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key points based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . contrary to the predictions , experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of particles called photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a metal surface , and the value of $ \phi $ depends on the metal . the energy of the incident photon must be equal to the sum of the metal 's work function and the photoelectron kinetic energy : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ introduction : what is the photoelectric effect ? when light shines on a metal , electrons can be ejected from the surface of the metal in a phenomenon known as the photoelectric effect . this process is also often referred to as photoemission , and the electrons that are ejected from the metal are called photoelectrons . in terms of their behavior and their properties , photoelectrons are no different from other electrons . the prefix , photo- , simply tells us that the electrons have been ejected from a metal surface by incident light . in this article , we will discuss how 19th century physicists attempted ( but failed ! ) to explain the photoelectric effect using classical physics . this ultimately led to the development of the modern description of electromagnetic radiation , which has both wave-like and particle-like properties . predictions based on light as a wave to explain the photoelectric effect , 19th-century physicists theorized that the oscillating electric field of the incoming light wave was heating the electrons and causing them to vibrate , eventually freeing them from the metal surface . this hypothesis was based on the assumption that light traveled purely as a wave through space . ( see this article for more information about the basic properties of light . ) scientists also believed that the energy of the light wave was proportional to its brightness , which is related to the wave 's amplitude . in order to test their hypotheses , they performed experiments to look at the effect of light amplitude and frequency on the rate of electron ejection , as well as the kinetic energy of the photoelectrons . based on the classical description of light as a wave , they made the following predictions : the kinetic energy of emitted photoelectrons should increase with the light amplitude . the rate of electron emission , which is proportional to the measured electric current , should increase as the light frequency is increased . to help us understand why they made these predictions , we can compare a light wave to a water wave . imagine some beach balls sitting on a dock that extends out into the ocean . the dock represents a metal surface , the beach balls represent electrons , and the ocean waves represent light waves . if a single large wave were to shake the dock , we would expect the energy from the big wave would send the beach balls flying off the dock with much more kinetic energy compared to a single , small wave . this is also what physicists believed would happen if the light intensity was increased . light amplitude was expected to be proportional to the light energy , so higher amplitude light was predicted to result in photoelectrons with more kinetic energy . classical physicists also predicted that increasing the frequency of light waves ( at a constant amplitude ) would increase the rate of electrons being ejected , and thus increase the measured electric current . using our beach ball analogy , we would expect waves hitting the dock more frequently would result in more beach balls being knocked off the dock compared to the same sized waves hitting the dock less often . now that we know what physicists thought would happen , let 's look at what they actually observed experimentally ! when intuition fails : photons to the rescue ! when experiments were performed to look at the effect of light amplitude and frequency , the following results were observed : the kinetic energy of photoelectrons increases with light frequency . electric current remains constant as light frequency increases . electric current increases with light amplitude . the kinetic energy of photoelectrons remains constant as light amplitude increases . these results were completely at odds with the predictions based on the classical description of light as a wave ! in order to explain what was happening , it turned out that an entirely new model of light was needed . that model was developed by albert einstein , who proposed that light sometimes behaved as particles of electromagnetic energy which we now call photons . the energy of a photon could be calculated using planck 's equation : $ \text { e } _ { \text { photon } } =h\nu $ where $ \text { e } _ { \text { photon } } $ is the energy of a photon in joules ( $ \text { j } $ ) , $ h $ is planck 's constant $ ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) $ , and $ \nu $ is the frequency of the light in $ \text { hz } $ . according to planck 's equation , the energy of a photon is proportional to the frequency of the light , $ \nu $ . the amplitude of the light is then proportional to the number of photons with a given frequency . concept check : as the wavelength of a photon increases , what happens to the photon 's energy ? light frequency and the threshold frequency $ \nu_0 $ we can think of the incident light as a stream of photons with an energy determined by the light frequency . when a photon hits the metal surface , the photon 's energy is absorbed by an electron in the metal . the graphic below illustrates the relationship between light frequency and the kinetic energy of ejected electrons . the scientists observed that if the incident light had a frequency less than a minimum frequency $ \nu_0 $ , then no electrons were ejected regardless of the light amplitude . this minimum frequency is also called the threshold frequency , and the value of $ \nu_0 $ depends on the metal . for frequencies greater than $ \nu_0 $ , electrons would be ejected from the metal . furthermore , the kinetic energy of the photoelectrons was proportional to the light frequency . the relationship between photoelectron kinetic energy and light frequency is shown in graph ( a ) below . because the light amplitude was kept constant as the light frequency increased , the number of photons being absorbed by the metal remained constant . thus , the rate at which electrons were ejected from the metal ( or the electric current ) remained constant as well . the relationship between electron current and light frequency is illustrated in graph ( b ) above . is n't there more math somewhere ? we can analyze the frequency relationship using the law of conservation of energy . the total energy of the incoming photon , $ \text { e } \text { photon } $ , must be equal to the kinetic energy of the ejected electron , $ \text { ke } { \text { electron } } $ , plus the energy required to eject the electron from the metal . the energy required to free the electron from a particular metal is also called the metal 's work function , which is represented by the symbol $ \phi $ ( in units of $ \text j $ ) : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ like the threshold frequency $ \nu_0 $ , the value of $ \phi $ also changes depending on the metal . we can now write the energy of the photon in terms of the light frequency using planck 's equation : $ \text { e } \text { photon } =h\nu=\text { ke } \text { electron } +\phi $ rearranging this equation in terms of the electron 's kinetic energy , we get : $ \text { ke } _\text { electron } =h\nu-\phi $ we can see that kinetic energy of the photoelectron increases linearly with $ \nu $ as long as the photon energy is greater than the work function $ \phi $ , which is exactly the relationship shown in graph ( a ) above . we can also use this equation to find the photoelectron velocity $ \text v $ , which is related to $ \text { ke } _\text { electron } $ as follows : $ \text { ke } _\text { electron } =h\nu-\phi=\dfrac { 1 } { 2 } m_e\text v^2 $ where $ m_e $ is the rest mass of an electron , $ 9.1094 \times 10^ { -31 } \ , \text { kg } $ . exploring the wave amplitude trends in terms of photons , higher amplitude light means more photons hitting the metal surface . this results in more electrons ejected over a given time period . as long as the light frequency is greater than $ \nu_0 $ , increasing the light amplitude will cause the electron current to increase proportionally as shown in graph ( a ) below . since increasing the light amplitude has no effect on the energy of the incoming photon , the photoelectron kinetic energy remains constant as the light amplitude is increased ( see graph ( b ) above ) . if we try to explain this result using our dock-and-beach-balls analogy , the relationship in graph ( b ) indicates that no matter the height of the wave hitting the dock $ - $ whether it 's a tiny swell , or a huge tsunami $ - $ the individual beach balls would be launched off the dock with the exact same speed ! thus , our intuition and analogy do n't do a very good job of explaining these particular experiments . example $ 1 $ : the photoelectric effect for copper the work function of copper metal is $ \phi=7.53\times10^ { -19 } \text { j } $ . if we shine light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ on copper metal , will the photoelectric effect be observed ? in order to eject electrons , we need the energy of the photons to be greater than the work function of copper . we can use planck 's equation to calculate the energy of the photon , $ \text { e } _ { \text { photon } } $ : $ \begin { align } \text { e } _\text { photon } & amp ; = h\nu \ & amp ; = ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) ( 3.0\times10^ { 16 } \text { hz } ) ~~~~\text { plug in values for $ h $ and $ \nu $ } \ & amp ; = 2.0\times10^ { -17 } \text { j } \end { align } $ if we compare our calculated photon energy , $ \text { e } _\text { photon } $ , to copper 's work function , we see that the photon energy is greater than $ \phi $ : $ ~2.0\times10^ { -17 } \text { j } ~ & gt ; ~7.53\times10^ { -19 } \text { j } $ $ ~~~~~~~~\text { e } _\text { photon } ~~~~~~~~~~~~~~~~~~~\phi $ thus , we would expect to see photoelectrons ejected from the copper . next , we will calculate the kinetic energy of the photoelectrons . example $ 2 $ : calculating the kinetic energy of a photoelectron what is the kinetic energy of the photoelectrons ejected from the copper by the light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ ? we can calculate the kinetic energy of the photoelectron using the equation that relates $ \text { ke } \text { electron } $ to the energy of the photon , $ \text { e } \text { photon } $ , and the work function , $ \phi $ : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ since we want to know $ \text { ke } _\text { electron } $ , we can start by rearranging the equation so that we will be solving for the kinetic energy of the electron : $ \text { ke } \text { electron } =\text { e } \text { photon } -\phi $ now we can insert our known values for $ \text { e } _\text { photon } $ and $ \phi $ from example 1 : $ \text { ke } _\text { electron } = ( 2.0\times10^ { -17 } \text { j } ) - ( 7.53\times10^ { -19 } \text { j } ) =1.9\times10^ { -17 } \text { j } $ therefore , each photoelectron has a kinetic energy of $ 1.9\times10^ { -17 } \text { j } $ . summary based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a specific metal surface . the energy of the incident photon must be equal to the sum of the work function and the kinetic energy of a photoelectron : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ try it ! when we shine light with a frequency of $ 6.20 \times 10^ { 14 } \ , \text { hz } $ on a mystery metal , we observe the ejected electrons have a kinetic energy of $ 3.28\times 10^ { -20 } \ , \text j $ . some possible candidates for the mystery metal are shown in the table below : metal | work function $ \phi $ ( joules , $ \text j $ ) : - : | : - : calcium , $ \text { ca } $ | $ 4.60\times 10^ { -19 } $ tin , $ \text { sn } $ | $ 7.08\times 10^ { -19 } $ sodium , $ \text { na } $ | $ 3.78\times 10^ { -19 } $ hafnium , $ \text { hf } $ | $ 6.25\times 10^ { -19 } $ samarium , $ \text { sm } $ | $ 4.33\times 10^ { -19 } $ based on this information , what is the most likely identity of our mystery metal ?
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based on these findings , einstein proposed that light behaved like a stream of photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a specific metal surface . the energy of the incident photon must be equal to the sum of the work function and the kinetic energy of a photoelectron : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ try it !
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if the energy of light incident on the metal is lesser than the work function of the metal , then do the electrons absorb energy and get excited into the next energy level ?
