well , the reason our eyes see 3d is because they 're spaced a little bit apart . they each get a different , slightly different image . that makes us see in 3d . we can play the same trick on our eye if we have the polarization like this . if light , if some of the light from the movie theater screen is coming in with one polarization , and the other light 's coming in with the other polarization , we can send two different images to our eyes at the same time . if you took these off , it 'd look like garbage because you 'd be getting both of these slightly different images , it 'd look all blurry . and it does . if you take off your 3d glasses and look at a 3d movie , looks terrible , because now both eyes are getting both images . but if you put your glasses back on , now this eye only gets the orientation that it 's supposed to get , and this eye only gets the orientation that it 's supposed to get , and you get a 3d image . so it 's useful in many ways . let me show you one more thing here . let 's come back here . this light was polarized vertically . so that 's called linear polarization . any time ... same with these . these are all linear polarization because , just up and down , one linear direction , just diagonal . this is also linear . all of these are linear . you can get circular polarized light . so if we come back to here , we 've got our electric field pointing up , like that . now let 's say we sent in another light ray , another light ray that also had a polarization , but not in this direction . let 's say our other light ray had polarization in this direction , so it looks like this , kind of like what our magnetic field would have looked like . but this is a completely different light ray with its own polarization and its own magnetic field . so we send this in . what would happen ? well , at this point , you 'd have a electric field that points this way . at this point , you 'd have a electric field that points that way . what would your eye see if you were over here ? let 's see . if i draw our axis here . all right , when this point right here gets to your eye , what am i going to see ? well , i 'm going to have a light ray that 's one part of a light ray . one component points up . that 's this electric field . one component points left . that 's this electric field . so the total , my total electric field , would point this way . i could to the pythagorean theorem if i wanted to figure out the size of it , but i just want to know the direction for now . and then it gets to here , and look at it : they both have zero . this light ray has zero electric field , this one has zero electric fields . so then it 'd just be at zero . now what happens over here ? well , i 've got light . this one points to the right at that point , this pink one , and then this red one would be pointing down . so what would i have at that point ? i 'd have light that went this way , and it would just be doing this over and over . it would just be ... i 'd just have diagonally polarized light . this is n't giving me anything new . you might think this is dumb . why do this ? why send in two different waves to just get diagonally polarized light ? i could have just sent in one wave that was diagonally polarized and got the same thing . the reason is , if you shift this purple wave , this pink wave , by 90 degrees of phase , by pi over two in phase , something magical happens . let me show you what happens here , if we move this to here . now we do n't just get diagonally linear polarized light . what we 're going to get is ... let me get rid of this . okay , so we start off with red , right ? the red electric field points up , and then this pink wave 's electric field is zero at that point . so this is all i have . my total electric field would just be up . i 'm going to draw it right here . the green 'll be the total . now i come over to here , and at this point , there 's some red electric field that points up , but there 's some of this other electric field that points this way . so i 'd have a total electric field that would point that way . and then i get over to here , and i 'd have all of the electric field from the pink one , none from the red one . it would point all left then . look what 's happening . the polarization of this light , if i shift this , if i 'm sitting here , looking with my eye , as my eye receives this light , i 'm going to see this light rotate its polarization . the polarization i 'm going to notice swings around in a circular pattern . and because of this , we call this circular polarization . so this is another type of polarization , where the actual angle of polarization rotates smoothly as this light ray enters your eye . and you know what ? er , drrr ... all right , actually , i sent you to receive this one first . that makes no sense . you 're going to receive the ones closes to you first in this light ray going this way . so you 'd actually receive this one first , then that one , then this one , then this one . because of that , you would n't see this going in a counterclockwise way , you 'd see this going in a clockwise circularly polarized way . sorry about that . you might think , `` okay , why ? `` why even bother with circular polarization ? '' well , i kind of lied earlier . turns out , in the movie theater example , they do n't actually do it like this , typically . oftentimes in the movie theaters , we do n't have just linearly polarized sunglasses . this would be a problem because , when you look at the movie theater screen , and if you were to tilt your head just a little bit ... think about it . this one 's not really going to get the right image anymore . it 's going to get some of both . and this one 's going to get some of both . it 's going to be blurry . your head would have to be perfectly level the whole time , which might be annoying . so what we do is , instead , we create circular polarized glasses , so that this one would only get one polarization , this one would get the other direction . this way , even if you tilt your head a little bit ... shoot , clockwise is clockwise , counterclockwise is counterclockwise . by using circular polarization for 3d movies , it can make it a little easier on you eyes to see a better 3d image , even if your head 's tilted a little bit .
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sometimes it could be . it could be completely polarized , but often it 's just partially polarized . but that 's pretty cool , because now you know what we can do .
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when does it gets partially polarized & when ... fully polarised ?
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- let 's talk about polarization of light . we know what light waves are ; they 're electromagnetic waves . so they 're made out of electric fields . and that 's not good enough . we know there 's not just electric fields . that could n't sustain itself . there 's got to be magnetic fields there , as well , that are changing . those are perpendicular , so you can kind of draw them . it 's hard , on something two-dimensional , but you can kind of imagine those looking something like this . and those magnetic fields would point at a right angle to the electric fields . but this gets really messy if i try to draw both the electric and magnetic fields at the same time . so we 're going to leave the magnetic fields out . it 's often good enough to just know the direction of the electric field when we focus on the electric field . so what does polarization mean ? polarization refers to the fact that , if this light ray was heading straight toward your eye , or a detector , over here , what would you see ? well , if i draw an axis over here , and this point here , in the middle , this is this line -- so imagine we 're looking straight down that line -- and then up and down is up and down , and then left and right , that direction i have the magnetic field , would be this way and that way . what would my eye see ? well , my eye 's only going to see electric fields that either point up or electric fields that point down . they might have different values , but i 'm only going to see electric fields that point up or down . because of that , this light ray is polarized . so polarized light is light where the electric field is only oscillating in one direction . up or down , that 's one direction -- vertically . or it could be polarized horizontally . or it could be polarized diagonally . but either way , you could have this wave polarized along any direction . i mean , a light ray like this , if we had it coming in diagonal , this light ray that 's oscillating like this , where the electric field oscillates like that , that also polarized . these are both polarized because there 's only one direction that the electric field is oscillating in . and you might thing , `` pff , how could you ever have `` a light ray that 's not polarized ? '' easy . most light that you get is not polarized . that is to say , light that 's coming from the sun , straight from the sun -- typically not polarized . light from a lightbulb , an old incandescent light bulb , this thing 's hot . you can get light polarized in any direction , all at once , all overlapping . so if we draw this case for a light bulb , just a random incandescent light bulb , you might get light , some of the light , hitting you eye , you can get some light that 's got that direction , you got light that 's got this direction , you got light in all these directions at any given moment . i mean , you 'd have to add these up to get the total , and they might not all be the same value . but what i 'm trying to say is , at any given moment , you do n't know what direction the electric field 's going to be hitting your eye at from a random source . it could be in any direction . so this is not polarized . this diagram represents light that is not polarized . at some point , the field might be pointing this way , at some later point it 's this way ; it 's just random . you never know which way the electric field 's going to be pointing . whereas these over here , these are polarized . so how could you polarize this light ? let 's say you wanted light that was polarized . you were doing an experiment . you needed polarized light . well , that 's easy . you can use what 's called a polarizer . and this is a material that lets light through , but it only lets light through in one orientation , so you 're going to have a polarizer that , for instance , only lets through vertically polarized light . so this is a polarizer . these are cheap : thin , plastic , configured in a way so that it only lets light through that 's vertically polarized . any light coming in here that 's not vertically polarized gets blocked , or absorbed . so what that means is , if you used this polarizer and held it in between your eye and this light bulb , you would only get this light . all the rest of it would get blocked . or you could just rotate this thing and imagine a polarizer that only lets through horizontal light . now it would only let through light that was this way , and so you would only get this part of the light . or you could just orient it at any angle you want and block everything but the certain angle that this polarizer is defined as letting light through . so you can do this . and once you hold this up , you get polarized light , light that 's only got one orientation . so that 's what polarization means . but why do we care about polarization ? well , let me get rid of this for a minute . you 've heard of polarized sunglasses . so imagine you 're standing near water , or maybe you 're standing on ice or snow or something reflective . there 's a problem . say the sun 's out . it 's shining . it 's a beautiful day -- except there 's going to be glare . let 's say you 're looking down at something here on the ground . it 's going to get light reflecting off of it from just ... you know , light 's coming in from all direction . but it also gets this direct light from the sun . so it gets light from reflected off the clouds and whatever , whatever 's nearby , ambient light . and there 's also this direct sunlight . that 's harsh . if that reflects straight up to your eye , that hurts . you do n't like that . it blocks our vision . it 's hard to see , it 's glare . we do n't want this glare . so what can we do ? well , it just so happens that , when light reflects off of a surface , even though the light from the sun is not polarized , once it reflects , it does get polarized or at least partially polarized . so this surface here , once this light reflects , it 's coming in at all orientations . you got electric field ... you never know what electric field you 're going to get straight from the sun . and when it reflects , though , you mostly get , upon reflection , the direction of polarization defined by the plane of the surface that it hit . so because the floor is horizontal , when this light ray hits the ground and reflects , that reflected light gets partially polarized . this horizontal component of the electric field is going to be more present than the other components . maybe not completely . sometimes it could be . it could be completely polarized , but often it 's just partially polarized . but that 's pretty cool , because now you know what we can do . i know how to block this . we should get some sunglasses . we put some sunglasses on and we make our glasses so that these are polarized . and how do we want these polarized ? i want to get rid of the glare . so what i do is , i make sure my sunglasses only let through vertically polarized light . here 's some polarizers . that way , a lot of this glare gets blocked because it does not have a vertical orientation , it has a horizontal orientation . and then we can block it . so that 's one good thing that polarization does for us , and understanding it , we can get rid of glare . also , fishermen like it because , if you 're trying to look in the water at fish , you want to see in through the water , you want to see this light from the fish getting to you . you do n't want to see the glare off of the sun getting to you . so polarized sunglasses are useful . also , we can play a trick on our eye , if we really wanted to . you could take one of these , make one eye have a vertical orientation for the polarization , have the other eye with a horizontal ... and you 're thinking , `` this is stupid . `` why would you do this for ? '' `` this eye 's going to get a lot of glare . '' we would n't use these outside , when you 're , like , skiing or fishing , but you could play a trick on your eyes if you went to the movies and you went and watched a movie . well , the reason our eyes see 3d is because they 're spaced a little bit apart . they each get a different , slightly different image . that makes us see in 3d . we can play the same trick on our eye if we have the polarization like this . if light , if some of the light from the movie theater screen is coming in with one polarization , and the other light 's coming in with the other polarization , we can send two different images to our eyes at the same time . if you took these off , it 'd look like garbage because you 'd be getting both of these slightly different images , it 'd look all blurry . and it does . if you take off your 3d glasses and look at a 3d movie , looks terrible , because now both eyes are getting both images . but if you put your glasses back on , now this eye only gets the orientation that it 's supposed to get , and this eye only gets the orientation that it 's supposed to get , and you get a 3d image . so it 's useful in many ways . let me show you one more thing here . let 's come back here . this light was polarized vertically . so that 's called linear polarization . any time ... same with these . these are all linear polarization because , just up and down , one linear direction , just diagonal . this is also linear . all of these are linear . you can get circular polarized light . so if we come back to here , we 've got our electric field pointing up , like that . now let 's say we sent in another light ray , another light ray that also had a polarization , but not in this direction . let 's say our other light ray had polarization in this direction , so it looks like this , kind of like what our magnetic field would have looked like . but this is a completely different light ray with its own polarization and its own magnetic field . so we send this in . what would happen ? well , at this point , you 'd have a electric field that points this way . at this point , you 'd have a electric field that points that way . what would your eye see if you were over here ? let 's see . if i draw our axis here . all right , when this point right here gets to your eye , what am i going to see ? well , i 'm going to have a light ray that 's one part of a light ray . one component points up . that 's this electric field . one component points left . that 's this electric field . so the total , my total electric field , would point this way . i could to the pythagorean theorem if i wanted to figure out the size of it , but i just want to know the direction for now . and then it gets to here , and look at it : they both have zero . this light ray has zero electric field , this one has zero electric fields . so then it 'd just be at zero . now what happens over here ? well , i 've got light . this one points to the right at that point , this pink one , and then this red one would be pointing down . so what would i have at that point ? i 'd have light that went this way , and it would just be doing this over and over . it would just be ... i 'd just have diagonally polarized light . this is n't giving me anything new . you might think this is dumb . why do this ? why send in two different waves to just get diagonally polarized light ? i could have just sent in one wave that was diagonally polarized and got the same thing . the reason is , if you shift this purple wave , this pink wave , by 90 degrees of phase , by pi over two in phase , something magical happens . let me show you what happens here , if we move this to here . now we do n't just get diagonally linear polarized light . what we 're going to get is ... let me get rid of this . okay , so we start off with red , right ? the red electric field points up , and then this pink wave 's electric field is zero at that point . so this is all i have . my total electric field would just be up . i 'm going to draw it right here . the green 'll be the total . now i come over to here , and at this point , there 's some red electric field that points up , but there 's some of this other electric field that points this way . so i 'd have a total electric field that would point that way . and then i get over to here , and i 'd have all of the electric field from the pink one , none from the red one . it would point all left then . look what 's happening . the polarization of this light , if i shift this , if i 'm sitting here , looking with my eye , as my eye receives this light , i 'm going to see this light rotate its polarization . the polarization i 'm going to notice swings around in a circular pattern . and because of this , we call this circular polarization . so this is another type of polarization , where the actual angle of polarization rotates smoothly as this light ray enters your eye . and you know what ? er , drrr ... all right , actually , i sent you to receive this one first . that makes no sense . you 're going to receive the ones closes to you first in this light ray going this way . so you 'd actually receive this one first , then that one , then this one , then this one . because of that , you would n't see this going in a counterclockwise way , you 'd see this going in a clockwise circularly polarized way . sorry about that . you might think , `` okay , why ? `` why even bother with circular polarization ? '' well , i kind of lied earlier . turns out , in the movie theater example , they do n't actually do it like this , typically . oftentimes in the movie theaters , we do n't have just linearly polarized sunglasses . this would be a problem because , when you look at the movie theater screen , and if you were to tilt your head just a little bit ... think about it . this one 's not really going to get the right image anymore . it 's going to get some of both . and this one 's going to get some of both . it 's going to be blurry . your head would have to be perfectly level the whole time , which might be annoying . so what we do is , instead , we create circular polarized glasses , so that this one would only get one polarization , this one would get the other direction . this way , even if you tilt your head a little bit ... shoot , clockwise is clockwise , counterclockwise is counterclockwise . by using circular polarization for 3d movies , it can make it a little easier on you eyes to see a better 3d image , even if your head 's tilted a little bit .
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and this is a material that lets light through , but it only lets light through in one orientation , so you 're going to have a polarizer that , for instance , only lets through vertically polarized light . so this is a polarizer . these are cheap : thin , plastic , configured in a way so that it only lets light through that 's vertically polarized .
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are the materials used for polarizer , itself polarizing , or should it be modified in any way that it gets the property ?
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- let 's talk about polarization of light . we know what light waves are ; they 're electromagnetic waves . so they 're made out of electric fields . and that 's not good enough . we know there 's not just electric fields . that could n't sustain itself . there 's got to be magnetic fields there , as well , that are changing . those are perpendicular , so you can kind of draw them . it 's hard , on something two-dimensional , but you can kind of imagine those looking something like this . and those magnetic fields would point at a right angle to the electric fields . but this gets really messy if i try to draw both the electric and magnetic fields at the same time . so we 're going to leave the magnetic fields out . it 's often good enough to just know the direction of the electric field when we focus on the electric field . so what does polarization mean ? polarization refers to the fact that , if this light ray was heading straight toward your eye , or a detector , over here , what would you see ? well , if i draw an axis over here , and this point here , in the middle , this is this line -- so imagine we 're looking straight down that line -- and then up and down is up and down , and then left and right , that direction i have the magnetic field , would be this way and that way . what would my eye see ? well , my eye 's only going to see electric fields that either point up or electric fields that point down . they might have different values , but i 'm only going to see electric fields that point up or down . because of that , this light ray is polarized . so polarized light is light where the electric field is only oscillating in one direction . up or down , that 's one direction -- vertically . or it could be polarized horizontally . or it could be polarized diagonally . but either way , you could have this wave polarized along any direction . i mean , a light ray like this , if we had it coming in diagonal , this light ray that 's oscillating like this , where the electric field oscillates like that , that also polarized . these are both polarized because there 's only one direction that the electric field is oscillating in . and you might thing , `` pff , how could you ever have `` a light ray that 's not polarized ? '' easy . most light that you get is not polarized . that is to say , light that 's coming from the sun , straight from the sun -- typically not polarized . light from a lightbulb , an old incandescent light bulb , this thing 's hot . you can get light polarized in any direction , all at once , all overlapping . so if we draw this case for a light bulb , just a random incandescent light bulb , you might get light , some of the light , hitting you eye , you can get some light that 's got that direction , you got light that 's got this direction , you got light in all these directions at any given moment . i mean , you 'd have to add these up to get the total , and they might not all be the same value . but what i 'm trying to say is , at any given moment , you do n't know what direction the electric field 's going to be hitting your eye at from a random source . it could be in any direction . so this is not polarized . this diagram represents light that is not polarized . at some point , the field might be pointing this way , at some later point it 's this way ; it 's just random . you never know which way the electric field 's going to be pointing . whereas these over here , these are polarized . so how could you polarize this light ? let 's say you wanted light that was polarized . you were doing an experiment . you needed polarized light . well , that 's easy . you can use what 's called a polarizer . and this is a material that lets light through , but it only lets light through in one orientation , so you 're going to have a polarizer that , for instance , only lets through vertically polarized light . so this is a polarizer . these are cheap : thin , plastic , configured in a way so that it only lets light through that 's vertically polarized . any light coming in here that 's not vertically polarized gets blocked , or absorbed . so what that means is , if you used this polarizer and held it in between your eye and this light bulb , you would only get this light . all the rest of it would get blocked . or you could just rotate this thing and imagine a polarizer that only lets through horizontal light . now it would only let through light that was this way , and so you would only get this part of the light . or you could just orient it at any angle you want and block everything but the certain angle that this polarizer is defined as letting light through . so you can do this . and once you hold this up , you get polarized light , light that 's only got one orientation . so that 's what polarization means . but why do we care about polarization ? well , let me get rid of this for a minute . you 've heard of polarized sunglasses . so imagine you 're standing near water , or maybe you 're standing on ice or snow or something reflective . there 's a problem . say the sun 's out . it 's shining . it 's a beautiful day -- except there 's going to be glare . let 's say you 're looking down at something here on the ground . it 's going to get light reflecting off of it from just ... you know , light 's coming in from all direction . but it also gets this direct light from the sun . so it gets light from reflected off the clouds and whatever , whatever 's nearby , ambient light . and there 's also this direct sunlight . that 's harsh . if that reflects straight up to your eye , that hurts . you do n't like that . it blocks our vision . it 's hard to see , it 's glare . we do n't want this glare . so what can we do ? well , it just so happens that , when light reflects off of a surface , even though the light from the sun is not polarized , once it reflects , it does get polarized or at least partially polarized . so this surface here , once this light reflects , it 's coming in at all orientations . you got electric field ... you never know what electric field you 're going to get straight from the sun . and when it reflects , though , you mostly get , upon reflection , the direction of polarization defined by the plane of the surface that it hit . so because the floor is horizontal , when this light ray hits the ground and reflects , that reflected light gets partially polarized . this horizontal component of the electric field is going to be more present than the other components . maybe not completely . sometimes it could be . it could be completely polarized , but often it 's just partially polarized . but that 's pretty cool , because now you know what we can do . i know how to block this . we should get some sunglasses . we put some sunglasses on and we make our glasses so that these are polarized . and how do we want these polarized ? i want to get rid of the glare . so what i do is , i make sure my sunglasses only let through vertically polarized light . here 's some polarizers . that way , a lot of this glare gets blocked because it does not have a vertical orientation , it has a horizontal orientation . and then we can block it . so that 's one good thing that polarization does for us , and understanding it , we can get rid of glare . also , fishermen like it because , if you 're trying to look in the water at fish , you want to see in through the water , you want to see this light from the fish getting to you . you do n't want to see the glare off of the sun getting to you . so polarized sunglasses are useful . also , we can play a trick on our eye , if we really wanted to . you could take one of these , make one eye have a vertical orientation for the polarization , have the other eye with a horizontal ... and you 're thinking , `` this is stupid . `` why would you do this for ? '' `` this eye 's going to get a lot of glare . '' we would n't use these outside , when you 're , like , skiing or fishing , but you could play a trick on your eyes if you went to the movies and you went and watched a movie . well , the reason our eyes see 3d is because they 're spaced a little bit apart . they each get a different , slightly different image . that makes us see in 3d . we can play the same trick on our eye if we have the polarization like this . if light , if some of the light from the movie theater screen is coming in with one polarization , and the other light 's coming in with the other polarization , we can send two different images to our eyes at the same time . if you took these off , it 'd look like garbage because you 'd be getting both of these slightly different images , it 'd look all blurry . and it does . if you take off your 3d glasses and look at a 3d movie , looks terrible , because now both eyes are getting both images . but if you put your glasses back on , now this eye only gets the orientation that it 's supposed to get , and this eye only gets the orientation that it 's supposed to get , and you get a 3d image . so it 's useful in many ways . let me show you one more thing here . let 's come back here . this light was polarized vertically . so that 's called linear polarization . any time ... same with these . these are all linear polarization because , just up and down , one linear direction , just diagonal . this is also linear . all of these are linear . you can get circular polarized light . so if we come back to here , we 've got our electric field pointing up , like that . now let 's say we sent in another light ray , another light ray that also had a polarization , but not in this direction . let 's say our other light ray had polarization in this direction , so it looks like this , kind of like what our magnetic field would have looked like . but this is a completely different light ray with its own polarization and its own magnetic field . so we send this in . what would happen ? well , at this point , you 'd have a electric field that points this way . at this point , you 'd have a electric field that points that way . what would your eye see if you were over here ? let 's see . if i draw our axis here . all right , when this point right here gets to your eye , what am i going to see ? well , i 'm going to have a light ray that 's one part of a light ray . one component points up . that 's this electric field . one component points left . that 's this electric field . so the total , my total electric field , would point this way . i could to the pythagorean theorem if i wanted to figure out the size of it , but i just want to know the direction for now . and then it gets to here , and look at it : they both have zero . this light ray has zero electric field , this one has zero electric fields . so then it 'd just be at zero . now what happens over here ? well , i 've got light . this one points to the right at that point , this pink one , and then this red one would be pointing down . so what would i have at that point ? i 'd have light that went this way , and it would just be doing this over and over . it would just be ... i 'd just have diagonally polarized light . this is n't giving me anything new . you might think this is dumb . why do this ? why send in two different waves to just get diagonally polarized light ? i could have just sent in one wave that was diagonally polarized and got the same thing . the reason is , if you shift this purple wave , this pink wave , by 90 degrees of phase , by pi over two in phase , something magical happens . let me show you what happens here , if we move this to here . now we do n't just get diagonally linear polarized light . what we 're going to get is ... let me get rid of this . okay , so we start off with red , right ? the red electric field points up , and then this pink wave 's electric field is zero at that point . so this is all i have . my total electric field would just be up . i 'm going to draw it right here . the green 'll be the total . now i come over to here , and at this point , there 's some red electric field that points up , but there 's some of this other electric field that points this way . so i 'd have a total electric field that would point that way . and then i get over to here , and i 'd have all of the electric field from the pink one , none from the red one . it would point all left then . look what 's happening . the polarization of this light , if i shift this , if i 'm sitting here , looking with my eye , as my eye receives this light , i 'm going to see this light rotate its polarization . the polarization i 'm going to notice swings around in a circular pattern . and because of this , we call this circular polarization . so this is another type of polarization , where the actual angle of polarization rotates smoothly as this light ray enters your eye . and you know what ? er , drrr ... all right , actually , i sent you to receive this one first . that makes no sense . you 're going to receive the ones closes to you first in this light ray going this way . so you 'd actually receive this one first , then that one , then this one , then this one . because of that , you would n't see this going in a counterclockwise way , you 'd see this going in a clockwise circularly polarized way . sorry about that . you might think , `` okay , why ? `` why even bother with circular polarization ? '' well , i kind of lied earlier . turns out , in the movie theater example , they do n't actually do it like this , typically . oftentimes in the movie theaters , we do n't have just linearly polarized sunglasses . this would be a problem because , when you look at the movie theater screen , and if you were to tilt your head just a little bit ... think about it . this one 's not really going to get the right image anymore . it 's going to get some of both . and this one 's going to get some of both . it 's going to be blurry . your head would have to be perfectly level the whole time , which might be annoying . so what we do is , instead , we create circular polarized glasses , so that this one would only get one polarization , this one would get the other direction . this way , even if you tilt your head a little bit ... shoot , clockwise is clockwise , counterclockwise is counterclockwise . by using circular polarization for 3d movies , it can make it a little easier on you eyes to see a better 3d image , even if your head 's tilted a little bit .
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- let 's talk about polarization of light . we know what light waves are ; they 're electromagnetic waves . so they 're made out of electric fields .
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i thought that when people draw the waves with two waves intersecting each other , that was the quantum superposition of light rays , if thats not quantum superposition then how does it work , does it exists somewhere else or works in another kinda dimention ?
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- let 's talk about polarization of light . we know what light waves are ; they 're electromagnetic waves . so they 're made out of electric fields . and that 's not good enough . we know there 's not just electric fields . that could n't sustain itself . there 's got to be magnetic fields there , as well , that are changing . those are perpendicular , so you can kind of draw them . it 's hard , on something two-dimensional , but you can kind of imagine those looking something like this . and those magnetic fields would point at a right angle to the electric fields . but this gets really messy if i try to draw both the electric and magnetic fields at the same time . so we 're going to leave the magnetic fields out . it 's often good enough to just know the direction of the electric field when we focus on the electric field . so what does polarization mean ? polarization refers to the fact that , if this light ray was heading straight toward your eye , or a detector , over here , what would you see ? well , if i draw an axis over here , and this point here , in the middle , this is this line -- so imagine we 're looking straight down that line -- and then up and down is up and down , and then left and right , that direction i have the magnetic field , would be this way and that way . what would my eye see ? well , my eye 's only going to see electric fields that either point up or electric fields that point down . they might have different values , but i 'm only going to see electric fields that point up or down . because of that , this light ray is polarized . so polarized light is light where the electric field is only oscillating in one direction . up or down , that 's one direction -- vertically . or it could be polarized horizontally . or it could be polarized diagonally . but either way , you could have this wave polarized along any direction . i mean , a light ray like this , if we had it coming in diagonal , this light ray that 's oscillating like this , where the electric field oscillates like that , that also polarized . these are both polarized because there 's only one direction that the electric field is oscillating in . and you might thing , `` pff , how could you ever have `` a light ray that 's not polarized ? '' easy . most light that you get is not polarized . that is to say , light that 's coming from the sun , straight from the sun -- typically not polarized . light from a lightbulb , an old incandescent light bulb , this thing 's hot . you can get light polarized in any direction , all at once , all overlapping . so if we draw this case for a light bulb , just a random incandescent light bulb , you might get light , some of the light , hitting you eye , you can get some light that 's got that direction , you got light that 's got this direction , you got light in all these directions at any given moment . i mean , you 'd have to add these up to get the total , and they might not all be the same value . but what i 'm trying to say is , at any given moment , you do n't know what direction the electric field 's going to be hitting your eye at from a random source . it could be in any direction . so this is not polarized . this diagram represents light that is not polarized . at some point , the field might be pointing this way , at some later point it 's this way ; it 's just random . you never know which way the electric field 's going to be pointing . whereas these over here , these are polarized . so how could you polarize this light ? let 's say you wanted light that was polarized . you were doing an experiment . you needed polarized light . well , that 's easy . you can use what 's called a polarizer . and this is a material that lets light through , but it only lets light through in one orientation , so you 're going to have a polarizer that , for instance , only lets through vertically polarized light . so this is a polarizer . these are cheap : thin , plastic , configured in a way so that it only lets light through that 's vertically polarized . any light coming in here that 's not vertically polarized gets blocked , or absorbed . so what that means is , if you used this polarizer and held it in between your eye and this light bulb , you would only get this light . all the rest of it would get blocked . or you could just rotate this thing and imagine a polarizer that only lets through horizontal light . now it would only let through light that was this way , and so you would only get this part of the light . or you could just orient it at any angle you want and block everything but the certain angle that this polarizer is defined as letting light through . so you can do this . and once you hold this up , you get polarized light , light that 's only got one orientation . so that 's what polarization means . but why do we care about polarization ? well , let me get rid of this for a minute . you 've heard of polarized sunglasses . so imagine you 're standing near water , or maybe you 're standing on ice or snow or something reflective . there 's a problem . say the sun 's out . it 's shining . it 's a beautiful day -- except there 's going to be glare . let 's say you 're looking down at something here on the ground . it 's going to get light reflecting off of it from just ... you know , light 's coming in from all direction . but it also gets this direct light from the sun . so it gets light from reflected off the clouds and whatever , whatever 's nearby , ambient light . and there 's also this direct sunlight . that 's harsh . if that reflects straight up to your eye , that hurts . you do n't like that . it blocks our vision . it 's hard to see , it 's glare . we do n't want this glare . so what can we do ? well , it just so happens that , when light reflects off of a surface , even though the light from the sun is not polarized , once it reflects , it does get polarized or at least partially polarized . so this surface here , once this light reflects , it 's coming in at all orientations . you got electric field ... you never know what electric field you 're going to get straight from the sun . and when it reflects , though , you mostly get , upon reflection , the direction of polarization defined by the plane of the surface that it hit . so because the floor is horizontal , when this light ray hits the ground and reflects , that reflected light gets partially polarized . this horizontal component of the electric field is going to be more present than the other components . maybe not completely . sometimes it could be . it could be completely polarized , but often it 's just partially polarized . but that 's pretty cool , because now you know what we can do . i know how to block this . we should get some sunglasses . we put some sunglasses on and we make our glasses so that these are polarized . and how do we want these polarized ? i want to get rid of the glare . so what i do is , i make sure my sunglasses only let through vertically polarized light . here 's some polarizers . that way , a lot of this glare gets blocked because it does not have a vertical orientation , it has a horizontal orientation . and then we can block it . so that 's one good thing that polarization does for us , and understanding it , we can get rid of glare . also , fishermen like it because , if you 're trying to look in the water at fish , you want to see in through the water , you want to see this light from the fish getting to you . you do n't want to see the glare off of the sun getting to you . so polarized sunglasses are useful . also , we can play a trick on our eye , if we really wanted to . you could take one of these , make one eye have a vertical orientation for the polarization , have the other eye with a horizontal ... and you 're thinking , `` this is stupid . `` why would you do this for ? '' `` this eye 's going to get a lot of glare . '' we would n't use these outside , when you 're , like , skiing or fishing , but you could play a trick on your eyes if you went to the movies and you went and watched a movie . well , the reason our eyes see 3d is because they 're spaced a little bit apart . they each get a different , slightly different image . that makes us see in 3d . we can play the same trick on our eye if we have the polarization like this . if light , if some of the light from the movie theater screen is coming in with one polarization , and the other light 's coming in with the other polarization , we can send two different images to our eyes at the same time . if you took these off , it 'd look like garbage because you 'd be getting both of these slightly different images , it 'd look all blurry . and it does . if you take off your 3d glasses and look at a 3d movie , looks terrible , because now both eyes are getting both images . but if you put your glasses back on , now this eye only gets the orientation that it 's supposed to get , and this eye only gets the orientation that it 's supposed to get , and you get a 3d image . so it 's useful in many ways . let me show you one more thing here . let 's come back here . this light was polarized vertically . so that 's called linear polarization . any time ... same with these . these are all linear polarization because , just up and down , one linear direction , just diagonal . this is also linear . all of these are linear . you can get circular polarized light . so if we come back to here , we 've got our electric field pointing up , like that . now let 's say we sent in another light ray , another light ray that also had a polarization , but not in this direction . let 's say our other light ray had polarization in this direction , so it looks like this , kind of like what our magnetic field would have looked like . but this is a completely different light ray with its own polarization and its own magnetic field . so we send this in . what would happen ? well , at this point , you 'd have a electric field that points this way . at this point , you 'd have a electric field that points that way . what would your eye see if you were over here ? let 's see . if i draw our axis here . all right , when this point right here gets to your eye , what am i going to see ? well , i 'm going to have a light ray that 's one part of a light ray . one component points up . that 's this electric field . one component points left . that 's this electric field . so the total , my total electric field , would point this way . i could to the pythagorean theorem if i wanted to figure out the size of it , but i just want to know the direction for now . and then it gets to here , and look at it : they both have zero . this light ray has zero electric field , this one has zero electric fields . so then it 'd just be at zero . now what happens over here ? well , i 've got light . this one points to the right at that point , this pink one , and then this red one would be pointing down . so what would i have at that point ? i 'd have light that went this way , and it would just be doing this over and over . it would just be ... i 'd just have diagonally polarized light . this is n't giving me anything new . you might think this is dumb . why do this ? why send in two different waves to just get diagonally polarized light ? i could have just sent in one wave that was diagonally polarized and got the same thing . the reason is , if you shift this purple wave , this pink wave , by 90 degrees of phase , by pi over two in phase , something magical happens . let me show you what happens here , if we move this to here . now we do n't just get diagonally linear polarized light . what we 're going to get is ... let me get rid of this . okay , so we start off with red , right ? the red electric field points up , and then this pink wave 's electric field is zero at that point . so this is all i have . my total electric field would just be up . i 'm going to draw it right here . the green 'll be the total . now i come over to here , and at this point , there 's some red electric field that points up , but there 's some of this other electric field that points this way . so i 'd have a total electric field that would point that way . and then i get over to here , and i 'd have all of the electric field from the pink one , none from the red one . it would point all left then . look what 's happening . the polarization of this light , if i shift this , if i 'm sitting here , looking with my eye , as my eye receives this light , i 'm going to see this light rotate its polarization . the polarization i 'm going to notice swings around in a circular pattern . and because of this , we call this circular polarization . so this is another type of polarization , where the actual angle of polarization rotates smoothly as this light ray enters your eye . and you know what ? er , drrr ... all right , actually , i sent you to receive this one first . that makes no sense . you 're going to receive the ones closes to you first in this light ray going this way . so you 'd actually receive this one first , then that one , then this one , then this one . because of that , you would n't see this going in a counterclockwise way , you 'd see this going in a clockwise circularly polarized way . sorry about that . you might think , `` okay , why ? `` why even bother with circular polarization ? '' well , i kind of lied earlier . turns out , in the movie theater example , they do n't actually do it like this , typically . oftentimes in the movie theaters , we do n't have just linearly polarized sunglasses . this would be a problem because , when you look at the movie theater screen , and if you were to tilt your head just a little bit ... think about it . this one 's not really going to get the right image anymore . it 's going to get some of both . and this one 's going to get some of both . it 's going to be blurry . your head would have to be perfectly level the whole time , which might be annoying . so what we do is , instead , we create circular polarized glasses , so that this one would only get one polarization , this one would get the other direction . this way , even if you tilt your head a little bit ... shoot , clockwise is clockwise , counterclockwise is counterclockwise . by using circular polarization for 3d movies , it can make it a little easier on you eyes to see a better 3d image , even if your head 's tilted a little bit .
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it 's hard , on something two-dimensional , but you can kind of imagine those looking something like this . and those magnetic fields would point at a right angle to the electric fields . but this gets really messy if i try to draw both the electric and magnetic fields at the same time .
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so does that mean we can see electric and magnetic fields if we can sense emr ?