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key points based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . contrary to the predictions , experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of particles called photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a metal surface , and the value of $ \phi $ depends on the metal . the energy of the incident photon must be equal to the sum of the metal 's work function and the photoelectron kinetic energy : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ introduction : what is the photoelectric effect ? when light shines on a metal , electrons can be ejected from the surface of the metal in a phenomenon known as the photoelectric effect . this process is also often referred to as photoemission , and the electrons that are ejected from the metal are called photoelectrons . in terms of their behavior and their properties , photoelectrons are no different from other electrons . the prefix , photo- , simply tells us that the electrons have been ejected from a metal surface by incident light . in this article , we will discuss how 19th century physicists attempted ( but failed ! ) to explain the photoelectric effect using classical physics . this ultimately led to the development of the modern description of electromagnetic radiation , which has both wave-like and particle-like properties . predictions based on light as a wave to explain the photoelectric effect , 19th-century physicists theorized that the oscillating electric field of the incoming light wave was heating the electrons and causing them to vibrate , eventually freeing them from the metal surface . this hypothesis was based on the assumption that light traveled purely as a wave through space . ( see this article for more information about the basic properties of light . ) scientists also believed that the energy of the light wave was proportional to its brightness , which is related to the wave 's amplitude . in order to test their hypotheses , they performed experiments to look at the effect of light amplitude and frequency on the rate of electron ejection , as well as the kinetic energy of the photoelectrons . based on the classical description of light as a wave , they made the following predictions : the kinetic energy of emitted photoelectrons should increase with the light amplitude . the rate of electron emission , which is proportional to the measured electric current , should increase as the light frequency is increased . to help us understand why they made these predictions , we can compare a light wave to a water wave . imagine some beach balls sitting on a dock that extends out into the ocean . the dock represents a metal surface , the beach balls represent electrons , and the ocean waves represent light waves . if a single large wave were to shake the dock , we would expect the energy from the big wave would send the beach balls flying off the dock with much more kinetic energy compared to a single , small wave . this is also what physicists believed would happen if the light intensity was increased . light amplitude was expected to be proportional to the light energy , so higher amplitude light was predicted to result in photoelectrons with more kinetic energy . classical physicists also predicted that increasing the frequency of light waves ( at a constant amplitude ) would increase the rate of electrons being ejected , and thus increase the measured electric current . using our beach ball analogy , we would expect waves hitting the dock more frequently would result in more beach balls being knocked off the dock compared to the same sized waves hitting the dock less often . now that we know what physicists thought would happen , let 's look at what they actually observed experimentally ! when intuition fails : photons to the rescue ! when experiments were performed to look at the effect of light amplitude and frequency , the following results were observed : the kinetic energy of photoelectrons increases with light frequency . electric current remains constant as light frequency increases . electric current increases with light amplitude . the kinetic energy of photoelectrons remains constant as light amplitude increases . these results were completely at odds with the predictions based on the classical description of light as a wave ! in order to explain what was happening , it turned out that an entirely new model of light was needed . that model was developed by albert einstein , who proposed that light sometimes behaved as particles of electromagnetic energy which we now call photons . the energy of a photon could be calculated using planck 's equation : $ \text { e } _ { \text { photon } } =h\nu $ where $ \text { e } _ { \text { photon } } $ is the energy of a photon in joules ( $ \text { j } $ ) , $ h $ is planck 's constant $ ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) $ , and $ \nu $ is the frequency of the light in $ \text { hz } $ . according to planck 's equation , the energy of a photon is proportional to the frequency of the light , $ \nu $ . the amplitude of the light is then proportional to the number of photons with a given frequency . concept check : as the wavelength of a photon increases , what happens to the photon 's energy ? light frequency and the threshold frequency $ \nu_0 $ we can think of the incident light as a stream of photons with an energy determined by the light frequency . when a photon hits the metal surface , the photon 's energy is absorbed by an electron in the metal . the graphic below illustrates the relationship between light frequency and the kinetic energy of ejected electrons . the scientists observed that if the incident light had a frequency less than a minimum frequency $ \nu_0 $ , then no electrons were ejected regardless of the light amplitude . this minimum frequency is also called the threshold frequency , and the value of $ \nu_0 $ depends on the metal . for frequencies greater than $ \nu_0 $ , electrons would be ejected from the metal . furthermore , the kinetic energy of the photoelectrons was proportional to the light frequency . the relationship between photoelectron kinetic energy and light frequency is shown in graph ( a ) below . because the light amplitude was kept constant as the light frequency increased , the number of photons being absorbed by the metal remained constant . thus , the rate at which electrons were ejected from the metal ( or the electric current ) remained constant as well . the relationship between electron current and light frequency is illustrated in graph ( b ) above . is n't there more math somewhere ? we can analyze the frequency relationship using the law of conservation of energy . the total energy of the incoming photon , $ \text { e } \text { photon } $ , must be equal to the kinetic energy of the ejected electron , $ \text { ke } { \text { electron } } $ , plus the energy required to eject the electron from the metal . the energy required to free the electron from a particular metal is also called the metal 's work function , which is represented by the symbol $ \phi $ ( in units of $ \text j $ ) : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ like the threshold frequency $ \nu_0 $ , the value of $ \phi $ also changes depending on the metal . we can now write the energy of the photon in terms of the light frequency using planck 's equation : $ \text { e } \text { photon } =h\nu=\text { ke } \text { electron } +\phi $ rearranging this equation in terms of the electron 's kinetic energy , we get : $ \text { ke } _\text { electron } =h\nu-\phi $ we can see that kinetic energy of the photoelectron increases linearly with $ \nu $ as long as the photon energy is greater than the work function $ \phi $ , which is exactly the relationship shown in graph ( a ) above . we can also use this equation to find the photoelectron velocity $ \text v $ , which is related to $ \text { ke } _\text { electron } $ as follows : $ \text { ke } _\text { electron } =h\nu-\phi=\dfrac { 1 } { 2 } m_e\text v^2 $ where $ m_e $ is the rest mass of an electron , $ 9.1094 \times 10^ { -31 } \ , \text { kg } $ . exploring the wave amplitude trends in terms of photons , higher amplitude light means more photons hitting the metal surface . this results in more electrons ejected over a given time period . as long as the light frequency is greater than $ \nu_0 $ , increasing the light amplitude will cause the electron current to increase proportionally as shown in graph ( a ) below . since increasing the light amplitude has no effect on the energy of the incoming photon , the photoelectron kinetic energy remains constant as the light amplitude is increased ( see graph ( b ) above ) . if we try to explain this result using our dock-and-beach-balls analogy , the relationship in graph ( b ) indicates that no matter the height of the wave hitting the dock $ - $ whether it 's a tiny swell , or a huge tsunami $ - $ the individual beach balls would be launched off the dock with the exact same speed ! thus , our intuition and analogy do n't do a very good job of explaining these particular experiments . example $ 1 $ : the photoelectric effect for copper the work function of copper metal is $ \phi=7.53\times10^ { -19 } \text { j } $ . if we shine light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ on copper metal , will the photoelectric effect be observed ? in order to eject electrons , we need the energy of the photons to be greater than the work function of copper . we can use planck 's equation to calculate the energy of the photon , $ \text { e } _ { \text { photon } } $ : $ \begin { align } \text { e } _\text { photon } & amp ; = h\nu \ & amp ; = ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) ( 3.0\times10^ { 16 } \text { hz } ) ~~~~\text { plug in values for $ h $ and $ \nu $ } \ & amp ; = 2.0\times10^ { -17 } \text { j } \end { align } $ if we compare our calculated photon energy , $ \text { e } _\text { photon } $ , to copper 's work function , we see that the photon energy is greater than $ \phi $ : $ ~2.0\times10^ { -17 } \text { j } ~ & gt ; ~7.53\times10^ { -19 } \text { j } $ $ ~~~~~~~~\text { e } _\text { photon } ~~~~~~~~~~~~~~~~~~~\phi $ thus , we would expect to see photoelectrons ejected from the copper . next , we will calculate the kinetic energy of the photoelectrons . example $ 2 $ : calculating the kinetic energy of a photoelectron what is the kinetic energy of the photoelectrons ejected from the copper by the light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ ? we can calculate the kinetic energy of the photoelectron using the equation that relates $ \text { ke } \text { electron } $ to the energy of the photon , $ \text { e } \text { photon } $ , and the work function , $ \phi $ : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ since we want to know $ \text { ke } _\text { electron } $ , we can start by rearranging the equation so that we will be solving for the kinetic energy of the electron : $ \text { ke } \text { electron } =\text { e } \text { photon } -\phi $ now we can insert our known values for $ \text { e } _\text { photon } $ and $ \phi $ from example 1 : $ \text { ke } _\text { electron } = ( 2.0\times10^ { -17 } \text { j } ) - ( 7.53\times10^ { -19 } \text { j } ) =1.9\times10^ { -17 } \text { j } $ therefore , each photoelectron has a kinetic energy of $ 1.9\times10^ { -17 } \text { j } $ . summary based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a specific metal surface . the energy of the incident photon must be equal to the sum of the work function and the kinetic energy of a photoelectron : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ try it ! when we shine light with a frequency of $ 6.20 \times 10^ { 14 } \ , \text { hz } $ on a mystery metal , we observe the ejected electrons have a kinetic energy of $ 3.28\times 10^ { -20 } \ , \text j $ . some possible candidates for the mystery metal are shown in the table below : metal | work function $ \phi $ ( joules , $ \text j $ ) : - : | : - : calcium , $ \text { ca } $ | $ 4.60\times 10^ { -19 } $ tin , $ \text { sn } $ | $ 7.08\times 10^ { -19 } $ sodium , $ \text { na } $ | $ 3.78\times 10^ { -19 } $ hafnium , $ \text { hf } $ | $ 6.25\times 10^ { -19 } $ samarium , $ \text { sm } $ | $ 4.33\times 10^ { -19 } $ based on this information , what is the most likely identity of our mystery metal ?
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if a single large wave were to shake the dock , we would expect the energy from the big wave would send the beach balls flying off the dock with much more kinetic energy compared to a single , small wave . this is also what physicists believed would happen if the light intensity was increased . light amplitude was expected to be proportional to the light energy , so higher amplitude light was predicted to result in photoelectrons with more kinetic energy .
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is intensity the same as brightness ?