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- let 's talk about polarization of light . we know what light waves are ; they 're electromagnetic waves . so they 're made out of electric fields . and that 's not good enough . we know there 's not just electric fields . that could n't sustain itself . there 's got to be magnetic fields there , as well , that are changing . those are perpendicular , so you can kind of draw them . it 's hard , on something two-dimensional , but you can kind of imagine those looking something like this . and those magnetic fields would point at a right angle to the electric fields . but this gets really messy if i try to draw both the electric and magnetic fields at the same time . so we 're going to leave the magnetic fields out . it 's often good enough to just know the direction of the electric field when we focus on the electric field . so what does polarization mean ? polarization refers to the fact that , if this light ray was heading straight toward your eye , or a detector , over here , what would you see ? well , if i draw an axis over here , and this point here , in the middle , this is this line -- so imagine we 're looking straight down that line -- and then up and down is up and down , and then left and right , that direction i have the magnetic field , would be this way and that way . what would my eye see ? well , my eye 's only going to see electric fields that either point up or electric fields that point down . they might have different values , but i 'm only going to see electric fields that point up or down . because of that , this light ray is polarized . so polarized light is light where the electric field is only oscillating in one direction . up or down , that 's one direction -- vertically . or it could be polarized horizontally . or it could be polarized diagonally . but either way , you could have this wave polarized along any direction . i mean , a light ray like this , if we had it coming in diagonal , this light ray that 's oscillating like this , where the electric field oscillates like that , that also polarized . these are both polarized because there 's only one direction that the electric field is oscillating in . and you might thing , `` pff , how could you ever have `` a light ray that 's not polarized ? '' easy . most light that you get is not polarized . that is to say , light that 's coming from the sun , straight from the sun -- typically not polarized . light from a lightbulb , an old incandescent light bulb , this thing 's hot . you can get light polarized in any direction , all at once , all overlapping . so if we draw this case for a light bulb , just a random incandescent light bulb , you might get light , some of the light , hitting you eye , you can get some light that 's got that direction , you got light that 's got this direction , you got light in all these directions at any given moment . i mean , you 'd have to add these up to get the total , and they might not all be the same value . but what i 'm trying to say is , at any given moment , you do n't know what direction the electric field 's going to be hitting your eye at from a random source . it could be in any direction . so this is not polarized . this diagram represents light that is not polarized . at some point , the field might be pointing this way , at some later point it 's this way ; it 's just random . you never know which way the electric field 's going to be pointing . whereas these over here , these are polarized . so how could you polarize this light ? let 's say you wanted light that was polarized . you were doing an experiment . you needed polarized light . well , that 's easy . you can use what 's called a polarizer . and this is a material that lets light through , but it only lets light through in one orientation , so you 're going to have a polarizer that , for instance , only lets through vertically polarized light . so this is a polarizer . these are cheap : thin , plastic , configured in a way so that it only lets light through that 's vertically polarized . any light coming in here that 's not vertically polarized gets blocked , or absorbed . so what that means is , if you used this polarizer and held it in between your eye and this light bulb , you would only get this light . all the rest of it would get blocked . or you could just rotate this thing and imagine a polarizer that only lets through horizontal light . now it would only let through light that was this way , and so you would only get this part of the light . or you could just orient it at any angle you want and block everything but the certain angle that this polarizer is defined as letting light through . so you can do this . and once you hold this up , you get polarized light , light that 's only got one orientation . so that 's what polarization means . but why do we care about polarization ? well , let me get rid of this for a minute . you 've heard of polarized sunglasses . so imagine you 're standing near water , or maybe you 're standing on ice or snow or something reflective . there 's a problem . say the sun 's out . it 's shining . it 's a beautiful day -- except there 's going to be glare . let 's say you 're looking down at something here on the ground . it 's going to get light reflecting off of it from just ... you know , light 's coming in from all direction . but it also gets this direct light from the sun . so it gets light from reflected off the clouds and whatever , whatever 's nearby , ambient light . and there 's also this direct sunlight . that 's harsh . if that reflects straight up to your eye , that hurts . you do n't like that . it blocks our vision . it 's hard to see , it 's glare . we do n't want this glare . so what can we do ? well , it just so happens that , when light reflects off of a surface , even though the light from the sun is not polarized , once it reflects , it does get polarized or at least partially polarized . so this surface here , once this light reflects , it 's coming in at all orientations . you got electric field ... you never know what electric field you 're going to get straight from the sun . and when it reflects , though , you mostly get , upon reflection , the direction of polarization defined by the plane of the surface that it hit . so because the floor is horizontal , when this light ray hits the ground and reflects , that reflected light gets partially polarized . this horizontal component of the electric field is going to be more present than the other components . maybe not completely . sometimes it could be . it could be completely polarized , but often it 's just partially polarized . but that 's pretty cool , because now you know what we can do . i know how to block this . we should get some sunglasses . we put some sunglasses on and we make our glasses so that these are polarized . and how do we want these polarized ? i want to get rid of the glare . so what i do is , i make sure my sunglasses only let through vertically polarized light . here 's some polarizers . that way , a lot of this glare gets blocked because it does not have a vertical orientation , it has a horizontal orientation . and then we can block it . so that 's one good thing that polarization does for us , and understanding it , we can get rid of glare . also , fishermen like it because , if you 're trying to look in the water at fish , you want to see in through the water , you want to see this light from the fish getting to you . you do n't want to see the glare off of the sun getting to you . so polarized sunglasses are useful . also , we can play a trick on our eye , if we really wanted to . you could take one of these , make one eye have a vertical orientation for the polarization , have the other eye with a horizontal ... and you 're thinking , `` this is stupid . `` why would you do this for ? '' `` this eye 's going to get a lot of glare . '' we would n't use these outside , when you 're , like , skiing or fishing , but you could play a trick on your eyes if you went to the movies and you went and watched a movie . well , the reason our eyes see 3d is because they 're spaced a little bit apart . they each get a different , slightly different image . that makes us see in 3d . we can play the same trick on our eye if we have the polarization like this . if light , if some of the light from the movie theater screen is coming in with one polarization , and the other light 's coming in with the other polarization , we can send two different images to our eyes at the same time . if you took these off , it 'd look like garbage because you 'd be getting both of these slightly different images , it 'd look all blurry . and it does . if you take off your 3d glasses and look at a 3d movie , looks terrible , because now both eyes are getting both images . but if you put your glasses back on , now this eye only gets the orientation that it 's supposed to get , and this eye only gets the orientation that it 's supposed to get , and you get a 3d image . so it 's useful in many ways . let me show you one more thing here . let 's come back here . this light was polarized vertically . so that 's called linear polarization . any time ... same with these . these are all linear polarization because , just up and down , one linear direction , just diagonal . this is also linear . all of these are linear . you can get circular polarized light . so if we come back to here , we 've got our electric field pointing up , like that . now let 's say we sent in another light ray , another light ray that also had a polarization , but not in this direction . let 's say our other light ray had polarization in this direction , so it looks like this , kind of like what our magnetic field would have looked like . but this is a completely different light ray with its own polarization and its own magnetic field . so we send this in . what would happen ? well , at this point , you 'd have a electric field that points this way . at this point , you 'd have a electric field that points that way . what would your eye see if you were over here ? let 's see . if i draw our axis here . all right , when this point right here gets to your eye , what am i going to see ? well , i 'm going to have a light ray that 's one part of a light ray . one component points up . that 's this electric field . one component points left . that 's this electric field . so the total , my total electric field , would point this way . i could to the pythagorean theorem if i wanted to figure out the size of it , but i just want to know the direction for now . and then it gets to here , and look at it : they both have zero . this light ray has zero electric field , this one has zero electric fields . so then it 'd just be at zero . now what happens over here ? well , i 've got light . this one points to the right at that point , this pink one , and then this red one would be pointing down . so what would i have at that point ? i 'd have light that went this way , and it would just be doing this over and over . it would just be ... i 'd just have diagonally polarized light . this is n't giving me anything new . you might think this is dumb . why do this ? why send in two different waves to just get diagonally polarized light ? i could have just sent in one wave that was diagonally polarized and got the same thing . the reason is , if you shift this purple wave , this pink wave , by 90 degrees of phase , by pi over two in phase , something magical happens . let me show you what happens here , if we move this to here . now we do n't just get diagonally linear polarized light . what we 're going to get is ... let me get rid of this . okay , so we start off with red , right ? the red electric field points up , and then this pink wave 's electric field is zero at that point . so this is all i have . my total electric field would just be up . i 'm going to draw it right here . the green 'll be the total . now i come over to here , and at this point , there 's some red electric field that points up , but there 's some of this other electric field that points this way . so i 'd have a total electric field that would point that way . and then i get over to here , and i 'd have all of the electric field from the pink one , none from the red one . it would point all left then . look what 's happening . the polarization of this light , if i shift this , if i 'm sitting here , looking with my eye , as my eye receives this light , i 'm going to see this light rotate its polarization . the polarization i 'm going to notice swings around in a circular pattern . and because of this , we call this circular polarization . so this is another type of polarization , where the actual angle of polarization rotates smoothly as this light ray enters your eye . and you know what ? er , drrr ... all right , actually , i sent you to receive this one first . that makes no sense . you 're going to receive the ones closes to you first in this light ray going this way . so you 'd actually receive this one first , then that one , then this one , then this one . because of that , you would n't see this going in a counterclockwise way , you 'd see this going in a clockwise circularly polarized way . sorry about that . you might think , `` okay , why ? `` why even bother with circular polarization ? '' well , i kind of lied earlier . turns out , in the movie theater example , they do n't actually do it like this , typically . oftentimes in the movie theaters , we do n't have just linearly polarized sunglasses . this would be a problem because , when you look at the movie theater screen , and if you were to tilt your head just a little bit ... think about it . this one 's not really going to get the right image anymore . it 's going to get some of both . and this one 's going to get some of both . it 's going to be blurry . your head would have to be perfectly level the whole time , which might be annoying . so what we do is , instead , we create circular polarized glasses , so that this one would only get one polarization , this one would get the other direction . this way , even if you tilt your head a little bit ... shoot , clockwise is clockwise , counterclockwise is counterclockwise . by using circular polarization for 3d movies , it can make it a little easier on you eyes to see a better 3d image , even if your head 's tilted a little bit .
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all right , when this point right here gets to your eye , what am i going to see ? well , i 'm going to have a light ray that 's one part of a light ray . one component points up .
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how can be reflected light ray isolated to a single axis ?
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- let 's talk about polarization of light . we know what light waves are ; they 're electromagnetic waves . so they 're made out of electric fields . and that 's not good enough . we know there 's not just electric fields . that could n't sustain itself . there 's got to be magnetic fields there , as well , that are changing . those are perpendicular , so you can kind of draw them . it 's hard , on something two-dimensional , but you can kind of imagine those looking something like this . and those magnetic fields would point at a right angle to the electric fields . but this gets really messy if i try to draw both the electric and magnetic fields at the same time . so we 're going to leave the magnetic fields out . it 's often good enough to just know the direction of the electric field when we focus on the electric field . so what does polarization mean ? polarization refers to the fact that , if this light ray was heading straight toward your eye , or a detector , over here , what would you see ? well , if i draw an axis over here , and this point here , in the middle , this is this line -- so imagine we 're looking straight down that line -- and then up and down is up and down , and then left and right , that direction i have the magnetic field , would be this way and that way . what would my eye see ? well , my eye 's only going to see electric fields that either point up or electric fields that point down . they might have different values , but i 'm only going to see electric fields that point up or down . because of that , this light ray is polarized . so polarized light is light where the electric field is only oscillating in one direction . up or down , that 's one direction -- vertically . or it could be polarized horizontally . or it could be polarized diagonally . but either way , you could have this wave polarized along any direction . i mean , a light ray like this , if we had it coming in diagonal , this light ray that 's oscillating like this , where the electric field oscillates like that , that also polarized . these are both polarized because there 's only one direction that the electric field is oscillating in . and you might thing , `` pff , how could you ever have `` a light ray that 's not polarized ? '' easy . most light that you get is not polarized . that is to say , light that 's coming from the sun , straight from the sun -- typically not polarized . light from a lightbulb , an old incandescent light bulb , this thing 's hot . you can get light polarized in any direction , all at once , all overlapping . so if we draw this case for a light bulb , just a random incandescent light bulb , you might get light , some of the light , hitting you eye , you can get some light that 's got that direction , you got light that 's got this direction , you got light in all these directions at any given moment . i mean , you 'd have to add these up to get the total , and they might not all be the same value . but what i 'm trying to say is , at any given moment , you do n't know what direction the electric field 's going to be hitting your eye at from a random source . it could be in any direction . so this is not polarized . this diagram represents light that is not polarized . at some point , the field might be pointing this way , at some later point it 's this way ; it 's just random . you never know which way the electric field 's going to be pointing . whereas these over here , these are polarized . so how could you polarize this light ? let 's say you wanted light that was polarized . you were doing an experiment . you needed polarized light . well , that 's easy . you can use what 's called a polarizer . and this is a material that lets light through , but it only lets light through in one orientation , so you 're going to have a polarizer that , for instance , only lets through vertically polarized light . so this is a polarizer . these are cheap : thin , plastic , configured in a way so that it only lets light through that 's vertically polarized . any light coming in here that 's not vertically polarized gets blocked , or absorbed . so what that means is , if you used this polarizer and held it in between your eye and this light bulb , you would only get this light . all the rest of it would get blocked . or you could just rotate this thing and imagine a polarizer that only lets through horizontal light . now it would only let through light that was this way , and so you would only get this part of the light . or you could just orient it at any angle you want and block everything but the certain angle that this polarizer is defined as letting light through . so you can do this . and once you hold this up , you get polarized light , light that 's only got one orientation . so that 's what polarization means . but why do we care about polarization ? well , let me get rid of this for a minute . you 've heard of polarized sunglasses . so imagine you 're standing near water , or maybe you 're standing on ice or snow or something reflective . there 's a problem . say the sun 's out . it 's shining . it 's a beautiful day -- except there 's going to be glare . let 's say you 're looking down at something here on the ground . it 's going to get light reflecting off of it from just ... you know , light 's coming in from all direction . but it also gets this direct light from the sun . so it gets light from reflected off the clouds and whatever , whatever 's nearby , ambient light . and there 's also this direct sunlight . that 's harsh . if that reflects straight up to your eye , that hurts . you do n't like that . it blocks our vision . it 's hard to see , it 's glare . we do n't want this glare . so what can we do ? well , it just so happens that , when light reflects off of a surface , even though the light from the sun is not polarized , once it reflects , it does get polarized or at least partially polarized . so this surface here , once this light reflects , it 's coming in at all orientations . you got electric field ... you never know what electric field you 're going to get straight from the sun . and when it reflects , though , you mostly get , upon reflection , the direction of polarization defined by the plane of the surface that it hit . so because the floor is horizontal , when this light ray hits the ground and reflects , that reflected light gets partially polarized . this horizontal component of the electric field is going to be more present than the other components . maybe not completely . sometimes it could be . it could be completely polarized , but often it 's just partially polarized . but that 's pretty cool , because now you know what we can do . i know how to block this . we should get some sunglasses . we put some sunglasses on and we make our glasses so that these are polarized . and how do we want these polarized ? i want to get rid of the glare . so what i do is , i make sure my sunglasses only let through vertically polarized light . here 's some polarizers . that way , a lot of this glare gets blocked because it does not have a vertical orientation , it has a horizontal orientation . and then we can block it . so that 's one good thing that polarization does for us , and understanding it , we can get rid of glare . also , fishermen like it because , if you 're trying to look in the water at fish , you want to see in through the water , you want to see this light from the fish getting to you . you do n't want to see the glare off of the sun getting to you . so polarized sunglasses are useful . also , we can play a trick on our eye , if we really wanted to . you could take one of these , make one eye have a vertical orientation for the polarization , have the other eye with a horizontal ... and you 're thinking , `` this is stupid . `` why would you do this for ? '' `` this eye 's going to get a lot of glare . '' we would n't use these outside , when you 're , like , skiing or fishing , but you could play a trick on your eyes if you went to the movies and you went and watched a movie . well , the reason our eyes see 3d is because they 're spaced a little bit apart . they each get a different , slightly different image . that makes us see in 3d . we can play the same trick on our eye if we have the polarization like this . if light , if some of the light from the movie theater screen is coming in with one polarization , and the other light 's coming in with the other polarization , we can send two different images to our eyes at the same time . if you took these off , it 'd look like garbage because you 'd be getting both of these slightly different images , it 'd look all blurry . and it does . if you take off your 3d glasses and look at a 3d movie , looks terrible , because now both eyes are getting both images . but if you put your glasses back on , now this eye only gets the orientation that it 's supposed to get , and this eye only gets the orientation that it 's supposed to get , and you get a 3d image . so it 's useful in many ways . let me show you one more thing here . let 's come back here . this light was polarized vertically . so that 's called linear polarization . any time ... same with these . these are all linear polarization because , just up and down , one linear direction , just diagonal . this is also linear . all of these are linear . you can get circular polarized light . so if we come back to here , we 've got our electric field pointing up , like that . now let 's say we sent in another light ray , another light ray that also had a polarization , but not in this direction . let 's say our other light ray had polarization in this direction , so it looks like this , kind of like what our magnetic field would have looked like . but this is a completely different light ray with its own polarization and its own magnetic field . so we send this in . what would happen ? well , at this point , you 'd have a electric field that points this way . at this point , you 'd have a electric field that points that way . what would your eye see if you were over here ? let 's see . if i draw our axis here . all right , when this point right here gets to your eye , what am i going to see ? well , i 'm going to have a light ray that 's one part of a light ray . one component points up . that 's this electric field . one component points left . that 's this electric field . so the total , my total electric field , would point this way . i could to the pythagorean theorem if i wanted to figure out the size of it , but i just want to know the direction for now . and then it gets to here , and look at it : they both have zero . this light ray has zero electric field , this one has zero electric fields . so then it 'd just be at zero . now what happens over here ? well , i 've got light . this one points to the right at that point , this pink one , and then this red one would be pointing down . so what would i have at that point ? i 'd have light that went this way , and it would just be doing this over and over . it would just be ... i 'd just have diagonally polarized light . this is n't giving me anything new . you might think this is dumb . why do this ? why send in two different waves to just get diagonally polarized light ? i could have just sent in one wave that was diagonally polarized and got the same thing . the reason is , if you shift this purple wave , this pink wave , by 90 degrees of phase , by pi over two in phase , something magical happens . let me show you what happens here , if we move this to here . now we do n't just get diagonally linear polarized light . what we 're going to get is ... let me get rid of this . okay , so we start off with red , right ? the red electric field points up , and then this pink wave 's electric field is zero at that point . so this is all i have . my total electric field would just be up . i 'm going to draw it right here . the green 'll be the total . now i come over to here , and at this point , there 's some red electric field that points up , but there 's some of this other electric field that points this way . so i 'd have a total electric field that would point that way . and then i get over to here , and i 'd have all of the electric field from the pink one , none from the red one . it would point all left then . look what 's happening . the polarization of this light , if i shift this , if i 'm sitting here , looking with my eye , as my eye receives this light , i 'm going to see this light rotate its polarization . the polarization i 'm going to notice swings around in a circular pattern . and because of this , we call this circular polarization . so this is another type of polarization , where the actual angle of polarization rotates smoothly as this light ray enters your eye . and you know what ? er , drrr ... all right , actually , i sent you to receive this one first . that makes no sense . you 're going to receive the ones closes to you first in this light ray going this way . so you 'd actually receive this one first , then that one , then this one , then this one . because of that , you would n't see this going in a counterclockwise way , you 'd see this going in a clockwise circularly polarized way . sorry about that . you might think , `` okay , why ? `` why even bother with circular polarization ? '' well , i kind of lied earlier . turns out , in the movie theater example , they do n't actually do it like this , typically . oftentimes in the movie theaters , we do n't have just linearly polarized sunglasses . this would be a problem because , when you look at the movie theater screen , and if you were to tilt your head just a little bit ... think about it . this one 's not really going to get the right image anymore . it 's going to get some of both . and this one 's going to get some of both . it 's going to be blurry . your head would have to be perfectly level the whole time , which might be annoying . so what we do is , instead , we create circular polarized glasses , so that this one would only get one polarization , this one would get the other direction . this way , even if you tilt your head a little bit ... shoot , clockwise is clockwise , counterclockwise is counterclockwise . by using circular polarization for 3d movies , it can make it a little easier on you eyes to see a better 3d image , even if your head 's tilted a little bit .
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but either way , you could have this wave polarized along any direction . i mean , a light ray like this , if we had it coming in diagonal , this light ray that 's oscillating like this , where the electric field oscillates like that , that also polarized . these are both polarized because there 's only one direction that the electric field is oscillating in .
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does the reflected ray behaves like the light coming out of polarizer ?
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- let 's talk about polarization of light . we know what light waves are ; they 're electromagnetic waves . so they 're made out of electric fields . and that 's not good enough . we know there 's not just electric fields . that could n't sustain itself . there 's got to be magnetic fields there , as well , that are changing . those are perpendicular , so you can kind of draw them . it 's hard , on something two-dimensional , but you can kind of imagine those looking something like this . and those magnetic fields would point at a right angle to the electric fields . but this gets really messy if i try to draw both the electric and magnetic fields at the same time . so we 're going to leave the magnetic fields out . it 's often good enough to just know the direction of the electric field when we focus on the electric field . so what does polarization mean ? polarization refers to the fact that , if this light ray was heading straight toward your eye , or a detector , over here , what would you see ? well , if i draw an axis over here , and this point here , in the middle , this is this line -- so imagine we 're looking straight down that line -- and then up and down is up and down , and then left and right , that direction i have the magnetic field , would be this way and that way . what would my eye see ? well , my eye 's only going to see electric fields that either point up or electric fields that point down . they might have different values , but i 'm only going to see electric fields that point up or down . because of that , this light ray is polarized . so polarized light is light where the electric field is only oscillating in one direction . up or down , that 's one direction -- vertically . or it could be polarized horizontally . or it could be polarized diagonally . but either way , you could have this wave polarized along any direction . i mean , a light ray like this , if we had it coming in diagonal , this light ray that 's oscillating like this , where the electric field oscillates like that , that also polarized . these are both polarized because there 's only one direction that the electric field is oscillating in . and you might thing , `` pff , how could you ever have `` a light ray that 's not polarized ? '' easy . most light that you get is not polarized . that is to say , light that 's coming from the sun , straight from the sun -- typically not polarized . light from a lightbulb , an old incandescent light bulb , this thing 's hot . you can get light polarized in any direction , all at once , all overlapping . so if we draw this case for a light bulb , just a random incandescent light bulb , you might get light , some of the light , hitting you eye , you can get some light that 's got that direction , you got light that 's got this direction , you got light in all these directions at any given moment . i mean , you 'd have to add these up to get the total , and they might not all be the same value . but what i 'm trying to say is , at any given moment , you do n't know what direction the electric field 's going to be hitting your eye at from a random source . it could be in any direction . so this is not polarized . this diagram represents light that is not polarized . at some point , the field might be pointing this way , at some later point it 's this way ; it 's just random . you never know which way the electric field 's going to be pointing . whereas these over here , these are polarized . so how could you polarize this light ? let 's say you wanted light that was polarized . you were doing an experiment . you needed polarized light . well , that 's easy . you can use what 's called a polarizer . and this is a material that lets light through , but it only lets light through in one orientation , so you 're going to have a polarizer that , for instance , only lets through vertically polarized light . so this is a polarizer . these are cheap : thin , plastic , configured in a way so that it only lets light through that 's vertically polarized . any light coming in here that 's not vertically polarized gets blocked , or absorbed . so what that means is , if you used this polarizer and held it in between your eye and this light bulb , you would only get this light . all the rest of it would get blocked . or you could just rotate this thing and imagine a polarizer that only lets through horizontal light . now it would only let through light that was this way , and so you would only get this part of the light . or you could just orient it at any angle you want and block everything but the certain angle that this polarizer is defined as letting light through . so you can do this . and once you hold this up , you get polarized light , light that 's only got one orientation . so that 's what polarization means . but why do we care about polarization ? well , let me get rid of this for a minute . you 've heard of polarized sunglasses . so imagine you 're standing near water , or maybe you 're standing on ice or snow or something reflective . there 's a problem . say the sun 's out . it 's shining . it 's a beautiful day -- except there 's going to be glare . let 's say you 're looking down at something here on the ground . it 's going to get light reflecting off of it from just ... you know , light 's coming in from all direction . but it also gets this direct light from the sun . so it gets light from reflected off the clouds and whatever , whatever 's nearby , ambient light . and there 's also this direct sunlight . that 's harsh . if that reflects straight up to your eye , that hurts . you do n't like that . it blocks our vision . it 's hard to see , it 's glare . we do n't want this glare . so what can we do ? well , it just so happens that , when light reflects off of a surface , even though the light from the sun is not polarized , once it reflects , it does get polarized or at least partially polarized . so this surface here , once this light reflects , it 's coming in at all orientations . you got electric field ... you never know what electric field you 're going to get straight from the sun . and when it reflects , though , you mostly get , upon reflection , the direction of polarization defined by the plane of the surface that it hit . so because the floor is horizontal , when this light ray hits the ground and reflects , that reflected light gets partially polarized . this horizontal component of the electric field is going to be more present than the other components . maybe not completely . sometimes it could be . it could be completely polarized , but often it 's just partially polarized . but that 's pretty cool , because now you know what we can do . i know how to block this . we should get some sunglasses . we put some sunglasses on and we make our glasses so that these are polarized . and how do we want these polarized ? i want to get rid of the glare . so what i do is , i make sure my sunglasses only let through vertically polarized light . here 's some polarizers . that way , a lot of this glare gets blocked because it does not have a vertical orientation , it has a horizontal orientation . and then we can block it . so that 's one good thing that polarization does for us , and understanding it , we can get rid of glare . also , fishermen like it because , if you 're trying to look in the water at fish , you want to see in through the water , you want to see this light from the fish getting to you . you do n't want to see the glare off of the sun getting to you . so polarized sunglasses are useful . also , we can play a trick on our eye , if we really wanted to . you could take one of these , make one eye have a vertical orientation for the polarization , have the other eye with a horizontal ... and you 're thinking , `` this is stupid . `` why would you do this for ? '' `` this eye 's going to get a lot of glare . '' we would n't use these outside , when you 're , like , skiing or fishing , but you could play a trick on your eyes if you went to the movies and you went and watched a movie . well , the reason our eyes see 3d is because they 're spaced a little bit apart . they each get a different , slightly different image . that makes us see in 3d . we can play the same trick on our eye if we have the polarization like this . if light , if some of the light from the movie theater screen is coming in with one polarization , and the other light 's coming in with the other polarization , we can send two different images to our eyes at the same time . if you took these off , it 'd look like garbage because you 'd be getting both of these slightly different images , it 'd look all blurry . and it does . if you take off your 3d glasses and look at a 3d movie , looks terrible , because now both eyes are getting both images . but if you put your glasses back on , now this eye only gets the orientation that it 's supposed to get , and this eye only gets the orientation that it 's supposed to get , and you get a 3d image . so it 's useful in many ways . let me show you one more thing here . let 's come back here . this light was polarized vertically . so that 's called linear polarization . any time ... same with these . these are all linear polarization because , just up and down , one linear direction , just diagonal . this is also linear . all of these are linear . you can get circular polarized light . so if we come back to here , we 've got our electric field pointing up , like that . now let 's say we sent in another light ray , another light ray that also had a polarization , but not in this direction . let 's say our other light ray had polarization in this direction , so it looks like this , kind of like what our magnetic field would have looked like . but this is a completely different light ray with its own polarization and its own magnetic field . so we send this in . what would happen ? well , at this point , you 'd have a electric field that points this way . at this point , you 'd have a electric field that points that way . what would your eye see if you were over here ? let 's see . if i draw our axis here . all right , when this point right here gets to your eye , what am i going to see ? well , i 'm going to have a light ray that 's one part of a light ray . one component points up . that 's this electric field . one component points left . that 's this electric field . so the total , my total electric field , would point this way . i could to the pythagorean theorem if i wanted to figure out the size of it , but i just want to know the direction for now . and then it gets to here , and look at it : they both have zero . this light ray has zero electric field , this one has zero electric fields . so then it 'd just be at zero . now what happens over here ? well , i 've got light . this one points to the right at that point , this pink one , and then this red one would be pointing down . so what would i have at that point ? i 'd have light that went this way , and it would just be doing this over and over . it would just be ... i 'd just have diagonally polarized light . this is n't giving me anything new . you might think this is dumb . why do this ? why send in two different waves to just get diagonally polarized light ? i could have just sent in one wave that was diagonally polarized and got the same thing . the reason is , if you shift this purple wave , this pink wave , by 90 degrees of phase , by pi over two in phase , something magical happens . let me show you what happens here , if we move this to here . now we do n't just get diagonally linear polarized light . what we 're going to get is ... let me get rid of this . okay , so we start off with red , right ? the red electric field points up , and then this pink wave 's electric field is zero at that point . so this is all i have . my total electric field would just be up . i 'm going to draw it right here . the green 'll be the total . now i come over to here , and at this point , there 's some red electric field that points up , but there 's some of this other electric field that points this way . so i 'd have a total electric field that would point that way . and then i get over to here , and i 'd have all of the electric field from the pink one , none from the red one . it would point all left then . look what 's happening . the polarization of this light , if i shift this , if i 'm sitting here , looking with my eye , as my eye receives this light , i 'm going to see this light rotate its polarization . the polarization i 'm going to notice swings around in a circular pattern . and because of this , we call this circular polarization . so this is another type of polarization , where the actual angle of polarization rotates smoothly as this light ray enters your eye . and you know what ? er , drrr ... all right , actually , i sent you to receive this one first . that makes no sense . you 're going to receive the ones closes to you first in this light ray going this way . so you 'd actually receive this one first , then that one , then this one , then this one . because of that , you would n't see this going in a counterclockwise way , you 'd see this going in a clockwise circularly polarized way . sorry about that . you might think , `` okay , why ? `` why even bother with circular polarization ? '' well , i kind of lied earlier . turns out , in the movie theater example , they do n't actually do it like this , typically . oftentimes in the movie theaters , we do n't have just linearly polarized sunglasses . this would be a problem because , when you look at the movie theater screen , and if you were to tilt your head just a little bit ... think about it . this one 's not really going to get the right image anymore . it 's going to get some of both . and this one 's going to get some of both . it 's going to be blurry . your head would have to be perfectly level the whole time , which might be annoying . so what we do is , instead , we create circular polarized glasses , so that this one would only get one polarization , this one would get the other direction . this way , even if you tilt your head a little bit ... shoot , clockwise is clockwise , counterclockwise is counterclockwise . by using circular polarization for 3d movies , it can make it a little easier on you eyes to see a better 3d image , even if your head 's tilted a little bit .
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they might have different values , but i 'm only going to see electric fields that point up or down . because of that , this light ray is polarized . so polarized light is light where the electric field is only oscillating in one direction .
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what experiment was michael faraday doing with the polarized light ray ?
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- let 's talk about polarization of light . we know what light waves are ; they 're electromagnetic waves . so they 're made out of electric fields . and that 's not good enough . we know there 's not just electric fields . that could n't sustain itself . there 's got to be magnetic fields there , as well , that are changing . those are perpendicular , so you can kind of draw them . it 's hard , on something two-dimensional , but you can kind of imagine those looking something like this . and those magnetic fields would point at a right angle to the electric fields . but this gets really messy if i try to draw both the electric and magnetic fields at the same time . so we 're going to leave the magnetic fields out . it 's often good enough to just know the direction of the electric field when we focus on the electric field . so what does polarization mean ? polarization refers to the fact that , if this light ray was heading straight toward your eye , or a detector , over here , what would you see ? well , if i draw an axis over here , and this point here , in the middle , this is this line -- so imagine we 're looking straight down that line -- and then up and down is up and down , and then left and right , that direction i have the magnetic field , would be this way and that way . what would my eye see ? well , my eye 's only going to see electric fields that either point up or electric fields that point down . they might have different values , but i 'm only going to see electric fields that point up or down . because of that , this light ray is polarized . so polarized light is light where the electric field is only oscillating in one direction . up or down , that 's one direction -- vertically . or it could be polarized horizontally . or it could be polarized diagonally . but either way , you could have this wave polarized along any direction . i mean , a light ray like this , if we had it coming in diagonal , this light ray that 's oscillating like this , where the electric field oscillates like that , that also polarized . these are both polarized because there 's only one direction that the electric field is oscillating in . and you might thing , `` pff , how could you ever have `` a light ray that 's not polarized ? '' easy . most light that you get is not polarized . that is to say , light that 's coming from the sun , straight from the sun -- typically not polarized . light from a lightbulb , an old incandescent light bulb , this thing 's hot . you can get light polarized in any direction , all at once , all overlapping . so if we draw this case for a light bulb , just a random incandescent light bulb , you might get light , some of the light , hitting you eye , you can get some light that 's got that direction , you got light that 's got this direction , you got light in all these directions at any given moment . i mean , you 'd have to add these up to get the total , and they might not all be the same value . but what i 'm trying to say is , at any given moment , you do n't know what direction the electric field 's going to be hitting your eye at from a random source . it could be in any direction . so this is not polarized . this diagram represents light that is not polarized . at some point , the field might be pointing this way , at some later point it 's this way ; it 's just random . you never know which way the electric field 's going to be pointing . whereas these over here , these are polarized . so how could you polarize this light ? let 's say you wanted light that was polarized . you were doing an experiment . you needed polarized light . well , that 's easy . you can use what 's called a polarizer . and this is a material that lets light through , but it only lets light through in one orientation , so you 're going to have a polarizer that , for instance , only lets through vertically polarized light . so this is a polarizer . these are cheap : thin , plastic , configured in a way so that it only lets light through that 's vertically polarized . any light coming in here that 's not vertically polarized gets blocked , or absorbed . so what that means is , if you used this polarizer and held it in between your eye and this light bulb , you would only get this light . all the rest of it would get blocked . or you could just rotate this thing and imagine a polarizer that only lets through horizontal light . now it would only let through light that was this way , and so you would only get this part of the light . or you could just orient it at any angle you want and block everything but the certain angle that this polarizer is defined as letting light through . so you can do this . and once you hold this up , you get polarized light , light that 's only got one orientation . so that 's what polarization means . but why do we care about polarization ? well , let me get rid of this for a minute . you 've heard of polarized sunglasses . so imagine you 're standing near water , or maybe you 're standing on ice or snow or something reflective . there 's a problem . say the sun 's out . it 's shining . it 's a beautiful day -- except there 's going to be glare . let 's say you 're looking down at something here on the ground . it 's going to get light reflecting off of it from just ... you know , light 's coming in from all direction . but it also gets this direct light from the sun . so it gets light from reflected off the clouds and whatever , whatever 's nearby , ambient light . and there 's also this direct sunlight . that 's harsh . if that reflects straight up to your eye , that hurts . you do n't like that . it blocks our vision . it 's hard to see , it 's glare . we do n't want this glare . so what can we do ? well , it just so happens that , when light reflects off of a surface , even though the light from the sun is not polarized , once it reflects , it does get polarized or at least partially polarized . so this surface here , once this light reflects , it 's coming in at all orientations . you got electric field ... you never know what electric field you 're going to get straight from the sun . and when it reflects , though , you mostly get , upon reflection , the direction of polarization defined by the plane of the surface that it hit . so because the floor is horizontal , when this light ray hits the ground and reflects , that reflected light gets partially polarized . this horizontal component of the electric field is going to be more present than the other components . maybe not completely . sometimes it could be . it could be completely polarized , but often it 's just partially polarized . but that 's pretty cool , because now you know what we can do . i know how to block this . we should get some sunglasses . we put some sunglasses on and we make our glasses so that these are polarized . and how do we want these polarized ? i want to get rid of the glare . so what i do is , i make sure my sunglasses only let through vertically polarized light . here 's some polarizers . that way , a lot of this glare gets blocked because it does not have a vertical orientation , it has a horizontal orientation . and then we can block it . so that 's one good thing that polarization does for us , and understanding it , we can get rid of glare . also , fishermen like it because , if you 're trying to look in the water at fish , you want to see in through the water , you want to see this light from the fish getting to you . you do n't want to see the glare off of the sun getting to you . so polarized sunglasses are useful . also , we can play a trick on our eye , if we really wanted to . you could take one of these , make one eye have a vertical orientation for the polarization , have the other eye with a horizontal ... and you 're thinking , `` this is stupid . `` why would you do this for ? '' `` this eye 's going to get a lot of glare . '' we would n't use these outside , when you 're , like , skiing or fishing , but you could play a trick on your eyes if you went to the movies and you went and watched a movie . well , the reason our eyes see 3d is because they 're spaced a little bit apart . they each get a different , slightly different image . that makes us see in 3d . we can play the same trick on our eye if we have the polarization like this . if light , if some of the light from the movie theater screen is coming in with one polarization , and the other light 's coming in with the other polarization , we can send two different images to our eyes at the same time . if you took these off , it 'd look like garbage because you 'd be getting both of these slightly different images , it 'd look all blurry . and it does . if you take off your 3d glasses and look at a 3d movie , looks terrible , because now both eyes are getting both images . but if you put your glasses back on , now this eye only gets the orientation that it 's supposed to get , and this eye only gets the orientation that it 's supposed to get , and you get a 3d image . so it 's useful in many ways . let me show you one more thing here . let 's come back here . this light was polarized vertically . so that 's called linear polarization . any time ... same with these . these are all linear polarization because , just up and down , one linear direction , just diagonal . this is also linear . all of these are linear . you can get circular polarized light . so if we come back to here , we 've got our electric field pointing up , like that . now let 's say we sent in another light ray , another light ray that also had a polarization , but not in this direction . let 's say our other light ray had polarization in this direction , so it looks like this , kind of like what our magnetic field would have looked like . but this is a completely different light ray with its own polarization and its own magnetic field . so we send this in . what would happen ? well , at this point , you 'd have a electric field that points this way . at this point , you 'd have a electric field that points that way . what would your eye see if you were over here ? let 's see . if i draw our axis here . all right , when this point right here gets to your eye , what am i going to see ? well , i 'm going to have a light ray that 's one part of a light ray . one component points up . that 's this electric field . one component points left . that 's this electric field . so the total , my total electric field , would point this way . i could to the pythagorean theorem if i wanted to figure out the size of it , but i just want to know the direction for now . and then it gets to here , and look at it : they both have zero . this light ray has zero electric field , this one has zero electric fields . so then it 'd just be at zero . now what happens over here ? well , i 've got light . this one points to the right at that point , this pink one , and then this red one would be pointing down . so what would i have at that point ? i 'd have light that went this way , and it would just be doing this over and over . it would just be ... i 'd just have diagonally polarized light . this is n't giving me anything new . you might think this is dumb . why do this ? why send in two different waves to just get diagonally polarized light ? i could have just sent in one wave that was diagonally polarized and got the same thing . the reason is , if you shift this purple wave , this pink wave , by 90 degrees of phase , by pi over two in phase , something magical happens . let me show you what happens here , if we move this to here . now we do n't just get diagonally linear polarized light . what we 're going to get is ... let me get rid of this . okay , so we start off with red , right ? the red electric field points up , and then this pink wave 's electric field is zero at that point . so this is all i have . my total electric field would just be up . i 'm going to draw it right here . the green 'll be the total . now i come over to here , and at this point , there 's some red electric field that points up , but there 's some of this other electric field that points this way . so i 'd have a total electric field that would point that way . and then i get over to here , and i 'd have all of the electric field from the pink one , none from the red one . it would point all left then . look what 's happening . the polarization of this light , if i shift this , if i 'm sitting here , looking with my eye , as my eye receives this light , i 'm going to see this light rotate its polarization . the polarization i 'm going to notice swings around in a circular pattern . and because of this , we call this circular polarization . so this is another type of polarization , where the actual angle of polarization rotates smoothly as this light ray enters your eye . and you know what ? er , drrr ... all right , actually , i sent you to receive this one first . that makes no sense . you 're going to receive the ones closes to you first in this light ray going this way . so you 'd actually receive this one first , then that one , then this one , then this one . because of that , you would n't see this going in a counterclockwise way , you 'd see this going in a clockwise circularly polarized way . sorry about that . you might think , `` okay , why ? `` why even bother with circular polarization ? '' well , i kind of lied earlier . turns out , in the movie theater example , they do n't actually do it like this , typically . oftentimes in the movie theaters , we do n't have just linearly polarized sunglasses . this would be a problem because , when you look at the movie theater screen , and if you were to tilt your head just a little bit ... think about it . this one 's not really going to get the right image anymore . it 's going to get some of both . and this one 's going to get some of both . it 's going to be blurry . your head would have to be perfectly level the whole time , which might be annoying . so what we do is , instead , we create circular polarized glasses , so that this one would only get one polarization , this one would get the other direction . this way , even if you tilt your head a little bit ... shoot , clockwise is clockwise , counterclockwise is counterclockwise . by using circular polarization for 3d movies , it can make it a little easier on you eyes to see a better 3d image , even if your head 's tilted a little bit .
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you do n't want to see the glare off of the sun getting to you . so polarized sunglasses are useful . also , we can play a trick on our eye , if we really wanted to .
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how exactly do polarized sunglasses work ?
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- let 's talk about polarization of light . we know what light waves are ; they 're electromagnetic waves . so they 're made out of electric fields . and that 's not good enough . we know there 's not just electric fields . that could n't sustain itself . there 's got to be magnetic fields there , as well , that are changing . those are perpendicular , so you can kind of draw them . it 's hard , on something two-dimensional , but you can kind of imagine those looking something like this . and those magnetic fields would point at a right angle to the electric fields . but this gets really messy if i try to draw both the electric and magnetic fields at the same time . so we 're going to leave the magnetic fields out . it 's often good enough to just know the direction of the electric field when we focus on the electric field . so what does polarization mean ? polarization refers to the fact that , if this light ray was heading straight toward your eye , or a detector , over here , what would you see ? well , if i draw an axis over here , and this point here , in the middle , this is this line -- so imagine we 're looking straight down that line -- and then up and down is up and down , and then left and right , that direction i have the magnetic field , would be this way and that way . what would my eye see ? well , my eye 's only going to see electric fields that either point up or electric fields that point down . they might have different values , but i 'm only going to see electric fields that point up or down . because of that , this light ray is polarized . so polarized light is light where the electric field is only oscillating in one direction . up or down , that 's one direction -- vertically . or it could be polarized horizontally . or it could be polarized diagonally . but either way , you could have this wave polarized along any direction . i mean , a light ray like this , if we had it coming in diagonal , this light ray that 's oscillating like this , where the electric field oscillates like that , that also polarized . these are both polarized because there 's only one direction that the electric field is oscillating in . and you might thing , `` pff , how could you ever have `` a light ray that 's not polarized ? '' easy . most light that you get is not polarized . that is to say , light that 's coming from the sun , straight from the sun -- typically not polarized . light from a lightbulb , an old incandescent light bulb , this thing 's hot . you can get light polarized in any direction , all at once , all overlapping . so if we draw this case for a light bulb , just a random incandescent light bulb , you might get light , some of the light , hitting you eye , you can get some light that 's got that direction , you got light that 's got this direction , you got light in all these directions at any given moment . i mean , you 'd have to add these up to get the total , and they might not all be the same value . but what i 'm trying to say is , at any given moment , you do n't know what direction the electric field 's going to be hitting your eye at from a random source . it could be in any direction . so this is not polarized . this diagram represents light that is not polarized . at some point , the field might be pointing this way , at some later point it 's this way ; it 's just random . you never know which way the electric field 's going to be pointing . whereas these over here , these are polarized . so how could you polarize this light ? let 's say you wanted light that was polarized . you were doing an experiment . you needed polarized light . well , that 's easy . you can use what 's called a polarizer . and this is a material that lets light through , but it only lets light through in one orientation , so you 're going to have a polarizer that , for instance , only lets through vertically polarized light . so this is a polarizer . these are cheap : thin , plastic , configured in a way so that it only lets light through that 's vertically polarized . any light coming in here that 's not vertically polarized gets blocked , or absorbed . so what that means is , if you used this polarizer and held it in between your eye and this light bulb , you would only get this light . all the rest of it would get blocked . or you could just rotate this thing and imagine a polarizer that only lets through horizontal light . now it would only let through light that was this way , and so you would only get this part of the light . or you could just orient it at any angle you want and block everything but the certain angle that this polarizer is defined as letting light through . so you can do this . and once you hold this up , you get polarized light , light that 's only got one orientation . so that 's what polarization means . but why do we care about polarization ? well , let me get rid of this for a minute . you 've heard of polarized sunglasses . so imagine you 're standing near water , or maybe you 're standing on ice or snow or something reflective . there 's a problem . say the sun 's out . it 's shining . it 's a beautiful day -- except there 's going to be glare . let 's say you 're looking down at something here on the ground . it 's going to get light reflecting off of it from just ... you know , light 's coming in from all direction . but it also gets this direct light from the sun . so it gets light from reflected off the clouds and whatever , whatever 's nearby , ambient light . and there 's also this direct sunlight . that 's harsh . if that reflects straight up to your eye , that hurts . you do n't like that . it blocks our vision . it 's hard to see , it 's glare . we do n't want this glare . so what can we do ? well , it just so happens that , when light reflects off of a surface , even though the light from the sun is not polarized , once it reflects , it does get polarized or at least partially polarized . so this surface here , once this light reflects , it 's coming in at all orientations . you got electric field ... you never know what electric field you 're going to get straight from the sun . and when it reflects , though , you mostly get , upon reflection , the direction of polarization defined by the plane of the surface that it hit . so because the floor is horizontal , when this light ray hits the ground and reflects , that reflected light gets partially polarized . this horizontal component of the electric field is going to be more present than the other components . maybe not completely . sometimes it could be . it could be completely polarized , but often it 's just partially polarized . but that 's pretty cool , because now you know what we can do . i know how to block this . we should get some sunglasses . we put some sunglasses on and we make our glasses so that these are polarized . and how do we want these polarized ? i want to get rid of the glare . so what i do is , i make sure my sunglasses only let through vertically polarized light . here 's some polarizers . that way , a lot of this glare gets blocked because it does not have a vertical orientation , it has a horizontal orientation . and then we can block it . so that 's one good thing that polarization does for us , and understanding it , we can get rid of glare . also , fishermen like it because , if you 're trying to look in the water at fish , you want to see in through the water , you want to see this light from the fish getting to you . you do n't want to see the glare off of the sun getting to you . so polarized sunglasses are useful . also , we can play a trick on our eye , if we really wanted to . you could take one of these , make one eye have a vertical orientation for the polarization , have the other eye with a horizontal ... and you 're thinking , `` this is stupid . `` why would you do this for ? '' `` this eye 's going to get a lot of glare . '' we would n't use these outside , when you 're , like , skiing or fishing , but you could play a trick on your eyes if you went to the movies and you went and watched a movie . well , the reason our eyes see 3d is because they 're spaced a little bit apart . they each get a different , slightly different image . that makes us see in 3d . we can play the same trick on our eye if we have the polarization like this . if light , if some of the light from the movie theater screen is coming in with one polarization , and the other light 's coming in with the other polarization , we can send two different images to our eyes at the same time . if you took these off , it 'd look like garbage because you 'd be getting both of these slightly different images , it 'd look all blurry . and it does . if you take off your 3d glasses and look at a 3d movie , looks terrible , because now both eyes are getting both images . but if you put your glasses back on , now this eye only gets the orientation that it 's supposed to get , and this eye only gets the orientation that it 's supposed to get , and you get a 3d image . so it 's useful in many ways . let me show you one more thing here . let 's come back here . this light was polarized vertically . so that 's called linear polarization . any time ... same with these . these are all linear polarization because , just up and down , one linear direction , just diagonal . this is also linear . all of these are linear . you can get circular polarized light . so if we come back to here , we 've got our electric field pointing up , like that . now let 's say we sent in another light ray , another light ray that also had a polarization , but not in this direction . let 's say our other light ray had polarization in this direction , so it looks like this , kind of like what our magnetic field would have looked like . but this is a completely different light ray with its own polarization and its own magnetic field . so we send this in . what would happen ? well , at this point , you 'd have a electric field that points this way . at this point , you 'd have a electric field that points that way . what would your eye see if you were over here ? let 's see . if i draw our axis here . all right , when this point right here gets to your eye , what am i going to see ? well , i 'm going to have a light ray that 's one part of a light ray . one component points up . that 's this electric field . one component points left . that 's this electric field . so the total , my total electric field , would point this way . i could to the pythagorean theorem if i wanted to figure out the size of it , but i just want to know the direction for now . and then it gets to here , and look at it : they both have zero . this light ray has zero electric field , this one has zero electric fields . so then it 'd just be at zero . now what happens over here ? well , i 've got light . this one points to the right at that point , this pink one , and then this red one would be pointing down . so what would i have at that point ? i 'd have light that went this way , and it would just be doing this over and over . it would just be ... i 'd just have diagonally polarized light . this is n't giving me anything new . you might think this is dumb . why do this ? why send in two different waves to just get diagonally polarized light ? i could have just sent in one wave that was diagonally polarized and got the same thing . the reason is , if you shift this purple wave , this pink wave , by 90 degrees of phase , by pi over two in phase , something magical happens . let me show you what happens here , if we move this to here . now we do n't just get diagonally linear polarized light . what we 're going to get is ... let me get rid of this . okay , so we start off with red , right ? the red electric field points up , and then this pink wave 's electric field is zero at that point . so this is all i have . my total electric field would just be up . i 'm going to draw it right here . the green 'll be the total . now i come over to here , and at this point , there 's some red electric field that points up , but there 's some of this other electric field that points this way . so i 'd have a total electric field that would point that way . and then i get over to here , and i 'd have all of the electric field from the pink one , none from the red one . it would point all left then . look what 's happening . the polarization of this light , if i shift this , if i 'm sitting here , looking with my eye , as my eye receives this light , i 'm going to see this light rotate its polarization . the polarization i 'm going to notice swings around in a circular pattern . and because of this , we call this circular polarization . so this is another type of polarization , where the actual angle of polarization rotates smoothly as this light ray enters your eye . and you know what ? er , drrr ... all right , actually , i sent you to receive this one first . that makes no sense . you 're going to receive the ones closes to you first in this light ray going this way . so you 'd actually receive this one first , then that one , then this one , then this one . because of that , you would n't see this going in a counterclockwise way , you 'd see this going in a clockwise circularly polarized way . sorry about that . you might think , `` okay , why ? `` why even bother with circular polarization ? '' well , i kind of lied earlier . turns out , in the movie theater example , they do n't actually do it like this , typically . oftentimes in the movie theaters , we do n't have just linearly polarized sunglasses . this would be a problem because , when you look at the movie theater screen , and if you were to tilt your head just a little bit ... think about it . this one 's not really going to get the right image anymore . it 's going to get some of both . and this one 's going to get some of both . it 's going to be blurry . your head would have to be perfectly level the whole time , which might be annoying . so what we do is , instead , we create circular polarized glasses , so that this one would only get one polarization , this one would get the other direction . this way , even if you tilt your head a little bit ... shoot , clockwise is clockwise , counterclockwise is counterclockwise . by using circular polarization for 3d movies , it can make it a little easier on you eyes to see a better 3d image , even if your head 's tilted a little bit .
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you do n't want to see the glare off of the sun getting to you . so polarized sunglasses are useful . also , we can play a trick on our eye , if we really wanted to .
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do polarized sunglasses have something to do with the sun 's rays or just its reflection ?
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- let 's talk about polarization of light . we know what light waves are ; they 're electromagnetic waves . so they 're made out of electric fields . and that 's not good enough . we know there 's not just electric fields . that could n't sustain itself . there 's got to be magnetic fields there , as well , that are changing . those are perpendicular , so you can kind of draw them . it 's hard , on something two-dimensional , but you can kind of imagine those looking something like this . and those magnetic fields would point at a right angle to the electric fields . but this gets really messy if i try to draw both the electric and magnetic fields at the same time . so we 're going to leave the magnetic fields out . it 's often good enough to just know the direction of the electric field when we focus on the electric field . so what does polarization mean ? polarization refers to the fact that , if this light ray was heading straight toward your eye , or a detector , over here , what would you see ? well , if i draw an axis over here , and this point here , in the middle , this is this line -- so imagine we 're looking straight down that line -- and then up and down is up and down , and then left and right , that direction i have the magnetic field , would be this way and that way . what would my eye see ? well , my eye 's only going to see electric fields that either point up or electric fields that point down . they might have different values , but i 'm only going to see electric fields that point up or down . because of that , this light ray is polarized . so polarized light is light where the electric field is only oscillating in one direction . up or down , that 's one direction -- vertically . or it could be polarized horizontally . or it could be polarized diagonally . but either way , you could have this wave polarized along any direction . i mean , a light ray like this , if we had it coming in diagonal , this light ray that 's oscillating like this , where the electric field oscillates like that , that also polarized . these are both polarized because there 's only one direction that the electric field is oscillating in . and you might thing , `` pff , how could you ever have `` a light ray that 's not polarized ? '' easy . most light that you get is not polarized . that is to say , light that 's coming from the sun , straight from the sun -- typically not polarized . light from a lightbulb , an old incandescent light bulb , this thing 's hot . you can get light polarized in any direction , all at once , all overlapping . so if we draw this case for a light bulb , just a random incandescent light bulb , you might get light , some of the light , hitting you eye , you can get some light that 's got that direction , you got light that 's got this direction , you got light in all these directions at any given moment . i mean , you 'd have to add these up to get the total , and they might not all be the same value . but what i 'm trying to say is , at any given moment , you do n't know what direction the electric field 's going to be hitting your eye at from a random source . it could be in any direction . so this is not polarized . this diagram represents light that is not polarized . at some point , the field might be pointing this way , at some later point it 's this way ; it 's just random . you never know which way the electric field 's going to be pointing . whereas these over here , these are polarized . so how could you polarize this light ? let 's say you wanted light that was polarized . you were doing an experiment . you needed polarized light . well , that 's easy . you can use what 's called a polarizer . and this is a material that lets light through , but it only lets light through in one orientation , so you 're going to have a polarizer that , for instance , only lets through vertically polarized light . so this is a polarizer . these are cheap : thin , plastic , configured in a way so that it only lets light through that 's vertically polarized . any light coming in here that 's not vertically polarized gets blocked , or absorbed . so what that means is , if you used this polarizer and held it in between your eye and this light bulb , you would only get this light . all the rest of it would get blocked . or you could just rotate this thing and imagine a polarizer that only lets through horizontal light . now it would only let through light that was this way , and so you would only get this part of the light . or you could just orient it at any angle you want and block everything but the certain angle that this polarizer is defined as letting light through . so you can do this . and once you hold this up , you get polarized light , light that 's only got one orientation . so that 's what polarization means . but why do we care about polarization ? well , let me get rid of this for a minute . you 've heard of polarized sunglasses . so imagine you 're standing near water , or maybe you 're standing on ice or snow or something reflective . there 's a problem . say the sun 's out . it 's shining . it 's a beautiful day -- except there 's going to be glare . let 's say you 're looking down at something here on the ground . it 's going to get light reflecting off of it from just ... you know , light 's coming in from all direction . but it also gets this direct light from the sun . so it gets light from reflected off the clouds and whatever , whatever 's nearby , ambient light . and there 's also this direct sunlight . that 's harsh . if that reflects straight up to your eye , that hurts . you do n't like that . it blocks our vision . it 's hard to see , it 's glare . we do n't want this glare . so what can we do ? well , it just so happens that , when light reflects off of a surface , even though the light from the sun is not polarized , once it reflects , it does get polarized or at least partially polarized . so this surface here , once this light reflects , it 's coming in at all orientations . you got electric field ... you never know what electric field you 're going to get straight from the sun . and when it reflects , though , you mostly get , upon reflection , the direction of polarization defined by the plane of the surface that it hit . so because the floor is horizontal , when this light ray hits the ground and reflects , that reflected light gets partially polarized . this horizontal component of the electric field is going to be more present than the other components . maybe not completely . sometimes it could be . it could be completely polarized , but often it 's just partially polarized . but that 's pretty cool , because now you know what we can do . i know how to block this . we should get some sunglasses . we put some sunglasses on and we make our glasses so that these are polarized . and how do we want these polarized ? i want to get rid of the glare . so what i do is , i make sure my sunglasses only let through vertically polarized light . here 's some polarizers . that way , a lot of this glare gets blocked because it does not have a vertical orientation , it has a horizontal orientation . and then we can block it . so that 's one good thing that polarization does for us , and understanding it , we can get rid of glare . also , fishermen like it because , if you 're trying to look in the water at fish , you want to see in through the water , you want to see this light from the fish getting to you . you do n't want to see the glare off of the sun getting to you . so polarized sunglasses are useful . also , we can play a trick on our eye , if we really wanted to . you could take one of these , make one eye have a vertical orientation for the polarization , have the other eye with a horizontal ... and you 're thinking , `` this is stupid . `` why would you do this for ? '' `` this eye 's going to get a lot of glare . '' we would n't use these outside , when you 're , like , skiing or fishing , but you could play a trick on your eyes if you went to the movies and you went and watched a movie . well , the reason our eyes see 3d is because they 're spaced a little bit apart . they each get a different , slightly different image . that makes us see in 3d . we can play the same trick on our eye if we have the polarization like this . if light , if some of the light from the movie theater screen is coming in with one polarization , and the other light 's coming in with the other polarization , we can send two different images to our eyes at the same time . if you took these off , it 'd look like garbage because you 'd be getting both of these slightly different images , it 'd look all blurry . and it does . if you take off your 3d glasses and look at a 3d movie , looks terrible , because now both eyes are getting both images . but if you put your glasses back on , now this eye only gets the orientation that it 's supposed to get , and this eye only gets the orientation that it 's supposed to get , and you get a 3d image . so it 's useful in many ways . let me show you one more thing here . let 's come back here . this light was polarized vertically . so that 's called linear polarization . any time ... same with these . these are all linear polarization because , just up and down , one linear direction , just diagonal . this is also linear . all of these are linear . you can get circular polarized light . so if we come back to here , we 've got our electric field pointing up , like that . now let 's say we sent in another light ray , another light ray that also had a polarization , but not in this direction . let 's say our other light ray had polarization in this direction , so it looks like this , kind of like what our magnetic field would have looked like . but this is a completely different light ray with its own polarization and its own magnetic field . so we send this in . what would happen ? well , at this point , you 'd have a electric field that points this way . at this point , you 'd have a electric field that points that way . what would your eye see if you were over here ? let 's see . if i draw our axis here . all right , when this point right here gets to your eye , what am i going to see ? well , i 'm going to have a light ray that 's one part of a light ray . one component points up . that 's this electric field . one component points left . that 's this electric field . so the total , my total electric field , would point this way . i could to the pythagorean theorem if i wanted to figure out the size of it , but i just want to know the direction for now . and then it gets to here , and look at it : they both have zero . this light ray has zero electric field , this one has zero electric fields . so then it 'd just be at zero . now what happens over here ? well , i 've got light . this one points to the right at that point , this pink one , and then this red one would be pointing down . so what would i have at that point ? i 'd have light that went this way , and it would just be doing this over and over . it would just be ... i 'd just have diagonally polarized light . this is n't giving me anything new . you might think this is dumb . why do this ? why send in two different waves to just get diagonally polarized light ? i could have just sent in one wave that was diagonally polarized and got the same thing . the reason is , if you shift this purple wave , this pink wave , by 90 degrees of phase , by pi over two in phase , something magical happens . let me show you what happens here , if we move this to here . now we do n't just get diagonally linear polarized light . what we 're going to get is ... let me get rid of this . okay , so we start off with red , right ? the red electric field points up , and then this pink wave 's electric field is zero at that point . so this is all i have . my total electric field would just be up . i 'm going to draw it right here . the green 'll be the total . now i come over to here , and at this point , there 's some red electric field that points up , but there 's some of this other electric field that points this way . so i 'd have a total electric field that would point that way . and then i get over to here , and i 'd have all of the electric field from the pink one , none from the red one . it would point all left then . look what 's happening . the polarization of this light , if i shift this , if i 'm sitting here , looking with my eye , as my eye receives this light , i 'm going to see this light rotate its polarization . the polarization i 'm going to notice swings around in a circular pattern . and because of this , we call this circular polarization . so this is another type of polarization , where the actual angle of polarization rotates smoothly as this light ray enters your eye . and you know what ? er , drrr ... all right , actually , i sent you to receive this one first . that makes no sense . you 're going to receive the ones closes to you first in this light ray going this way . so you 'd actually receive this one first , then that one , then this one , then this one . because of that , you would n't see this going in a counterclockwise way , you 'd see this going in a clockwise circularly polarized way . sorry about that . you might think , `` okay , why ? `` why even bother with circular polarization ? '' well , i kind of lied earlier . turns out , in the movie theater example , they do n't actually do it like this , typically . oftentimes in the movie theaters , we do n't have just linearly polarized sunglasses . this would be a problem because , when you look at the movie theater screen , and if you were to tilt your head just a little bit ... think about it . this one 's not really going to get the right image anymore . it 's going to get some of both . and this one 's going to get some of both . it 's going to be blurry . your head would have to be perfectly level the whole time , which might be annoying . so what we do is , instead , we create circular polarized glasses , so that this one would only get one polarization , this one would get the other direction . this way , even if you tilt your head a little bit ... shoot , clockwise is clockwise , counterclockwise is counterclockwise . by using circular polarization for 3d movies , it can make it a little easier on you eyes to see a better 3d image , even if your head 's tilted a little bit .
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- let 's talk about polarization of light . we know what light waves are ; they 're electromagnetic waves .
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where did the energy go ?
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- let 's talk about polarization of light . we know what light waves are ; they 're electromagnetic waves . so they 're made out of electric fields . and that 's not good enough . we know there 's not just electric fields . that could n't sustain itself . there 's got to be magnetic fields there , as well , that are changing . those are perpendicular , so you can kind of draw them . it 's hard , on something two-dimensional , but you can kind of imagine those looking something like this . and those magnetic fields would point at a right angle to the electric fields . but this gets really messy if i try to draw both the electric and magnetic fields at the same time . so we 're going to leave the magnetic fields out . it 's often good enough to just know the direction of the electric field when we focus on the electric field . so what does polarization mean ? polarization refers to the fact that , if this light ray was heading straight toward your eye , or a detector , over here , what would you see ? well , if i draw an axis over here , and this point here , in the middle , this is this line -- so imagine we 're looking straight down that line -- and then up and down is up and down , and then left and right , that direction i have the magnetic field , would be this way and that way . what would my eye see ? well , my eye 's only going to see electric fields that either point up or electric fields that point down . they might have different values , but i 'm only going to see electric fields that point up or down . because of that , this light ray is polarized . so polarized light is light where the electric field is only oscillating in one direction . up or down , that 's one direction -- vertically . or it could be polarized horizontally . or it could be polarized diagonally . but either way , you could have this wave polarized along any direction . i mean , a light ray like this , if we had it coming in diagonal , this light ray that 's oscillating like this , where the electric field oscillates like that , that also polarized . these are both polarized because there 's only one direction that the electric field is oscillating in . and you might thing , `` pff , how could you ever have `` a light ray that 's not polarized ? '' easy . most light that you get is not polarized . that is to say , light that 's coming from the sun , straight from the sun -- typically not polarized . light from a lightbulb , an old incandescent light bulb , this thing 's hot . you can get light polarized in any direction , all at once , all overlapping . so if we draw this case for a light bulb , just a random incandescent light bulb , you might get light , some of the light , hitting you eye , you can get some light that 's got that direction , you got light that 's got this direction , you got light in all these directions at any given moment . i mean , you 'd have to add these up to get the total , and they might not all be the same value . but what i 'm trying to say is , at any given moment , you do n't know what direction the electric field 's going to be hitting your eye at from a random source . it could be in any direction . so this is not polarized . this diagram represents light that is not polarized . at some point , the field might be pointing this way , at some later point it 's this way ; it 's just random . you never know which way the electric field 's going to be pointing . whereas these over here , these are polarized . so how could you polarize this light ? let 's say you wanted light that was polarized . you were doing an experiment . you needed polarized light . well , that 's easy . you can use what 's called a polarizer . and this is a material that lets light through , but it only lets light through in one orientation , so you 're going to have a polarizer that , for instance , only lets through vertically polarized light . so this is a polarizer . these are cheap : thin , plastic , configured in a way so that it only lets light through that 's vertically polarized . any light coming in here that 's not vertically polarized gets blocked , or absorbed . so what that means is , if you used this polarizer and held it in between your eye and this light bulb , you would only get this light . all the rest of it would get blocked . or you could just rotate this thing and imagine a polarizer that only lets through horizontal light . now it would only let through light that was this way , and so you would only get this part of the light . or you could just orient it at any angle you want and block everything but the certain angle that this polarizer is defined as letting light through . so you can do this . and once you hold this up , you get polarized light , light that 's only got one orientation . so that 's what polarization means . but why do we care about polarization ? well , let me get rid of this for a minute . you 've heard of polarized sunglasses . so imagine you 're standing near water , or maybe you 're standing on ice or snow or something reflective . there 's a problem . say the sun 's out . it 's shining . it 's a beautiful day -- except there 's going to be glare . let 's say you 're looking down at something here on the ground . it 's going to get light reflecting off of it from just ... you know , light 's coming in from all direction . but it also gets this direct light from the sun . so it gets light from reflected off the clouds and whatever , whatever 's nearby , ambient light . and there 's also this direct sunlight . that 's harsh . if that reflects straight up to your eye , that hurts . you do n't like that . it blocks our vision . it 's hard to see , it 's glare . we do n't want this glare . so what can we do ? well , it just so happens that , when light reflects off of a surface , even though the light from the sun is not polarized , once it reflects , it does get polarized or at least partially polarized . so this surface here , once this light reflects , it 's coming in at all orientations . you got electric field ... you never know what electric field you 're going to get straight from the sun . and when it reflects , though , you mostly get , upon reflection , the direction of polarization defined by the plane of the surface that it hit . so because the floor is horizontal , when this light ray hits the ground and reflects , that reflected light gets partially polarized . this horizontal component of the electric field is going to be more present than the other components . maybe not completely . sometimes it could be . it could be completely polarized , but often it 's just partially polarized . but that 's pretty cool , because now you know what we can do . i know how to block this . we should get some sunglasses . we put some sunglasses on and we make our glasses so that these are polarized . and how do we want these polarized ? i want to get rid of the glare . so what i do is , i make sure my sunglasses only let through vertically polarized light . here 's some polarizers . that way , a lot of this glare gets blocked because it does not have a vertical orientation , it has a horizontal orientation . and then we can block it . so that 's one good thing that polarization does for us , and understanding it , we can get rid of glare . also , fishermen like it because , if you 're trying to look in the water at fish , you want to see in through the water , you want to see this light from the fish getting to you . you do n't want to see the glare off of the sun getting to you . so polarized sunglasses are useful . also , we can play a trick on our eye , if we really wanted to . you could take one of these , make one eye have a vertical orientation for the polarization , have the other eye with a horizontal ... and you 're thinking , `` this is stupid . `` why would you do this for ? '' `` this eye 's going to get a lot of glare . '' we would n't use these outside , when you 're , like , skiing or fishing , but you could play a trick on your eyes if you went to the movies and you went and watched a movie . well , the reason our eyes see 3d is because they 're spaced a little bit apart . they each get a different , slightly different image . that makes us see in 3d . we can play the same trick on our eye if we have the polarization like this . if light , if some of the light from the movie theater screen is coming in with one polarization , and the other light 's coming in with the other polarization , we can send two different images to our eyes at the same time . if you took these off , it 'd look like garbage because you 'd be getting both of these slightly different images , it 'd look all blurry . and it does . if you take off your 3d glasses and look at a 3d movie , looks terrible , because now both eyes are getting both images . but if you put your glasses back on , now this eye only gets the orientation that it 's supposed to get , and this eye only gets the orientation that it 's supposed to get , and you get a 3d image . so it 's useful in many ways . let me show you one more thing here . let 's come back here . this light was polarized vertically . so that 's called linear polarization . any time ... same with these . these are all linear polarization because , just up and down , one linear direction , just diagonal . this is also linear . all of these are linear . you can get circular polarized light . so if we come back to here , we 've got our electric field pointing up , like that . now let 's say we sent in another light ray , another light ray that also had a polarization , but not in this direction . let 's say our other light ray had polarization in this direction , so it looks like this , kind of like what our magnetic field would have looked like . but this is a completely different light ray with its own polarization and its own magnetic field . so we send this in . what would happen ? well , at this point , you 'd have a electric field that points this way . at this point , you 'd have a electric field that points that way . what would your eye see if you were over here ? let 's see . if i draw our axis here . all right , when this point right here gets to your eye , what am i going to see ? well , i 'm going to have a light ray that 's one part of a light ray . one component points up . that 's this electric field . one component points left . that 's this electric field . so the total , my total electric field , would point this way . i could to the pythagorean theorem if i wanted to figure out the size of it , but i just want to know the direction for now . and then it gets to here , and look at it : they both have zero . this light ray has zero electric field , this one has zero electric fields . so then it 'd just be at zero . now what happens over here ? well , i 've got light . this one points to the right at that point , this pink one , and then this red one would be pointing down . so what would i have at that point ? i 'd have light that went this way , and it would just be doing this over and over . it would just be ... i 'd just have diagonally polarized light . this is n't giving me anything new . you might think this is dumb . why do this ? why send in two different waves to just get diagonally polarized light ? i could have just sent in one wave that was diagonally polarized and got the same thing . the reason is , if you shift this purple wave , this pink wave , by 90 degrees of phase , by pi over two in phase , something magical happens . let me show you what happens here , if we move this to here . now we do n't just get diagonally linear polarized light . what we 're going to get is ... let me get rid of this . okay , so we start off with red , right ? the red electric field points up , and then this pink wave 's electric field is zero at that point . so this is all i have . my total electric field would just be up . i 'm going to draw it right here . the green 'll be the total . now i come over to here , and at this point , there 's some red electric field that points up , but there 's some of this other electric field that points this way . so i 'd have a total electric field that would point that way . and then i get over to here , and i 'd have all of the electric field from the pink one , none from the red one . it would point all left then . look what 's happening . the polarization of this light , if i shift this , if i 'm sitting here , looking with my eye , as my eye receives this light , i 'm going to see this light rotate its polarization . the polarization i 'm going to notice swings around in a circular pattern . and because of this , we call this circular polarization . so this is another type of polarization , where the actual angle of polarization rotates smoothly as this light ray enters your eye . and you know what ? er , drrr ... all right , actually , i sent you to receive this one first . that makes no sense . you 're going to receive the ones closes to you first in this light ray going this way . so you 'd actually receive this one first , then that one , then this one , then this one . because of that , you would n't see this going in a counterclockwise way , you 'd see this going in a clockwise circularly polarized way . sorry about that . you might think , `` okay , why ? `` why even bother with circular polarization ? '' well , i kind of lied earlier . turns out , in the movie theater example , they do n't actually do it like this , typically . oftentimes in the movie theaters , we do n't have just linearly polarized sunglasses . this would be a problem because , when you look at the movie theater screen , and if you were to tilt your head just a little bit ... think about it . this one 's not really going to get the right image anymore . it 's going to get some of both . and this one 's going to get some of both . it 's going to be blurry . your head would have to be perfectly level the whole time , which might be annoying . so what we do is , instead , we create circular polarized glasses , so that this one would only get one polarization , this one would get the other direction . this way , even if you tilt your head a little bit ... shoot , clockwise is clockwise , counterclockwise is counterclockwise . by using circular polarization for 3d movies , it can make it a little easier on you eyes to see a better 3d image , even if your head 's tilted a little bit .
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you can get light polarized in any direction , all at once , all overlapping . so if we draw this case for a light bulb , just a random incandescent light bulb , you might get light , some of the light , hitting you eye , you can get some light that 's got that direction , you got light that 's got this direction , you got light in all these directions at any given moment . i mean , you 'd have to add these up to get the total , and they might not all be the same value .
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if yes , then why do we see light because light is composed of both the fields ?