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key points based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . contrary to the predictions , experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of particles called photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a metal surface , and the value of $ \phi $ depends on the metal . the energy of the incident photon must be equal to the sum of the metal 's work function and the photoelectron kinetic energy : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ introduction : what is the photoelectric effect ? when light shines on a metal , electrons can be ejected from the surface of the metal in a phenomenon known as the photoelectric effect . this process is also often referred to as photoemission , and the electrons that are ejected from the metal are called photoelectrons . in terms of their behavior and their properties , photoelectrons are no different from other electrons . the prefix , photo- , simply tells us that the electrons have been ejected from a metal surface by incident light . in this article , we will discuss how 19th century physicists attempted ( but failed ! ) to explain the photoelectric effect using classical physics . this ultimately led to the development of the modern description of electromagnetic radiation , which has both wave-like and particle-like properties . predictions based on light as a wave to explain the photoelectric effect , 19th-century physicists theorized that the oscillating electric field of the incoming light wave was heating the electrons and causing them to vibrate , eventually freeing them from the metal surface . this hypothesis was based on the assumption that light traveled purely as a wave through space . ( see this article for more information about the basic properties of light . ) scientists also believed that the energy of the light wave was proportional to its brightness , which is related to the wave 's amplitude . in order to test their hypotheses , they performed experiments to look at the effect of light amplitude and frequency on the rate of electron ejection , as well as the kinetic energy of the photoelectrons . based on the classical description of light as a wave , they made the following predictions : the kinetic energy of emitted photoelectrons should increase with the light amplitude . the rate of electron emission , which is proportional to the measured electric current , should increase as the light frequency is increased . to help us understand why they made these predictions , we can compare a light wave to a water wave . imagine some beach balls sitting on a dock that extends out into the ocean . the dock represents a metal surface , the beach balls represent electrons , and the ocean waves represent light waves . if a single large wave were to shake the dock , we would expect the energy from the big wave would send the beach balls flying off the dock with much more kinetic energy compared to a single , small wave . this is also what physicists believed would happen if the light intensity was increased . light amplitude was expected to be proportional to the light energy , so higher amplitude light was predicted to result in photoelectrons with more kinetic energy . classical physicists also predicted that increasing the frequency of light waves ( at a constant amplitude ) would increase the rate of electrons being ejected , and thus increase the measured electric current . using our beach ball analogy , we would expect waves hitting the dock more frequently would result in more beach balls being knocked off the dock compared to the same sized waves hitting the dock less often . now that we know what physicists thought would happen , let 's look at what they actually observed experimentally ! when intuition fails : photons to the rescue ! when experiments were performed to look at the effect of light amplitude and frequency , the following results were observed : the kinetic energy of photoelectrons increases with light frequency . electric current remains constant as light frequency increases . electric current increases with light amplitude . the kinetic energy of photoelectrons remains constant as light amplitude increases . these results were completely at odds with the predictions based on the classical description of light as a wave ! in order to explain what was happening , it turned out that an entirely new model of light was needed . that model was developed by albert einstein , who proposed that light sometimes behaved as particles of electromagnetic energy which we now call photons . the energy of a photon could be calculated using planck 's equation : $ \text { e } _ { \text { photon } } =h\nu $ where $ \text { e } _ { \text { photon } } $ is the energy of a photon in joules ( $ \text { j } $ ) , $ h $ is planck 's constant $ ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) $ , and $ \nu $ is the frequency of the light in $ \text { hz } $ . according to planck 's equation , the energy of a photon is proportional to the frequency of the light , $ \nu $ . the amplitude of the light is then proportional to the number of photons with a given frequency . concept check : as the wavelength of a photon increases , what happens to the photon 's energy ? light frequency and the threshold frequency $ \nu_0 $ we can think of the incident light as a stream of photons with an energy determined by the light frequency . when a photon hits the metal surface , the photon 's energy is absorbed by an electron in the metal . the graphic below illustrates the relationship between light frequency and the kinetic energy of ejected electrons . the scientists observed that if the incident light had a frequency less than a minimum frequency $ \nu_0 $ , then no electrons were ejected regardless of the light amplitude . this minimum frequency is also called the threshold frequency , and the value of $ \nu_0 $ depends on the metal . for frequencies greater than $ \nu_0 $ , electrons would be ejected from the metal . furthermore , the kinetic energy of the photoelectrons was proportional to the light frequency . the relationship between photoelectron kinetic energy and light frequency is shown in graph ( a ) below . because the light amplitude was kept constant as the light frequency increased , the number of photons being absorbed by the metal remained constant . thus , the rate at which electrons were ejected from the metal ( or the electric current ) remained constant as well . the relationship between electron current and light frequency is illustrated in graph ( b ) above . is n't there more math somewhere ? we can analyze the frequency relationship using the law of conservation of energy . the total energy of the incoming photon , $ \text { e } \text { photon } $ , must be equal to the kinetic energy of the ejected electron , $ \text { ke } { \text { electron } } $ , plus the energy required to eject the electron from the metal . the energy required to free the electron from a particular metal is also called the metal 's work function , which is represented by the symbol $ \phi $ ( in units of $ \text j $ ) : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ like the threshold frequency $ \nu_0 $ , the value of $ \phi $ also changes depending on the metal . we can now write the energy of the photon in terms of the light frequency using planck 's equation : $ \text { e } \text { photon } =h\nu=\text { ke } \text { electron } +\phi $ rearranging this equation in terms of the electron 's kinetic energy , we get : $ \text { ke } _\text { electron } =h\nu-\phi $ we can see that kinetic energy of the photoelectron increases linearly with $ \nu $ as long as the photon energy is greater than the work function $ \phi $ , which is exactly the relationship shown in graph ( a ) above . we can also use this equation to find the photoelectron velocity $ \text v $ , which is related to $ \text { ke } _\text { electron } $ as follows : $ \text { ke } _\text { electron } =h\nu-\phi=\dfrac { 1 } { 2 } m_e\text v^2 $ where $ m_e $ is the rest mass of an electron , $ 9.1094 \times 10^ { -31 } \ , \text { kg } $ . exploring the wave amplitude trends in terms of photons , higher amplitude light means more photons hitting the metal surface . this results in more electrons ejected over a given time period . as long as the light frequency is greater than $ \nu_0 $ , increasing the light amplitude will cause the electron current to increase proportionally as shown in graph ( a ) below . since increasing the light amplitude has no effect on the energy of the incoming photon , the photoelectron kinetic energy remains constant as the light amplitude is increased ( see graph ( b ) above ) . if we try to explain this result using our dock-and-beach-balls analogy , the relationship in graph ( b ) indicates that no matter the height of the wave hitting the dock $ - $ whether it 's a tiny swell , or a huge tsunami $ - $ the individual beach balls would be launched off the dock with the exact same speed ! thus , our intuition and analogy do n't do a very good job of explaining these particular experiments . example $ 1 $ : the photoelectric effect for copper the work function of copper metal is $ \phi=7.53\times10^ { -19 } \text { j } $ . if we shine light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ on copper metal , will the photoelectric effect be observed ? in order to eject electrons , we need the energy of the photons to be greater than the work function of copper . we can use planck 's equation to calculate the energy of the photon , $ \text { e } _ { \text { photon } } $ : $ \begin { align } \text { e } _\text { photon } & amp ; = h\nu \ & amp ; = ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) ( 3.0\times10^ { 16 } \text { hz } ) ~~~~\text { plug in values for $ h $ and $ \nu $ } \ & amp ; = 2.0\times10^ { -17 } \text { j } \end { align } $ if we compare our calculated photon energy , $ \text { e } _\text { photon } $ , to copper 's work function , we see that the photon energy is greater than $ \phi $ : $ ~2.0\times10^ { -17 } \text { j } ~ & gt ; ~7.53\times10^ { -19 } \text { j } $ $ ~~~~~~~~\text { e } _\text { photon } ~~~~~~~~~~~~~~~~~~~\phi $ thus , we would expect to see photoelectrons ejected from the copper . next , we will calculate the kinetic energy of the photoelectrons . example $ 2 $ : calculating the kinetic energy of a photoelectron what is the kinetic energy of the photoelectrons ejected from the copper by the light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ ? we can calculate the kinetic energy of the photoelectron using the equation that relates $ \text { ke } \text { electron } $ to the energy of the photon , $ \text { e } \text { photon } $ , and the work function , $ \phi $ : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ since we want to know $ \text { ke } _\text { electron } $ , we can start by rearranging the equation so that we will be solving for the kinetic energy of the electron : $ \text { ke } \text { electron } =\text { e } \text { photon } -\phi $ now we can insert our known values for $ \text { e } _\text { photon } $ and $ \phi $ from example 1 : $ \text { ke } _\text { electron } = ( 2.0\times10^ { -17 } \text { j } ) - ( 7.53\times10^ { -19 } \text { j } ) =1.9\times10^ { -17 } \text { j } $ therefore , each photoelectron has a kinetic energy of $ 1.9\times10^ { -17 } \text { j } $ . summary based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a specific metal surface . the energy of the incident photon must be equal to the sum of the work function and the kinetic energy of a photoelectron : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ try it ! when we shine light with a frequency of $ 6.20 \times 10^ { 14 } \ , \text { hz } $ on a mystery metal , we observe the ejected electrons have a kinetic energy of $ 3.28\times 10^ { -20 } \ , \text j $ . some possible candidates for the mystery metal are shown in the table below : metal | work function $ \phi $ ( joules , $ \text j $ ) : - : | : - : calcium , $ \text { ca } $ | $ 4.60\times 10^ { -19 } $ tin , $ \text { sn } $ | $ 7.08\times 10^ { -19 } $ sodium , $ \text { na } $ | $ 3.78\times 10^ { -19 } $ hafnium , $ \text { hf } $ | $ 6.25\times 10^ { -19 } $ samarium , $ \text { sm } $ | $ 4.33\times 10^ { -19 } $ based on this information , what is the most likely identity of our mystery metal ?
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electric current remains constant as light frequency increases . electric current increases with light amplitude . the kinetic energy of photoelectrons remains constant as light amplitude increases . these results were completely at odds with the predictions based on the classical description of light as a wave !
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however , why does the current not increase when the kinetic energy increases ?