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- let 's talk about polarization of light . we know what light waves are ; they 're electromagnetic waves . so they 're made out of electric fields . and that 's not good enough . we know there 's not just electric fields . that could n't sustain itself . there 's got to be magnetic fields there , as well , that are changing . those are perpendicular , so you can kind of draw them . it 's hard , on something two-dimensional , but you can kind of imagine those looking something like this . and those magnetic fields would point at a right angle to the electric fields . but this gets really messy if i try to draw both the electric and magnetic fields at the same time . so we 're going to leave the magnetic fields out . it 's often good enough to just know the direction of the electric field when we focus on the electric field . so what does polarization mean ? polarization refers to the fact that , if this light ray was heading straight toward your eye , or a detector , over here , what would you see ? well , if i draw an axis over here , and this point here , in the middle , this is this line -- so imagine we 're looking straight down that line -- and then up and down is up and down , and then left and right , that direction i have the magnetic field , would be this way and that way . what would my eye see ? well , my eye 's only going to see electric fields that either point up or electric fields that point down . they might have different values , but i 'm only going to see electric fields that point up or down . because of that , this light ray is polarized . so polarized light is light where the electric field is only oscillating in one direction . up or down , that 's one direction -- vertically . or it could be polarized horizontally . or it could be polarized diagonally . but either way , you could have this wave polarized along any direction . i mean , a light ray like this , if we had it coming in diagonal , this light ray that 's oscillating like this , where the electric field oscillates like that , that also polarized . these are both polarized because there 's only one direction that the electric field is oscillating in . and you might thing , `` pff , how could you ever have `` a light ray that 's not polarized ? '' easy . most light that you get is not polarized . that is to say , light that 's coming from the sun , straight from the sun -- typically not polarized . light from a lightbulb , an old incandescent light bulb , this thing 's hot . you can get light polarized in any direction , all at once , all overlapping . so if we draw this case for a light bulb , just a random incandescent light bulb , you might get light , some of the light , hitting you eye , you can get some light that 's got that direction , you got light that 's got this direction , you got light in all these directions at any given moment . i mean , you 'd have to add these up to get the total , and they might not all be the same value . but what i 'm trying to say is , at any given moment , you do n't know what direction the electric field 's going to be hitting your eye at from a random source . it could be in any direction . so this is not polarized . this diagram represents light that is not polarized . at some point , the field might be pointing this way , at some later point it 's this way ; it 's just random . you never know which way the electric field 's going to be pointing . whereas these over here , these are polarized . so how could you polarize this light ? let 's say you wanted light that was polarized . you were doing an experiment . you needed polarized light . well , that 's easy . you can use what 's called a polarizer . and this is a material that lets light through , but it only lets light through in one orientation , so you 're going to have a polarizer that , for instance , only lets through vertically polarized light . so this is a polarizer . these are cheap : thin , plastic , configured in a way so that it only lets light through that 's vertically polarized . any light coming in here that 's not vertically polarized gets blocked , or absorbed . so what that means is , if you used this polarizer and held it in between your eye and this light bulb , you would only get this light . all the rest of it would get blocked . or you could just rotate this thing and imagine a polarizer that only lets through horizontal light . now it would only let through light that was this way , and so you would only get this part of the light . or you could just orient it at any angle you want and block everything but the certain angle that this polarizer is defined as letting light through . so you can do this . and once you hold this up , you get polarized light , light that 's only got one orientation . so that 's what polarization means . but why do we care about polarization ? well , let me get rid of this for a minute . you 've heard of polarized sunglasses . so imagine you 're standing near water , or maybe you 're standing on ice or snow or something reflective . there 's a problem . say the sun 's out . it 's shining . it 's a beautiful day -- except there 's going to be glare . let 's say you 're looking down at something here on the ground . it 's going to get light reflecting off of it from just ... you know , light 's coming in from all direction . but it also gets this direct light from the sun . so it gets light from reflected off the clouds and whatever , whatever 's nearby , ambient light . and there 's also this direct sunlight . that 's harsh . if that reflects straight up to your eye , that hurts . you do n't like that . it blocks our vision . it 's hard to see , it 's glare . we do n't want this glare . so what can we do ? well , it just so happens that , when light reflects off of a surface , even though the light from the sun is not polarized , once it reflects , it does get polarized or at least partially polarized . so this surface here , once this light reflects , it 's coming in at all orientations . you got electric field ... you never know what electric field you 're going to get straight from the sun . and when it reflects , though , you mostly get , upon reflection , the direction of polarization defined by the plane of the surface that it hit . so because the floor is horizontal , when this light ray hits the ground and reflects , that reflected light gets partially polarized . this horizontal component of the electric field is going to be more present than the other components . maybe not completely . sometimes it could be . it could be completely polarized , but often it 's just partially polarized . but that 's pretty cool , because now you know what we can do . i know how to block this . we should get some sunglasses . we put some sunglasses on and we make our glasses so that these are polarized . and how do we want these polarized ? i want to get rid of the glare . so what i do is , i make sure my sunglasses only let through vertically polarized light . here 's some polarizers . that way , a lot of this glare gets blocked because it does not have a vertical orientation , it has a horizontal orientation . and then we can block it . so that 's one good thing that polarization does for us , and understanding it , we can get rid of glare . also , fishermen like it because , if you 're trying to look in the water at fish , you want to see in through the water , you want to see this light from the fish getting to you . you do n't want to see the glare off of the sun getting to you . so polarized sunglasses are useful . also , we can play a trick on our eye , if we really wanted to . you could take one of these , make one eye have a vertical orientation for the polarization , have the other eye with a horizontal ... and you 're thinking , `` this is stupid . `` why would you do this for ? '' `` this eye 's going to get a lot of glare . '' we would n't use these outside , when you 're , like , skiing or fishing , but you could play a trick on your eyes if you went to the movies and you went and watched a movie . well , the reason our eyes see 3d is because they 're spaced a little bit apart . they each get a different , slightly different image . that makes us see in 3d . we can play the same trick on our eye if we have the polarization like this . if light , if some of the light from the movie theater screen is coming in with one polarization , and the other light 's coming in with the other polarization , we can send two different images to our eyes at the same time . if you took these off , it 'd look like garbage because you 'd be getting both of these slightly different images , it 'd look all blurry . and it does . if you take off your 3d glasses and look at a 3d movie , looks terrible , because now both eyes are getting both images . but if you put your glasses back on , now this eye only gets the orientation that it 's supposed to get , and this eye only gets the orientation that it 's supposed to get , and you get a 3d image . so it 's useful in many ways . let me show you one more thing here . let 's come back here . this light was polarized vertically . so that 's called linear polarization . any time ... same with these . these are all linear polarization because , just up and down , one linear direction , just diagonal . this is also linear . all of these are linear . you can get circular polarized light . so if we come back to here , we 've got our electric field pointing up , like that . now let 's say we sent in another light ray , another light ray that also had a polarization , but not in this direction . let 's say our other light ray had polarization in this direction , so it looks like this , kind of like what our magnetic field would have looked like . but this is a completely different light ray with its own polarization and its own magnetic field . so we send this in . what would happen ? well , at this point , you 'd have a electric field that points this way . at this point , you 'd have a electric field that points that way . what would your eye see if you were over here ? let 's see . if i draw our axis here . all right , when this point right here gets to your eye , what am i going to see ? well , i 'm going to have a light ray that 's one part of a light ray . one component points up . that 's this electric field . one component points left . that 's this electric field . so the total , my total electric field , would point this way . i could to the pythagorean theorem if i wanted to figure out the size of it , but i just want to know the direction for now . and then it gets to here , and look at it : they both have zero . this light ray has zero electric field , this one has zero electric fields . so then it 'd just be at zero . now what happens over here ? well , i 've got light . this one points to the right at that point , this pink one , and then this red one would be pointing down . so what would i have at that point ? i 'd have light that went this way , and it would just be doing this over and over . it would just be ... i 'd just have diagonally polarized light . this is n't giving me anything new . you might think this is dumb . why do this ? why send in two different waves to just get diagonally polarized light ? i could have just sent in one wave that was diagonally polarized and got the same thing . the reason is , if you shift this purple wave , this pink wave , by 90 degrees of phase , by pi over two in phase , something magical happens . let me show you what happens here , if we move this to here . now we do n't just get diagonally linear polarized light . what we 're going to get is ... let me get rid of this . okay , so we start off with red , right ? the red electric field points up , and then this pink wave 's electric field is zero at that point . so this is all i have . my total electric field would just be up . i 'm going to draw it right here . the green 'll be the total . now i come over to here , and at this point , there 's some red electric field that points up , but there 's some of this other electric field that points this way . so i 'd have a total electric field that would point that way . and then i get over to here , and i 'd have all of the electric field from the pink one , none from the red one . it would point all left then . look what 's happening . the polarization of this light , if i shift this , if i 'm sitting here , looking with my eye , as my eye receives this light , i 'm going to see this light rotate its polarization . the polarization i 'm going to notice swings around in a circular pattern . and because of this , we call this circular polarization . so this is another type of polarization , where the actual angle of polarization rotates smoothly as this light ray enters your eye . and you know what ? er , drrr ... all right , actually , i sent you to receive this one first . that makes no sense . you 're going to receive the ones closes to you first in this light ray going this way . so you 'd actually receive this one first , then that one , then this one , then this one . because of that , you would n't see this going in a counterclockwise way , you 'd see this going in a clockwise circularly polarized way . sorry about that . you might think , `` okay , why ? `` why even bother with circular polarization ? '' well , i kind of lied earlier . turns out , in the movie theater example , they do n't actually do it like this , typically . oftentimes in the movie theaters , we do n't have just linearly polarized sunglasses . this would be a problem because , when you look at the movie theater screen , and if you were to tilt your head just a little bit ... think about it . this one 's not really going to get the right image anymore . it 's going to get some of both . and this one 's going to get some of both . it 's going to be blurry . your head would have to be perfectly level the whole time , which might be annoying . so what we do is , instead , we create circular polarized glasses , so that this one would only get one polarization , this one would get the other direction . this way , even if you tilt your head a little bit ... shoot , clockwise is clockwise , counterclockwise is counterclockwise . by using circular polarization for 3d movies , it can make it a little easier on you eyes to see a better 3d image , even if your head 's tilted a little bit .
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you were doing an experiment . you needed polarized light . well , that 's easy .
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so light is an electromagnetic wave , does it mean that if you put a compass and shine a beam of polarized light beside it , it can affect the direction the compass needle points at ?
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- let 's talk about polarization of light . we know what light waves are ; they 're electromagnetic waves . so they 're made out of electric fields . and that 's not good enough . we know there 's not just electric fields . that could n't sustain itself . there 's got to be magnetic fields there , as well , that are changing . those are perpendicular , so you can kind of draw them . it 's hard , on something two-dimensional , but you can kind of imagine those looking something like this . and those magnetic fields would point at a right angle to the electric fields . but this gets really messy if i try to draw both the electric and magnetic fields at the same time . so we 're going to leave the magnetic fields out . it 's often good enough to just know the direction of the electric field when we focus on the electric field . so what does polarization mean ? polarization refers to the fact that , if this light ray was heading straight toward your eye , or a detector , over here , what would you see ? well , if i draw an axis over here , and this point here , in the middle , this is this line -- so imagine we 're looking straight down that line -- and then up and down is up and down , and then left and right , that direction i have the magnetic field , would be this way and that way . what would my eye see ? well , my eye 's only going to see electric fields that either point up or electric fields that point down . they might have different values , but i 'm only going to see electric fields that point up or down . because of that , this light ray is polarized . so polarized light is light where the electric field is only oscillating in one direction . up or down , that 's one direction -- vertically . or it could be polarized horizontally . or it could be polarized diagonally . but either way , you could have this wave polarized along any direction . i mean , a light ray like this , if we had it coming in diagonal , this light ray that 's oscillating like this , where the electric field oscillates like that , that also polarized . these are both polarized because there 's only one direction that the electric field is oscillating in . and you might thing , `` pff , how could you ever have `` a light ray that 's not polarized ? '' easy . most light that you get is not polarized . that is to say , light that 's coming from the sun , straight from the sun -- typically not polarized . light from a lightbulb , an old incandescent light bulb , this thing 's hot . you can get light polarized in any direction , all at once , all overlapping . so if we draw this case for a light bulb , just a random incandescent light bulb , you might get light , some of the light , hitting you eye , you can get some light that 's got that direction , you got light that 's got this direction , you got light in all these directions at any given moment . i mean , you 'd have to add these up to get the total , and they might not all be the same value . but what i 'm trying to say is , at any given moment , you do n't know what direction the electric field 's going to be hitting your eye at from a random source . it could be in any direction . so this is not polarized . this diagram represents light that is not polarized . at some point , the field might be pointing this way , at some later point it 's this way ; it 's just random . you never know which way the electric field 's going to be pointing . whereas these over here , these are polarized . so how could you polarize this light ? let 's say you wanted light that was polarized . you were doing an experiment . you needed polarized light . well , that 's easy . you can use what 's called a polarizer . and this is a material that lets light through , but it only lets light through in one orientation , so you 're going to have a polarizer that , for instance , only lets through vertically polarized light . so this is a polarizer . these are cheap : thin , plastic , configured in a way so that it only lets light through that 's vertically polarized . any light coming in here that 's not vertically polarized gets blocked , or absorbed . so what that means is , if you used this polarizer and held it in between your eye and this light bulb , you would only get this light . all the rest of it would get blocked . or you could just rotate this thing and imagine a polarizer that only lets through horizontal light . now it would only let through light that was this way , and so you would only get this part of the light . or you could just orient it at any angle you want and block everything but the certain angle that this polarizer is defined as letting light through . so you can do this . and once you hold this up , you get polarized light , light that 's only got one orientation . so that 's what polarization means . but why do we care about polarization ? well , let me get rid of this for a minute . you 've heard of polarized sunglasses . so imagine you 're standing near water , or maybe you 're standing on ice or snow or something reflective . there 's a problem . say the sun 's out . it 's shining . it 's a beautiful day -- except there 's going to be glare . let 's say you 're looking down at something here on the ground . it 's going to get light reflecting off of it from just ... you know , light 's coming in from all direction . but it also gets this direct light from the sun . so it gets light from reflected off the clouds and whatever , whatever 's nearby , ambient light . and there 's also this direct sunlight . that 's harsh . if that reflects straight up to your eye , that hurts . you do n't like that . it blocks our vision . it 's hard to see , it 's glare . we do n't want this glare . so what can we do ? well , it just so happens that , when light reflects off of a surface , even though the light from the sun is not polarized , once it reflects , it does get polarized or at least partially polarized . so this surface here , once this light reflects , it 's coming in at all orientations . you got electric field ... you never know what electric field you 're going to get straight from the sun . and when it reflects , though , you mostly get , upon reflection , the direction of polarization defined by the plane of the surface that it hit . so because the floor is horizontal , when this light ray hits the ground and reflects , that reflected light gets partially polarized . this horizontal component of the electric field is going to be more present than the other components . maybe not completely . sometimes it could be . it could be completely polarized , but often it 's just partially polarized . but that 's pretty cool , because now you know what we can do . i know how to block this . we should get some sunglasses . we put some sunglasses on and we make our glasses so that these are polarized . and how do we want these polarized ? i want to get rid of the glare . so what i do is , i make sure my sunglasses only let through vertically polarized light . here 's some polarizers . that way , a lot of this glare gets blocked because it does not have a vertical orientation , it has a horizontal orientation . and then we can block it . so that 's one good thing that polarization does for us , and understanding it , we can get rid of glare . also , fishermen like it because , if you 're trying to look in the water at fish , you want to see in through the water , you want to see this light from the fish getting to you . you do n't want to see the glare off of the sun getting to you . so polarized sunglasses are useful . also , we can play a trick on our eye , if we really wanted to . you could take one of these , make one eye have a vertical orientation for the polarization , have the other eye with a horizontal ... and you 're thinking , `` this is stupid . `` why would you do this for ? '' `` this eye 's going to get a lot of glare . '' we would n't use these outside , when you 're , like , skiing or fishing , but you could play a trick on your eyes if you went to the movies and you went and watched a movie . well , the reason our eyes see 3d is because they 're spaced a little bit apart . they each get a different , slightly different image . that makes us see in 3d . we can play the same trick on our eye if we have the polarization like this . if light , if some of the light from the movie theater screen is coming in with one polarization , and the other light 's coming in with the other polarization , we can send two different images to our eyes at the same time . if you took these off , it 'd look like garbage because you 'd be getting both of these slightly different images , it 'd look all blurry . and it does . if you take off your 3d glasses and look at a 3d movie , looks terrible , because now both eyes are getting both images . but if you put your glasses back on , now this eye only gets the orientation that it 's supposed to get , and this eye only gets the orientation that it 's supposed to get , and you get a 3d image . so it 's useful in many ways . let me show you one more thing here . let 's come back here . this light was polarized vertically . so that 's called linear polarization . any time ... same with these . these are all linear polarization because , just up and down , one linear direction , just diagonal . this is also linear . all of these are linear . you can get circular polarized light . so if we come back to here , we 've got our electric field pointing up , like that . now let 's say we sent in another light ray , another light ray that also had a polarization , but not in this direction . let 's say our other light ray had polarization in this direction , so it looks like this , kind of like what our magnetic field would have looked like . but this is a completely different light ray with its own polarization and its own magnetic field . so we send this in . what would happen ? well , at this point , you 'd have a electric field that points this way . at this point , you 'd have a electric field that points that way . what would your eye see if you were over here ? let 's see . if i draw our axis here . all right , when this point right here gets to your eye , what am i going to see ? well , i 'm going to have a light ray that 's one part of a light ray . one component points up . that 's this electric field . one component points left . that 's this electric field . so the total , my total electric field , would point this way . i could to the pythagorean theorem if i wanted to figure out the size of it , but i just want to know the direction for now . and then it gets to here , and look at it : they both have zero . this light ray has zero electric field , this one has zero electric fields . so then it 'd just be at zero . now what happens over here ? well , i 've got light . this one points to the right at that point , this pink one , and then this red one would be pointing down . so what would i have at that point ? i 'd have light that went this way , and it would just be doing this over and over . it would just be ... i 'd just have diagonally polarized light . this is n't giving me anything new . you might think this is dumb . why do this ? why send in two different waves to just get diagonally polarized light ? i could have just sent in one wave that was diagonally polarized and got the same thing . the reason is , if you shift this purple wave , this pink wave , by 90 degrees of phase , by pi over two in phase , something magical happens . let me show you what happens here , if we move this to here . now we do n't just get diagonally linear polarized light . what we 're going to get is ... let me get rid of this . okay , so we start off with red , right ? the red electric field points up , and then this pink wave 's electric field is zero at that point . so this is all i have . my total electric field would just be up . i 'm going to draw it right here . the green 'll be the total . now i come over to here , and at this point , there 's some red electric field that points up , but there 's some of this other electric field that points this way . so i 'd have a total electric field that would point that way . and then i get over to here , and i 'd have all of the electric field from the pink one , none from the red one . it would point all left then . look what 's happening . the polarization of this light , if i shift this , if i 'm sitting here , looking with my eye , as my eye receives this light , i 'm going to see this light rotate its polarization . the polarization i 'm going to notice swings around in a circular pattern . and because of this , we call this circular polarization . so this is another type of polarization , where the actual angle of polarization rotates smoothly as this light ray enters your eye . and you know what ? er , drrr ... all right , actually , i sent you to receive this one first . that makes no sense . you 're going to receive the ones closes to you first in this light ray going this way . so you 'd actually receive this one first , then that one , then this one , then this one . because of that , you would n't see this going in a counterclockwise way , you 'd see this going in a clockwise circularly polarized way . sorry about that . you might think , `` okay , why ? `` why even bother with circular polarization ? '' well , i kind of lied earlier . turns out , in the movie theater example , they do n't actually do it like this , typically . oftentimes in the movie theaters , we do n't have just linearly polarized sunglasses . this would be a problem because , when you look at the movie theater screen , and if you were to tilt your head just a little bit ... think about it . this one 's not really going to get the right image anymore . it 's going to get some of both . and this one 's going to get some of both . it 's going to be blurry . your head would have to be perfectly level the whole time , which might be annoying . so what we do is , instead , we create circular polarized glasses , so that this one would only get one polarization , this one would get the other direction . this way , even if you tilt your head a little bit ... shoot , clockwise is clockwise , counterclockwise is counterclockwise . by using circular polarization for 3d movies , it can make it a little easier on you eyes to see a better 3d image , even if your head 's tilted a little bit .
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it 's often good enough to just know the direction of the electric field when we focus on the electric field . so what does polarization mean ? polarization refers to the fact that , if this light ray was heading straight toward your eye , or a detector , over here , what would you see ?
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what is the opposite of polarization ?
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- let 's talk about polarization of light . we know what light waves are ; they 're electromagnetic waves . so they 're made out of electric fields . and that 's not good enough . we know there 's not just electric fields . that could n't sustain itself . there 's got to be magnetic fields there , as well , that are changing . those are perpendicular , so you can kind of draw them . it 's hard , on something two-dimensional , but you can kind of imagine those looking something like this . and those magnetic fields would point at a right angle to the electric fields . but this gets really messy if i try to draw both the electric and magnetic fields at the same time . so we 're going to leave the magnetic fields out . it 's often good enough to just know the direction of the electric field when we focus on the electric field . so what does polarization mean ? polarization refers to the fact that , if this light ray was heading straight toward your eye , or a detector , over here , what would you see ? well , if i draw an axis over here , and this point here , in the middle , this is this line -- so imagine we 're looking straight down that line -- and then up and down is up and down , and then left and right , that direction i have the magnetic field , would be this way and that way . what would my eye see ? well , my eye 's only going to see electric fields that either point up or electric fields that point down . they might have different values , but i 'm only going to see electric fields that point up or down . because of that , this light ray is polarized . so polarized light is light where the electric field is only oscillating in one direction . up or down , that 's one direction -- vertically . or it could be polarized horizontally . or it could be polarized diagonally . but either way , you could have this wave polarized along any direction . i mean , a light ray like this , if we had it coming in diagonal , this light ray that 's oscillating like this , where the electric field oscillates like that , that also polarized . these are both polarized because there 's only one direction that the electric field is oscillating in . and you might thing , `` pff , how could you ever have `` a light ray that 's not polarized ? '' easy . most light that you get is not polarized . that is to say , light that 's coming from the sun , straight from the sun -- typically not polarized . light from a lightbulb , an old incandescent light bulb , this thing 's hot . you can get light polarized in any direction , all at once , all overlapping . so if we draw this case for a light bulb , just a random incandescent light bulb , you might get light , some of the light , hitting you eye , you can get some light that 's got that direction , you got light that 's got this direction , you got light in all these directions at any given moment . i mean , you 'd have to add these up to get the total , and they might not all be the same value . but what i 'm trying to say is , at any given moment , you do n't know what direction the electric field 's going to be hitting your eye at from a random source . it could be in any direction . so this is not polarized . this diagram represents light that is not polarized . at some point , the field might be pointing this way , at some later point it 's this way ; it 's just random . you never know which way the electric field 's going to be pointing . whereas these over here , these are polarized . so how could you polarize this light ? let 's say you wanted light that was polarized . you were doing an experiment . you needed polarized light . well , that 's easy . you can use what 's called a polarizer . and this is a material that lets light through , but it only lets light through in one orientation , so you 're going to have a polarizer that , for instance , only lets through vertically polarized light . so this is a polarizer . these are cheap : thin , plastic , configured in a way so that it only lets light through that 's vertically polarized . any light coming in here that 's not vertically polarized gets blocked , or absorbed . so what that means is , if you used this polarizer and held it in between your eye and this light bulb , you would only get this light . all the rest of it would get blocked . or you could just rotate this thing and imagine a polarizer that only lets through horizontal light . now it would only let through light that was this way , and so you would only get this part of the light . or you could just orient it at any angle you want and block everything but the certain angle that this polarizer is defined as letting light through . so you can do this . and once you hold this up , you get polarized light , light that 's only got one orientation . so that 's what polarization means . but why do we care about polarization ? well , let me get rid of this for a minute . you 've heard of polarized sunglasses . so imagine you 're standing near water , or maybe you 're standing on ice or snow or something reflective . there 's a problem . say the sun 's out . it 's shining . it 's a beautiful day -- except there 's going to be glare . let 's say you 're looking down at something here on the ground . it 's going to get light reflecting off of it from just ... you know , light 's coming in from all direction . but it also gets this direct light from the sun . so it gets light from reflected off the clouds and whatever , whatever 's nearby , ambient light . and there 's also this direct sunlight . that 's harsh . if that reflects straight up to your eye , that hurts . you do n't like that . it blocks our vision . it 's hard to see , it 's glare . we do n't want this glare . so what can we do ? well , it just so happens that , when light reflects off of a surface , even though the light from the sun is not polarized , once it reflects , it does get polarized or at least partially polarized . so this surface here , once this light reflects , it 's coming in at all orientations . you got electric field ... you never know what electric field you 're going to get straight from the sun . and when it reflects , though , you mostly get , upon reflection , the direction of polarization defined by the plane of the surface that it hit . so because the floor is horizontal , when this light ray hits the ground and reflects , that reflected light gets partially polarized . this horizontal component of the electric field is going to be more present than the other components . maybe not completely . sometimes it could be . it could be completely polarized , but often it 's just partially polarized . but that 's pretty cool , because now you know what we can do . i know how to block this . we should get some sunglasses . we put some sunglasses on and we make our glasses so that these are polarized . and how do we want these polarized ? i want to get rid of the glare . so what i do is , i make sure my sunglasses only let through vertically polarized light . here 's some polarizers . that way , a lot of this glare gets blocked because it does not have a vertical orientation , it has a horizontal orientation . and then we can block it . so that 's one good thing that polarization does for us , and understanding it , we can get rid of glare . also , fishermen like it because , if you 're trying to look in the water at fish , you want to see in through the water , you want to see this light from the fish getting to you . you do n't want to see the glare off of the sun getting to you . so polarized sunglasses are useful . also , we can play a trick on our eye , if we really wanted to . you could take one of these , make one eye have a vertical orientation for the polarization , have the other eye with a horizontal ... and you 're thinking , `` this is stupid . `` why would you do this for ? '' `` this eye 's going to get a lot of glare . '' we would n't use these outside , when you 're , like , skiing or fishing , but you could play a trick on your eyes if you went to the movies and you went and watched a movie . well , the reason our eyes see 3d is because they 're spaced a little bit apart . they each get a different , slightly different image . that makes us see in 3d . we can play the same trick on our eye if we have the polarization like this . if light , if some of the light from the movie theater screen is coming in with one polarization , and the other light 's coming in with the other polarization , we can send two different images to our eyes at the same time . if you took these off , it 'd look like garbage because you 'd be getting both of these slightly different images , it 'd look all blurry . and it does . if you take off your 3d glasses and look at a 3d movie , looks terrible , because now both eyes are getting both images . but if you put your glasses back on , now this eye only gets the orientation that it 's supposed to get , and this eye only gets the orientation that it 's supposed to get , and you get a 3d image . so it 's useful in many ways . let me show you one more thing here . let 's come back here . this light was polarized vertically . so that 's called linear polarization . any time ... same with these . these are all linear polarization because , just up and down , one linear direction , just diagonal . this is also linear . all of these are linear . you can get circular polarized light . so if we come back to here , we 've got our electric field pointing up , like that . now let 's say we sent in another light ray , another light ray that also had a polarization , but not in this direction . let 's say our other light ray had polarization in this direction , so it looks like this , kind of like what our magnetic field would have looked like . but this is a completely different light ray with its own polarization and its own magnetic field . so we send this in . what would happen ? well , at this point , you 'd have a electric field that points this way . at this point , you 'd have a electric field that points that way . what would your eye see if you were over here ? let 's see . if i draw our axis here . all right , when this point right here gets to your eye , what am i going to see ? well , i 'm going to have a light ray that 's one part of a light ray . one component points up . that 's this electric field . one component points left . that 's this electric field . so the total , my total electric field , would point this way . i could to the pythagorean theorem if i wanted to figure out the size of it , but i just want to know the direction for now . and then it gets to here , and look at it : they both have zero . this light ray has zero electric field , this one has zero electric fields . so then it 'd just be at zero . now what happens over here ? well , i 've got light . this one points to the right at that point , this pink one , and then this red one would be pointing down . so what would i have at that point ? i 'd have light that went this way , and it would just be doing this over and over . it would just be ... i 'd just have diagonally polarized light . this is n't giving me anything new . you might think this is dumb . why do this ? why send in two different waves to just get diagonally polarized light ? i could have just sent in one wave that was diagonally polarized and got the same thing . the reason is , if you shift this purple wave , this pink wave , by 90 degrees of phase , by pi over two in phase , something magical happens . let me show you what happens here , if we move this to here . now we do n't just get diagonally linear polarized light . what we 're going to get is ... let me get rid of this . okay , so we start off with red , right ? the red electric field points up , and then this pink wave 's electric field is zero at that point . so this is all i have . my total electric field would just be up . i 'm going to draw it right here . the green 'll be the total . now i come over to here , and at this point , there 's some red electric field that points up , but there 's some of this other electric field that points this way . so i 'd have a total electric field that would point that way . and then i get over to here , and i 'd have all of the electric field from the pink one , none from the red one . it would point all left then . look what 's happening . the polarization of this light , if i shift this , if i 'm sitting here , looking with my eye , as my eye receives this light , i 'm going to see this light rotate its polarization . the polarization i 'm going to notice swings around in a circular pattern . and because of this , we call this circular polarization . so this is another type of polarization , where the actual angle of polarization rotates smoothly as this light ray enters your eye . and you know what ? er , drrr ... all right , actually , i sent you to receive this one first . that makes no sense . you 're going to receive the ones closes to you first in this light ray going this way . so you 'd actually receive this one first , then that one , then this one , then this one . because of that , you would n't see this going in a counterclockwise way , you 'd see this going in a clockwise circularly polarized way . sorry about that . you might think , `` okay , why ? `` why even bother with circular polarization ? '' well , i kind of lied earlier . turns out , in the movie theater example , they do n't actually do it like this , typically . oftentimes in the movie theaters , we do n't have just linearly polarized sunglasses . this would be a problem because , when you look at the movie theater screen , and if you were to tilt your head just a little bit ... think about it . this one 's not really going to get the right image anymore . it 's going to get some of both . and this one 's going to get some of both . it 's going to be blurry . your head would have to be perfectly level the whole time , which might be annoying . so what we do is , instead , we create circular polarized glasses , so that this one would only get one polarization , this one would get the other direction . this way , even if you tilt your head a little bit ... shoot , clockwise is clockwise , counterclockwise is counterclockwise . by using circular polarization for 3d movies , it can make it a little easier on you eyes to see a better 3d image , even if your head 's tilted a little bit .
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why do this ? why send in two different waves to just get diagonally polarized light ? i could have just sent in one wave that was diagonally polarized and got the same thing .
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or is it how we perceive two different light sources oscillating at pi/2 phase that it looks like it 's diagonally polarized ?
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- let 's talk about polarization of light . we know what light waves are ; they 're electromagnetic waves . so they 're made out of electric fields . and that 's not good enough . we know there 's not just electric fields . that could n't sustain itself . there 's got to be magnetic fields there , as well , that are changing . those are perpendicular , so you can kind of draw them . it 's hard , on something two-dimensional , but you can kind of imagine those looking something like this . and those magnetic fields would point at a right angle to the electric fields . but this gets really messy if i try to draw both the electric and magnetic fields at the same time . so we 're going to leave the magnetic fields out . it 's often good enough to just know the direction of the electric field when we focus on the electric field . so what does polarization mean ? polarization refers to the fact that , if this light ray was heading straight toward your eye , or a detector , over here , what would you see ? well , if i draw an axis over here , and this point here , in the middle , this is this line -- so imagine we 're looking straight down that line -- and then up and down is up and down , and then left and right , that direction i have the magnetic field , would be this way and that way . what would my eye see ? well , my eye 's only going to see electric fields that either point up or electric fields that point down . they might have different values , but i 'm only going to see electric fields that point up or down . because of that , this light ray is polarized . so polarized light is light where the electric field is only oscillating in one direction . up or down , that 's one direction -- vertically . or it could be polarized horizontally . or it could be polarized diagonally . but either way , you could have this wave polarized along any direction . i mean , a light ray like this , if we had it coming in diagonal , this light ray that 's oscillating like this , where the electric field oscillates like that , that also polarized . these are both polarized because there 's only one direction that the electric field is oscillating in . and you might thing , `` pff , how could you ever have `` a light ray that 's not polarized ? '' easy . most light that you get is not polarized . that is to say , light that 's coming from the sun , straight from the sun -- typically not polarized . light from a lightbulb , an old incandescent light bulb , this thing 's hot . you can get light polarized in any direction , all at once , all overlapping . so if we draw this case for a light bulb , just a random incandescent light bulb , you might get light , some of the light , hitting you eye , you can get some light that 's got that direction , you got light that 's got this direction , you got light in all these directions at any given moment . i mean , you 'd have to add these up to get the total , and they might not all be the same value . but what i 'm trying to say is , at any given moment , you do n't know what direction the electric field 's going to be hitting your eye at from a random source . it could be in any direction . so this is not polarized . this diagram represents light that is not polarized . at some point , the field might be pointing this way , at some later point it 's this way ; it 's just random . you never know which way the electric field 's going to be pointing . whereas these over here , these are polarized . so how could you polarize this light ? let 's say you wanted light that was polarized . you were doing an experiment . you needed polarized light . well , that 's easy . you can use what 's called a polarizer . and this is a material that lets light through , but it only lets light through in one orientation , so you 're going to have a polarizer that , for instance , only lets through vertically polarized light . so this is a polarizer . these are cheap : thin , plastic , configured in a way so that it only lets light through that 's vertically polarized . any light coming in here that 's not vertically polarized gets blocked , or absorbed . so what that means is , if you used this polarizer and held it in between your eye and this light bulb , you would only get this light . all the rest of it would get blocked . or you could just rotate this thing and imagine a polarizer that only lets through horizontal light . now it would only let through light that was this way , and so you would only get this part of the light . or you could just orient it at any angle you want and block everything but the certain angle that this polarizer is defined as letting light through . so you can do this . and once you hold this up , you get polarized light , light that 's only got one orientation . so that 's what polarization means . but why do we care about polarization ? well , let me get rid of this for a minute . you 've heard of polarized sunglasses . so imagine you 're standing near water , or maybe you 're standing on ice or snow or something reflective . there 's a problem . say the sun 's out . it 's shining . it 's a beautiful day -- except there 's going to be glare . let 's say you 're looking down at something here on the ground . it 's going to get light reflecting off of it from just ... you know , light 's coming in from all direction . but it also gets this direct light from the sun . so it gets light from reflected off the clouds and whatever , whatever 's nearby , ambient light . and there 's also this direct sunlight . that 's harsh . if that reflects straight up to your eye , that hurts . you do n't like that . it blocks our vision . it 's hard to see , it 's glare . we do n't want this glare . so what can we do ? well , it just so happens that , when light reflects off of a surface , even though the light from the sun is not polarized , once it reflects , it does get polarized or at least partially polarized . so this surface here , once this light reflects , it 's coming in at all orientations . you got electric field ... you never know what electric field you 're going to get straight from the sun . and when it reflects , though , you mostly get , upon reflection , the direction of polarization defined by the plane of the surface that it hit . so because the floor is horizontal , when this light ray hits the ground and reflects , that reflected light gets partially polarized . this horizontal component of the electric field is going to be more present than the other components . maybe not completely . sometimes it could be . it could be completely polarized , but often it 's just partially polarized . but that 's pretty cool , because now you know what we can do . i know how to block this . we should get some sunglasses . we put some sunglasses on and we make our glasses so that these are polarized . and how do we want these polarized ? i want to get rid of the glare . so what i do is , i make sure my sunglasses only let through vertically polarized light . here 's some polarizers . that way , a lot of this glare gets blocked because it does not have a vertical orientation , it has a horizontal orientation . and then we can block it . so that 's one good thing that polarization does for us , and understanding it , we can get rid of glare . also , fishermen like it because , if you 're trying to look in the water at fish , you want to see in through the water , you want to see this light from the fish getting to you . you do n't want to see the glare off of the sun getting to you . so polarized sunglasses are useful . also , we can play a trick on our eye , if we really wanted to . you could take one of these , make one eye have a vertical orientation for the polarization , have the other eye with a horizontal ... and you 're thinking , `` this is stupid . `` why would you do this for ? '' `` this eye 's going to get a lot of glare . '' we would n't use these outside , when you 're , like , skiing or fishing , but you could play a trick on your eyes if you went to the movies and you went and watched a movie . well , the reason our eyes see 3d is because they 're spaced a little bit apart . they each get a different , slightly different image . that makes us see in 3d . we can play the same trick on our eye if we have the polarization like this . if light , if some of the light from the movie theater screen is coming in with one polarization , and the other light 's coming in with the other polarization , we can send two different images to our eyes at the same time . if you took these off , it 'd look like garbage because you 'd be getting both of these slightly different images , it 'd look all blurry . and it does . if you take off your 3d glasses and look at a 3d movie , looks terrible , because now both eyes are getting both images . but if you put your glasses back on , now this eye only gets the orientation that it 's supposed to get , and this eye only gets the orientation that it 's supposed to get , and you get a 3d image . so it 's useful in many ways . let me show you one more thing here . let 's come back here . this light was polarized vertically . so that 's called linear polarization . any time ... same with these . these are all linear polarization because , just up and down , one linear direction , just diagonal . this is also linear . all of these are linear . you can get circular polarized light . so if we come back to here , we 've got our electric field pointing up , like that . now let 's say we sent in another light ray , another light ray that also had a polarization , but not in this direction . let 's say our other light ray had polarization in this direction , so it looks like this , kind of like what our magnetic field would have looked like . but this is a completely different light ray with its own polarization and its own magnetic field . so we send this in . what would happen ? well , at this point , you 'd have a electric field that points this way . at this point , you 'd have a electric field that points that way . what would your eye see if you were over here ? let 's see . if i draw our axis here . all right , when this point right here gets to your eye , what am i going to see ? well , i 'm going to have a light ray that 's one part of a light ray . one component points up . that 's this electric field . one component points left . that 's this electric field . so the total , my total electric field , would point this way . i could to the pythagorean theorem if i wanted to figure out the size of it , but i just want to know the direction for now . and then it gets to here , and look at it : they both have zero . this light ray has zero electric field , this one has zero electric fields . so then it 'd just be at zero . now what happens over here ? well , i 've got light . this one points to the right at that point , this pink one , and then this red one would be pointing down . so what would i have at that point ? i 'd have light that went this way , and it would just be doing this over and over . it would just be ... i 'd just have diagonally polarized light . this is n't giving me anything new . you might think this is dumb . why do this ? why send in two different waves to just get diagonally polarized light ? i could have just sent in one wave that was diagonally polarized and got the same thing . the reason is , if you shift this purple wave , this pink wave , by 90 degrees of phase , by pi over two in phase , something magical happens . let me show you what happens here , if we move this to here . now we do n't just get diagonally linear polarized light . what we 're going to get is ... let me get rid of this . okay , so we start off with red , right ? the red electric field points up , and then this pink wave 's electric field is zero at that point . so this is all i have . my total electric field would just be up . i 'm going to draw it right here . the green 'll be the total . now i come over to here , and at this point , there 's some red electric field that points up , but there 's some of this other electric field that points this way . so i 'd have a total electric field that would point that way . and then i get over to here , and i 'd have all of the electric field from the pink one , none from the red one . it would point all left then . look what 's happening . the polarization of this light , if i shift this , if i 'm sitting here , looking with my eye , as my eye receives this light , i 'm going to see this light rotate its polarization . the polarization i 'm going to notice swings around in a circular pattern . and because of this , we call this circular polarization . so this is another type of polarization , where the actual angle of polarization rotates smoothly as this light ray enters your eye . and you know what ? er , drrr ... all right , actually , i sent you to receive this one first . that makes no sense . you 're going to receive the ones closes to you first in this light ray going this way . so you 'd actually receive this one first , then that one , then this one , then this one . because of that , you would n't see this going in a counterclockwise way , you 'd see this going in a clockwise circularly polarized way . sorry about that . you might think , `` okay , why ? `` why even bother with circular polarization ? '' well , i kind of lied earlier . turns out , in the movie theater example , they do n't actually do it like this , typically . oftentimes in the movie theaters , we do n't have just linearly polarized sunglasses . this would be a problem because , when you look at the movie theater screen , and if you were to tilt your head just a little bit ... think about it . this one 's not really going to get the right image anymore . it 's going to get some of both . and this one 's going to get some of both . it 's going to be blurry . your head would have to be perfectly level the whole time , which might be annoying . so what we do is , instead , we create circular polarized glasses , so that this one would only get one polarization , this one would get the other direction . this way , even if you tilt your head a little bit ... shoot , clockwise is clockwise , counterclockwise is counterclockwise . by using circular polarization for 3d movies , it can make it a little easier on you eyes to see a better 3d image , even if your head 's tilted a little bit .