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key points based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . contrary to the predictions , experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of particles called photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a metal surface , and the value of $ \phi $ depends on the metal . the energy of the incident photon must be equal to the sum of the metal 's work function and the photoelectron kinetic energy : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ introduction : what is the photoelectric effect ? when light shines on a metal , electrons can be ejected from the surface of the metal in a phenomenon known as the photoelectric effect . this process is also often referred to as photoemission , and the electrons that are ejected from the metal are called photoelectrons . in terms of their behavior and their properties , photoelectrons are no different from other electrons . the prefix , photo- , simply tells us that the electrons have been ejected from a metal surface by incident light . in this article , we will discuss how 19th century physicists attempted ( but failed ! ) to explain the photoelectric effect using classical physics . this ultimately led to the development of the modern description of electromagnetic radiation , which has both wave-like and particle-like properties . predictions based on light as a wave to explain the photoelectric effect , 19th-century physicists theorized that the oscillating electric field of the incoming light wave was heating the electrons and causing them to vibrate , eventually freeing them from the metal surface . this hypothesis was based on the assumption that light traveled purely as a wave through space . ( see this article for more information about the basic properties of light . ) scientists also believed that the energy of the light wave was proportional to its brightness , which is related to the wave 's amplitude . in order to test their hypotheses , they performed experiments to look at the effect of light amplitude and frequency on the rate of electron ejection , as well as the kinetic energy of the photoelectrons . based on the classical description of light as a wave , they made the following predictions : the kinetic energy of emitted photoelectrons should increase with the light amplitude . the rate of electron emission , which is proportional to the measured electric current , should increase as the light frequency is increased . to help us understand why they made these predictions , we can compare a light wave to a water wave . imagine some beach balls sitting on a dock that extends out into the ocean . the dock represents a metal surface , the beach balls represent electrons , and the ocean waves represent light waves . if a single large wave were to shake the dock , we would expect the energy from the big wave would send the beach balls flying off the dock with much more kinetic energy compared to a single , small wave . this is also what physicists believed would happen if the light intensity was increased . light amplitude was expected to be proportional to the light energy , so higher amplitude light was predicted to result in photoelectrons with more kinetic energy . classical physicists also predicted that increasing the frequency of light waves ( at a constant amplitude ) would increase the rate of electrons being ejected , and thus increase the measured electric current . using our beach ball analogy , we would expect waves hitting the dock more frequently would result in more beach balls being knocked off the dock compared to the same sized waves hitting the dock less often . now that we know what physicists thought would happen , let 's look at what they actually observed experimentally ! when intuition fails : photons to the rescue ! when experiments were performed to look at the effect of light amplitude and frequency , the following results were observed : the kinetic energy of photoelectrons increases with light frequency . electric current remains constant as light frequency increases . electric current increases with light amplitude . the kinetic energy of photoelectrons remains constant as light amplitude increases . these results were completely at odds with the predictions based on the classical description of light as a wave ! in order to explain what was happening , it turned out that an entirely new model of light was needed . that model was developed by albert einstein , who proposed that light sometimes behaved as particles of electromagnetic energy which we now call photons . the energy of a photon could be calculated using planck 's equation : $ \text { e } _ { \text { photon } } =h\nu $ where $ \text { e } _ { \text { photon } } $ is the energy of a photon in joules ( $ \text { j } $ ) , $ h $ is planck 's constant $ ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) $ , and $ \nu $ is the frequency of the light in $ \text { hz } $ . according to planck 's equation , the energy of a photon is proportional to the frequency of the light , $ \nu $ . the amplitude of the light is then proportional to the number of photons with a given frequency . concept check : as the wavelength of a photon increases , what happens to the photon 's energy ? light frequency and the threshold frequency $ \nu_0 $ we can think of the incident light as a stream of photons with an energy determined by the light frequency . when a photon hits the metal surface , the photon 's energy is absorbed by an electron in the metal . the graphic below illustrates the relationship between light frequency and the kinetic energy of ejected electrons . the scientists observed that if the incident light had a frequency less than a minimum frequency $ \nu_0 $ , then no electrons were ejected regardless of the light amplitude . this minimum frequency is also called the threshold frequency , and the value of $ \nu_0 $ depends on the metal . for frequencies greater than $ \nu_0 $ , electrons would be ejected from the metal . furthermore , the kinetic energy of the photoelectrons was proportional to the light frequency . the relationship between photoelectron kinetic energy and light frequency is shown in graph ( a ) below . because the light amplitude was kept constant as the light frequency increased , the number of photons being absorbed by the metal remained constant . thus , the rate at which electrons were ejected from the metal ( or the electric current ) remained constant as well . the relationship between electron current and light frequency is illustrated in graph ( b ) above . is n't there more math somewhere ? we can analyze the frequency relationship using the law of conservation of energy . the total energy of the incoming photon , $ \text { e } \text { photon } $ , must be equal to the kinetic energy of the ejected electron , $ \text { ke } { \text { electron } } $ , plus the energy required to eject the electron from the metal . the energy required to free the electron from a particular metal is also called the metal 's work function , which is represented by the symbol $ \phi $ ( in units of $ \text j $ ) : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ like the threshold frequency $ \nu_0 $ , the value of $ \phi $ also changes depending on the metal . we can now write the energy of the photon in terms of the light frequency using planck 's equation : $ \text { e } \text { photon } =h\nu=\text { ke } \text { electron } +\phi $ rearranging this equation in terms of the electron 's kinetic energy , we get : $ \text { ke } _\text { electron } =h\nu-\phi $ we can see that kinetic energy of the photoelectron increases linearly with $ \nu $ as long as the photon energy is greater than the work function $ \phi $ , which is exactly the relationship shown in graph ( a ) above . we can also use this equation to find the photoelectron velocity $ \text v $ , which is related to $ \text { ke } _\text { electron } $ as follows : $ \text { ke } _\text { electron } =h\nu-\phi=\dfrac { 1 } { 2 } m_e\text v^2 $ where $ m_e $ is the rest mass of an electron , $ 9.1094 \times 10^ { -31 } \ , \text { kg } $ . exploring the wave amplitude trends in terms of photons , higher amplitude light means more photons hitting the metal surface . this results in more electrons ejected over a given time period . as long as the light frequency is greater than $ \nu_0 $ , increasing the light amplitude will cause the electron current to increase proportionally as shown in graph ( a ) below . since increasing the light amplitude has no effect on the energy of the incoming photon , the photoelectron kinetic energy remains constant as the light amplitude is increased ( see graph ( b ) above ) . if we try to explain this result using our dock-and-beach-balls analogy , the relationship in graph ( b ) indicates that no matter the height of the wave hitting the dock $ - $ whether it 's a tiny swell , or a huge tsunami $ - $ the individual beach balls would be launched off the dock with the exact same speed ! thus , our intuition and analogy do n't do a very good job of explaining these particular experiments . example $ 1 $ : the photoelectric effect for copper the work function of copper metal is $ \phi=7.53\times10^ { -19 } \text { j } $ . if we shine light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ on copper metal , will the photoelectric effect be observed ? in order to eject electrons , we need the energy of the photons to be greater than the work function of copper . we can use planck 's equation to calculate the energy of the photon , $ \text { e } _ { \text { photon } } $ : $ \begin { align } \text { e } _\text { photon } & amp ; = h\nu \ & amp ; = ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) ( 3.0\times10^ { 16 } \text { hz } ) ~~~~\text { plug in values for $ h $ and $ \nu $ } \ & amp ; = 2.0\times10^ { -17 } \text { j } \end { align } $ if we compare our calculated photon energy , $ \text { e } _\text { photon } $ , to copper 's work function , we see that the photon energy is greater than $ \phi $ : $ ~2.0\times10^ { -17 } \text { j } ~ & gt ; ~7.53\times10^ { -19 } \text { j } $ $ ~~~~~~~~\text { e } _\text { photon } ~~~~~~~~~~~~~~~~~~~\phi $ thus , we would expect to see photoelectrons ejected from the copper . next , we will calculate the kinetic energy of the photoelectrons . example $ 2 $ : calculating the kinetic energy of a photoelectron what is the kinetic energy of the photoelectrons ejected from the copper by the light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ ? we can calculate the kinetic energy of the photoelectron using the equation that relates $ \text { ke } \text { electron } $ to the energy of the photon , $ \text { e } \text { photon } $ , and the work function , $ \phi $ : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ since we want to know $ \text { ke } _\text { electron } $ , we can start by rearranging the equation so that we will be solving for the kinetic energy of the electron : $ \text { ke } \text { electron } =\text { e } \text { photon } -\phi $ now we can insert our known values for $ \text { e } _\text { photon } $ and $ \phi $ from example 1 : $ \text { ke } _\text { electron } = ( 2.0\times10^ { -17 } \text { j } ) - ( 7.53\times10^ { -19 } \text { j } ) =1.9\times10^ { -17 } \text { j } $ therefore , each photoelectron has a kinetic energy of $ 1.9\times10^ { -17 } \text { j } $ . summary based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a specific metal surface . the energy of the incident photon must be equal to the sum of the work function and the kinetic energy of a photoelectron : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ try it ! when we shine light with a frequency of $ 6.20 \times 10^ { 14 } \ , \text { hz } $ on a mystery metal , we observe the ejected electrons have a kinetic energy of $ 3.28\times 10^ { -20 } \ , \text j $ . some possible candidates for the mystery metal are shown in the table below : metal | work function $ \phi $ ( joules , $ \text j $ ) : - : | : - : calcium , $ \text { ca } $ | $ 4.60\times 10^ { -19 } $ tin , $ \text { sn } $ | $ 7.08\times 10^ { -19 } $ sodium , $ \text { na } $ | $ 3.78\times 10^ { -19 } $ hafnium , $ \text { hf } $ | $ 6.25\times 10^ { -19 } $ samarium , $ \text { sm } $ | $ 4.33\times 10^ { -19 } $ based on this information , what is the most likely identity of our mystery metal ?
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we can calculate the kinetic energy of the photoelectron using the equation that relates $ \text { ke } \text { electron } $ to the energy of the photon , $ \text { e } \text { photon } $ , and the work function , $ \phi $ : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ since we want to know $ \text { ke } _\text { electron } $ , we can start by rearranging the equation so that we will be solving for the kinetic energy of the electron : $ \text { ke } \text { electron } =\text { e } \text { photon } -\phi $ now we can insert our known values for $ \text { e } _\text { photon } $ and $ \phi $ from example 1 : $ \text { ke } _\text { electron } = ( 2.0\times10^ { -17 } \text { j } ) - ( 7.53\times10^ { -19 } \text { j } ) =1.9\times10^ { -17 } \text { j } $ therefore , each photoelectron has a kinetic energy of $ 1.9\times10^ { -17 } \text { j } $ . summary based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current .
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if the particles are moving faster , would n't that speed up the current ?