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so we send this in . what would happen ? well , at this point , you 'd have a electric field that points this way .
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so where and when do this vector addition happen ?
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- let 's talk about polarization of light . we know what light waves are ; they 're electromagnetic waves . so they 're made out of electric fields . and that 's not good enough . we know there 's not just electric fields . that could n't sustain itself . there 's got to be magnetic fields there , as well , that are changing . those are perpendicular , so you can kind of draw them . it 's hard , on something two-dimensional , but you can kind of imagine those looking something like this . and those magnetic fields would point at a right angle to the electric fields . but this gets really messy if i try to draw both the electric and magnetic fields at the same time . so we 're going to leave the magnetic fields out . it 's often good enough to just know the direction of the electric field when we focus on the electric field . so what does polarization mean ? polarization refers to the fact that , if this light ray was heading straight toward your eye , or a detector , over here , what would you see ? well , if i draw an axis over here , and this point here , in the middle , this is this line -- so imagine we 're looking straight down that line -- and then up and down is up and down , and then left and right , that direction i have the magnetic field , would be this way and that way . what would my eye see ? well , my eye 's only going to see electric fields that either point up or electric fields that point down . they might have different values , but i 'm only going to see electric fields that point up or down . because of that , this light ray is polarized . so polarized light is light where the electric field is only oscillating in one direction . up or down , that 's one direction -- vertically . or it could be polarized horizontally . or it could be polarized diagonally . but either way , you could have this wave polarized along any direction . i mean , a light ray like this , if we had it coming in diagonal , this light ray that 's oscillating like this , where the electric field oscillates like that , that also polarized . these are both polarized because there 's only one direction that the electric field is oscillating in . and you might thing , `` pff , how could you ever have `` a light ray that 's not polarized ? '' easy . most light that you get is not polarized . that is to say , light that 's coming from the sun , straight from the sun -- typically not polarized . light from a lightbulb , an old incandescent light bulb , this thing 's hot . you can get light polarized in any direction , all at once , all overlapping . so if we draw this case for a light bulb , just a random incandescent light bulb , you might get light , some of the light , hitting you eye , you can get some light that 's got that direction , you got light that 's got this direction , you got light in all these directions at any given moment . i mean , you 'd have to add these up to get the total , and they might not all be the same value . but what i 'm trying to say is , at any given moment , you do n't know what direction the electric field 's going to be hitting your eye at from a random source . it could be in any direction . so this is not polarized . this diagram represents light that is not polarized . at some point , the field might be pointing this way , at some later point it 's this way ; it 's just random . you never know which way the electric field 's going to be pointing . whereas these over here , these are polarized . so how could you polarize this light ? let 's say you wanted light that was polarized . you were doing an experiment . you needed polarized light . well , that 's easy . you can use what 's called a polarizer . and this is a material that lets light through , but it only lets light through in one orientation , so you 're going to have a polarizer that , for instance , only lets through vertically polarized light . so this is a polarizer . these are cheap : thin , plastic , configured in a way so that it only lets light through that 's vertically polarized . any light coming in here that 's not vertically polarized gets blocked , or absorbed . so what that means is , if you used this polarizer and held it in between your eye and this light bulb , you would only get this light . all the rest of it would get blocked . or you could just rotate this thing and imagine a polarizer that only lets through horizontal light . now it would only let through light that was this way , and so you would only get this part of the light . or you could just orient it at any angle you want and block everything but the certain angle that this polarizer is defined as letting light through . so you can do this . and once you hold this up , you get polarized light , light that 's only got one orientation . so that 's what polarization means . but why do we care about polarization ? well , let me get rid of this for a minute . you 've heard of polarized sunglasses . so imagine you 're standing near water , or maybe you 're standing on ice or snow or something reflective . there 's a problem . say the sun 's out . it 's shining . it 's a beautiful day -- except there 's going to be glare . let 's say you 're looking down at something here on the ground . it 's going to get light reflecting off of it from just ... you know , light 's coming in from all direction . but it also gets this direct light from the sun . so it gets light from reflected off the clouds and whatever , whatever 's nearby , ambient light . and there 's also this direct sunlight . that 's harsh . if that reflects straight up to your eye , that hurts . you do n't like that . it blocks our vision . it 's hard to see , it 's glare . we do n't want this glare . so what can we do ? well , it just so happens that , when light reflects off of a surface , even though the light from the sun is not polarized , once it reflects , it does get polarized or at least partially polarized . so this surface here , once this light reflects , it 's coming in at all orientations . you got electric field ... you never know what electric field you 're going to get straight from the sun . and when it reflects , though , you mostly get , upon reflection , the direction of polarization defined by the plane of the surface that it hit . so because the floor is horizontal , when this light ray hits the ground and reflects , that reflected light gets partially polarized . this horizontal component of the electric field is going to be more present than the other components . maybe not completely . sometimes it could be . it could be completely polarized , but often it 's just partially polarized . but that 's pretty cool , because now you know what we can do . i know how to block this . we should get some sunglasses . we put some sunglasses on and we make our glasses so that these are polarized . and how do we want these polarized ? i want to get rid of the glare . so what i do is , i make sure my sunglasses only let through vertically polarized light . here 's some polarizers . that way , a lot of this glare gets blocked because it does not have a vertical orientation , it has a horizontal orientation . and then we can block it . so that 's one good thing that polarization does for us , and understanding it , we can get rid of glare . also , fishermen like it because , if you 're trying to look in the water at fish , you want to see in through the water , you want to see this light from the fish getting to you . you do n't want to see the glare off of the sun getting to you . so polarized sunglasses are useful . also , we can play a trick on our eye , if we really wanted to . you could take one of these , make one eye have a vertical orientation for the polarization , have the other eye with a horizontal ... and you 're thinking , `` this is stupid . `` why would you do this for ? '' `` this eye 's going to get a lot of glare . '' we would n't use these outside , when you 're , like , skiing or fishing , but you could play a trick on your eyes if you went to the movies and you went and watched a movie . well , the reason our eyes see 3d is because they 're spaced a little bit apart . they each get a different , slightly different image . that makes us see in 3d . we can play the same trick on our eye if we have the polarization like this . if light , if some of the light from the movie theater screen is coming in with one polarization , and the other light 's coming in with the other polarization , we can send two different images to our eyes at the same time . if you took these off , it 'd look like garbage because you 'd be getting both of these slightly different images , it 'd look all blurry . and it does . if you take off your 3d glasses and look at a 3d movie , looks terrible , because now both eyes are getting both images . but if you put your glasses back on , now this eye only gets the orientation that it 's supposed to get , and this eye only gets the orientation that it 's supposed to get , and you get a 3d image . so it 's useful in many ways . let me show you one more thing here . let 's come back here . this light was polarized vertically . so that 's called linear polarization . any time ... same with these . these are all linear polarization because , just up and down , one linear direction , just diagonal . this is also linear . all of these are linear . you can get circular polarized light . so if we come back to here , we 've got our electric field pointing up , like that . now let 's say we sent in another light ray , another light ray that also had a polarization , but not in this direction . let 's say our other light ray had polarization in this direction , so it looks like this , kind of like what our magnetic field would have looked like . but this is a completely different light ray with its own polarization and its own magnetic field . so we send this in . what would happen ? well , at this point , you 'd have a electric field that points this way . at this point , you 'd have a electric field that points that way . what would your eye see if you were over here ? let 's see . if i draw our axis here . all right , when this point right here gets to your eye , what am i going to see ? well , i 'm going to have a light ray that 's one part of a light ray . one component points up . that 's this electric field . one component points left . that 's this electric field . so the total , my total electric field , would point this way . i could to the pythagorean theorem if i wanted to figure out the size of it , but i just want to know the direction for now . and then it gets to here , and look at it : they both have zero . this light ray has zero electric field , this one has zero electric fields . so then it 'd just be at zero . now what happens over here ? well , i 've got light . this one points to the right at that point , this pink one , and then this red one would be pointing down . so what would i have at that point ? i 'd have light that went this way , and it would just be doing this over and over . it would just be ... i 'd just have diagonally polarized light . this is n't giving me anything new . you might think this is dumb . why do this ? why send in two different waves to just get diagonally polarized light ? i could have just sent in one wave that was diagonally polarized and got the same thing . the reason is , if you shift this purple wave , this pink wave , by 90 degrees of phase , by pi over two in phase , something magical happens . let me show you what happens here , if we move this to here . now we do n't just get diagonally linear polarized light . what we 're going to get is ... let me get rid of this . okay , so we start off with red , right ? the red electric field points up , and then this pink wave 's electric field is zero at that point . so this is all i have . my total electric field would just be up . i 'm going to draw it right here . the green 'll be the total . now i come over to here , and at this point , there 's some red electric field that points up , but there 's some of this other electric field that points this way . so i 'd have a total electric field that would point that way . and then i get over to here , and i 'd have all of the electric field from the pink one , none from the red one . it would point all left then . look what 's happening . the polarization of this light , if i shift this , if i 'm sitting here , looking with my eye , as my eye receives this light , i 'm going to see this light rotate its polarization . the polarization i 'm going to notice swings around in a circular pattern . and because of this , we call this circular polarization . so this is another type of polarization , where the actual angle of polarization rotates smoothly as this light ray enters your eye . and you know what ? er , drrr ... all right , actually , i sent you to receive this one first . that makes no sense . you 're going to receive the ones closes to you first in this light ray going this way . so you 'd actually receive this one first , then that one , then this one , then this one . because of that , you would n't see this going in a counterclockwise way , you 'd see this going in a clockwise circularly polarized way . sorry about that . you might think , `` okay , why ? `` why even bother with circular polarization ? '' well , i kind of lied earlier . turns out , in the movie theater example , they do n't actually do it like this , typically . oftentimes in the movie theaters , we do n't have just linearly polarized sunglasses . this would be a problem because , when you look at the movie theater screen , and if you were to tilt your head just a little bit ... think about it . this one 's not really going to get the right image anymore . it 's going to get some of both . and this one 's going to get some of both . it 's going to be blurry . your head would have to be perfectly level the whole time , which might be annoying . so what we do is , instead , we create circular polarized glasses , so that this one would only get one polarization , this one would get the other direction . this way , even if you tilt your head a little bit ... shoot , clockwise is clockwise , counterclockwise is counterclockwise . by using circular polarization for 3d movies , it can make it a little easier on you eyes to see a better 3d image , even if your head 's tilted a little bit .
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- let 's talk about polarization of light . we know what light waves are ; they 're electromagnetic waves . so they 're made out of electric fields .
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why would u send in 2 dif waves ?
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- let 's talk about polarization of light . we know what light waves are ; they 're electromagnetic waves . so they 're made out of electric fields . and that 's not good enough . we know there 's not just electric fields . that could n't sustain itself . there 's got to be magnetic fields there , as well , that are changing . those are perpendicular , so you can kind of draw them . it 's hard , on something two-dimensional , but you can kind of imagine those looking something like this . and those magnetic fields would point at a right angle to the electric fields . but this gets really messy if i try to draw both the electric and magnetic fields at the same time . so we 're going to leave the magnetic fields out . it 's often good enough to just know the direction of the electric field when we focus on the electric field . so what does polarization mean ? polarization refers to the fact that , if this light ray was heading straight toward your eye , or a detector , over here , what would you see ? well , if i draw an axis over here , and this point here , in the middle , this is this line -- so imagine we 're looking straight down that line -- and then up and down is up and down , and then left and right , that direction i have the magnetic field , would be this way and that way . what would my eye see ? well , my eye 's only going to see electric fields that either point up or electric fields that point down . they might have different values , but i 'm only going to see electric fields that point up or down . because of that , this light ray is polarized . so polarized light is light where the electric field is only oscillating in one direction . up or down , that 's one direction -- vertically . or it could be polarized horizontally . or it could be polarized diagonally . but either way , you could have this wave polarized along any direction . i mean , a light ray like this , if we had it coming in diagonal , this light ray that 's oscillating like this , where the electric field oscillates like that , that also polarized . these are both polarized because there 's only one direction that the electric field is oscillating in . and you might thing , `` pff , how could you ever have `` a light ray that 's not polarized ? '' easy . most light that you get is not polarized . that is to say , light that 's coming from the sun , straight from the sun -- typically not polarized . light from a lightbulb , an old incandescent light bulb , this thing 's hot . you can get light polarized in any direction , all at once , all overlapping . so if we draw this case for a light bulb , just a random incandescent light bulb , you might get light , some of the light , hitting you eye , you can get some light that 's got that direction , you got light that 's got this direction , you got light in all these directions at any given moment . i mean , you 'd have to add these up to get the total , and they might not all be the same value . but what i 'm trying to say is , at any given moment , you do n't know what direction the electric field 's going to be hitting your eye at from a random source . it could be in any direction . so this is not polarized . this diagram represents light that is not polarized . at some point , the field might be pointing this way , at some later point it 's this way ; it 's just random . you never know which way the electric field 's going to be pointing . whereas these over here , these are polarized . so how could you polarize this light ? let 's say you wanted light that was polarized . you were doing an experiment . you needed polarized light . well , that 's easy . you can use what 's called a polarizer . and this is a material that lets light through , but it only lets light through in one orientation , so you 're going to have a polarizer that , for instance , only lets through vertically polarized light . so this is a polarizer . these are cheap : thin , plastic , configured in a way so that it only lets light through that 's vertically polarized . any light coming in here that 's not vertically polarized gets blocked , or absorbed . so what that means is , if you used this polarizer and held it in between your eye and this light bulb , you would only get this light . all the rest of it would get blocked . or you could just rotate this thing and imagine a polarizer that only lets through horizontal light . now it would only let through light that was this way , and so you would only get this part of the light . or you could just orient it at any angle you want and block everything but the certain angle that this polarizer is defined as letting light through . so you can do this . and once you hold this up , you get polarized light , light that 's only got one orientation . so that 's what polarization means . but why do we care about polarization ? well , let me get rid of this for a minute . you 've heard of polarized sunglasses . so imagine you 're standing near water , or maybe you 're standing on ice or snow or something reflective . there 's a problem . say the sun 's out . it 's shining . it 's a beautiful day -- except there 's going to be glare . let 's say you 're looking down at something here on the ground . it 's going to get light reflecting off of it from just ... you know , light 's coming in from all direction . but it also gets this direct light from the sun . so it gets light from reflected off the clouds and whatever , whatever 's nearby , ambient light . and there 's also this direct sunlight . that 's harsh . if that reflects straight up to your eye , that hurts . you do n't like that . it blocks our vision . it 's hard to see , it 's glare . we do n't want this glare . so what can we do ? well , it just so happens that , when light reflects off of a surface , even though the light from the sun is not polarized , once it reflects , it does get polarized or at least partially polarized . so this surface here , once this light reflects , it 's coming in at all orientations . you got electric field ... you never know what electric field you 're going to get straight from the sun . and when it reflects , though , you mostly get , upon reflection , the direction of polarization defined by the plane of the surface that it hit . so because the floor is horizontal , when this light ray hits the ground and reflects , that reflected light gets partially polarized . this horizontal component of the electric field is going to be more present than the other components . maybe not completely . sometimes it could be . it could be completely polarized , but often it 's just partially polarized . but that 's pretty cool , because now you know what we can do . i know how to block this . we should get some sunglasses . we put some sunglasses on and we make our glasses so that these are polarized . and how do we want these polarized ? i want to get rid of the glare . so what i do is , i make sure my sunglasses only let through vertically polarized light . here 's some polarizers . that way , a lot of this glare gets blocked because it does not have a vertical orientation , it has a horizontal orientation . and then we can block it . so that 's one good thing that polarization does for us , and understanding it , we can get rid of glare . also , fishermen like it because , if you 're trying to look in the water at fish , you want to see in through the water , you want to see this light from the fish getting to you . you do n't want to see the glare off of the sun getting to you . so polarized sunglasses are useful . also , we can play a trick on our eye , if we really wanted to . you could take one of these , make one eye have a vertical orientation for the polarization , have the other eye with a horizontal ... and you 're thinking , `` this is stupid . `` why would you do this for ? '' `` this eye 's going to get a lot of glare . '' we would n't use these outside , when you 're , like , skiing or fishing , but you could play a trick on your eyes if you went to the movies and you went and watched a movie . well , the reason our eyes see 3d is because they 're spaced a little bit apart . they each get a different , slightly different image . that makes us see in 3d . we can play the same trick on our eye if we have the polarization like this . if light , if some of the light from the movie theater screen is coming in with one polarization , and the other light 's coming in with the other polarization , we can send two different images to our eyes at the same time . if you took these off , it 'd look like garbage because you 'd be getting both of these slightly different images , it 'd look all blurry . and it does . if you take off your 3d glasses and look at a 3d movie , looks terrible , because now both eyes are getting both images . but if you put your glasses back on , now this eye only gets the orientation that it 's supposed to get , and this eye only gets the orientation that it 's supposed to get , and you get a 3d image . so it 's useful in many ways . let me show you one more thing here . let 's come back here . this light was polarized vertically . so that 's called linear polarization . any time ... same with these . these are all linear polarization because , just up and down , one linear direction , just diagonal . this is also linear . all of these are linear . you can get circular polarized light . so if we come back to here , we 've got our electric field pointing up , like that . now let 's say we sent in another light ray , another light ray that also had a polarization , but not in this direction . let 's say our other light ray had polarization in this direction , so it looks like this , kind of like what our magnetic field would have looked like . but this is a completely different light ray with its own polarization and its own magnetic field . so we send this in . what would happen ? well , at this point , you 'd have a electric field that points this way . at this point , you 'd have a electric field that points that way . what would your eye see if you were over here ? let 's see . if i draw our axis here . all right , when this point right here gets to your eye , what am i going to see ? well , i 'm going to have a light ray that 's one part of a light ray . one component points up . that 's this electric field . one component points left . that 's this electric field . so the total , my total electric field , would point this way . i could to the pythagorean theorem if i wanted to figure out the size of it , but i just want to know the direction for now . and then it gets to here , and look at it : they both have zero . this light ray has zero electric field , this one has zero electric fields . so then it 'd just be at zero . now what happens over here ? well , i 've got light . this one points to the right at that point , this pink one , and then this red one would be pointing down . so what would i have at that point ? i 'd have light that went this way , and it would just be doing this over and over . it would just be ... i 'd just have diagonally polarized light . this is n't giving me anything new . you might think this is dumb . why do this ? why send in two different waves to just get diagonally polarized light ? i could have just sent in one wave that was diagonally polarized and got the same thing . the reason is , if you shift this purple wave , this pink wave , by 90 degrees of phase , by pi over two in phase , something magical happens . let me show you what happens here , if we move this to here . now we do n't just get diagonally linear polarized light . what we 're going to get is ... let me get rid of this . okay , so we start off with red , right ? the red electric field points up , and then this pink wave 's electric field is zero at that point . so this is all i have . my total electric field would just be up . i 'm going to draw it right here . the green 'll be the total . now i come over to here , and at this point , there 's some red electric field that points up , but there 's some of this other electric field that points this way . so i 'd have a total electric field that would point that way . and then i get over to here , and i 'd have all of the electric field from the pink one , none from the red one . it would point all left then . look what 's happening . the polarization of this light , if i shift this , if i 'm sitting here , looking with my eye , as my eye receives this light , i 'm going to see this light rotate its polarization . the polarization i 'm going to notice swings around in a circular pattern . and because of this , we call this circular polarization . so this is another type of polarization , where the actual angle of polarization rotates smoothly as this light ray enters your eye . and you know what ? er , drrr ... all right , actually , i sent you to receive this one first . that makes no sense . you 're going to receive the ones closes to you first in this light ray going this way . so you 'd actually receive this one first , then that one , then this one , then this one . because of that , you would n't see this going in a counterclockwise way , you 'd see this going in a clockwise circularly polarized way . sorry about that . you might think , `` okay , why ? `` why even bother with circular polarization ? '' well , i kind of lied earlier . turns out , in the movie theater example , they do n't actually do it like this , typically . oftentimes in the movie theaters , we do n't have just linearly polarized sunglasses . this would be a problem because , when you look at the movie theater screen , and if you were to tilt your head just a little bit ... think about it . this one 's not really going to get the right image anymore . it 's going to get some of both . and this one 's going to get some of both . it 's going to be blurry . your head would have to be perfectly level the whole time , which might be annoying . so what we do is , instead , we create circular polarized glasses , so that this one would only get one polarization , this one would get the other direction . this way , even if you tilt your head a little bit ... shoot , clockwise is clockwise , counterclockwise is counterclockwise . by using circular polarization for 3d movies , it can make it a little easier on you eyes to see a better 3d image , even if your head 's tilted a little bit .
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so we send this in . what would happen ? well , at this point , you 'd have a electric field that points this way .
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what would happen if instead of only two waves used in movie theaters there were three of them ?
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- let 's talk about polarization of light . we know what light waves are ; they 're electromagnetic waves . so they 're made out of electric fields . and that 's not good enough . we know there 's not just electric fields . that could n't sustain itself . there 's got to be magnetic fields there , as well , that are changing . those are perpendicular , so you can kind of draw them . it 's hard , on something two-dimensional , but you can kind of imagine those looking something like this . and those magnetic fields would point at a right angle to the electric fields . but this gets really messy if i try to draw both the electric and magnetic fields at the same time . so we 're going to leave the magnetic fields out . it 's often good enough to just know the direction of the electric field when we focus on the electric field . so what does polarization mean ? polarization refers to the fact that , if this light ray was heading straight toward your eye , or a detector , over here , what would you see ? well , if i draw an axis over here , and this point here , in the middle , this is this line -- so imagine we 're looking straight down that line -- and then up and down is up and down , and then left and right , that direction i have the magnetic field , would be this way and that way . what would my eye see ? well , my eye 's only going to see electric fields that either point up or electric fields that point down . they might have different values , but i 'm only going to see electric fields that point up or down . because of that , this light ray is polarized . so polarized light is light where the electric field is only oscillating in one direction . up or down , that 's one direction -- vertically . or it could be polarized horizontally . or it could be polarized diagonally . but either way , you could have this wave polarized along any direction . i mean , a light ray like this , if we had it coming in diagonal , this light ray that 's oscillating like this , where the electric field oscillates like that , that also polarized . these are both polarized because there 's only one direction that the electric field is oscillating in . and you might thing , `` pff , how could you ever have `` a light ray that 's not polarized ? '' easy . most light that you get is not polarized . that is to say , light that 's coming from the sun , straight from the sun -- typically not polarized . light from a lightbulb , an old incandescent light bulb , this thing 's hot . you can get light polarized in any direction , all at once , all overlapping . so if we draw this case for a light bulb , just a random incandescent light bulb , you might get light , some of the light , hitting you eye , you can get some light that 's got that direction , you got light that 's got this direction , you got light in all these directions at any given moment . i mean , you 'd have to add these up to get the total , and they might not all be the same value . but what i 'm trying to say is , at any given moment , you do n't know what direction the electric field 's going to be hitting your eye at from a random source . it could be in any direction . so this is not polarized . this diagram represents light that is not polarized . at some point , the field might be pointing this way , at some later point it 's this way ; it 's just random . you never know which way the electric field 's going to be pointing . whereas these over here , these are polarized . so how could you polarize this light ? let 's say you wanted light that was polarized . you were doing an experiment . you needed polarized light . well , that 's easy . you can use what 's called a polarizer . and this is a material that lets light through , but it only lets light through in one orientation , so you 're going to have a polarizer that , for instance , only lets through vertically polarized light . so this is a polarizer . these are cheap : thin , plastic , configured in a way so that it only lets light through that 's vertically polarized . any light coming in here that 's not vertically polarized gets blocked , or absorbed . so what that means is , if you used this polarizer and held it in between your eye and this light bulb , you would only get this light . all the rest of it would get blocked . or you could just rotate this thing and imagine a polarizer that only lets through horizontal light . now it would only let through light that was this way , and so you would only get this part of the light . or you could just orient it at any angle you want and block everything but the certain angle that this polarizer is defined as letting light through . so you can do this . and once you hold this up , you get polarized light , light that 's only got one orientation . so that 's what polarization means . but why do we care about polarization ? well , let me get rid of this for a minute . you 've heard of polarized sunglasses . so imagine you 're standing near water , or maybe you 're standing on ice or snow or something reflective . there 's a problem . say the sun 's out . it 's shining . it 's a beautiful day -- except there 's going to be glare . let 's say you 're looking down at something here on the ground . it 's going to get light reflecting off of it from just ... you know , light 's coming in from all direction . but it also gets this direct light from the sun . so it gets light from reflected off the clouds and whatever , whatever 's nearby , ambient light . and there 's also this direct sunlight . that 's harsh . if that reflects straight up to your eye , that hurts . you do n't like that . it blocks our vision . it 's hard to see , it 's glare . we do n't want this glare . so what can we do ? well , it just so happens that , when light reflects off of a surface , even though the light from the sun is not polarized , once it reflects , it does get polarized or at least partially polarized . so this surface here , once this light reflects , it 's coming in at all orientations . you got electric field ... you never know what electric field you 're going to get straight from the sun . and when it reflects , though , you mostly get , upon reflection , the direction of polarization defined by the plane of the surface that it hit . so because the floor is horizontal , when this light ray hits the ground and reflects , that reflected light gets partially polarized . this horizontal component of the electric field is going to be more present than the other components . maybe not completely . sometimes it could be . it could be completely polarized , but often it 's just partially polarized . but that 's pretty cool , because now you know what we can do . i know how to block this . we should get some sunglasses . we put some sunglasses on and we make our glasses so that these are polarized . and how do we want these polarized ? i want to get rid of the glare . so what i do is , i make sure my sunglasses only let through vertically polarized light . here 's some polarizers . that way , a lot of this glare gets blocked because it does not have a vertical orientation , it has a horizontal orientation . and then we can block it . so that 's one good thing that polarization does for us , and understanding it , we can get rid of glare . also , fishermen like it because , if you 're trying to look in the water at fish , you want to see in through the water , you want to see this light from the fish getting to you . you do n't want to see the glare off of the sun getting to you . so polarized sunglasses are useful . also , we can play a trick on our eye , if we really wanted to . you could take one of these , make one eye have a vertical orientation for the polarization , have the other eye with a horizontal ... and you 're thinking , `` this is stupid . `` why would you do this for ? '' `` this eye 's going to get a lot of glare . '' we would n't use these outside , when you 're , like , skiing or fishing , but you could play a trick on your eyes if you went to the movies and you went and watched a movie . well , the reason our eyes see 3d is because they 're spaced a little bit apart . they each get a different , slightly different image . that makes us see in 3d . we can play the same trick on our eye if we have the polarization like this . if light , if some of the light from the movie theater screen is coming in with one polarization , and the other light 's coming in with the other polarization , we can send two different images to our eyes at the same time . if you took these off , it 'd look like garbage because you 'd be getting both of these slightly different images , it 'd look all blurry . and it does . if you take off your 3d glasses and look at a 3d movie , looks terrible , because now both eyes are getting both images . but if you put your glasses back on , now this eye only gets the orientation that it 's supposed to get , and this eye only gets the orientation that it 's supposed to get , and you get a 3d image . so it 's useful in many ways . let me show you one more thing here . let 's come back here . this light was polarized vertically . so that 's called linear polarization . any time ... same with these . these are all linear polarization because , just up and down , one linear direction , just diagonal . this is also linear . all of these are linear . you can get circular polarized light . so if we come back to here , we 've got our electric field pointing up , like that . now let 's say we sent in another light ray , another light ray that also had a polarization , but not in this direction . let 's say our other light ray had polarization in this direction , so it looks like this , kind of like what our magnetic field would have looked like . but this is a completely different light ray with its own polarization and its own magnetic field . so we send this in . what would happen ? well , at this point , you 'd have a electric field that points this way . at this point , you 'd have a electric field that points that way . what would your eye see if you were over here ? let 's see . if i draw our axis here . all right , when this point right here gets to your eye , what am i going to see ? well , i 'm going to have a light ray that 's one part of a light ray . one component points up . that 's this electric field . one component points left . that 's this electric field . so the total , my total electric field , would point this way . i could to the pythagorean theorem if i wanted to figure out the size of it , but i just want to know the direction for now . and then it gets to here , and look at it : they both have zero . this light ray has zero electric field , this one has zero electric fields . so then it 'd just be at zero . now what happens over here ? well , i 've got light . this one points to the right at that point , this pink one , and then this red one would be pointing down . so what would i have at that point ? i 'd have light that went this way , and it would just be doing this over and over . it would just be ... i 'd just have diagonally polarized light . this is n't giving me anything new . you might think this is dumb . why do this ? why send in two different waves to just get diagonally polarized light ? i could have just sent in one wave that was diagonally polarized and got the same thing . the reason is , if you shift this purple wave , this pink wave , by 90 degrees of phase , by pi over two in phase , something magical happens . let me show you what happens here , if we move this to here . now we do n't just get diagonally linear polarized light . what we 're going to get is ... let me get rid of this . okay , so we start off with red , right ? the red electric field points up , and then this pink wave 's electric field is zero at that point . so this is all i have . my total electric field would just be up . i 'm going to draw it right here . the green 'll be the total . now i come over to here , and at this point , there 's some red electric field that points up , but there 's some of this other electric field that points this way . so i 'd have a total electric field that would point that way . and then i get over to here , and i 'd have all of the electric field from the pink one , none from the red one . it would point all left then . look what 's happening . the polarization of this light , if i shift this , if i 'm sitting here , looking with my eye , as my eye receives this light , i 'm going to see this light rotate its polarization . the polarization i 'm going to notice swings around in a circular pattern . and because of this , we call this circular polarization . so this is another type of polarization , where the actual angle of polarization rotates smoothly as this light ray enters your eye . and you know what ? er , drrr ... all right , actually , i sent you to receive this one first . that makes no sense . you 're going to receive the ones closes to you first in this light ray going this way . so you 'd actually receive this one first , then that one , then this one , then this one . because of that , you would n't see this going in a counterclockwise way , you 'd see this going in a clockwise circularly polarized way . sorry about that . you might think , `` okay , why ? `` why even bother with circular polarization ? '' well , i kind of lied earlier . turns out , in the movie theater example , they do n't actually do it like this , typically . oftentimes in the movie theaters , we do n't have just linearly polarized sunglasses . this would be a problem because , when you look at the movie theater screen , and if you were to tilt your head just a little bit ... think about it . this one 's not really going to get the right image anymore . it 's going to get some of both . and this one 's going to get some of both . it 's going to be blurry . your head would have to be perfectly level the whole time , which might be annoying . so what we do is , instead , we create circular polarized glasses , so that this one would only get one polarization , this one would get the other direction . this way , even if you tilt your head a little bit ... shoot , clockwise is clockwise , counterclockwise is counterclockwise . by using circular polarization for 3d movies , it can make it a little easier on you eyes to see a better 3d image , even if your head 's tilted a little bit .
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so we send this in . what would happen ? well , at this point , you 'd have a electric field that points this way .
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how would we receive the polarization and the image ?
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- let 's talk about polarization of light . we know what light waves are ; they 're electromagnetic waves . so they 're made out of electric fields . and that 's not good enough . we know there 's not just electric fields . that could n't sustain itself . there 's got to be magnetic fields there , as well , that are changing . those are perpendicular , so you can kind of draw them . it 's hard , on something two-dimensional , but you can kind of imagine those looking something like this . and those magnetic fields would point at a right angle to the electric fields . but this gets really messy if i try to draw both the electric and magnetic fields at the same time . so we 're going to leave the magnetic fields out . it 's often good enough to just know the direction of the electric field when we focus on the electric field . so what does polarization mean ? polarization refers to the fact that , if this light ray was heading straight toward your eye , or a detector , over here , what would you see ? well , if i draw an axis over here , and this point here , in the middle , this is this line -- so imagine we 're looking straight down that line -- and then up and down is up and down , and then left and right , that direction i have the magnetic field , would be this way and that way . what would my eye see ? well , my eye 's only going to see electric fields that either point up or electric fields that point down . they might have different values , but i 'm only going to see electric fields that point up or down . because of that , this light ray is polarized . so polarized light is light where the electric field is only oscillating in one direction . up or down , that 's one direction -- vertically . or it could be polarized horizontally . or it could be polarized diagonally . but either way , you could have this wave polarized along any direction . i mean , a light ray like this , if we had it coming in diagonal , this light ray that 's oscillating like this , where the electric field oscillates like that , that also polarized . these are both polarized because there 's only one direction that the electric field is oscillating in . and you might thing , `` pff , how could you ever have `` a light ray that 's not polarized ? '' easy . most light that you get is not polarized . that is to say , light that 's coming from the sun , straight from the sun -- typically not polarized . light from a lightbulb , an old incandescent light bulb , this thing 's hot . you can get light polarized in any direction , all at once , all overlapping . so if we draw this case for a light bulb , just a random incandescent light bulb , you might get light , some of the light , hitting you eye , you can get some light that 's got that direction , you got light that 's got this direction , you got light in all these directions at any given moment . i mean , you 'd have to add these up to get the total , and they might not all be the same value . but what i 'm trying to say is , at any given moment , you do n't know what direction the electric field 's going to be hitting your eye at from a random source . it could be in any direction . so this is not polarized . this diagram represents light that is not polarized . at some point , the field might be pointing this way , at some later point it 's this way ; it 's just random . you never know which way the electric field 's going to be pointing . whereas these over here , these are polarized . so how could you polarize this light ? let 's say you wanted light that was polarized . you were doing an experiment . you needed polarized light . well , that 's easy . you can use what 's called a polarizer . and this is a material that lets light through , but it only lets light through in one orientation , so you 're going to have a polarizer that , for instance , only lets through vertically polarized light . so this is a polarizer . these are cheap : thin , plastic , configured in a way so that it only lets light through that 's vertically polarized . any light coming in here that 's not vertically polarized gets blocked , or absorbed . so what that means is , if you used this polarizer and held it in between your eye and this light bulb , you would only get this light . all the rest of it would get blocked . or you could just rotate this thing and imagine a polarizer that only lets through horizontal light . now it would only let through light that was this way , and so you would only get this part of the light . or you could just orient it at any angle you want and block everything but the certain angle that this polarizer is defined as letting light through . so you can do this . and once you hold this up , you get polarized light , light that 's only got one orientation . so that 's what polarization means . but why do we care about polarization ? well , let me get rid of this for a minute . you 've heard of polarized sunglasses . so imagine you 're standing near water , or maybe you 're standing on ice or snow or something reflective . there 's a problem . say the sun 's out . it 's shining . it 's a beautiful day -- except there 's going to be glare . let 's say you 're looking down at something here on the ground . it 's going to get light reflecting off of it from just ... you know , light 's coming in from all direction . but it also gets this direct light from the sun . so it gets light from reflected off the clouds and whatever , whatever 's nearby , ambient light . and there 's also this direct sunlight . that 's harsh . if that reflects straight up to your eye , that hurts . you do n't like that . it blocks our vision . it 's hard to see , it 's glare . we do n't want this glare . so what can we do ? well , it just so happens that , when light reflects off of a surface , even though the light from the sun is not polarized , once it reflects , it does get polarized or at least partially polarized . so this surface here , once this light reflects , it 's coming in at all orientations . you got electric field ... you never know what electric field you 're going to get straight from the sun . and when it reflects , though , you mostly get , upon reflection , the direction of polarization defined by the plane of the surface that it hit . so because the floor is horizontal , when this light ray hits the ground and reflects , that reflected light gets partially polarized . this horizontal component of the electric field is going to be more present than the other components . maybe not completely . sometimes it could be . it could be completely polarized , but often it 's just partially polarized . but that 's pretty cool , because now you know what we can do . i know how to block this . we should get some sunglasses . we put some sunglasses on and we make our glasses so that these are polarized . and how do we want these polarized ? i want to get rid of the glare . so what i do is , i make sure my sunglasses only let through vertically polarized light . here 's some polarizers . that way , a lot of this glare gets blocked because it does not have a vertical orientation , it has a horizontal orientation . and then we can block it . so that 's one good thing that polarization does for us , and understanding it , we can get rid of glare . also , fishermen like it because , if you 're trying to look in the water at fish , you want to see in through the water , you want to see this light from the fish getting to you . you do n't want to see the glare off of the sun getting to you . so polarized sunglasses are useful . also , we can play a trick on our eye , if we really wanted to . you could take one of these , make one eye have a vertical orientation for the polarization , have the other eye with a horizontal ... and you 're thinking , `` this is stupid . `` why would you do this for ? '' `` this eye 's going to get a lot of glare . '' we would n't use these outside , when you 're , like , skiing or fishing , but you could play a trick on your eyes if you went to the movies and you went and watched a movie . well , the reason our eyes see 3d is because they 're spaced a little bit apart . they each get a different , slightly different image . that makes us see in 3d . we can play the same trick on our eye if we have the polarization like this . if light , if some of the light from the movie theater screen is coming in with one polarization , and the other light 's coming in with the other polarization , we can send two different images to our eyes at the same time . if you took these off , it 'd look like garbage because you 'd be getting both of these slightly different images , it 'd look all blurry . and it does . if you take off your 3d glasses and look at a 3d movie , looks terrible , because now both eyes are getting both images . but if you put your glasses back on , now this eye only gets the orientation that it 's supposed to get , and this eye only gets the orientation that it 's supposed to get , and you get a 3d image . so it 's useful in many ways . let me show you one more thing here . let 's come back here . this light was polarized vertically . so that 's called linear polarization . any time ... same with these . these are all linear polarization because , just up and down , one linear direction , just diagonal . this is also linear . all of these are linear . you can get circular polarized light . so if we come back to here , we 've got our electric field pointing up , like that . now let 's say we sent in another light ray , another light ray that also had a polarization , but not in this direction . let 's say our other light ray had polarization in this direction , so it looks like this , kind of like what our magnetic field would have looked like . but this is a completely different light ray with its own polarization and its own magnetic field . so we send this in . what would happen ? well , at this point , you 'd have a electric field that points this way . at this point , you 'd have a electric field that points that way . what would your eye see if you were over here ? let 's see . if i draw our axis here . all right , when this point right here gets to your eye , what am i going to see ? well , i 'm going to have a light ray that 's one part of a light ray . one component points up . that 's this electric field . one component points left . that 's this electric field . so the total , my total electric field , would point this way . i could to the pythagorean theorem if i wanted to figure out the size of it , but i just want to know the direction for now . and then it gets to here , and look at it : they both have zero . this light ray has zero electric field , this one has zero electric fields . so then it 'd just be at zero . now what happens over here ? well , i 've got light . this one points to the right at that point , this pink one , and then this red one would be pointing down . so what would i have at that point ? i 'd have light that went this way , and it would just be doing this over and over . it would just be ... i 'd just have diagonally polarized light . this is n't giving me anything new . you might think this is dumb . why do this ? why send in two different waves to just get diagonally polarized light ? i could have just sent in one wave that was diagonally polarized and got the same thing . the reason is , if you shift this purple wave , this pink wave , by 90 degrees of phase , by pi over two in phase , something magical happens . let me show you what happens here , if we move this to here . now we do n't just get diagonally linear polarized light . what we 're going to get is ... let me get rid of this . okay , so we start off with red , right ? the red electric field points up , and then this pink wave 's electric field is zero at that point . so this is all i have . my total electric field would just be up . i 'm going to draw it right here . the green 'll be the total . now i come over to here , and at this point , there 's some red electric field that points up , but there 's some of this other electric field that points this way . so i 'd have a total electric field that would point that way . and then i get over to here , and i 'd have all of the electric field from the pink one , none from the red one . it would point all left then . look what 's happening . the polarization of this light , if i shift this , if i 'm sitting here , looking with my eye , as my eye receives this light , i 'm going to see this light rotate its polarization . the polarization i 'm going to notice swings around in a circular pattern . and because of this , we call this circular polarization . so this is another type of polarization , where the actual angle of polarization rotates smoothly as this light ray enters your eye . and you know what ? er , drrr ... all right , actually , i sent you to receive this one first . that makes no sense . you 're going to receive the ones closes to you first in this light ray going this way . so you 'd actually receive this one first , then that one , then this one , then this one . because of that , you would n't see this going in a counterclockwise way , you 'd see this going in a clockwise circularly polarized way . sorry about that . you might think , `` okay , why ? `` why even bother with circular polarization ? '' well , i kind of lied earlier . turns out , in the movie theater example , they do n't actually do it like this , typically . oftentimes in the movie theaters , we do n't have just linearly polarized sunglasses . this would be a problem because , when you look at the movie theater screen , and if you were to tilt your head just a little bit ... think about it . this one 's not really going to get the right image anymore . it 's going to get some of both . and this one 's going to get some of both . it 's going to be blurry . your head would have to be perfectly level the whole time , which might be annoying . so what we do is , instead , we create circular polarized glasses , so that this one would only get one polarization , this one would get the other direction . this way , even if you tilt your head a little bit ... shoot , clockwise is clockwise , counterclockwise is counterclockwise . by using circular polarization for 3d movies , it can make it a little easier on you eyes to see a better 3d image , even if your head 's tilted a little bit .
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it 's often good enough to just know the direction of the electric field when we focus on the electric field . so what does polarization mean ? polarization refers to the fact that , if this light ray was heading straight toward your eye , or a detector , over here , what would you see ?
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what is the definition of polarization ?
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- let 's talk about polarization of light . we know what light waves are ; they 're electromagnetic waves . so they 're made out of electric fields . and that 's not good enough . we know there 's not just electric fields . that could n't sustain itself . there 's got to be magnetic fields there , as well , that are changing . those are perpendicular , so you can kind of draw them . it 's hard , on something two-dimensional , but you can kind of imagine those looking something like this . and those magnetic fields would point at a right angle to the electric fields . but this gets really messy if i try to draw both the electric and magnetic fields at the same time . so we 're going to leave the magnetic fields out . it 's often good enough to just know the direction of the electric field when we focus on the electric field . so what does polarization mean ? polarization refers to the fact that , if this light ray was heading straight toward your eye , or a detector , over here , what would you see ? well , if i draw an axis over here , and this point here , in the middle , this is this line -- so imagine we 're looking straight down that line -- and then up and down is up and down , and then left and right , that direction i have the magnetic field , would be this way and that way . what would my eye see ? well , my eye 's only going to see electric fields that either point up or electric fields that point down . they might have different values , but i 'm only going to see electric fields that point up or down . because of that , this light ray is polarized . so polarized light is light where the electric field is only oscillating in one direction . up or down , that 's one direction -- vertically . or it could be polarized horizontally . or it could be polarized diagonally . but either way , you could have this wave polarized along any direction . i mean , a light ray like this , if we had it coming in diagonal , this light ray that 's oscillating like this , where the electric field oscillates like that , that also polarized . these are both polarized because there 's only one direction that the electric field is oscillating in . and you might thing , `` pff , how could you ever have `` a light ray that 's not polarized ? '' easy . most light that you get is not polarized . that is to say , light that 's coming from the sun , straight from the sun -- typically not polarized . light from a lightbulb , an old incandescent light bulb , this thing 's hot . you can get light polarized in any direction , all at once , all overlapping . so if we draw this case for a light bulb , just a random incandescent light bulb , you might get light , some of the light , hitting you eye , you can get some light that 's got that direction , you got light that 's got this direction , you got light in all these directions at any given moment . i mean , you 'd have to add these up to get the total , and they might not all be the same value . but what i 'm trying to say is , at any given moment , you do n't know what direction the electric field 's going to be hitting your eye at from a random source . it could be in any direction . so this is not polarized . this diagram represents light that is not polarized . at some point , the field might be pointing this way , at some later point it 's this way ; it 's just random . you never know which way the electric field 's going to be pointing . whereas these over here , these are polarized . so how could you polarize this light ? let 's say you wanted light that was polarized . you were doing an experiment . you needed polarized light . well , that 's easy . you can use what 's called a polarizer . and this is a material that lets light through , but it only lets light through in one orientation , so you 're going to have a polarizer that , for instance , only lets through vertically polarized light . so this is a polarizer . these are cheap : thin , plastic , configured in a way so that it only lets light through that 's vertically polarized . any light coming in here that 's not vertically polarized gets blocked , or absorbed . so what that means is , if you used this polarizer and held it in between your eye and this light bulb , you would only get this light . all the rest of it would get blocked . or you could just rotate this thing and imagine a polarizer that only lets through horizontal light . now it would only let through light that was this way , and so you would only get this part of the light . or you could just orient it at any angle you want and block everything but the certain angle that this polarizer is defined as letting light through . so you can do this . and once you hold this up , you get polarized light , light that 's only got one orientation . so that 's what polarization means . but why do we care about polarization ? well , let me get rid of this for a minute . you 've heard of polarized sunglasses . so imagine you 're standing near water , or maybe you 're standing on ice or snow or something reflective . there 's a problem . say the sun 's out . it 's shining . it 's a beautiful day -- except there 's going to be glare . let 's say you 're looking down at something here on the ground . it 's going to get light reflecting off of it from just ... you know , light 's coming in from all direction . but it also gets this direct light from the sun . so it gets light from reflected off the clouds and whatever , whatever 's nearby , ambient light . and there 's also this direct sunlight . that 's harsh . if that reflects straight up to your eye , that hurts . you do n't like that . it blocks our vision . it 's hard to see , it 's glare . we do n't want this glare . so what can we do ? well , it just so happens that , when light reflects off of a surface , even though the light from the sun is not polarized , once it reflects , it does get polarized or at least partially polarized . so this surface here , once this light reflects , it 's coming in at all orientations . you got electric field ... you never know what electric field you 're going to get straight from the sun . and when it reflects , though , you mostly get , upon reflection , the direction of polarization defined by the plane of the surface that it hit . so because the floor is horizontal , when this light ray hits the ground and reflects , that reflected light gets partially polarized . this horizontal component of the electric field is going to be more present than the other components . maybe not completely . sometimes it could be . it could be completely polarized , but often it 's just partially polarized . but that 's pretty cool , because now you know what we can do . i know how to block this . we should get some sunglasses . we put some sunglasses on and we make our glasses so that these are polarized . and how do we want these polarized ? i want to get rid of the glare . so what i do is , i make sure my sunglasses only let through vertically polarized light . here 's some polarizers . that way , a lot of this glare gets blocked because it does not have a vertical orientation , it has a horizontal orientation . and then we can block it . so that 's one good thing that polarization does for us , and understanding it , we can get rid of glare . also , fishermen like it because , if you 're trying to look in the water at fish , you want to see in through the water , you want to see this light from the fish getting to you . you do n't want to see the glare off of the sun getting to you . so polarized sunglasses are useful . also , we can play a trick on our eye , if we really wanted to . you could take one of these , make one eye have a vertical orientation for the polarization , have the other eye with a horizontal ... and you 're thinking , `` this is stupid . `` why would you do this for ? '' `` this eye 's going to get a lot of glare . '' we would n't use these outside , when you 're , like , skiing or fishing , but you could play a trick on your eyes if you went to the movies and you went and watched a movie . well , the reason our eyes see 3d is because they 're spaced a little bit apart . they each get a different , slightly different image . that makes us see in 3d . we can play the same trick on our eye if we have the polarization like this . if light , if some of the light from the movie theater screen is coming in with one polarization , and the other light 's coming in with the other polarization , we can send two different images to our eyes at the same time . if you took these off , it 'd look like garbage because you 'd be getting both of these slightly different images , it 'd look all blurry . and it does . if you take off your 3d glasses and look at a 3d movie , looks terrible , because now both eyes are getting both images . but if you put your glasses back on , now this eye only gets the orientation that it 's supposed to get , and this eye only gets the orientation that it 's supposed to get , and you get a 3d image . so it 's useful in many ways . let me show you one more thing here . let 's come back here . this light was polarized vertically . so that 's called linear polarization . any time ... same with these . these are all linear polarization because , just up and down , one linear direction , just diagonal . this is also linear . all of these are linear . you can get circular polarized light . so if we come back to here , we 've got our electric field pointing up , like that . now let 's say we sent in another light ray , another light ray that also had a polarization , but not in this direction . let 's say our other light ray had polarization in this direction , so it looks like this , kind of like what our magnetic field would have looked like . but this is a completely different light ray with its own polarization and its own magnetic field . so we send this in . what would happen ? well , at this point , you 'd have a electric field that points this way . at this point , you 'd have a electric field that points that way . what would your eye see if you were over here ? let 's see . if i draw our axis here . all right , when this point right here gets to your eye , what am i going to see ? well , i 'm going to have a light ray that 's one part of a light ray . one component points up . that 's this electric field . one component points left . that 's this electric field . so the total , my total electric field , would point this way . i could to the pythagorean theorem if i wanted to figure out the size of it , but i just want to know the direction for now . and then it gets to here , and look at it : they both have zero . this light ray has zero electric field , this one has zero electric fields . so then it 'd just be at zero . now what happens over here ? well , i 've got light . this one points to the right at that point , this pink one , and then this red one would be pointing down . so what would i have at that point ? i 'd have light that went this way , and it would just be doing this over and over . it would just be ... i 'd just have diagonally polarized light . this is n't giving me anything new . you might think this is dumb . why do this ? why send in two different waves to just get diagonally polarized light ? i could have just sent in one wave that was diagonally polarized and got the same thing . the reason is , if you shift this purple wave , this pink wave , by 90 degrees of phase , by pi over two in phase , something magical happens . let me show you what happens here , if we move this to here . now we do n't just get diagonally linear polarized light . what we 're going to get is ... let me get rid of this . okay , so we start off with red , right ? the red electric field points up , and then this pink wave 's electric field is zero at that point . so this is all i have . my total electric field would just be up . i 'm going to draw it right here . the green 'll be the total . now i come over to here , and at this point , there 's some red electric field that points up , but there 's some of this other electric field that points this way . so i 'd have a total electric field that would point that way . and then i get over to here , and i 'd have all of the electric field from the pink one , none from the red one . it would point all left then . look what 's happening . the polarization of this light , if i shift this , if i 'm sitting here , looking with my eye , as my eye receives this light , i 'm going to see this light rotate its polarization . the polarization i 'm going to notice swings around in a circular pattern . and because of this , we call this circular polarization . so this is another type of polarization , where the actual angle of polarization rotates smoothly as this light ray enters your eye . and you know what ? er , drrr ... all right , actually , i sent you to receive this one first . that makes no sense . you 're going to receive the ones closes to you first in this light ray going this way . so you 'd actually receive this one first , then that one , then this one , then this one . because of that , you would n't see this going in a counterclockwise way , you 'd see this going in a clockwise circularly polarized way . sorry about that . you might think , `` okay , why ? `` why even bother with circular polarization ? '' well , i kind of lied earlier . turns out , in the movie theater example , they do n't actually do it like this , typically . oftentimes in the movie theaters , we do n't have just linearly polarized sunglasses . this would be a problem because , when you look at the movie theater screen , and if you were to tilt your head just a little bit ... think about it . this one 's not really going to get the right image anymore . it 's going to get some of both . and this one 's going to get some of both . it 's going to be blurry . your head would have to be perfectly level the whole time , which might be annoying . so what we do is , instead , we create circular polarized glasses , so that this one would only get one polarization , this one would get the other direction . this way , even if you tilt your head a little bit ... shoot , clockwise is clockwise , counterclockwise is counterclockwise . by using circular polarization for 3d movies , it can make it a little easier on you eyes to see a better 3d image , even if your head 's tilted a little bit .
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- let 's talk about polarization of light . we know what light waves are ; they 're electromagnetic waves .
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how can radiation be related to ecology ?
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- let 's talk about polarization of light . we know what light waves are ; they 're electromagnetic waves . so they 're made out of electric fields . and that 's not good enough . we know there 's not just electric fields . that could n't sustain itself . there 's got to be magnetic fields there , as well , that are changing . those are perpendicular , so you can kind of draw them . it 's hard , on something two-dimensional , but you can kind of imagine those looking something like this . and those magnetic fields would point at a right angle to the electric fields . but this gets really messy if i try to draw both the electric and magnetic fields at the same time . so we 're going to leave the magnetic fields out . it 's often good enough to just know the direction of the electric field when we focus on the electric field . so what does polarization mean ? polarization refers to the fact that , if this light ray was heading straight toward your eye , or a detector , over here , what would you see ? well , if i draw an axis over here , and this point here , in the middle , this is this line -- so imagine we 're looking straight down that line -- and then up and down is up and down , and then left and right , that direction i have the magnetic field , would be this way and that way . what would my eye see ? well , my eye 's only going to see electric fields that either point up or electric fields that point down . they might have different values , but i 'm only going to see electric fields that point up or down . because of that , this light ray is polarized . so polarized light is light where the electric field is only oscillating in one direction . up or down , that 's one direction -- vertically . or it could be polarized horizontally . or it could be polarized diagonally . but either way , you could have this wave polarized along any direction . i mean , a light ray like this , if we had it coming in diagonal , this light ray that 's oscillating like this , where the electric field oscillates like that , that also polarized . these are both polarized because there 's only one direction that the electric field is oscillating in . and you might thing , `` pff , how could you ever have `` a light ray that 's not polarized ? '' easy . most light that you get is not polarized . that is to say , light that 's coming from the sun , straight from the sun -- typically not polarized . light from a lightbulb , an old incandescent light bulb , this thing 's hot . you can get light polarized in any direction , all at once , all overlapping . so if we draw this case for a light bulb , just a random incandescent light bulb , you might get light , some of the light , hitting you eye , you can get some light that 's got that direction , you got light that 's got this direction , you got light in all these directions at any given moment . i mean , you 'd have to add these up to get the total , and they might not all be the same value . but what i 'm trying to say is , at any given moment , you do n't know what direction the electric field 's going to be hitting your eye at from a random source . it could be in any direction . so this is not polarized . this diagram represents light that is not polarized . at some point , the field might be pointing this way , at some later point it 's this way ; it 's just random . you never know which way the electric field 's going to be pointing . whereas these over here , these are polarized . so how could you polarize this light ? let 's say you wanted light that was polarized . you were doing an experiment . you needed polarized light . well , that 's easy . you can use what 's called a polarizer . and this is a material that lets light through , but it only lets light through in one orientation , so you 're going to have a polarizer that , for instance , only lets through vertically polarized light . so this is a polarizer . these are cheap : thin , plastic , configured in a way so that it only lets light through that 's vertically polarized . any light coming in here that 's not vertically polarized gets blocked , or absorbed . so what that means is , if you used this polarizer and held it in between your eye and this light bulb , you would only get this light . all the rest of it would get blocked . or you could just rotate this thing and imagine a polarizer that only lets through horizontal light . now it would only let through light that was this way , and so you would only get this part of the light . or you could just orient it at any angle you want and block everything but the certain angle that this polarizer is defined as letting light through . so you can do this . and once you hold this up , you get polarized light , light that 's only got one orientation . so that 's what polarization means . but why do we care about polarization ? well , let me get rid of this for a minute . you 've heard of polarized sunglasses . so imagine you 're standing near water , or maybe you 're standing on ice or snow or something reflective . there 's a problem . say the sun 's out . it 's shining . it 's a beautiful day -- except there 's going to be glare . let 's say you 're looking down at something here on the ground . it 's going to get light reflecting off of it from just ... you know , light 's coming in from all direction . but it also gets this direct light from the sun . so it gets light from reflected off the clouds and whatever , whatever 's nearby , ambient light . and there 's also this direct sunlight . that 's harsh . if that reflects straight up to your eye , that hurts . you do n't like that . it blocks our vision . it 's hard to see , it 's glare . we do n't want this glare . so what can we do ? well , it just so happens that , when light reflects off of a surface , even though the light from the sun is not polarized , once it reflects , it does get polarized or at least partially polarized . so this surface here , once this light reflects , it 's coming in at all orientations . you got electric field ... you never know what electric field you 're going to get straight from the sun . and when it reflects , though , you mostly get , upon reflection , the direction of polarization defined by the plane of the surface that it hit . so because the floor is horizontal , when this light ray hits the ground and reflects , that reflected light gets partially polarized . this horizontal component of the electric field is going to be more present than the other components . maybe not completely . sometimes it could be . it could be completely polarized , but often it 's just partially polarized . but that 's pretty cool , because now you know what we can do . i know how to block this . we should get some sunglasses . we put some sunglasses on and we make our glasses so that these are polarized . and how do we want these polarized ? i want to get rid of the glare . so what i do is , i make sure my sunglasses only let through vertically polarized light . here 's some polarizers . that way , a lot of this glare gets blocked because it does not have a vertical orientation , it has a horizontal orientation . and then we can block it . so that 's one good thing that polarization does for us , and understanding it , we can get rid of glare . also , fishermen like it because , if you 're trying to look in the water at fish , you want to see in through the water , you want to see this light from the fish getting to you . you do n't want to see the glare off of the sun getting to you . so polarized sunglasses are useful . also , we can play a trick on our eye , if we really wanted to . you could take one of these , make one eye have a vertical orientation for the polarization , have the other eye with a horizontal ... and you 're thinking , `` this is stupid . `` why would you do this for ? '' `` this eye 's going to get a lot of glare . '' we would n't use these outside , when you 're , like , skiing or fishing , but you could play a trick on your eyes if you went to the movies and you went and watched a movie . well , the reason our eyes see 3d is because they 're spaced a little bit apart . they each get a different , slightly different image . that makes us see in 3d . we can play the same trick on our eye if we have the polarization like this . if light , if some of the light from the movie theater screen is coming in with one polarization , and the other light 's coming in with the other polarization , we can send two different images to our eyes at the same time . if you took these off , it 'd look like garbage because you 'd be getting both of these slightly different images , it 'd look all blurry . and it does . if you take off your 3d glasses and look at a 3d movie , looks terrible , because now both eyes are getting both images . but if you put your glasses back on , now this eye only gets the orientation that it 's supposed to get , and this eye only gets the orientation that it 's supposed to get , and you get a 3d image . so it 's useful in many ways . let me show you one more thing here . let 's come back here . this light was polarized vertically . so that 's called linear polarization . any time ... same with these . these are all linear polarization because , just up and down , one linear direction , just diagonal . this is also linear . all of these are linear . you can get circular polarized light . so if we come back to here , we 've got our electric field pointing up , like that . now let 's say we sent in another light ray , another light ray that also had a polarization , but not in this direction . let 's say our other light ray had polarization in this direction , so it looks like this , kind of like what our magnetic field would have looked like . but this is a completely different light ray with its own polarization and its own magnetic field . so we send this in . what would happen ? well , at this point , you 'd have a electric field that points this way . at this point , you 'd have a electric field that points that way . what would your eye see if you were over here ? let 's see . if i draw our axis here . all right , when this point right here gets to your eye , what am i going to see ? well , i 'm going to have a light ray that 's one part of a light ray . one component points up . that 's this electric field . one component points left . that 's this electric field . so the total , my total electric field , would point this way . i could to the pythagorean theorem if i wanted to figure out the size of it , but i just want to know the direction for now . and then it gets to here , and look at it : they both have zero . this light ray has zero electric field , this one has zero electric fields . so then it 'd just be at zero . now what happens over here ? well , i 've got light . this one points to the right at that point , this pink one , and then this red one would be pointing down . so what would i have at that point ? i 'd have light that went this way , and it would just be doing this over and over . it would just be ... i 'd just have diagonally polarized light . this is n't giving me anything new . you might think this is dumb . why do this ? why send in two different waves to just get diagonally polarized light ? i could have just sent in one wave that was diagonally polarized and got the same thing . the reason is , if you shift this purple wave , this pink wave , by 90 degrees of phase , by pi over two in phase , something magical happens . let me show you what happens here , if we move this to here . now we do n't just get diagonally linear polarized light . what we 're going to get is ... let me get rid of this . okay , so we start off with red , right ? the red electric field points up , and then this pink wave 's electric field is zero at that point . so this is all i have . my total electric field would just be up . i 'm going to draw it right here . the green 'll be the total . now i come over to here , and at this point , there 's some red electric field that points up , but there 's some of this other electric field that points this way . so i 'd have a total electric field that would point that way . and then i get over to here , and i 'd have all of the electric field from the pink one , none from the red one . it would point all left then . look what 's happening . the polarization of this light , if i shift this , if i 'm sitting here , looking with my eye , as my eye receives this light , i 'm going to see this light rotate its polarization . the polarization i 'm going to notice swings around in a circular pattern . and because of this , we call this circular polarization . so this is another type of polarization , where the actual angle of polarization rotates smoothly as this light ray enters your eye . and you know what ? er , drrr ... all right , actually , i sent you to receive this one first . that makes no sense . you 're going to receive the ones closes to you first in this light ray going this way . so you 'd actually receive this one first , then that one , then this one , then this one . because of that , you would n't see this going in a counterclockwise way , you 'd see this going in a clockwise circularly polarized way . sorry about that . you might think , `` okay , why ? `` why even bother with circular polarization ? '' well , i kind of lied earlier . turns out , in the movie theater example , they do n't actually do it like this , typically . oftentimes in the movie theaters , we do n't have just linearly polarized sunglasses . this would be a problem because , when you look at the movie theater screen , and if you were to tilt your head just a little bit ... think about it . this one 's not really going to get the right image anymore . it 's going to get some of both . and this one 's going to get some of both . it 's going to be blurry . your head would have to be perfectly level the whole time , which might be annoying . so what we do is , instead , we create circular polarized glasses , so that this one would only get one polarization , this one would get the other direction . this way , even if you tilt your head a little bit ... shoot , clockwise is clockwise , counterclockwise is counterclockwise . by using circular polarization for 3d movies , it can make it a little easier on you eyes to see a better 3d image , even if your head 's tilted a little bit .
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i could have just sent in one wave that was diagonally polarized and got the same thing . the reason is , if you shift this purple wave , this pink wave , by 90 degrees of phase , by pi over two in phase , something magical happens . let me show you what happens here , if we move this to here .
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how do you shift the same wave of light by 90 degrees of phase to circularly polarize it once it goes through the glasses to your eye ?
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- let 's talk about polarization of light . we know what light waves are ; they 're electromagnetic waves . so they 're made out of electric fields . and that 's not good enough . we know there 's not just electric fields . that could n't sustain itself . there 's got to be magnetic fields there , as well , that are changing . those are perpendicular , so you can kind of draw them . it 's hard , on something two-dimensional , but you can kind of imagine those looking something like this . and those magnetic fields would point at a right angle to the electric fields . but this gets really messy if i try to draw both the electric and magnetic fields at the same time . so we 're going to leave the magnetic fields out . it 's often good enough to just know the direction of the electric field when we focus on the electric field . so what does polarization mean ? polarization refers to the fact that , if this light ray was heading straight toward your eye , or a detector , over here , what would you see ? well , if i draw an axis over here , and this point here , in the middle , this is this line -- so imagine we 're looking straight down that line -- and then up and down is up and down , and then left and right , that direction i have the magnetic field , would be this way and that way . what would my eye see ? well , my eye 's only going to see electric fields that either point up or electric fields that point down . they might have different values , but i 'm only going to see electric fields that point up or down . because of that , this light ray is polarized . so polarized light is light where the electric field is only oscillating in one direction . up or down , that 's one direction -- vertically . or it could be polarized horizontally . or it could be polarized diagonally . but either way , you could have this wave polarized along any direction . i mean , a light ray like this , if we had it coming in diagonal , this light ray that 's oscillating like this , where the electric field oscillates like that , that also polarized . these are both polarized because there 's only one direction that the electric field is oscillating in . and you might thing , `` pff , how could you ever have `` a light ray that 's not polarized ? '' easy . most light that you get is not polarized . that is to say , light that 's coming from the sun , straight from the sun -- typically not polarized . light from a lightbulb , an old incandescent light bulb , this thing 's hot . you can get light polarized in any direction , all at once , all overlapping . so if we draw this case for a light bulb , just a random incandescent light bulb , you might get light , some of the light , hitting you eye , you can get some light that 's got that direction , you got light that 's got this direction , you got light in all these directions at any given moment . i mean , you 'd have to add these up to get the total , and they might not all be the same value . but what i 'm trying to say is , at any given moment , you do n't know what direction the electric field 's going to be hitting your eye at from a random source . it could be in any direction . so this is not polarized . this diagram represents light that is not polarized . at some point , the field might be pointing this way , at some later point it 's this way ; it 's just random . you never know which way the electric field 's going to be pointing . whereas these over here , these are polarized . so how could you polarize this light ? let 's say you wanted light that was polarized . you were doing an experiment . you needed polarized light . well , that 's easy . you can use what 's called a polarizer . and this is a material that lets light through , but it only lets light through in one orientation , so you 're going to have a polarizer that , for instance , only lets through vertically polarized light . so this is a polarizer . these are cheap : thin , plastic , configured in a way so that it only lets light through that 's vertically polarized . any light coming in here that 's not vertically polarized gets blocked , or absorbed . so what that means is , if you used this polarizer and held it in between your eye and this light bulb , you would only get this light . all the rest of it would get blocked . or you could just rotate this thing and imagine a polarizer that only lets through horizontal light . now it would only let through light that was this way , and so you would only get this part of the light . or you could just orient it at any angle you want and block everything but the certain angle that this polarizer is defined as letting light through . so you can do this . and once you hold this up , you get polarized light , light that 's only got one orientation . so that 's what polarization means . but why do we care about polarization ? well , let me get rid of this for a minute . you 've heard of polarized sunglasses . so imagine you 're standing near water , or maybe you 're standing on ice or snow or something reflective . there 's a problem . say the sun 's out . it 's shining . it 's a beautiful day -- except there 's going to be glare . let 's say you 're looking down at something here on the ground . it 's going to get light reflecting off of it from just ... you know , light 's coming in from all direction . but it also gets this direct light from the sun . so it gets light from reflected off the clouds and whatever , whatever 's nearby , ambient light . and there 's also this direct sunlight . that 's harsh . if that reflects straight up to your eye , that hurts . you do n't like that . it blocks our vision . it 's hard to see , it 's glare . we do n't want this glare . so what can we do ? well , it just so happens that , when light reflects off of a surface , even though the light from the sun is not polarized , once it reflects , it does get polarized or at least partially polarized . so this surface here , once this light reflects , it 's coming in at all orientations . you got electric field ... you never know what electric field you 're going to get straight from the sun . and when it reflects , though , you mostly get , upon reflection , the direction of polarization defined by the plane of the surface that it hit . so because the floor is horizontal , when this light ray hits the ground and reflects , that reflected light gets partially polarized . this horizontal component of the electric field is going to be more present than the other components . maybe not completely . sometimes it could be . it could be completely polarized , but often it 's just partially polarized . but that 's pretty cool , because now you know what we can do . i know how to block this . we should get some sunglasses . we put some sunglasses on and we make our glasses so that these are polarized . and how do we want these polarized ? i want to get rid of the glare . so what i do is , i make sure my sunglasses only let through vertically polarized light . here 's some polarizers . that way , a lot of this glare gets blocked because it does not have a vertical orientation , it has a horizontal orientation . and then we can block it . so that 's one good thing that polarization does for us , and understanding it , we can get rid of glare . also , fishermen like it because , if you 're trying to look in the water at fish , you want to see in through the water , you want to see this light from the fish getting to you . you do n't want to see the glare off of the sun getting to you . so polarized sunglasses are useful . also , we can play a trick on our eye , if we really wanted to . you could take one of these , make one eye have a vertical orientation for the polarization , have the other eye with a horizontal ... and you 're thinking , `` this is stupid . `` why would you do this for ? '' `` this eye 's going to get a lot of glare . '' we would n't use these outside , when you 're , like , skiing or fishing , but you could play a trick on your eyes if you went to the movies and you went and watched a movie . well , the reason our eyes see 3d is because they 're spaced a little bit apart . they each get a different , slightly different image . that makes us see in 3d . we can play the same trick on our eye if we have the polarization like this . if light , if some of the light from the movie theater screen is coming in with one polarization , and the other light 's coming in with the other polarization , we can send two different images to our eyes at the same time . if you took these off , it 'd look like garbage because you 'd be getting both of these slightly different images , it 'd look all blurry . and it does . if you take off your 3d glasses and look at a 3d movie , looks terrible , because now both eyes are getting both images . but if you put your glasses back on , now this eye only gets the orientation that it 's supposed to get , and this eye only gets the orientation that it 's supposed to get , and you get a 3d image . so it 's useful in many ways . let me show you one more thing here . let 's come back here . this light was polarized vertically . so that 's called linear polarization . any time ... same with these . these are all linear polarization because , just up and down , one linear direction , just diagonal . this is also linear . all of these are linear . you can get circular polarized light . so if we come back to here , we 've got our electric field pointing up , like that . now let 's say we sent in another light ray , another light ray that also had a polarization , but not in this direction . let 's say our other light ray had polarization in this direction , so it looks like this , kind of like what our magnetic field would have looked like . but this is a completely different light ray with its own polarization and its own magnetic field . so we send this in . what would happen ? well , at this point , you 'd have a electric field that points this way . at this point , you 'd have a electric field that points that way . what would your eye see if you were over here ? let 's see . if i draw our axis here . all right , when this point right here gets to your eye , what am i going to see ? well , i 'm going to have a light ray that 's one part of a light ray . one component points up . that 's this electric field . one component points left . that 's this electric field . so the total , my total electric field , would point this way . i could to the pythagorean theorem if i wanted to figure out the size of it , but i just want to know the direction for now . and then it gets to here , and look at it : they both have zero . this light ray has zero electric field , this one has zero electric fields . so then it 'd just be at zero . now what happens over here ? well , i 've got light . this one points to the right at that point , this pink one , and then this red one would be pointing down . so what would i have at that point ? i 'd have light that went this way , and it would just be doing this over and over . it would just be ... i 'd just have diagonally polarized light . this is n't giving me anything new . you might think this is dumb . why do this ? why send in two different waves to just get diagonally polarized light ? i could have just sent in one wave that was diagonally polarized and got the same thing . the reason is , if you shift this purple wave , this pink wave , by 90 degrees of phase , by pi over two in phase , something magical happens . let me show you what happens here , if we move this to here . now we do n't just get diagonally linear polarized light . what we 're going to get is ... let me get rid of this . okay , so we start off with red , right ? the red electric field points up , and then this pink wave 's electric field is zero at that point . so this is all i have . my total electric field would just be up . i 'm going to draw it right here . the green 'll be the total . now i come over to here , and at this point , there 's some red electric field that points up , but there 's some of this other electric field that points this way . so i 'd have a total electric field that would point that way . and then i get over to here , and i 'd have all of the electric field from the pink one , none from the red one . it would point all left then . look what 's happening . the polarization of this light , if i shift this , if i 'm sitting here , looking with my eye , as my eye receives this light , i 'm going to see this light rotate its polarization . the polarization i 'm going to notice swings around in a circular pattern . and because of this , we call this circular polarization . so this is another type of polarization , where the actual angle of polarization rotates smoothly as this light ray enters your eye . and you know what ? er , drrr ... all right , actually , i sent you to receive this one first . that makes no sense . you 're going to receive the ones closes to you first in this light ray going this way . so you 'd actually receive this one first , then that one , then this one , then this one . because of that , you would n't see this going in a counterclockwise way , you 'd see this going in a clockwise circularly polarized way . sorry about that . you might think , `` okay , why ? `` why even bother with circular polarization ? '' well , i kind of lied earlier . turns out , in the movie theater example , they do n't actually do it like this , typically . oftentimes in the movie theaters , we do n't have just linearly polarized sunglasses . this would be a problem because , when you look at the movie theater screen , and if you were to tilt your head just a little bit ... think about it . this one 's not really going to get the right image anymore . it 's going to get some of both . and this one 's going to get some of both . it 's going to be blurry . your head would have to be perfectly level the whole time , which might be annoying . so what we do is , instead , we create circular polarized glasses , so that this one would only get one polarization , this one would get the other direction . this way , even if you tilt your head a little bit ... shoot , clockwise is clockwise , counterclockwise is counterclockwise . by using circular polarization for 3d movies , it can make it a little easier on you eyes to see a better 3d image , even if your head 's tilted a little bit .