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key points based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . contrary to the predictions , experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of particles called photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a metal surface , and the value of $ \phi $ depends on the metal . the energy of the incident photon must be equal to the sum of the metal 's work function and the photoelectron kinetic energy : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ introduction : what is the photoelectric effect ? when light shines on a metal , electrons can be ejected from the surface of the metal in a phenomenon known as the photoelectric effect . this process is also often referred to as photoemission , and the electrons that are ejected from the metal are called photoelectrons . in terms of their behavior and their properties , photoelectrons are no different from other electrons . the prefix , photo- , simply tells us that the electrons have been ejected from a metal surface by incident light . in this article , we will discuss how 19th century physicists attempted ( but failed ! ) to explain the photoelectric effect using classical physics . this ultimately led to the development of the modern description of electromagnetic radiation , which has both wave-like and particle-like properties . predictions based on light as a wave to explain the photoelectric effect , 19th-century physicists theorized that the oscillating electric field of the incoming light wave was heating the electrons and causing them to vibrate , eventually freeing them from the metal surface . this hypothesis was based on the assumption that light traveled purely as a wave through space . ( see this article for more information about the basic properties of light . ) scientists also believed that the energy of the light wave was proportional to its brightness , which is related to the wave 's amplitude . in order to test their hypotheses , they performed experiments to look at the effect of light amplitude and frequency on the rate of electron ejection , as well as the kinetic energy of the photoelectrons . based on the classical description of light as a wave , they made the following predictions : the kinetic energy of emitted photoelectrons should increase with the light amplitude . the rate of electron emission , which is proportional to the measured electric current , should increase as the light frequency is increased . to help us understand why they made these predictions , we can compare a light wave to a water wave . imagine some beach balls sitting on a dock that extends out into the ocean . the dock represents a metal surface , the beach balls represent electrons , and the ocean waves represent light waves . if a single large wave were to shake the dock , we would expect the energy from the big wave would send the beach balls flying off the dock with much more kinetic energy compared to a single , small wave . this is also what physicists believed would happen if the light intensity was increased . light amplitude was expected to be proportional to the light energy , so higher amplitude light was predicted to result in photoelectrons with more kinetic energy . classical physicists also predicted that increasing the frequency of light waves ( at a constant amplitude ) would increase the rate of electrons being ejected , and thus increase the measured electric current . using our beach ball analogy , we would expect waves hitting the dock more frequently would result in more beach balls being knocked off the dock compared to the same sized waves hitting the dock less often . now that we know what physicists thought would happen , let 's look at what they actually observed experimentally ! when intuition fails : photons to the rescue ! when experiments were performed to look at the effect of light amplitude and frequency , the following results were observed : the kinetic energy of photoelectrons increases with light frequency . electric current remains constant as light frequency increases . electric current increases with light amplitude . the kinetic energy of photoelectrons remains constant as light amplitude increases . these results were completely at odds with the predictions based on the classical description of light as a wave ! in order to explain what was happening , it turned out that an entirely new model of light was needed . that model was developed by albert einstein , who proposed that light sometimes behaved as particles of electromagnetic energy which we now call photons . the energy of a photon could be calculated using planck 's equation : $ \text { e } _ { \text { photon } } =h\nu $ where $ \text { e } _ { \text { photon } } $ is the energy of a photon in joules ( $ \text { j } $ ) , $ h $ is planck 's constant $ ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) $ , and $ \nu $ is the frequency of the light in $ \text { hz } $ . according to planck 's equation , the energy of a photon is proportional to the frequency of the light , $ \nu $ . the amplitude of the light is then proportional to the number of photons with a given frequency . concept check : as the wavelength of a photon increases , what happens to the photon 's energy ? light frequency and the threshold frequency $ \nu_0 $ we can think of the incident light as a stream of photons with an energy determined by the light frequency . when a photon hits the metal surface , the photon 's energy is absorbed by an electron in the metal . the graphic below illustrates the relationship between light frequency and the kinetic energy of ejected electrons . the scientists observed that if the incident light had a frequency less than a minimum frequency $ \nu_0 $ , then no electrons were ejected regardless of the light amplitude . this minimum frequency is also called the threshold frequency , and the value of $ \nu_0 $ depends on the metal . for frequencies greater than $ \nu_0 $ , electrons would be ejected from the metal . furthermore , the kinetic energy of the photoelectrons was proportional to the light frequency . the relationship between photoelectron kinetic energy and light frequency is shown in graph ( a ) below . because the light amplitude was kept constant as the light frequency increased , the number of photons being absorbed by the metal remained constant . thus , the rate at which electrons were ejected from the metal ( or the electric current ) remained constant as well . the relationship between electron current and light frequency is illustrated in graph ( b ) above . is n't there more math somewhere ? we can analyze the frequency relationship using the law of conservation of energy . the total energy of the incoming photon , $ \text { e } \text { photon } $ , must be equal to the kinetic energy of the ejected electron , $ \text { ke } { \text { electron } } $ , plus the energy required to eject the electron from the metal . the energy required to free the electron from a particular metal is also called the metal 's work function , which is represented by the symbol $ \phi $ ( in units of $ \text j $ ) : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ like the threshold frequency $ \nu_0 $ , the value of $ \phi $ also changes depending on the metal . we can now write the energy of the photon in terms of the light frequency using planck 's equation : $ \text { e } \text { photon } =h\nu=\text { ke } \text { electron } +\phi $ rearranging this equation in terms of the electron 's kinetic energy , we get : $ \text { ke } _\text { electron } =h\nu-\phi $ we can see that kinetic energy of the photoelectron increases linearly with $ \nu $ as long as the photon energy is greater than the work function $ \phi $ , which is exactly the relationship shown in graph ( a ) above . we can also use this equation to find the photoelectron velocity $ \text v $ , which is related to $ \text { ke } _\text { electron } $ as follows : $ \text { ke } _\text { electron } =h\nu-\phi=\dfrac { 1 } { 2 } m_e\text v^2 $ where $ m_e $ is the rest mass of an electron , $ 9.1094 \times 10^ { -31 } \ , \text { kg } $ . exploring the wave amplitude trends in terms of photons , higher amplitude light means more photons hitting the metal surface . this results in more electrons ejected over a given time period . as long as the light frequency is greater than $ \nu_0 $ , increasing the light amplitude will cause the electron current to increase proportionally as shown in graph ( a ) below . since increasing the light amplitude has no effect on the energy of the incoming photon , the photoelectron kinetic energy remains constant as the light amplitude is increased ( see graph ( b ) above ) . if we try to explain this result using our dock-and-beach-balls analogy , the relationship in graph ( b ) indicates that no matter the height of the wave hitting the dock $ - $ whether it 's a tiny swell , or a huge tsunami $ - $ the individual beach balls would be launched off the dock with the exact same speed ! thus , our intuition and analogy do n't do a very good job of explaining these particular experiments . example $ 1 $ : the photoelectric effect for copper the work function of copper metal is $ \phi=7.53\times10^ { -19 } \text { j } $ . if we shine light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ on copper metal , will the photoelectric effect be observed ? in order to eject electrons , we need the energy of the photons to be greater than the work function of copper . we can use planck 's equation to calculate the energy of the photon , $ \text { e } _ { \text { photon } } $ : $ \begin { align } \text { e } _\text { photon } & amp ; = h\nu \ & amp ; = ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) ( 3.0\times10^ { 16 } \text { hz } ) ~~~~\text { plug in values for $ h $ and $ \nu $ } \ & amp ; = 2.0\times10^ { -17 } \text { j } \end { align } $ if we compare our calculated photon energy , $ \text { e } _\text { photon } $ , to copper 's work function , we see that the photon energy is greater than $ \phi $ : $ ~2.0\times10^ { -17 } \text { j } ~ & gt ; ~7.53\times10^ { -19 } \text { j } $ $ ~~~~~~~~\text { e } _\text { photon } ~~~~~~~~~~~~~~~~~~~\phi $ thus , we would expect to see photoelectrons ejected from the copper . next , we will calculate the kinetic energy of the photoelectrons . example $ 2 $ : calculating the kinetic energy of a photoelectron what is the kinetic energy of the photoelectrons ejected from the copper by the light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ ? we can calculate the kinetic energy of the photoelectron using the equation that relates $ \text { ke } \text { electron } $ to the energy of the photon , $ \text { e } \text { photon } $ , and the work function , $ \phi $ : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ since we want to know $ \text { ke } _\text { electron } $ , we can start by rearranging the equation so that we will be solving for the kinetic energy of the electron : $ \text { ke } \text { electron } =\text { e } \text { photon } -\phi $ now we can insert our known values for $ \text { e } _\text { photon } $ and $ \phi $ from example 1 : $ \text { ke } _\text { electron } = ( 2.0\times10^ { -17 } \text { j } ) - ( 7.53\times10^ { -19 } \text { j } ) =1.9\times10^ { -17 } \text { j } $ therefore , each photoelectron has a kinetic energy of $ 1.9\times10^ { -17 } \text { j } $ . summary based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a specific metal surface . the energy of the incident photon must be equal to the sum of the work function and the kinetic energy of a photoelectron : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ try it ! when we shine light with a frequency of $ 6.20 \times 10^ { 14 } \ , \text { hz } $ on a mystery metal , we observe the ejected electrons have a kinetic energy of $ 3.28\times 10^ { -20 } \ , \text j $ . some possible candidates for the mystery metal are shown in the table below : metal | work function $ \phi $ ( joules , $ \text j $ ) : - : | : - : calcium , $ \text { ca } $ | $ 4.60\times 10^ { -19 } $ tin , $ \text { sn } $ | $ 7.08\times 10^ { -19 } $ sodium , $ \text { na } $ | $ 3.78\times 10^ { -19 } $ hafnium , $ \text { hf } $ | $ 6.25\times 10^ { -19 } $ samarium , $ \text { sm } $ | $ 4.33\times 10^ { -19 } $ based on this information , what is the most likely identity of our mystery metal ?
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to explain the photoelectric effect using classical physics . this ultimately led to the development of the modern description of electromagnetic radiation , which has both wave-like and particle-like properties . predictions based on light as a wave to explain the photoelectric effect , 19th-century physicists theorized that the oscillating electric field of the incoming light wave was heating the electrons and causing them to vibrate , eventually freeing them from the metal surface .
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is a photon a wave-like particle ?