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you do n't want to see the glare off of the sun getting to you . so polarized sunglasses are useful . also , we can play a trick on our eye , if we really wanted to .
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what is the pro and con of circular vs. linear polarized sunglasses ?
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- let 's talk about polarization of light . we know what light waves are ; they 're electromagnetic waves . so they 're made out of electric fields . and that 's not good enough . we know there 's not just electric fields . that could n't sustain itself . there 's got to be magnetic fields there , as well , that are changing . those are perpendicular , so you can kind of draw them . it 's hard , on something two-dimensional , but you can kind of imagine those looking something like this . and those magnetic fields would point at a right angle to the electric fields . but this gets really messy if i try to draw both the electric and magnetic fields at the same time . so we 're going to leave the magnetic fields out . it 's often good enough to just know the direction of the electric field when we focus on the electric field . so what does polarization mean ? polarization refers to the fact that , if this light ray was heading straight toward your eye , or a detector , over here , what would you see ? well , if i draw an axis over here , and this point here , in the middle , this is this line -- so imagine we 're looking straight down that line -- and then up and down is up and down , and then left and right , that direction i have the magnetic field , would be this way and that way . what would my eye see ? well , my eye 's only going to see electric fields that either point up or electric fields that point down . they might have different values , but i 'm only going to see electric fields that point up or down . because of that , this light ray is polarized . so polarized light is light where the electric field is only oscillating in one direction . up or down , that 's one direction -- vertically . or it could be polarized horizontally . or it could be polarized diagonally . but either way , you could have this wave polarized along any direction . i mean , a light ray like this , if we had it coming in diagonal , this light ray that 's oscillating like this , where the electric field oscillates like that , that also polarized . these are both polarized because there 's only one direction that the electric field is oscillating in . and you might thing , `` pff , how could you ever have `` a light ray that 's not polarized ? '' easy . most light that you get is not polarized . that is to say , light that 's coming from the sun , straight from the sun -- typically not polarized . light from a lightbulb , an old incandescent light bulb , this thing 's hot . you can get light polarized in any direction , all at once , all overlapping . so if we draw this case for a light bulb , just a random incandescent light bulb , you might get light , some of the light , hitting you eye , you can get some light that 's got that direction , you got light that 's got this direction , you got light in all these directions at any given moment . i mean , you 'd have to add these up to get the total , and they might not all be the same value . but what i 'm trying to say is , at any given moment , you do n't know what direction the electric field 's going to be hitting your eye at from a random source . it could be in any direction . so this is not polarized . this diagram represents light that is not polarized . at some point , the field might be pointing this way , at some later point it 's this way ; it 's just random . you never know which way the electric field 's going to be pointing . whereas these over here , these are polarized . so how could you polarize this light ? let 's say you wanted light that was polarized . you were doing an experiment . you needed polarized light . well , that 's easy . you can use what 's called a polarizer . and this is a material that lets light through , but it only lets light through in one orientation , so you 're going to have a polarizer that , for instance , only lets through vertically polarized light . so this is a polarizer . these are cheap : thin , plastic , configured in a way so that it only lets light through that 's vertically polarized . any light coming in here that 's not vertically polarized gets blocked , or absorbed . so what that means is , if you used this polarizer and held it in between your eye and this light bulb , you would only get this light . all the rest of it would get blocked . or you could just rotate this thing and imagine a polarizer that only lets through horizontal light . now it would only let through light that was this way , and so you would only get this part of the light . or you could just orient it at any angle you want and block everything but the certain angle that this polarizer is defined as letting light through . so you can do this . and once you hold this up , you get polarized light , light that 's only got one orientation . so that 's what polarization means . but why do we care about polarization ? well , let me get rid of this for a minute . you 've heard of polarized sunglasses . so imagine you 're standing near water , or maybe you 're standing on ice or snow or something reflective . there 's a problem . say the sun 's out . it 's shining . it 's a beautiful day -- except there 's going to be glare . let 's say you 're looking down at something here on the ground . it 's going to get light reflecting off of it from just ... you know , light 's coming in from all direction . but it also gets this direct light from the sun . so it gets light from reflected off the clouds and whatever , whatever 's nearby , ambient light . and there 's also this direct sunlight . that 's harsh . if that reflects straight up to your eye , that hurts . you do n't like that . it blocks our vision . it 's hard to see , it 's glare . we do n't want this glare . so what can we do ? well , it just so happens that , when light reflects off of a surface , even though the light from the sun is not polarized , once it reflects , it does get polarized or at least partially polarized . so this surface here , once this light reflects , it 's coming in at all orientations . you got electric field ... you never know what electric field you 're going to get straight from the sun . and when it reflects , though , you mostly get , upon reflection , the direction of polarization defined by the plane of the surface that it hit . so because the floor is horizontal , when this light ray hits the ground and reflects , that reflected light gets partially polarized . this horizontal component of the electric field is going to be more present than the other components . maybe not completely . sometimes it could be . it could be completely polarized , but often it 's just partially polarized . but that 's pretty cool , because now you know what we can do . i know how to block this . we should get some sunglasses . we put some sunglasses on and we make our glasses so that these are polarized . and how do we want these polarized ? i want to get rid of the glare . so what i do is , i make sure my sunglasses only let through vertically polarized light . here 's some polarizers . that way , a lot of this glare gets blocked because it does not have a vertical orientation , it has a horizontal orientation . and then we can block it . so that 's one good thing that polarization does for us , and understanding it , we can get rid of glare . also , fishermen like it because , if you 're trying to look in the water at fish , you want to see in through the water , you want to see this light from the fish getting to you . you do n't want to see the glare off of the sun getting to you . so polarized sunglasses are useful . also , we can play a trick on our eye , if we really wanted to . you could take one of these , make one eye have a vertical orientation for the polarization , have the other eye with a horizontal ... and you 're thinking , `` this is stupid . `` why would you do this for ? '' `` this eye 's going to get a lot of glare . '' we would n't use these outside , when you 're , like , skiing or fishing , but you could play a trick on your eyes if you went to the movies and you went and watched a movie . well , the reason our eyes see 3d is because they 're spaced a little bit apart . they each get a different , slightly different image . that makes us see in 3d . we can play the same trick on our eye if we have the polarization like this . if light , if some of the light from the movie theater screen is coming in with one polarization , and the other light 's coming in with the other polarization , we can send two different images to our eyes at the same time . if you took these off , it 'd look like garbage because you 'd be getting both of these slightly different images , it 'd look all blurry . and it does . if you take off your 3d glasses and look at a 3d movie , looks terrible , because now both eyes are getting both images . but if you put your glasses back on , now this eye only gets the orientation that it 's supposed to get , and this eye only gets the orientation that it 's supposed to get , and you get a 3d image . so it 's useful in many ways . let me show you one more thing here . let 's come back here . this light was polarized vertically . so that 's called linear polarization . any time ... same with these . these are all linear polarization because , just up and down , one linear direction , just diagonal . this is also linear . all of these are linear . you can get circular polarized light . so if we come back to here , we 've got our electric field pointing up , like that . now let 's say we sent in another light ray , another light ray that also had a polarization , but not in this direction . let 's say our other light ray had polarization in this direction , so it looks like this , kind of like what our magnetic field would have looked like . but this is a completely different light ray with its own polarization and its own magnetic field . so we send this in . what would happen ? well , at this point , you 'd have a electric field that points this way . at this point , you 'd have a electric field that points that way . what would your eye see if you were over here ? let 's see . if i draw our axis here . all right , when this point right here gets to your eye , what am i going to see ? well , i 'm going to have a light ray that 's one part of a light ray . one component points up . that 's this electric field . one component points left . that 's this electric field . so the total , my total electric field , would point this way . i could to the pythagorean theorem if i wanted to figure out the size of it , but i just want to know the direction for now . and then it gets to here , and look at it : they both have zero . this light ray has zero electric field , this one has zero electric fields . so then it 'd just be at zero . now what happens over here ? well , i 've got light . this one points to the right at that point , this pink one , and then this red one would be pointing down . so what would i have at that point ? i 'd have light that went this way , and it would just be doing this over and over . it would just be ... i 'd just have diagonally polarized light . this is n't giving me anything new . you might think this is dumb . why do this ? why send in two different waves to just get diagonally polarized light ? i could have just sent in one wave that was diagonally polarized and got the same thing . the reason is , if you shift this purple wave , this pink wave , by 90 degrees of phase , by pi over two in phase , something magical happens . let me show you what happens here , if we move this to here . now we do n't just get diagonally linear polarized light . what we 're going to get is ... let me get rid of this . okay , so we start off with red , right ? the red electric field points up , and then this pink wave 's electric field is zero at that point . so this is all i have . my total electric field would just be up . i 'm going to draw it right here . the green 'll be the total . now i come over to here , and at this point , there 's some red electric field that points up , but there 's some of this other electric field that points this way . so i 'd have a total electric field that would point that way . and then i get over to here , and i 'd have all of the electric field from the pink one , none from the red one . it would point all left then . look what 's happening . the polarization of this light , if i shift this , if i 'm sitting here , looking with my eye , as my eye receives this light , i 'm going to see this light rotate its polarization . the polarization i 'm going to notice swings around in a circular pattern . and because of this , we call this circular polarization . so this is another type of polarization , where the actual angle of polarization rotates smoothly as this light ray enters your eye . and you know what ? er , drrr ... all right , actually , i sent you to receive this one first . that makes no sense . you 're going to receive the ones closes to you first in this light ray going this way . so you 'd actually receive this one first , then that one , then this one , then this one . because of that , you would n't see this going in a counterclockwise way , you 'd see this going in a clockwise circularly polarized way . sorry about that . you might think , `` okay , why ? `` why even bother with circular polarization ? '' well , i kind of lied earlier . turns out , in the movie theater example , they do n't actually do it like this , typically . oftentimes in the movie theaters , we do n't have just linearly polarized sunglasses . this would be a problem because , when you look at the movie theater screen , and if you were to tilt your head just a little bit ... think about it . this one 's not really going to get the right image anymore . it 's going to get some of both . and this one 's going to get some of both . it 's going to be blurry . your head would have to be perfectly level the whole time , which might be annoying . so what we do is , instead , we create circular polarized glasses , so that this one would only get one polarization , this one would get the other direction . this way , even if you tilt your head a little bit ... shoot , clockwise is clockwise , counterclockwise is counterclockwise . by using circular polarization for 3d movies , it can make it a little easier on you eyes to see a better 3d image , even if your head 's tilted a little bit .
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so you 'd actually receive this one first , then that one , then this one , then this one . because of that , you would n't see this going in a counterclockwise way , you 'd see this going in a clockwise circularly polarized way . sorry about that .
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in what way polarization is going to help us ?
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- let 's talk about polarization of light . we know what light waves are ; they 're electromagnetic waves . so they 're made out of electric fields . and that 's not good enough . we know there 's not just electric fields . that could n't sustain itself . there 's got to be magnetic fields there , as well , that are changing . those are perpendicular , so you can kind of draw them . it 's hard , on something two-dimensional , but you can kind of imagine those looking something like this . and those magnetic fields would point at a right angle to the electric fields . but this gets really messy if i try to draw both the electric and magnetic fields at the same time . so we 're going to leave the magnetic fields out . it 's often good enough to just know the direction of the electric field when we focus on the electric field . so what does polarization mean ? polarization refers to the fact that , if this light ray was heading straight toward your eye , or a detector , over here , what would you see ? well , if i draw an axis over here , and this point here , in the middle , this is this line -- so imagine we 're looking straight down that line -- and then up and down is up and down , and then left and right , that direction i have the magnetic field , would be this way and that way . what would my eye see ? well , my eye 's only going to see electric fields that either point up or electric fields that point down . they might have different values , but i 'm only going to see electric fields that point up or down . because of that , this light ray is polarized . so polarized light is light where the electric field is only oscillating in one direction . up or down , that 's one direction -- vertically . or it could be polarized horizontally . or it could be polarized diagonally . but either way , you could have this wave polarized along any direction . i mean , a light ray like this , if we had it coming in diagonal , this light ray that 's oscillating like this , where the electric field oscillates like that , that also polarized . these are both polarized because there 's only one direction that the electric field is oscillating in . and you might thing , `` pff , how could you ever have `` a light ray that 's not polarized ? '' easy . most light that you get is not polarized . that is to say , light that 's coming from the sun , straight from the sun -- typically not polarized . light from a lightbulb , an old incandescent light bulb , this thing 's hot . you can get light polarized in any direction , all at once , all overlapping . so if we draw this case for a light bulb , just a random incandescent light bulb , you might get light , some of the light , hitting you eye , you can get some light that 's got that direction , you got light that 's got this direction , you got light in all these directions at any given moment . i mean , you 'd have to add these up to get the total , and they might not all be the same value . but what i 'm trying to say is , at any given moment , you do n't know what direction the electric field 's going to be hitting your eye at from a random source . it could be in any direction . so this is not polarized . this diagram represents light that is not polarized . at some point , the field might be pointing this way , at some later point it 's this way ; it 's just random . you never know which way the electric field 's going to be pointing . whereas these over here , these are polarized . so how could you polarize this light ? let 's say you wanted light that was polarized . you were doing an experiment . you needed polarized light . well , that 's easy . you can use what 's called a polarizer . and this is a material that lets light through , but it only lets light through in one orientation , so you 're going to have a polarizer that , for instance , only lets through vertically polarized light . so this is a polarizer . these are cheap : thin , plastic , configured in a way so that it only lets light through that 's vertically polarized . any light coming in here that 's not vertically polarized gets blocked , or absorbed . so what that means is , if you used this polarizer and held it in between your eye and this light bulb , you would only get this light . all the rest of it would get blocked . or you could just rotate this thing and imagine a polarizer that only lets through horizontal light . now it would only let through light that was this way , and so you would only get this part of the light . or you could just orient it at any angle you want and block everything but the certain angle that this polarizer is defined as letting light through . so you can do this . and once you hold this up , you get polarized light , light that 's only got one orientation . so that 's what polarization means . but why do we care about polarization ? well , let me get rid of this for a minute . you 've heard of polarized sunglasses . so imagine you 're standing near water , or maybe you 're standing on ice or snow or something reflective . there 's a problem . say the sun 's out . it 's shining . it 's a beautiful day -- except there 's going to be glare . let 's say you 're looking down at something here on the ground . it 's going to get light reflecting off of it from just ... you know , light 's coming in from all direction . but it also gets this direct light from the sun . so it gets light from reflected off the clouds and whatever , whatever 's nearby , ambient light . and there 's also this direct sunlight . that 's harsh . if that reflects straight up to your eye , that hurts . you do n't like that . it blocks our vision . it 's hard to see , it 's glare . we do n't want this glare . so what can we do ? well , it just so happens that , when light reflects off of a surface , even though the light from the sun is not polarized , once it reflects , it does get polarized or at least partially polarized . so this surface here , once this light reflects , it 's coming in at all orientations . you got electric field ... you never know what electric field you 're going to get straight from the sun . and when it reflects , though , you mostly get , upon reflection , the direction of polarization defined by the plane of the surface that it hit . so because the floor is horizontal , when this light ray hits the ground and reflects , that reflected light gets partially polarized . this horizontal component of the electric field is going to be more present than the other components . maybe not completely . sometimes it could be . it could be completely polarized , but often it 's just partially polarized . but that 's pretty cool , because now you know what we can do . i know how to block this . we should get some sunglasses . we put some sunglasses on and we make our glasses so that these are polarized . and how do we want these polarized ? i want to get rid of the glare . so what i do is , i make sure my sunglasses only let through vertically polarized light . here 's some polarizers . that way , a lot of this glare gets blocked because it does not have a vertical orientation , it has a horizontal orientation . and then we can block it . so that 's one good thing that polarization does for us , and understanding it , we can get rid of glare . also , fishermen like it because , if you 're trying to look in the water at fish , you want to see in through the water , you want to see this light from the fish getting to you . you do n't want to see the glare off of the sun getting to you . so polarized sunglasses are useful . also , we can play a trick on our eye , if we really wanted to . you could take one of these , make one eye have a vertical orientation for the polarization , have the other eye with a horizontal ... and you 're thinking , `` this is stupid . `` why would you do this for ? '' `` this eye 's going to get a lot of glare . '' we would n't use these outside , when you 're , like , skiing or fishing , but you could play a trick on your eyes if you went to the movies and you went and watched a movie . well , the reason our eyes see 3d is because they 're spaced a little bit apart . they each get a different , slightly different image . that makes us see in 3d . we can play the same trick on our eye if we have the polarization like this . if light , if some of the light from the movie theater screen is coming in with one polarization , and the other light 's coming in with the other polarization , we can send two different images to our eyes at the same time . if you took these off , it 'd look like garbage because you 'd be getting both of these slightly different images , it 'd look all blurry . and it does . if you take off your 3d glasses and look at a 3d movie , looks terrible , because now both eyes are getting both images . but if you put your glasses back on , now this eye only gets the orientation that it 's supposed to get , and this eye only gets the orientation that it 's supposed to get , and you get a 3d image . so it 's useful in many ways . let me show you one more thing here . let 's come back here . this light was polarized vertically . so that 's called linear polarization . any time ... same with these . these are all linear polarization because , just up and down , one linear direction , just diagonal . this is also linear . all of these are linear . you can get circular polarized light . so if we come back to here , we 've got our electric field pointing up , like that . now let 's say we sent in another light ray , another light ray that also had a polarization , but not in this direction . let 's say our other light ray had polarization in this direction , so it looks like this , kind of like what our magnetic field would have looked like . but this is a completely different light ray with its own polarization and its own magnetic field . so we send this in . what would happen ? well , at this point , you 'd have a electric field that points this way . at this point , you 'd have a electric field that points that way . what would your eye see if you were over here ? let 's see . if i draw our axis here . all right , when this point right here gets to your eye , what am i going to see ? well , i 'm going to have a light ray that 's one part of a light ray . one component points up . that 's this electric field . one component points left . that 's this electric field . so the total , my total electric field , would point this way . i could to the pythagorean theorem if i wanted to figure out the size of it , but i just want to know the direction for now . and then it gets to here , and look at it : they both have zero . this light ray has zero electric field , this one has zero electric fields . so then it 'd just be at zero . now what happens over here ? well , i 've got light . this one points to the right at that point , this pink one , and then this red one would be pointing down . so what would i have at that point ? i 'd have light that went this way , and it would just be doing this over and over . it would just be ... i 'd just have diagonally polarized light . this is n't giving me anything new . you might think this is dumb . why do this ? why send in two different waves to just get diagonally polarized light ? i could have just sent in one wave that was diagonally polarized and got the same thing . the reason is , if you shift this purple wave , this pink wave , by 90 degrees of phase , by pi over two in phase , something magical happens . let me show you what happens here , if we move this to here . now we do n't just get diagonally linear polarized light . what we 're going to get is ... let me get rid of this . okay , so we start off with red , right ? the red electric field points up , and then this pink wave 's electric field is zero at that point . so this is all i have . my total electric field would just be up . i 'm going to draw it right here . the green 'll be the total . now i come over to here , and at this point , there 's some red electric field that points up , but there 's some of this other electric field that points this way . so i 'd have a total electric field that would point that way . and then i get over to here , and i 'd have all of the electric field from the pink one , none from the red one . it would point all left then . look what 's happening . the polarization of this light , if i shift this , if i 'm sitting here , looking with my eye , as my eye receives this light , i 'm going to see this light rotate its polarization . the polarization i 'm going to notice swings around in a circular pattern . and because of this , we call this circular polarization . so this is another type of polarization , where the actual angle of polarization rotates smoothly as this light ray enters your eye . and you know what ? er , drrr ... all right , actually , i sent you to receive this one first . that makes no sense . you 're going to receive the ones closes to you first in this light ray going this way . so you 'd actually receive this one first , then that one , then this one , then this one . because of that , you would n't see this going in a counterclockwise way , you 'd see this going in a clockwise circularly polarized way . sorry about that . you might think , `` okay , why ? `` why even bother with circular polarization ? '' well , i kind of lied earlier . turns out , in the movie theater example , they do n't actually do it like this , typically . oftentimes in the movie theaters , we do n't have just linearly polarized sunglasses . this would be a problem because , when you look at the movie theater screen , and if you were to tilt your head just a little bit ... think about it . this one 's not really going to get the right image anymore . it 's going to get some of both . and this one 's going to get some of both . it 's going to be blurry . your head would have to be perfectly level the whole time , which might be annoying . so what we do is , instead , we create circular polarized glasses , so that this one would only get one polarization , this one would get the other direction . this way , even if you tilt your head a little bit ... shoot , clockwise is clockwise , counterclockwise is counterclockwise . by using circular polarization for 3d movies , it can make it a little easier on you eyes to see a better 3d image , even if your head 's tilted a little bit .
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one component points up . that 's this electric field . one component points left .
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wat is electro megnatic field ?
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- let 's talk about polarization of light . we know what light waves are ; they 're electromagnetic waves . so they 're made out of electric fields . and that 's not good enough . we know there 's not just electric fields . that could n't sustain itself . there 's got to be magnetic fields there , as well , that are changing . those are perpendicular , so you can kind of draw them . it 's hard , on something two-dimensional , but you can kind of imagine those looking something like this . and those magnetic fields would point at a right angle to the electric fields . but this gets really messy if i try to draw both the electric and magnetic fields at the same time . so we 're going to leave the magnetic fields out . it 's often good enough to just know the direction of the electric field when we focus on the electric field . so what does polarization mean ? polarization refers to the fact that , if this light ray was heading straight toward your eye , or a detector , over here , what would you see ? well , if i draw an axis over here , and this point here , in the middle , this is this line -- so imagine we 're looking straight down that line -- and then up and down is up and down , and then left and right , that direction i have the magnetic field , would be this way and that way . what would my eye see ? well , my eye 's only going to see electric fields that either point up or electric fields that point down . they might have different values , but i 'm only going to see electric fields that point up or down . because of that , this light ray is polarized . so polarized light is light where the electric field is only oscillating in one direction . up or down , that 's one direction -- vertically . or it could be polarized horizontally . or it could be polarized diagonally . but either way , you could have this wave polarized along any direction . i mean , a light ray like this , if we had it coming in diagonal , this light ray that 's oscillating like this , where the electric field oscillates like that , that also polarized . these are both polarized because there 's only one direction that the electric field is oscillating in . and you might thing , `` pff , how could you ever have `` a light ray that 's not polarized ? '' easy . most light that you get is not polarized . that is to say , light that 's coming from the sun , straight from the sun -- typically not polarized . light from a lightbulb , an old incandescent light bulb , this thing 's hot . you can get light polarized in any direction , all at once , all overlapping . so if we draw this case for a light bulb , just a random incandescent light bulb , you might get light , some of the light , hitting you eye , you can get some light that 's got that direction , you got light that 's got this direction , you got light in all these directions at any given moment . i mean , you 'd have to add these up to get the total , and they might not all be the same value . but what i 'm trying to say is , at any given moment , you do n't know what direction the electric field 's going to be hitting your eye at from a random source . it could be in any direction . so this is not polarized . this diagram represents light that is not polarized . at some point , the field might be pointing this way , at some later point it 's this way ; it 's just random . you never know which way the electric field 's going to be pointing . whereas these over here , these are polarized . so how could you polarize this light ? let 's say you wanted light that was polarized . you were doing an experiment . you needed polarized light . well , that 's easy . you can use what 's called a polarizer . and this is a material that lets light through , but it only lets light through in one orientation , so you 're going to have a polarizer that , for instance , only lets through vertically polarized light . so this is a polarizer . these are cheap : thin , plastic , configured in a way so that it only lets light through that 's vertically polarized . any light coming in here that 's not vertically polarized gets blocked , or absorbed . so what that means is , if you used this polarizer and held it in between your eye and this light bulb , you would only get this light . all the rest of it would get blocked . or you could just rotate this thing and imagine a polarizer that only lets through horizontal light . now it would only let through light that was this way , and so you would only get this part of the light . or you could just orient it at any angle you want and block everything but the certain angle that this polarizer is defined as letting light through . so you can do this . and once you hold this up , you get polarized light , light that 's only got one orientation . so that 's what polarization means . but why do we care about polarization ? well , let me get rid of this for a minute . you 've heard of polarized sunglasses . so imagine you 're standing near water , or maybe you 're standing on ice or snow or something reflective . there 's a problem . say the sun 's out . it 's shining . it 's a beautiful day -- except there 's going to be glare . let 's say you 're looking down at something here on the ground . it 's going to get light reflecting off of it from just ... you know , light 's coming in from all direction . but it also gets this direct light from the sun . so it gets light from reflected off the clouds and whatever , whatever 's nearby , ambient light . and there 's also this direct sunlight . that 's harsh . if that reflects straight up to your eye , that hurts . you do n't like that . it blocks our vision . it 's hard to see , it 's glare . we do n't want this glare . so what can we do ? well , it just so happens that , when light reflects off of a surface , even though the light from the sun is not polarized , once it reflects , it does get polarized or at least partially polarized . so this surface here , once this light reflects , it 's coming in at all orientations . you got electric field ... you never know what electric field you 're going to get straight from the sun . and when it reflects , though , you mostly get , upon reflection , the direction of polarization defined by the plane of the surface that it hit . so because the floor is horizontal , when this light ray hits the ground and reflects , that reflected light gets partially polarized . this horizontal component of the electric field is going to be more present than the other components . maybe not completely . sometimes it could be . it could be completely polarized , but often it 's just partially polarized . but that 's pretty cool , because now you know what we can do . i know how to block this . we should get some sunglasses . we put some sunglasses on and we make our glasses so that these are polarized . and how do we want these polarized ? i want to get rid of the glare . so what i do is , i make sure my sunglasses only let through vertically polarized light . here 's some polarizers . that way , a lot of this glare gets blocked because it does not have a vertical orientation , it has a horizontal orientation . and then we can block it . so that 's one good thing that polarization does for us , and understanding it , we can get rid of glare . also , fishermen like it because , if you 're trying to look in the water at fish , you want to see in through the water , you want to see this light from the fish getting to you . you do n't want to see the glare off of the sun getting to you . so polarized sunglasses are useful . also , we can play a trick on our eye , if we really wanted to . you could take one of these , make one eye have a vertical orientation for the polarization , have the other eye with a horizontal ... and you 're thinking , `` this is stupid . `` why would you do this for ? '' `` this eye 's going to get a lot of glare . '' we would n't use these outside , when you 're , like , skiing or fishing , but you could play a trick on your eyes if you went to the movies and you went and watched a movie . well , the reason our eyes see 3d is because they 're spaced a little bit apart . they each get a different , slightly different image . that makes us see in 3d . we can play the same trick on our eye if we have the polarization like this . if light , if some of the light from the movie theater screen is coming in with one polarization , and the other light 's coming in with the other polarization , we can send two different images to our eyes at the same time . if you took these off , it 'd look like garbage because you 'd be getting both of these slightly different images , it 'd look all blurry . and it does . if you take off your 3d glasses and look at a 3d movie , looks terrible , because now both eyes are getting both images . but if you put your glasses back on , now this eye only gets the orientation that it 's supposed to get , and this eye only gets the orientation that it 's supposed to get , and you get a 3d image . so it 's useful in many ways . let me show you one more thing here . let 's come back here . this light was polarized vertically . so that 's called linear polarization . any time ... same with these . these are all linear polarization because , just up and down , one linear direction , just diagonal . this is also linear . all of these are linear . you can get circular polarized light . so if we come back to here , we 've got our electric field pointing up , like that . now let 's say we sent in another light ray , another light ray that also had a polarization , but not in this direction . let 's say our other light ray had polarization in this direction , so it looks like this , kind of like what our magnetic field would have looked like . but this is a completely different light ray with its own polarization and its own magnetic field . so we send this in . what would happen ? well , at this point , you 'd have a electric field that points this way . at this point , you 'd have a electric field that points that way . what would your eye see if you were over here ? let 's see . if i draw our axis here . all right , when this point right here gets to your eye , what am i going to see ? well , i 'm going to have a light ray that 's one part of a light ray . one component points up . that 's this electric field . one component points left . that 's this electric field . so the total , my total electric field , would point this way . i could to the pythagorean theorem if i wanted to figure out the size of it , but i just want to know the direction for now . and then it gets to here , and look at it : they both have zero . this light ray has zero electric field , this one has zero electric fields . so then it 'd just be at zero . now what happens over here ? well , i 've got light . this one points to the right at that point , this pink one , and then this red one would be pointing down . so what would i have at that point ? i 'd have light that went this way , and it would just be doing this over and over . it would just be ... i 'd just have diagonally polarized light . this is n't giving me anything new . you might think this is dumb . why do this ? why send in two different waves to just get diagonally polarized light ? i could have just sent in one wave that was diagonally polarized and got the same thing . the reason is , if you shift this purple wave , this pink wave , by 90 degrees of phase , by pi over two in phase , something magical happens . let me show you what happens here , if we move this to here . now we do n't just get diagonally linear polarized light . what we 're going to get is ... let me get rid of this . okay , so we start off with red , right ? the red electric field points up , and then this pink wave 's electric field is zero at that point . so this is all i have . my total electric field would just be up . i 'm going to draw it right here . the green 'll be the total . now i come over to here , and at this point , there 's some red electric field that points up , but there 's some of this other electric field that points this way . so i 'd have a total electric field that would point that way . and then i get over to here , and i 'd have all of the electric field from the pink one , none from the red one . it would point all left then . look what 's happening . the polarization of this light , if i shift this , if i 'm sitting here , looking with my eye , as my eye receives this light , i 'm going to see this light rotate its polarization . the polarization i 'm going to notice swings around in a circular pattern . and because of this , we call this circular polarization . so this is another type of polarization , where the actual angle of polarization rotates smoothly as this light ray enters your eye . and you know what ? er , drrr ... all right , actually , i sent you to receive this one first . that makes no sense . you 're going to receive the ones closes to you first in this light ray going this way . so you 'd actually receive this one first , then that one , then this one , then this one . because of that , you would n't see this going in a counterclockwise way , you 'd see this going in a clockwise circularly polarized way . sorry about that . you might think , `` okay , why ? `` why even bother with circular polarization ? '' well , i kind of lied earlier . turns out , in the movie theater example , they do n't actually do it like this , typically . oftentimes in the movie theaters , we do n't have just linearly polarized sunglasses . this would be a problem because , when you look at the movie theater screen , and if you were to tilt your head just a little bit ... think about it . this one 's not really going to get the right image anymore . it 's going to get some of both . and this one 's going to get some of both . it 's going to be blurry . your head would have to be perfectly level the whole time , which might be annoying . so what we do is , instead , we create circular polarized glasses , so that this one would only get one polarization , this one would get the other direction . this way , even if you tilt your head a little bit ... shoot , clockwise is clockwise , counterclockwise is counterclockwise . by using circular polarization for 3d movies , it can make it a little easier on you eyes to see a better 3d image , even if your head 's tilted a little bit .
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- let 's talk about polarization of light . we know what light waves are ; they 're electromagnetic waves .
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how does a 3d image differ from a 4d image in terms of light , and how do their glasses differ in terms of polarization ?
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we 're asked to graph the circle which is centered at 3 , -2 and has a radius of 5 units . i got this exercise off of the khan academy graph a circle according to its features exercise . it 's a pretty neat little widget here , because what i can do is i can take this dot and i can move it around to redefine the center of the circle so it 's centered at 3 , -2 . so , x is 3 and y is -2 , so that 's its center . it has to have a radius of 5 . the way it 's drawn right now it has a radius of 1 . the distance between the center and the actual circle , the points that define the circle , right now it 's 1 . i need to make this radius equal to 5 . if i take that , so now the radius is equal to 2 , 3 , 4 and 5 . there you go . centered at 3 , -2 , radius of 5 . notice you go from the center to the actual circle it 's 5 no matter where you go . let 's do one more of these . graph the circle which is centered at -4 , 1 and which has the point 0 , 4 on it . once again , let 's drag the center , so it 's going to be -4 , x is -4 . y is 1 , so that 's the center . it has the point 0 , 4 on it . x is 0 , y is 4 . i have to drag , i have to increase the radius of the circle . let 's see , whoops , nope , i want to make sure i do n't change the center . i want to increase the radius of the circle until it includes this point right over here , 0,4 . i 'm not there quite yet , there you go . i 'm now including the point 0 , 4 . if we 're curious what the radius is , we could just go along the x axis . x = -4 is the x coordinate for the center and we see that this point ... this is -4,1 and we see that 1,1 is actually on the circle . the distance here is you go 4 then another 1 , it 's 5 . this has a radius of 5 . but either way , we did what they asked us to do .
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we 're asked to graph the circle which is centered at 3 , -2 and has a radius of 5 units . i got this exercise off of the khan academy graph a circle according to its features exercise .
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what should be the exact angle between the plane and cone to get a parabola ?