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key points based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . contrary to the predictions , experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of particles called photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a metal surface , and the value of $ \phi $ depends on the metal . the energy of the incident photon must be equal to the sum of the metal 's work function and the photoelectron kinetic energy : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ introduction : what is the photoelectric effect ? when light shines on a metal , electrons can be ejected from the surface of the metal in a phenomenon known as the photoelectric effect . this process is also often referred to as photoemission , and the electrons that are ejected from the metal are called photoelectrons . in terms of their behavior and their properties , photoelectrons are no different from other electrons . the prefix , photo- , simply tells us that the electrons have been ejected from a metal surface by incident light . in this article , we will discuss how 19th century physicists attempted ( but failed ! ) to explain the photoelectric effect using classical physics . this ultimately led to the development of the modern description of electromagnetic radiation , which has both wave-like and particle-like properties . predictions based on light as a wave to explain the photoelectric effect , 19th-century physicists theorized that the oscillating electric field of the incoming light wave was heating the electrons and causing them to vibrate , eventually freeing them from the metal surface . this hypothesis was based on the assumption that light traveled purely as a wave through space . ( see this article for more information about the basic properties of light . ) scientists also believed that the energy of the light wave was proportional to its brightness , which is related to the wave 's amplitude . in order to test their hypotheses , they performed experiments to look at the effect of light amplitude and frequency on the rate of electron ejection , as well as the kinetic energy of the photoelectrons . based on the classical description of light as a wave , they made the following predictions : the kinetic energy of emitted photoelectrons should increase with the light amplitude . the rate of electron emission , which is proportional to the measured electric current , should increase as the light frequency is increased . to help us understand why they made these predictions , we can compare a light wave to a water wave . imagine some beach balls sitting on a dock that extends out into the ocean . the dock represents a metal surface , the beach balls represent electrons , and the ocean waves represent light waves . if a single large wave were to shake the dock , we would expect the energy from the big wave would send the beach balls flying off the dock with much more kinetic energy compared to a single , small wave . this is also what physicists believed would happen if the light intensity was increased . light amplitude was expected to be proportional to the light energy , so higher amplitude light was predicted to result in photoelectrons with more kinetic energy . classical physicists also predicted that increasing the frequency of light waves ( at a constant amplitude ) would increase the rate of electrons being ejected , and thus increase the measured electric current . using our beach ball analogy , we would expect waves hitting the dock more frequently would result in more beach balls being knocked off the dock compared to the same sized waves hitting the dock less often . now that we know what physicists thought would happen , let 's look at what they actually observed experimentally ! when intuition fails : photons to the rescue ! when experiments were performed to look at the effect of light amplitude and frequency , the following results were observed : the kinetic energy of photoelectrons increases with light frequency . electric current remains constant as light frequency increases . electric current increases with light amplitude . the kinetic energy of photoelectrons remains constant as light amplitude increases . these results were completely at odds with the predictions based on the classical description of light as a wave ! in order to explain what was happening , it turned out that an entirely new model of light was needed . that model was developed by albert einstein , who proposed that light sometimes behaved as particles of electromagnetic energy which we now call photons . the energy of a photon could be calculated using planck 's equation : $ \text { e } _ { \text { photon } } =h\nu $ where $ \text { e } _ { \text { photon } } $ is the energy of a photon in joules ( $ \text { j } $ ) , $ h $ is planck 's constant $ ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) $ , and $ \nu $ is the frequency of the light in $ \text { hz } $ . according to planck 's equation , the energy of a photon is proportional to the frequency of the light , $ \nu $ . the amplitude of the light is then proportional to the number of photons with a given frequency . concept check : as the wavelength of a photon increases , what happens to the photon 's energy ? light frequency and the threshold frequency $ \nu_0 $ we can think of the incident light as a stream of photons with an energy determined by the light frequency . when a photon hits the metal surface , the photon 's energy is absorbed by an electron in the metal . the graphic below illustrates the relationship between light frequency and the kinetic energy of ejected electrons . the scientists observed that if the incident light had a frequency less than a minimum frequency $ \nu_0 $ , then no electrons were ejected regardless of the light amplitude . this minimum frequency is also called the threshold frequency , and the value of $ \nu_0 $ depends on the metal . for frequencies greater than $ \nu_0 $ , electrons would be ejected from the metal . furthermore , the kinetic energy of the photoelectrons was proportional to the light frequency . the relationship between photoelectron kinetic energy and light frequency is shown in graph ( a ) below . because the light amplitude was kept constant as the light frequency increased , the number of photons being absorbed by the metal remained constant . thus , the rate at which electrons were ejected from the metal ( or the electric current ) remained constant as well . the relationship between electron current and light frequency is illustrated in graph ( b ) above . is n't there more math somewhere ? we can analyze the frequency relationship using the law of conservation of energy . the total energy of the incoming photon , $ \text { e } \text { photon } $ , must be equal to the kinetic energy of the ejected electron , $ \text { ke } { \text { electron } } $ , plus the energy required to eject the electron from the metal . the energy required to free the electron from a particular metal is also called the metal 's work function , which is represented by the symbol $ \phi $ ( in units of $ \text j $ ) : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ like the threshold frequency $ \nu_0 $ , the value of $ \phi $ also changes depending on the metal . we can now write the energy of the photon in terms of the light frequency using planck 's equation : $ \text { e } \text { photon } =h\nu=\text { ke } \text { electron } +\phi $ rearranging this equation in terms of the electron 's kinetic energy , we get : $ \text { ke } _\text { electron } =h\nu-\phi $ we can see that kinetic energy of the photoelectron increases linearly with $ \nu $ as long as the photon energy is greater than the work function $ \phi $ , which is exactly the relationship shown in graph ( a ) above . we can also use this equation to find the photoelectron velocity $ \text v $ , which is related to $ \text { ke } _\text { electron } $ as follows : $ \text { ke } _\text { electron } =h\nu-\phi=\dfrac { 1 } { 2 } m_e\text v^2 $ where $ m_e $ is the rest mass of an electron , $ 9.1094 \times 10^ { -31 } \ , \text { kg } $ . exploring the wave amplitude trends in terms of photons , higher amplitude light means more photons hitting the metal surface . this results in more electrons ejected over a given time period . as long as the light frequency is greater than $ \nu_0 $ , increasing the light amplitude will cause the electron current to increase proportionally as shown in graph ( a ) below . since increasing the light amplitude has no effect on the energy of the incoming photon , the photoelectron kinetic energy remains constant as the light amplitude is increased ( see graph ( b ) above ) . if we try to explain this result using our dock-and-beach-balls analogy , the relationship in graph ( b ) indicates that no matter the height of the wave hitting the dock $ - $ whether it 's a tiny swell , or a huge tsunami $ - $ the individual beach balls would be launched off the dock with the exact same speed ! thus , our intuition and analogy do n't do a very good job of explaining these particular experiments . example $ 1 $ : the photoelectric effect for copper the work function of copper metal is $ \phi=7.53\times10^ { -19 } \text { j } $ . if we shine light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ on copper metal , will the photoelectric effect be observed ? in order to eject electrons , we need the energy of the photons to be greater than the work function of copper . we can use planck 's equation to calculate the energy of the photon , $ \text { e } _ { \text { photon } } $ : $ \begin { align } \text { e } _\text { photon } & amp ; = h\nu \ & amp ; = ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) ( 3.0\times10^ { 16 } \text { hz } ) ~~~~\text { plug in values for $ h $ and $ \nu $ } \ & amp ; = 2.0\times10^ { -17 } \text { j } \end { align } $ if we compare our calculated photon energy , $ \text { e } _\text { photon } $ , to copper 's work function , we see that the photon energy is greater than $ \phi $ : $ ~2.0\times10^ { -17 } \text { j } ~ & gt ; ~7.53\times10^ { -19 } \text { j } $ $ ~~~~~~~~\text { e } _\text { photon } ~~~~~~~~~~~~~~~~~~~\phi $ thus , we would expect to see photoelectrons ejected from the copper . next , we will calculate the kinetic energy of the photoelectrons . example $ 2 $ : calculating the kinetic energy of a photoelectron what is the kinetic energy of the photoelectrons ejected from the copper by the light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ ? we can calculate the kinetic energy of the photoelectron using the equation that relates $ \text { ke } \text { electron } $ to the energy of the photon , $ \text { e } \text { photon } $ , and the work function , $ \phi $ : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ since we want to know $ \text { ke } _\text { electron } $ , we can start by rearranging the equation so that we will be solving for the kinetic energy of the electron : $ \text { ke } \text { electron } =\text { e } \text { photon } -\phi $ now we can insert our known values for $ \text { e } _\text { photon } $ and $ \phi $ from example 1 : $ \text { ke } _\text { electron } = ( 2.0\times10^ { -17 } \text { j } ) - ( 7.53\times10^ { -19 } \text { j } ) =1.9\times10^ { -17 } \text { j } $ therefore , each photoelectron has a kinetic energy of $ 1.9\times10^ { -17 } \text { j } $ . summary based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a specific metal surface . the energy of the incident photon must be equal to the sum of the work function and the kinetic energy of a photoelectron : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ try it ! when we shine light with a frequency of $ 6.20 \times 10^ { 14 } \ , \text { hz } $ on a mystery metal , we observe the ejected electrons have a kinetic energy of $ 3.28\times 10^ { -20 } \ , \text j $ . some possible candidates for the mystery metal are shown in the table below : metal | work function $ \phi $ ( joules , $ \text j $ ) : - : | : - : calcium , $ \text { ca } $ | $ 4.60\times 10^ { -19 } $ tin , $ \text { sn } $ | $ 7.08\times 10^ { -19 } $ sodium , $ \text { na } $ | $ 3.78\times 10^ { -19 } $ hafnium , $ \text { hf } $ | $ 6.25\times 10^ { -19 } $ samarium , $ \text { sm } $ | $ 4.33\times 10^ { -19 } $ based on this information , what is the most likely identity of our mystery metal ?
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the relationship between electron current and light frequency is illustrated in graph ( b ) above . is n't there more math somewhere ? we can analyze the frequency relationship using the law of conservation of energy .
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so why do n't the metals in our home lose their electrons when we turn on the lights ?
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key points based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . contrary to the predictions , experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of particles called photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a metal surface , and the value of $ \phi $ depends on the metal . the energy of the incident photon must be equal to the sum of the metal 's work function and the photoelectron kinetic energy : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ introduction : what is the photoelectric effect ? when light shines on a metal , electrons can be ejected from the surface of the metal in a phenomenon known as the photoelectric effect . this process is also often referred to as photoemission , and the electrons that are ejected from the metal are called photoelectrons . in terms of their behavior and their properties , photoelectrons are no different from other electrons . the prefix , photo- , simply tells us that the electrons have been ejected from a metal surface by incident light . in this article , we will discuss how 19th century physicists attempted ( but failed ! ) to explain the photoelectric effect using classical physics . this ultimately led to the development of the modern description of electromagnetic radiation , which has both wave-like and particle-like properties . predictions based on light as a wave to explain the photoelectric effect , 19th-century physicists theorized that the oscillating electric field of the incoming light wave was heating the electrons and causing them to vibrate , eventually freeing them from the metal surface . this hypothesis was based on the assumption that light traveled purely as a wave through space . ( see this article for more information about the basic properties of light . ) scientists also believed that the energy of the light wave was proportional to its brightness , which is related to the wave 's amplitude . in order to test their hypotheses , they performed experiments to look at the effect of light amplitude and frequency on the rate of electron ejection , as well as the kinetic energy of the photoelectrons . based on the classical description of light as a wave , they made the following predictions : the kinetic energy of emitted photoelectrons should increase with the light amplitude . the rate of electron emission , which is proportional