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we 're asked to graph the circle which is centered at 3 , -2 and has a radius of 5 units . i got this exercise off of the khan academy graph a circle according to its features exercise . it 's a pretty neat little widget here , because what i can do is i can take this dot and i can move it around to redefine the center of the circle so it 's centered at 3 , -2 . so , x is 3 and y is -2 , so that 's its center . it has to have a radius of 5 . the way it 's drawn right now it has a radius of 1 . the distance between the center and the actual circle , the points that define the circle , right now it 's 1 . i need to make this radius equal to 5 . if i take that , so now the radius is equal to 2 , 3 , 4 and 5 . there you go . centered at 3 , -2 , radius of 5 . notice you go from the center to the actual circle it 's 5 no matter where you go . let 's do one more of these . graph the circle which is centered at -4 , 1 and which has the point 0 , 4 on it . once again , let 's drag the center , so it 's going to be -4 , x is -4 . y is 1 , so that 's the center . it has the point 0 , 4 on it . x is 0 , y is 4 . i have to drag , i have to increase the radius of the circle . let 's see , whoops , nope , i want to make sure i do n't change the center . i want to increase the radius of the circle until it includes this point right over here , 0,4 . i 'm not there quite yet , there you go . i 'm now including the point 0 , 4 . if we 're curious what the radius is , we could just go along the x axis . x = -4 is the x coordinate for the center and we see that this point ... this is -4,1 and we see that 1,1 is actually on the circle . the distance here is you go 4 then another 1 , it 's 5 . this has a radius of 5 . but either way , we did what they asked us to do .
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the way it 's drawn right now it has a radius of 1 . the distance between the center and the actual circle , the points that define the circle , right now it 's 1 . i need to make this radius equal to 5 .
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can a circle be considered a degenerate form of an ellipse ?
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we 're asked to graph the circle which is centered at 3 , -2 and has a radius of 5 units . i got this exercise off of the khan academy graph a circle according to its features exercise . it 's a pretty neat little widget here , because what i can do is i can take this dot and i can move it around to redefine the center of the circle so it 's centered at 3 , -2 . so , x is 3 and y is -2 , so that 's its center . it has to have a radius of 5 . the way it 's drawn right now it has a radius of 1 . the distance between the center and the actual circle , the points that define the circle , right now it 's 1 . i need to make this radius equal to 5 . if i take that , so now the radius is equal to 2 , 3 , 4 and 5 . there you go . centered at 3 , -2 , radius of 5 . notice you go from the center to the actual circle it 's 5 no matter where you go . let 's do one more of these . graph the circle which is centered at -4 , 1 and which has the point 0 , 4 on it . once again , let 's drag the center , so it 's going to be -4 , x is -4 . y is 1 , so that 's the center . it has the point 0 , 4 on it . x is 0 , y is 4 . i have to drag , i have to increase the radius of the circle . let 's see , whoops , nope , i want to make sure i do n't change the center . i want to increase the radius of the circle until it includes this point right over here , 0,4 . i 'm not there quite yet , there you go . i 'm now including the point 0 , 4 . if we 're curious what the radius is , we could just go along the x axis . x = -4 is the x coordinate for the center and we see that this point ... this is -4,1 and we see that 1,1 is actually on the circle . the distance here is you go 4 then another 1 , it 's 5 . this has a radius of 5 . but either way , we did what they asked us to do .
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the way it 's drawn right now it has a radius of 1 . the distance between the center and the actual circle , the points that define the circle , right now it 's 1 . i need to make this radius equal to 5 . if i take that , so now the radius is equal to 2 , 3 , 4 and 5 .
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does a radius touches the center of the circle ?
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we 're asked to graph the circle which is centered at 3 , -2 and has a radius of 5 units . i got this exercise off of the khan academy graph a circle according to its features exercise . it 's a pretty neat little widget here , because what i can do is i can take this dot and i can move it around to redefine the center of the circle so it 's centered at 3 , -2 . so , x is 3 and y is -2 , so that 's its center . it has to have a radius of 5 . the way it 's drawn right now it has a radius of 1 . the distance between the center and the actual circle , the points that define the circle , right now it 's 1 . i need to make this radius equal to 5 . if i take that , so now the radius is equal to 2 , 3 , 4 and 5 . there you go . centered at 3 , -2 , radius of 5 . notice you go from the center to the actual circle it 's 5 no matter where you go . let 's do one more of these . graph the circle which is centered at -4 , 1 and which has the point 0 , 4 on it . once again , let 's drag the center , so it 's going to be -4 , x is -4 . y is 1 , so that 's the center . it has the point 0 , 4 on it . x is 0 , y is 4 . i have to drag , i have to increase the radius of the circle . let 's see , whoops , nope , i want to make sure i do n't change the center . i want to increase the radius of the circle until it includes this point right over here , 0,4 . i 'm not there quite yet , there you go . i 'm now including the point 0 , 4 . if we 're curious what the radius is , we could just go along the x axis . x = -4 is the x coordinate for the center and we see that this point ... this is -4,1 and we see that 1,1 is actually on the circle . the distance here is you go 4 then another 1 , it 's 5 . this has a radius of 5 . but either way , we did what they asked us to do .
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the way it 's drawn right now it has a radius of 1 . the distance between the center and the actual circle , the points that define the circle , right now it 's 1 . i need to make this radius equal to 5 .
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if the given coordinates were the coordinates of the diameter of a circle ?
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we 're asked to graph the circle which is centered at 3 , -2 and has a radius of 5 units . i got this exercise off of the khan academy graph a circle according to its features exercise . it 's a pretty neat little widget here , because what i can do is i can take this dot and i can move it around to redefine the center of the circle so it 's centered at 3 , -2 . so , x is 3 and y is -2 , so that 's its center . it has to have a radius of 5 . the way it 's drawn right now it has a radius of 1 . the distance between the center and the actual circle , the points that define the circle , right now it 's 1 . i need to make this radius equal to 5 . if i take that , so now the radius is equal to 2 , 3 , 4 and 5 . there you go . centered at 3 , -2 , radius of 5 . notice you go from the center to the actual circle it 's 5 no matter where you go . let 's do one more of these . graph the circle which is centered at -4 , 1 and which has the point 0 , 4 on it . once again , let 's drag the center , so it 's going to be -4 , x is -4 . y is 1 , so that 's the center . it has the point 0 , 4 on it . x is 0 , y is 4 . i have to drag , i have to increase the radius of the circle . let 's see , whoops , nope , i want to make sure i do n't change the center . i want to increase the radius of the circle until it includes this point right over here , 0,4 . i 'm not there quite yet , there you go . i 'm now including the point 0 , 4 . if we 're curious what the radius is , we could just go along the x axis . x = -4 is the x coordinate for the center and we see that this point ... this is -4,1 and we see that 1,1 is actually on the circle . the distance here is you go 4 then another 1 , it 's 5 . this has a radius of 5 . but either way , we did what they asked us to do .
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let 's see , whoops , nope , i want to make sure i do n't change the center . i want to increase the radius of the circle until it includes this point right over here , 0,4 . i 'm not there quite yet , there you go .
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the point ( 0,4 ) for the circle radius was given but why was n't the circle on the x axis point zero ?
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let 's multiply 7 times 253 and see what we get . so just like in the last example , what i like to do is i like to rewrite the largest number first . so that 's 253 . and then write the smaller number below it and align the place value , the 7 . it only has a ones place , so i 'll put the 7 right over here below the ones place in 253 . and then put the multiplication symbol right over here . so you could read this as 253 times 7 , which we know is the same thing as 7 times 253 . and now we are ready to compute . and there are many ways of doing this , but this one you could call the standard way . so what i do is i start with my 7 . and i multiply it times each of the numbers up here , and i carry appropriately . so first i start with 7 times 3 . well , 7 times 3 we know is 21 . let me write that down . 7 times 3 is equal to 21 . you could do this part in your head , but i just want to make it clear where i 'm getting these numbers from . what i would do in the standard method is i would write the 1 into 21 down here , but then carry the 2 to the tens place . now i want to figure out what 7 times 5 is . we know from our multiplication tables that 7 times 5 is equal to 35 . now , we ca n't just somehow put the 35 down here . we still have to deal with this 2 that we carried . so we compute 7 times 5 is 35 , but then we also add that 2 . so it 's 35 plus 2 is 37 . now , we write the 7 right over here in the tens place and carry the 3 . now we need to compute what 7 times 2 is . we know that 7 times 2 is 14 from our multiplication tables . we ca n't just put a 14 down here . we have this 3 to add . so 7 times 2 is 14 , plus 3 is 17 . so now we can write the 17 down here , because 2 is the last number that we had to deal with . and so we have our answer . 7 times 253 is 1,771 .
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so you could read this as 253 times 7 , which we know is the same thing as 7 times 253 . and now we are ready to compute . and there are many ways of doing this , but this one you could call the standard way .
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math-wise what does compute mean ?
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let 's multiply 7 times 253 and see what we get . so just like in the last example , what i like to do is i like to rewrite the largest number first . so that 's 253 . and then write the smaller number below it and align the place value , the 7 . it only has a ones place , so i 'll put the 7 right over here below the ones place in 253 . and then put the multiplication symbol right over here . so you could read this as 253 times 7 , which we know is the same thing as 7 times 253 . and now we are ready to compute . and there are many ways of doing this , but this one you could call the standard way . so what i do is i start with my 7 . and i multiply it times each of the numbers up here , and i carry appropriately . so first i start with 7 times 3 . well , 7 times 3 we know is 21 . let me write that down . 7 times 3 is equal to 21 . you could do this part in your head , but i just want to make it clear where i 'm getting these numbers from . what i would do in the standard method is i would write the 1 into 21 down here , but then carry the 2 to the tens place . now i want to figure out what 7 times 5 is . we know from our multiplication tables that 7 times 5 is equal to 35 . now , we ca n't just somehow put the 35 down here . we still have to deal with this 2 that we carried . so we compute 7 times 5 is 35 , but then we also add that 2 . so it 's 35 plus 2 is 37 . now , we write the 7 right over here in the tens place and carry the 3 . now we need to compute what 7 times 2 is . we know that 7 times 2 is 14 from our multiplication tables . we ca n't just put a 14 down here . we have this 3 to add . so 7 times 2 is 14 , plus 3 is 17 . so now we can write the 17 down here , because 2 is the last number that we had to deal with . and so we have our answer . 7 times 253 is 1,771 .
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it only has a ones place , so i 'll put the 7 right over here below the ones place in 253 . and then put the multiplication symbol right over here . so you could read this as 253 times 7 , which we know is the same thing as 7 times 253 .
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at 0.18 why did you put large number at the upside ?
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let 's multiply 7 times 253 and see what we get . so just like in the last example , what i like to do is i like to rewrite the largest number first . so that 's 253 . and then write the smaller number below it and align the place value , the 7 . it only has a ones place , so i 'll put the 7 right over here below the ones place in 253 . and then put the multiplication symbol right over here . so you could read this as 253 times 7 , which we know is the same thing as 7 times 253 . and now we are ready to compute . and there are many ways of doing this , but this one you could call the standard way . so what i do is i start with my 7 . and i multiply it times each of the numbers up here , and i carry appropriately . so first i start with 7 times 3 . well , 7 times 3 we know is 21 . let me write that down . 7 times 3 is equal to 21 . you could do this part in your head , but i just want to make it clear where i 'm getting these numbers from . what i would do in the standard method is i would write the 1 into 21 down here , but then carry the 2 to the tens place . now i want to figure out what 7 times 5 is . we know from our multiplication tables that 7 times 5 is equal to 35 . now , we ca n't just somehow put the 35 down here . we still have to deal with this 2 that we carried . so we compute 7 times 5 is 35 , but then we also add that 2 . so it 's 35 plus 2 is 37 . now , we write the 7 right over here in the tens place and carry the 3 . now we need to compute what 7 times 2 is . we know that 7 times 2 is 14 from our multiplication tables . we ca n't just put a 14 down here . we have this 3 to add . so 7 times 2 is 14 , plus 3 is 17 . so now we can write the 17 down here , because 2 is the last number that we had to deal with . and so we have our answer . 7 times 253 is 1,771 .
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so that 's 253 . and then write the smaller number below it and align the place value , the 7 . it only has a ones place , so i 'll put the 7 right over here below the ones place in 253 .
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how is it possible that the area can be smaller than the perimeter ?
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let 's multiply 7 times 253 and see what we get . so just like in the last example , what i like to do is i like to rewrite the largest number first . so that 's 253 . and then write the smaller number below it and align the place value , the 7 . it only has a ones place , so i 'll put the 7 right over here below the ones place in 253 . and then put the multiplication symbol right over here . so you could read this as 253 times 7 , which we know is the same thing as 7 times 253 . and now we are ready to compute . and there are many ways of doing this , but this one you could call the standard way . so what i do is i start with my 7 . and i multiply it times each of the numbers up here , and i carry appropriately . so first i start with 7 times 3 . well , 7 times 3 we know is 21 . let me write that down . 7 times 3 is equal to 21 . you could do this part in your head , but i just want to make it clear where i 'm getting these numbers from . what i would do in the standard method is i would write the 1 into 21 down here , but then carry the 2 to the tens place . now i want to figure out what 7 times 5 is . we know from our multiplication tables that 7 times 5 is equal to 35 . now , we ca n't just somehow put the 35 down here . we still have to deal with this 2 that we carried . so we compute 7 times 5 is 35 , but then we also add that 2 . so it 's 35 plus 2 is 37 . now , we write the 7 right over here in the tens place and carry the 3 . now we need to compute what 7 times 2 is . we know that 7 times 2 is 14 from our multiplication tables . we ca n't just put a 14 down here . we have this 3 to add . so 7 times 2 is 14 , plus 3 is 17 . so now we can write the 17 down here , because 2 is the last number that we had to deal with . and so we have our answer . 7 times 253 is 1,771 .
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let 's multiply 7 times 253 and see what we get . so just like in the last example , what i like to do is i like to rewrite the largest number first .
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how does the negative * negative = positive work ?
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let 's multiply 7 times 253 and see what we get . so just like in the last example , what i like to do is i like to rewrite the largest number first . so that 's 253 . and then write the smaller number below it and align the place value , the 7 . it only has a ones place , so i 'll put the 7 right over here below the ones place in 253 . and then put the multiplication symbol right over here . so you could read this as 253 times 7 , which we know is the same thing as 7 times 253 . and now we are ready to compute . and there are many ways of doing this , but this one you could call the standard way . so what i do is i start with my 7 . and i multiply it times each of the numbers up here , and i carry appropriately . so first i start with 7 times 3 . well , 7 times 3 we know is 21 . let me write that down . 7 times 3 is equal to 21 . you could do this part in your head , but i just want to make it clear where i 'm getting these numbers from . what i would do in the standard method is i would write the 1 into 21 down here , but then carry the 2 to the tens place . now i want to figure out what 7 times 5 is . we know from our multiplication tables that 7 times 5 is equal to 35 . now , we ca n't just somehow put the 35 down here . we still have to deal with this 2 that we carried . so we compute 7 times 5 is 35 , but then we also add that 2 . so it 's 35 plus 2 is 37 . now , we write the 7 right over here in the tens place and carry the 3 . now we need to compute what 7 times 2 is . we know that 7 times 2 is 14 from our multiplication tables . we ca n't just put a 14 down here . we have this 3 to add . so 7 times 2 is 14 , plus 3 is 17 . so now we can write the 17 down here , because 2 is the last number that we had to deal with . and so we have our answer . 7 times 253 is 1,771 .
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let 's multiply 7 times 253 and see what we get . so just like in the last example , what i like to do is i like to rewrite the largest number first .
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what is 305 x 6 ?
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let 's multiply 7 times 253 and see what we get . so just like in the last example , what i like to do is i like to rewrite the largest number first . so that 's 253 . and then write the smaller number below it and align the place value , the 7 . it only has a ones place , so i 'll put the 7 right over here below the ones place in 253 . and then put the multiplication symbol right over here . so you could read this as 253 times 7 , which we know is the same thing as 7 times 253 . and now we are ready to compute . and there are many ways of doing this , but this one you could call the standard way . so what i do is i start with my 7 . and i multiply it times each of the numbers up here , and i carry appropriately . so first i start with 7 times 3 . well , 7 times 3 we know is 21 . let me write that down . 7 times 3 is equal to 21 . you could do this part in your head , but i just want to make it clear where i 'm getting these numbers from . what i would do in the standard method is i would write the 1 into 21 down here , but then carry the 2 to the tens place . now i want to figure out what 7 times 5 is . we know from our multiplication tables that 7 times 5 is equal to 35 . now , we ca n't just somehow put the 35 down here . we still have to deal with this 2 that we carried . so we compute 7 times 5 is 35 , but then we also add that 2 . so it 's 35 plus 2 is 37 . now , we write the 7 right over here in the tens place and carry the 3 . now we need to compute what 7 times 2 is . we know that 7 times 2 is 14 from our multiplication tables . we ca n't just put a 14 down here . we have this 3 to add . so 7 times 2 is 14 , plus 3 is 17 . so now we can write the 17 down here , because 2 is the last number that we had to deal with . and so we have our answer . 7 times 253 is 1,771 .
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let 's multiply 7 times 253 and see what we get . so just like in the last example , what i like to do is i like to rewrite the largest number first . so that 's 253 .
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how would i multiply equations like 543x23 or 123x345 ?
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let 's multiply 7 times 253 and see what we get . so just like in the last example , what i like to do is i like to rewrite the largest number first . so that 's 253 . and then write the smaller number below it and align the place value , the 7 . it only has a ones place , so i 'll put the 7 right over here below the ones place in 253 . and then put the multiplication symbol right over here . so you could read this as 253 times 7 , which we know is the same thing as 7 times 253 . and now we are ready to compute . and there are many ways of doing this , but this one you could call the standard way . so what i do is i start with my 7 . and i multiply it times each of the numbers up here , and i carry appropriately . so first i start with 7 times 3 . well , 7 times 3 we know is 21 . let me write that down . 7 times 3 is equal to 21 . you could do this part in your head , but i just want to make it clear where i 'm getting these numbers from . what i would do in the standard method is i would write the 1 into 21 down here , but then carry the 2 to the tens place . now i want to figure out what 7 times 5 is . we know from our multiplication tables that 7 times 5 is equal to 35 . now , we ca n't just somehow put the 35 down here . we still have to deal with this 2 that we carried . so we compute 7 times 5 is 35 , but then we also add that 2 . so it 's 35 plus 2 is 37 . now , we write the 7 right over here in the tens place and carry the 3 . now we need to compute what 7 times 2 is . we know that 7 times 2 is 14 from our multiplication tables . we ca n't just put a 14 down here . we have this 3 to add . so 7 times 2 is 14 , plus 3 is 17 . so now we can write the 17 down here , because 2 is the last number that we had to deal with . and so we have our answer . 7 times 253 is 1,771 .
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so that 's 253 . and then write the smaller number below it and align the place value , the 7 . it only has a ones place , so i 'll put the 7 right over here below the ones place in 253 .
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what happens when there is a zero in the number ?
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let 's multiply 7 times 253 and see what we get . so just like in the last example , what i like to do is i like to rewrite the largest number first . so that 's 253 . and then write the smaller number below it and align the place value , the 7 . it only has a ones place , so i 'll put the 7 right over here below the ones place in 253 . and then put the multiplication symbol right over here . so you could read this as 253 times 7 , which we know is the same thing as 7 times 253 . and now we are ready to compute . and there are many ways of doing this , but this one you could call the standard way . so what i do is i start with my 7 . and i multiply it times each of the numbers up here , and i carry appropriately . so first i start with 7 times 3 . well , 7 times 3 we know is 21 . let me write that down . 7 times 3 is equal to 21 . you could do this part in your head , but i just want to make it clear where i 'm getting these numbers from . what i would do in the standard method is i would write the 1 into 21 down here , but then carry the 2 to the tens place . now i want to figure out what 7 times 5 is . we know from our multiplication tables that 7 times 5 is equal to 35 . now , we ca n't just somehow put the 35 down here . we still have to deal with this 2 that we carried . so we compute 7 times 5 is 35 , but then we also add that 2 . so it 's 35 plus 2 is 37 . now , we write the 7 right over here in the tens place and carry the 3 . now we need to compute what 7 times 2 is . we know that 7 times 2 is 14 from our multiplication tables . we ca n't just put a 14 down here . we have this 3 to add . so 7 times 2 is 14 , plus 3 is 17 . so now we can write the 17 down here , because 2 is the last number that we had to deal with . and so we have our answer . 7 times 253 is 1,771 .
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so you could read this as 253 times 7 , which we know is the same thing as 7 times 253 . and now we are ready to compute . and there are many ways of doing this , but this one you could call the standard way .
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at 8 41 what does compute mean ?
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let 's multiply 7 times 253 and see what we get . so just like in the last example , what i like to do is i like to rewrite the largest number first . so that 's 253 . and then write the smaller number below it and align the place value , the 7 . it only has a ones place , so i 'll put the 7 right over here below the ones place in 253 . and then put the multiplication symbol right over here . so you could read this as 253 times 7 , which we know is the same thing as 7 times 253 . and now we are ready to compute . and there are many ways of doing this , but this one you could call the standard way . so what i do is i start with my 7 . and i multiply it times each of the numbers up here , and i carry appropriately . so first i start with 7 times 3 . well , 7 times 3 we know is 21 . let me write that down . 7 times 3 is equal to 21 . you could do this part in your head , but i just want to make it clear where i 'm getting these numbers from . what i would do in the standard method is i would write the 1 into 21 down here , but then carry the 2 to the tens place . now i want to figure out what 7 times 5 is . we know from our multiplication tables that 7 times 5 is equal to 35 . now , we ca n't just somehow put the 35 down here . we still have to deal with this 2 that we carried . so we compute 7 times 5 is 35 , but then we also add that 2 . so it 's 35 plus 2 is 37 . now , we write the 7 right over here in the tens place and carry the 3 . now we need to compute what 7 times 2 is . we know that 7 times 2 is 14 from our multiplication tables . we ca n't just put a 14 down here . we have this 3 to add . so 7 times 2 is 14 , plus 3 is 17 . so now we can write the 17 down here , because 2 is the last number that we had to deal with . and so we have our answer . 7 times 253 is 1,771 .
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so first i start with 7 times 3 . well , 7 times 3 we know is 21 . let me write that down .
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is multiplying a 5-6 or 4 digit number well at least almost the same as multiplying a 3 and 2 digit number ?
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let 's multiply 7 times 253 and see what we get . so just like in the last example , what i like to do is i like to rewrite the largest number first . so that 's 253 . and then write the smaller number below it and align the place value , the 7 . it only has a ones place , so i 'll put the 7 right over here below the ones place in 253 . and then put the multiplication symbol right over here . so you could read this as 253 times 7 , which we know is the same thing as 7 times 253 . and now we are ready to compute . and there are many ways of doing this , but this one you could call the standard way . so what i do is i start with my 7 . and i multiply it times each of the numbers up here , and i carry appropriately . so first i start with 7 times 3 . well , 7 times 3 we know is 21 . let me write that down . 7 times 3 is equal to 21 . you could do this part in your head , but i just want to make it clear where i 'm getting these numbers from . what i would do in the standard method is i would write the 1 into 21 down here , but then carry the 2 to the tens place . now i want to figure out what 7 times 5 is . we know from our multiplication tables that 7 times 5 is equal to 35 . now , we ca n't just somehow put the 35 down here . we still have to deal with this 2 that we carried . so we compute 7 times 5 is 35 , but then we also add that 2 . so it 's 35 plus 2 is 37 . now , we write the 7 right over here in the tens place and carry the 3 . now we need to compute what 7 times 2 is . we know that 7 times 2 is 14 from our multiplication tables . we ca n't just put a 14 down here . we have this 3 to add . so 7 times 2 is 14 , plus 3 is 17 . so now we can write the 17 down here , because 2 is the last number that we had to deal with . and so we have our answer . 7 times 253 is 1,771 .
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so what i do is i start with my 7 . and i multiply it times each of the numbers up here , and i carry appropriately . so first i start with 7 times 3 .
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when you multiply 5 or 4 digit numbers is it the same as multiplying 2 and 3 digit numbers ?
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let 's multiply 7 times 253 and see what we get . so just like in the last example , what i like to do is i like to rewrite the largest number first . so that 's 253 . and then write the smaller number below it and align the place value , the 7 . it only has a ones place , so i 'll put the 7 right over here below the ones place in 253 . and then put the multiplication symbol right over here . so you could read this as 253 times 7 , which we know is the same thing as 7 times 253 . and now we are ready to compute . and there are many ways of doing this , but this one you could call the standard way . so what i do is i start with my 7 . and i multiply it times each of the numbers up here , and i carry appropriately . so first i start with 7 times 3 . well , 7 times 3 we know is 21 . let me write that down . 7 times 3 is equal to 21 . you could do this part in your head , but i just want to make it clear where i 'm getting these numbers from . what i would do in the standard method is i would write the 1 into 21 down here , but then carry the 2 to the tens place . now i want to figure out what 7 times 5 is . we know from our multiplication tables that 7 times 5 is equal to 35 . now , we ca n't just somehow put the 35 down here . we still have to deal with this 2 that we carried . so we compute 7 times 5 is 35 , but then we also add that 2 . so it 's 35 plus 2 is 37 . now , we write the 7 right over here in the tens place and carry the 3 . now we need to compute what 7 times 2 is . we know that 7 times 2 is 14 from our multiplication tables . we ca n't just put a 14 down here . we have this 3 to add . so 7 times 2 is 14 , plus 3 is 17 . so now we can write the 17 down here , because 2 is the last number that we had to deal with . and so we have our answer . 7 times 253 is 1,771 .
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you could do this part in your head , but i just want to make it clear where i 'm getting these numbers from . what i would do in the standard method is i would write the 1 into 21 down here , but then carry the 2 to the tens place . now i want to figure out what 7 times 5 is .
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when you carry the tens over to the hundreds place , would it be 35 tens or 30 tens and 5 ones ?
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let 's multiply 7 times 253 and see what we get . so just like in the last example , what i like to do is i like to rewrite the largest number first . so that 's 253 . and then write the smaller number below it and align the place value , the 7 . it only has a ones place , so i 'll put the 7 right over here below the ones place in 253 . and then put the multiplication symbol right over here . so you could read this as 253 times 7 , which we know is the same thing as 7 times 253 . and now we are ready to compute . and there are many ways of doing this , but this one you could call the standard way . so what i do is i start with my 7 . and i multiply it times each of the numbers up here , and i carry appropriately . so first i start with 7 times 3 . well , 7 times 3 we know is 21 . let me write that down . 7 times 3 is equal to 21 . you could do this part in your head , but i just want to make it clear where i 'm getting these numbers from . what i would do in the standard method is i would write the 1 into 21 down here , but then carry the 2 to the tens place . now i want to figure out what 7 times 5 is . we know from our multiplication tables that 7 times 5 is equal to 35 . now , we ca n't just somehow put the 35 down here . we still have to deal with this 2 that we carried . so we compute 7 times 5 is 35 , but then we also add that 2 . so it 's 35 plus 2 is 37 . now , we write the 7 right over here in the tens place and carry the 3 . now we need to compute what 7 times 2 is . we know that 7 times 2 is 14 from our multiplication tables . we ca n't just put a 14 down here . we have this 3 to add . so 7 times 2 is 14 , plus 3 is 17 . so now we can write the 17 down here , because 2 is the last number that we had to deal with . and so we have our answer . 7 times 253 is 1,771 .
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let 's multiply 7 times 253 and see what we get . so just like in the last example , what i like to do is i like to rewrite the largest number first .
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what is a denominator and a numenador ?
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let 's multiply 7 times 253 and see what we get . so just like in the last example , what i like to do is i like to rewrite the largest number first . so that 's 253 . and then write the smaller number below it and align the place value , the 7 . it only has a ones place , so i 'll put the 7 right over here below the ones place in 253 . and then put the multiplication symbol right over here . so you could read this as 253 times 7 , which we know is the same thing as 7 times 253 . and now we are ready to compute . and there are many ways of doing this , but this one you could call the standard way . so what i do is i start with my 7 . and i multiply it times each of the numbers up here , and i carry appropriately . so first i start with 7 times 3 . well , 7 times 3 we know is 21 . let me write that down . 7 times 3 is equal to 21 . you could do this part in your head , but i just want to make it clear where i 'm getting these numbers from . what i would do in the standard method is i would write the 1 into 21 down here , but then carry the 2 to the tens place . now i want to figure out what 7 times 5 is . we know from our multiplication tables that 7 times 5 is equal to 35 . now , we ca n't just somehow put the 35 down here . we still have to deal with this 2 that we carried . so we compute 7 times 5 is 35 , but then we also add that 2 . so it 's 35 plus 2 is 37 . now , we write the 7 right over here in the tens place and carry the 3 . now we need to compute what 7 times 2 is . we know that 7 times 2 is 14 from our multiplication tables . we ca n't just put a 14 down here . we have this 3 to add . so 7 times 2 is 14 , plus 3 is 17 . so now we can write the 17 down here , because 2 is the last number that we had to deal with . and so we have our answer . 7 times 253 is 1,771 .
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let 's multiply 7 times 253 and see what we get . so just like in the last example , what i like to do is i like to rewrite the largest number first .
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how do you find divison area models ?
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let 's multiply 7 times 253 and see what we get . so just like in the last example , what i like to do is i like to rewrite the largest number first . so that 's 253 . and then write the smaller number below it and align the place value , the 7 . it only has a ones place , so i 'll put the 7 right over here below the ones place in 253 . and then put the multiplication symbol right over here . so you could read this as 253 times 7 , which we know is the same thing as 7 times 253 . and now we are ready to compute . and there are many ways of doing this , but this one you could call the standard way . so what i do is i start with my 7 . and i multiply it times each of the numbers up here , and i carry appropriately . so first i start with 7 times 3 . well , 7 times 3 we know is 21 . let me write that down . 7 times 3 is equal to 21 . you could do this part in your head , but i just want to make it clear where i 'm getting these numbers from . what i would do in the standard method is i would write the 1 into 21 down here , but then carry the 2 to the tens place . now i want to figure out what 7 times 5 is . we know from our multiplication tables that 7 times 5 is equal to 35 . now , we ca n't just somehow put the 35 down here . we still have to deal with this 2 that we carried . so we compute 7 times 5 is 35 , but then we also add that 2 . so it 's 35 plus 2 is 37 . now , we write the 7 right over here in the tens place and carry the 3 . now we need to compute what 7 times 2 is . we know that 7 times 2 is 14 from our multiplication tables . we ca n't just put a 14 down here . we have this 3 to add . so 7 times 2 is 14 , plus 3 is 17 . so now we can write the 17 down here , because 2 is the last number that we had to deal with . and so we have our answer . 7 times 253 is 1,771 .
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it only has a ones place , so i 'll put the 7 right over here below the ones place in 253 . and then put the multiplication symbol right over here . so you could read this as 253 times 7 , which we know is the same thing as 7 times 253 .
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why and and how can multiplication make a huge difference in life ?
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let 's multiply 7 times 253 and see what we get . so just like in the last example , what i like to do is i like to rewrite the largest number first . so that 's 253 . and then write the smaller number below it and align the place value , the 7 . it only has a ones place , so i 'll put the 7 right over here below the ones place in 253 . and then put the multiplication symbol right over here . so you could read this as 253 times 7 , which we know is the same thing as 7 times 253 . and now we are ready to compute . and there are many ways of doing this , but this one you could call the standard way . so what i do is i start with my 7 . and i multiply it times each of the numbers up here , and i carry appropriately . so first i start with 7 times 3 . well , 7 times 3 we know is 21 . let me write that down . 7 times 3 is equal to 21 . you could do this part in your head , but i just want to make it clear where i 'm getting these numbers from . what i would do in the standard method is i would write the 1 into 21 down here , but then carry the 2 to the tens place . now i want to figure out what 7 times 5 is . we know from our multiplication tables that 7 times 5 is equal to 35 . now , we ca n't just somehow put the 35 down here . we still have to deal with this 2 that we carried . so we compute 7 times 5 is 35 , but then we also add that 2 . so it 's 35 plus 2 is 37 . now , we write the 7 right over here in the tens place and carry the 3 . now we need to compute what 7 times 2 is . we know that 7 times 2 is 14 from our multiplication tables . we ca n't just put a 14 down here . we have this 3 to add . so 7 times 2 is 14 , plus 3 is 17 . so now we can write the 17 down here , because 2 is the last number that we had to deal with . and so we have our answer . 7 times 253 is 1,771 .
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we ca n't just put a 14 down here . we have this 3 to add . so 7 times 2 is 14 , plus 3 is 17 . so now we can write the 17 down here , because 2 is the last number that we had to deal with .
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when will you do 2 digits time 1,2,3,4 digits ?
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let 's multiply 7 times 253 and see what we get . so just like in the last example , what i like to do is i like to rewrite the largest number first . so that 's 253 . and then write the smaller number below it and align the place value , the 7 . it only has a ones place , so i 'll put the 7 right over here below the ones place in 253 . and then put the multiplication symbol right over here . so you could read this as 253 times 7 , which we know is the same thing as 7 times 253 . and now we are ready to compute . and there are many ways of doing this , but this one you could call the standard way . so what i do is i start with my 7 . and i multiply it times each of the numbers up here , and i carry appropriately . so first i start with 7 times 3 . well , 7 times 3 we know is 21 . let me write that down . 7 times 3 is equal to 21 . you could do this part in your head , but i just want to make it clear where i 'm getting these numbers from . what i would do in the standard method is i would write the 1 into 21 down here , but then carry the 2 to the tens place . now i want to figure out what 7 times 5 is . we know from our multiplication tables that 7 times 5 is equal to 35 . now , we ca n't just somehow put the 35 down here . we still have to deal with this 2 that we carried . so we compute 7 times 5 is 35 , but then we also add that 2 . so it 's 35 plus 2 is 37 . now , we write the 7 right over here in the tens place and carry the 3 . now we need to compute what 7 times 2 is . we know that 7 times 2 is 14 from our multiplication tables . we ca n't just put a 14 down here . we have this 3 to add . so 7 times 2 is 14 , plus 3 is 17 . so now we can write the 17 down here , because 2 is the last number that we had to deal with . and so we have our answer . 7 times 253 is 1,771 .
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and so we have our answer . 7 times 253 is 1,771 .
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what 's 114 -114 +115-1+1 ?
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- this is a rectangle . and yes , this is a rectangle . let 's measure the green line below using both rectangles and a centimeter ruler . so , we have this green line and we 're going to measure it in terms of rectangles and we 're going to measure it on this ruler . and you immediately see the green line is equal to one rectangle long , but if we measure it in centimeters it 's equal to six centimeters long . so we can say the line is one rectangle long , but it 's six centimeters long and that makes sense because the rectangle is much more than a centimeter . actually , the length of a rectangle is six centimeters . so , the length of a rectangle is longer than a centimeter . you see that . this is the length of the rectangle , it 's the same as the line , while centimeter is this length . the rectangle is actually six centimeters long . so it takes blank rectangles , than centimeters , to measure the line . well , since the rectangle is longer , it takes fewer rectangles than centimeters to measure the line . so it 's fewer rectangles than centimeters and you see that . fewer rectangles , one is fewer than six . it took one , it only took one rectangle to measure the line because a rectangle 's so long and it took six centimeters to measure the line . so it took fewer rectangles than centimeters to measure the line . let 's keep going . alright , so we have . this is a rectangle . yes , that is a rectangle . let 's measure the blue line below using both a rectangle and a centimeter ruler . so it 's a similar idea . so , when we look at this blue line , the line is now two of these green rectangles long . so it is two rectangles long . now , in terms of centimeters , it is four , four centimeters long . four centimeters long . the length of each rectangle is blank than a centimeter . well , each rectangle is more than a centimeter . it 's longer . you see , each rectangle is actually two centimeters . so , it 's longer than a centimeter . so it takes blank rectangles than centimeters to measure the line . well , since each rectangle is longer , it 's going to take fewer rectangles to measure the line . so we 'll select fewer right over there and you see that over here . it only took two rectangles to measure the line , but it took four centimeters . two is fewer than four . let 's see . let 's do one more of these . these are a lot of fun . alright , this is a rectangle . let 's measure the green line below . same idea . the line is four rectangles long . the line is seven centimeters long . the length of each rectangle is shorter , sorry , longer than a centimeter . you see that right here . each rectangle is more than one centimeter . so it takes fewer rectangles than centimeters to measure the line . so , we 've seen this , we 've seen this multiple times .
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- this is a rectangle . and yes , this is a rectangle .
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how can you tell when the units are different ?
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