to the measured electric current , should increase as the light frequency is increased . to help us understand why they made these predictions , we can compare a light wave to a water wave . imagine some beach balls sitting on a dock that extends out into the ocean . the dock represents a metal surface , the beach balls represent electrons , and the ocean waves represent light waves . if a single large wave were to shake the dock , we would expect the energy from the big wave would send the beach balls flying off the dock with much more kinetic energy compared to a single , small wave . this is also what physicists believed would happen if the light intensity was increased . light amplitude was expected to be proportional to the light energy , so higher amplitude light was predicted to result in photoelectrons with more kinetic energy . classical physicists also predicted that increasing the frequency of light waves ( at a constant amplitude ) would increase the rate of electrons being ejected , and thus increase the measured electric current . using our beach ball analogy , we would expect waves hitting the dock more frequently would result in more beach balls being knocked off the dock compared to the same sized waves hitting the dock less often . now that we know what physicists thought would happen , let 's look at what they actually observed experimentally ! when intuition fails : photons to the rescue ! when experiments were performed to look at the effect of light amplitude and frequency , the following results were observed : the kinetic energy of photoelectrons increases with light frequency . electric current remains constant as light frequency increases . electric current increases with light amplitude . the kinetic energy of photoelectrons remains constant as light amplitude increases . these results were completely at odds with the predictions based on the classical description of light as a wave ! in order to explain what was happening , it turned out that an entirely new model of light was needed . that model was developed by albert einstein , who proposed that light sometimes behaved as particles of electromagnetic energy which we now call photons . the energy of a photon could be calculated using planck 's equation : $ \text { e } _ { \text { photon } } =h\nu $ where $ \text { e } _ { \text { photon } } $ is the energy of a photon in joules ( $ \text { j } $ ) , $ h $ is planck 's constant $ ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) $ , and $ \nu $ is the frequency of the light in $ \text { hz } $ . according to planck 's equation , the energy of a photon is proportional to the frequency of the light , $ \nu $ . the amplitude of the light is then proportional to the number of photons with a given frequency . concept check : as the wavelength of a photon increases , what happens to the photon 's energy ? light frequency and the threshold frequency $ \nu_0 $ we can think of the incident light as a stream of photons with an energy determined by the light frequency . when a photon hits the metal surface , the photon 's energy is absorbed by an electron in the metal . the graphic below illustrates the relationship between light frequency and the kinetic energy of ejected electrons . the scientists observed that if the incident light had a frequency less than a minimum frequency $ \nu_0 $ , then no electrons were ejected regardless of the light amplitude . this minimum frequency is also called the threshold frequency , and the value of $ \nu_0 $ depends on the metal . for frequencies greater than $ \nu_0 $ , electrons would be ejected from the metal . furthermore , the kinetic energy of the photoelectrons was proportional to the light frequency . the relationship between photoelectron kinetic energy and light frequency is shown in graph ( a ) below . because the light amplitude was kept constant as the light frequency increased , the number of photons being absorbed by the metal remained constant . thus , the rate at which electrons were ejected from the metal ( or the electric current ) remained constant as well . the relationship between electron current and light frequency is illustrated in graph ( b ) above . is n't there more math somewhere ? we can analyze the frequency relationship using the law of conservation of energy . the total energy of the incoming photon , $ \text { e } \text { photon } $ , must be equal to the kinetic energy of the ejected electron , $ \text { ke } { \text { electron } } $ , plus the energy required to eject the electron from the metal . the energy required to free the electron from a particular metal is also called the metal 's work function , which is represented by the symbol $ \phi $ ( in units of $ \text j $ ) : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ like the threshold frequency $ \nu_0 $ , the value of $ \phi $ also changes depending on the metal . we can now write the energy of the photon in terms of the light frequency using planck 's equation : $ \text { e } \text { photon } =h\nu=\text { ke } \text { electron } +\phi $ rearranging this equation in terms of the electron 's kinetic energy , we get : $ \text { ke } _\text { electron } =h\nu-\phi $ we can see that kinetic energy of the photoelectron increases linearly with $ \nu $ as long as the photon energy is greater than the work function $ \phi $ , which is exactly the relationship shown in graph ( a ) above . we can also use this equation to find the photoelectron velocity $ \text v $ , which is related to $ \text { ke } _\text { electron } $ as follows : $ \text { ke } _\text { electron } =h\nu-\phi=\dfrac { 1 } { 2 } m_e\text v^2 $ where $ m_e $ is the rest mass of an electron , $ 9.1094 \times 10^ { -31 } \ , \text { kg } $ . exploring the wave amplitude trends in terms of photons , higher amplitude light means more photons hitting the metal surface . this results in more electrons ejected over a given time period . as long as the light frequency is greater than $ \nu_0 $ , increasing the light amplitude will cause the electron current to increase proportionally as shown in graph ( a ) below . since increasing the light amplitude has no effect on the energy of the incoming photon , the photoelectron kinetic energy remains constant as the light amplitude is increased ( see graph ( b ) above ) . if we try to explain this result using our dock-and-beach-balls analogy , the relationship in graph ( b ) indicates that no matter the height of the wave hitting the dock $ - $ whether it 's a tiny swell , or a huge tsunami $ - $ the individual beach balls would be launched off the dock with the exact same speed ! thus , our intuition and analogy do n't do a very good job of explaining these particular experiments . example $ 1 $ : the photoelectric effect for copper the work function of copper metal is $ \phi=7.53\times10^ { -19 } \text { j } $ . if we shine light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ on copper metal , will the photoelectric effect be observed ? in order to eject electrons , we need the energy of the photons to be greater than the work function of copper . we can use planck 's equation to calculate the energy of the photon , $ \text { e } _ { \text { photon } } $ : $ \begin { align } \text { e } _\text { photon } & amp ; = h\nu \ & amp ; = ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) ( 3.0\times10^ { 16 } \text { hz } ) ~~~~\text { plug in values for $ h $ and $ \nu $ } \ & amp ; = 2.0\times10^ { -17 } \text { j } \end { align } $ if we compare our calculated photon energy , $ \text { e } _\text { photon } $ , to copper 's work function , we see that the photon energy is greater than $ \phi $ : $ ~2.0\times10^ { -17 } \text { j } ~ & gt ; ~7.53\times10^ { -19 } \text { j } $ $ ~~~~~~~~\text { e } _\text { photon } ~~~~~~~~~~~~~~~~~~~\phi $ thus , we would expect to see photoelectrons ejected from the copper . next , we will calculate the kinetic energy of the photoelectrons . example $ 2 $ : calculating the kinetic energy of a photoelectron what is the kinetic energy of the photoelectrons ejected from the copper by the light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ ? we can calculate the kinetic energy of the photoelectron using the equation that relates $ \text { ke } \text { electron } $ to the energy of the photon , $ \text { e } \text { photon } $ , and the work function , $ \phi $ : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ since we want to know $ \text { ke } _\text { electron } $ , we can start by rearranging the equation so that we will be solving for the kinetic energy of the electron : $ \text { ke } \text { electron } =\text { e } \text { photon } -\phi $ now we can insert our known values for $ \text { e } _\text { photon } $ and $ \phi $ from example 1 : $ \text { ke } _\text { electron } = ( 2.0\times10^ { -17 } \text { j } ) - ( 7.53\times10^ { -19 } \text { j } ) =1.9\times10^ { -17 } \text { j } $ therefore , each photoelectron has a kinetic energy of $ 1.9\times10^ { -17 } \text { j } $ . summary based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a specific metal surface . the energy of the incident photon must be equal to the sum of the work function and the kinetic energy of a photoelectron : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ try it ! when we shine light with a frequency of $ 6.20 \times 10^ { 14 } \ , \text { hz } $ on a mystery metal , we observe the ejected electrons have a kinetic energy of $ 3.28\times 10^ { -20 } \ , \text j $ . some possible candidates for the mystery metal are shown in the table below : metal | work function $ \phi $ ( joules , $ \text j $ ) : - : | : - : calcium , $ \text { ca } $ | $ 4.60\times 10^ { -19 } $ tin , $ \text { sn } $ | $ 7.08\times 10^ { -19 } $ sodium , $ \text { na } $ | $ 3.78\times 10^ { -19 } $ hafnium , $ \text { hf } $ | $ 6.25\times 10^ { -19 } $ samarium , $ \text { sm } $ | $ 4.33\times 10^ { -19 } $ based on this information , what is the most likely identity of our mystery metal ?
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when experiments were performed to look at the effect of light amplitude and frequency , the following results were observed : the kinetic energy of photoelectrons increases with light frequency . electric current remains constant as light frequency increases . electric current increases with light amplitude . the kinetic energy of photoelectrons remains constant as light amplitude increases .
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what is current of electrons ?
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key points based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . contrary to the predictions , experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of particles called photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a metal surface , and the value of $ \phi $ depends on the metal . the energy of the incident photon must be equal to the sum of the metal 's work function and the photoelectron kinetic energy : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ introduction : what is the photoelectric effect ? when light shines on a metal , electrons can be ejected from the surface of the metal in a phenomenon known as the photoelectric effect . this process is also often referred to as photoemission , and the electrons that are ejected from the metal are called photoelectrons . in terms of their behavior and their properties , photoelectrons are no different from other electrons . the prefix , photo- , simply tells us that the electrons have been ejected from a metal surface by incident light . in this article , we will discuss how 19th century physicists attempted ( but failed ! ) to explain the photoelectric effect using classical physics . this ultimately led to the development of the modern description of electromagnetic radiation , which has both wave-like and particle-like properties . predictions based on light as a wave to explain the photoelectric effect , 19th-century physicists theorized that the oscillating electric field of the incoming light wave was heating the electrons and causing them to vibrate , eventually freeing them from the metal surface . this hypothesis was based on the assumption that light traveled purely as a wave through space . ( see this article for more information about the basic properties of light . ) scientists also believed that the energy of the light wave was proportional to its brightness , which is related to the wave 's amplitude . in order to test their hypotheses , they performed experiments to look at the effect of light amplitude and frequency on the rate of electron ejection , as well as the kinetic energy of the photoelectrons . based on the classical description of light as a wave , they made the following predictions : the kinetic energy of emitted photoelectrons should increase with the light amplitude . the rate of electron emission , which is proportional to the measured electric current , should increase as the light frequency is increased . to help us understand why they made these predictions , we can compare a light wave to a water wave . imagine some beach balls sitting on a dock that extends out into the ocean . the dock represents a metal surface , the beach balls represent electrons , and the ocean waves represent light waves . if a single large wave were to shake the dock , we would expect the energy from the big wave would send the beach balls flying off the dock with much more kinetic energy compared to a single , small wave . this is also what physicists believed would happen if the light intensity was increased . light amplitude was expected to be proportional to the light energy , so higher amplitude light was predicted to result in photoelectrons with more kinetic energy . classical physicists also predicted that increasing the frequency of light waves ( at a constant amplitude ) would increase the rate of electrons being ejected , and thus increase the measured electric current . using our beach ball analogy , we would expect waves hitting the dock more frequently would result in more beach balls being knocked off the dock compared to the same sized waves hitting the dock less often . now that we know what physicists thought would happen , let 's look at what they actually observed experimentally ! when intuition fails : photons to the rescue ! when experiments were performed to look at the effect of light amplitude and frequency , the following results were observed : the kinetic energy of photoelectrons increases with light frequency . electric current remains constant as light frequency increases . electric current increases with light amplitude . the kinetic energy of photoelectrons remains constant as light amplitude increases . these results were completely at odds with the predictions based on the classical description of light as a wave ! in order to explain what was happening , it turned out that an entirely new model of light was needed . that model was developed by albert einstein , who proposed that light sometimes behaved as particles of electromagnetic energy which we now call photons . the energy of a photon could be calculated using planck 's equation : $ \text { e } _ { \text { photon } } =h\nu $ where $ \text { e } _ { \text { photon } } $ is the energy of a photon in joules ( $ \text { j } $ ) , $ h $ is planck 's constant $ ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) $ , and $ \nu $ is the frequency of the light in $ \text { hz } $ . according to planck 's equation , the energy of a photon is proportional to the frequency of the light , $ \nu $ . the amplitude of the light is then proportional to the number of photons with a given frequency . concept check : as the wavelength of a photon increases , what happens to the photon 's energy ? light frequency and the threshold frequency $ \nu_0 $ we can think of the incident light as a stream of photons with an energy determined by the light frequency . when a photon hits the metal surface , the photon 's energy is absorbed by an electron in the metal . the graphic below illustrates the relationship between light frequency and the kinetic energy of ejected electrons . the scientists observed that if the incident light had a frequency less than a minimum frequency $ \nu_0 $ , then no electrons were ejected regardless of the light amplitude . this minimum frequency is also called the threshold frequency , and the value of $ \nu_0 $ depends on the metal . for frequencies greater than $ \nu_0 $ , electrons would be ejected from the metal . furthermore , the kinetic energy of the photoelectrons was proportional to the light frequency . the relationship between photoelectron kinetic energy and light frequency is shown in graph ( a ) below . because the light amplitude was kept constant as the light frequency increased , the number of photons being absorbed by the metal remained constant . thus , the rate at which electrons were ejected from the metal ( or the electric current ) remained constant as well . the relationship between electron current and light frequency is illustrated in graph ( b ) above . is n't there more math somewhere ? we can analyze the frequency relationship using the law of conservation of energy . the total energy of the incoming photon , $ \text { e } \text { photon } $ , must be equal to the kinetic energy of the ejected electron , $ \text { ke } { \text { electron } } $ , plus the energy required to eject the electron from the metal . the energy required to free the electron from a particular metal is also called the metal 's work function , which is represented by the symbol $ \phi $ ( in units of $ \text j $ ) : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ like the threshold frequency $ \nu_0 $ , the value of $ \phi $ also changes depending on the metal . we can now write the energy of the photon in terms of the light frequency using planck 's equation : $ \text { e } \text { photon } =h\nu=\text { ke } \text { electron } +\phi $ rearranging this equation in terms of the electron 's kinetic energy , we get : $ \text { ke } _\text { electron } =h\nu-\phi $ we can see that kinetic energy of the photoelectron increases linearly with $ \nu $ as long as the photon energy is greater than the work function $ \phi $ , which is exactly the relationship shown in graph ( a ) above . we can also use this equation to find the photoelectron velocity $ \text v $ , which is related to $ \text { ke } _\text { electron } $ as follows : $ \text { ke } _\text { electron } =h\nu-\phi=\dfrac { 1 } { 2 } m_e\text v^2 $ where $ m_e $ is the rest mass of an electron , $ 9.1094 \times 10^ { -31 } \ , \text { kg } $ . exploring the wave amplitude trends in terms of photons , higher amplitude light means more photons hitting the metal surface . this results in more electrons ejected over a given time period . as long as the light frequency is greater than $ \nu_0 $ , increasing the light amplitude will cause the electron current to increase proportionally as shown in graph ( a ) below . since increasing the light amplitude has no effect on the energy of the incoming photon , the photoelectron kinetic energy remains constant as the light amplitude is increased ( see graph ( b ) above ) . if we try to explain this result using our dock-and-beach-balls analogy , the relationship in graph ( b ) indicates that no matter the height of the wave hitting the dock $ - $ whether it 's a tiny swell , or a huge tsunami $ - $ the individual beach balls would be launched off the dock with the exact same speed ! thus , our intuition and analogy do n't do a very good job of explaining these particular experiments . example $ 1 $ : the photoelectric effect for copper the work function of copper metal is $ \phi=7.53\times10^ { -19 } \text { j } $ . if we shine light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ on copper metal , will the photoelectric effect be observed ? in order to eject electrons , we need the energy of the photons to be greater than the work function of copper . we can use planck 's equation to calculate the energy of the photon , $ \text { e } _ { \text { photon } } $ : $ \begin { align } \text { e } _\text { photon } & amp ; = h\nu \ & amp ; = ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) ( 3.0\times10^ { 16 } \text { hz } ) ~~~~\text { plug in values for $ h $ and $ \nu $ } \ & amp ; = 2.0\times10^ { -17 } \text { j } \end { align } $ if we compare our calculated photon energy , $ \text { e } _\text { photon } $ , to copper 's work function , we see that the photon energy is greater than $ \phi $ : $ ~2.0\times10^ { -17 } \text { j } ~ & gt ; ~7.53\times10^ { -19 } \text { j } $ $ ~~~~~~~~\text { e } _\text { photon } ~~~~~~~~~~~~~~~~~~~\phi $ thus , we would expect to see photoelectrons ejected from the copper . next , we will calculate the kinetic energy of the photoelectrons . example $ 2 $ : calculating the kinetic energy of a photoelectron what is the kinetic energy of the photoelectrons ejected from the copper by the light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ ? we can calculate the kinetic energy of the photoelectron using the equation that relates $ \text { ke } \text { electron } $ to the energy of the photon , $ \text { e } \text { photon } $ , and the work function , $ \phi $ : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ since we want to know $ \text { ke } _\text { electron } $ , we can start by rearranging the equation so that we will be solving for the kinetic energy of the electron : $ \text { ke } \text { electron } =\text { e } \text { photon } -\phi $ now we can insert our known values for $ \text { e } _\text { photon } $ and $ \phi $ from example 1 : $ \text { ke } _\text { electron } = ( 2.0\times10^ { -17 } \text { j } ) - ( 7.53\times10^ { -19 } \text { j } ) =1.9\times10^ { -17 } \text { j } $ therefore , each photoelectron has a kinetic energy of $ 1.9\times10^ { -17 } \text { j } $ . summary based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a specific metal surface . the energy of the incident photon must be equal to the sum of the work function and the kinetic energy of a photoelectron : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ try it ! when we shine light with a frequency of $ 6.20 \times 10^ { 14 } \ , \text { hz } $ on a mystery metal , we observe the ejected electrons have a kinetic energy of $ 3.28\times 10^ { -20 } \ , \text j $ . some possible candidates for the mystery metal are shown in the table below : metal | work function $ \phi $ ( joules , $ \text j $ ) : - : | : - : calcium , $ \text { ca } $ | $ 4.60\times 10^ { -19 } $ tin , $ \text { sn } $ | $ 7.08\times 10^ { -19 } $ sodium , $ \text { na } $ | $ 3.78\times 10^ { -19 } $ hafnium , $ \text { hf } $ | $ 6.25\times 10^ { -19 } $ samarium , $ \text { sm } $ | $ 4.33\times 10^ { -19 } $ based on this information , what is the most likely identity of our mystery metal ?
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light frequency and the threshold frequency $ \nu_0 $ we can think of the incident light as a stream of photons with an energy determined by the light frequency . when a photon hits the metal surface , the photon 's energy is absorbed by an electron in the metal . the graphic below illustrates the relationship between light frequency and the kinetic energy of ejected electrons .
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what will happen if the energy of the photon is just equal to the work function of the metal ?
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key points based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . contrary to the predictions , experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of particles called photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a metal surface , and the value of $ \phi $ depends on the metal . the energy of the incident photon must be equal to the sum of the metal 's work function and the photoelectron kinetic energy : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ introduction : what is the photoelectric effect ? when light shines on a metal , electrons can be ejected from the surface of the metal in a phenomenon known as the photoelectric effect . this process is also often referred to as photoemission , and the electrons that are ejected from the metal are called photoelectrons . in terms of their behavior and their properties , photoelectrons are no different from other electrons . the prefix , photo- , simply tells us that the electrons have been ejected from a metal surface by incident light . in this article , we will discuss how 19th century physicists attempted ( but failed ! ) to explain the photoelectric effect using classical physics . this ultimately led to the development of the modern description of electromagnetic radiation , which has both wave-like and particle-like properties . predictions based on light as a wave to explain the photoelectric effect , 19th-century physicists theorized that the oscillating electric field of the incoming light wave was heating the electrons and causing them to vibrate , eventually freeing them from the metal surface . this hypothesis was based on the assumption that light traveled purely as a wave through space . ( see this article for more information about the basic properties of light . ) scientists also believed that the energy of the light wave was proportional to its brightness , which is related to the wave 's amplitude . in order to test their hypotheses , they performed experiments to look at the effect of light amplitude and frequency on the rate of electron ejection , as well as the kinetic energy of the photoelectrons . based on the classical description of light as a wave , they made the following predictions : the kinetic energy of emitted photoelectrons should increase with the light amplitude . the rate of electron emission , which is proportional to the measured electric current , should increase as the light frequency is increased . to help us understand why they made these predictions , we can compare a light wave to a water wave . imagine some beach balls sitting on a dock that extends out into the ocean . the dock represents a metal surface , the beach balls represent electrons , and the ocean waves represent light waves . if a single large wave were to shake the dock , we would expect the energy from the big wave would send the beach balls flying off the dock with much more kinetic energy compared to a single , small wave . this is also what physicists believed would happen if the light intensity was increased . light amplitude was expected to be proportional to the light energy , so higher amplitude light was predicted to result in photoelectrons with more kinetic energy . classical physicists also predicted that increasing the frequency of light waves ( at a constant amplitude ) would increase the rate of electrons being ejected , and thus increase the measured electric current . using our beach ball analogy , we would expect waves hitting the dock more frequently would result in more beach balls being knocked off the dock compared to the same sized waves hitting the dock less often . now that we know what physicists thought would happen , let 's look at what they actually observed experimentally ! when intuition fails : photons to the rescue ! when experiments were performed to look at the effect of light amplitude and frequency , the following results were observed : the kinetic energy of photoelectrons increases with light frequency . electric current remains constant as light frequency increases . electric current increases with light amplitude . the kinetic energy of photoelectrons remains constant as light amplitude increases . these results were completely at odds with the predictions based on the classical description of light as a wave ! in order to explain what was happening , it turned out that an entirely new model of light was needed . that model was developed by albert einstein , who proposed that light sometimes behaved as particles of electromagnetic energy which we now call photons . the energy of a photon could be calculated using planck 's equation : $ \text { e } _ { \text { photon } } =h\nu $ where $ \text { e } _ { \text { photon } } $ is the energy of a photon in joules ( $ \text { j } $ ) , $ h $ is planck 's constant $ ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) $ , and $ \nu $ is the frequency of the light in $ \text { hz } $ . according to planck 's equation , the energy of a photon is proportional to the frequency of the light , $ \nu $ . the amplitude of the light is then proportional to the number of photons with a given frequency . concept check : as the wavelength of a photon increases , what happens to the photon 's energy ? light frequency and the threshold frequency $ \nu_0 $ we can think of the incident light as a stream of photons with an energy determined by the light frequency . when a photon hits the metal surface , the photon 's energy is absorbed by an electron in the metal . the graphic below illustrates the relationship between light frequency and the kinetic energy of ejected electrons . the scientists observed that if the incident light had a frequency less than a minimum frequency $ \nu_0 $ , then no electrons were ejected regardless of the light amplitude . this minimum frequency is also called the threshold frequency , and the value of $ \nu_0 $ depends on the metal . for frequencies greater than $ \nu_0 $ , electrons would be ejected from the metal . furthermore , the kinetic energy of the photoelectrons was proportional to the light frequency . the relationship between photoelectron kinetic energy and light frequency is shown in graph ( a ) below . because the light amplitude was kept constant as the light frequency increased , the number of photons being absorbed by the metal remained constant . thus , the rate at which electrons were ejected from the metal ( or the electric current ) remained constant as well . the relationship between electron current and light frequency is illustrated in graph ( b ) above . is n't there more math somewhere ? we can analyze the frequency relationship using the law of conservation of energy . the total energy of the incoming photon , $ \text { e } \text { photon } $ , must be equal to the kinetic energy of the ejected electron , $ \text { ke } { \text { electron } } $ , plus the energy required to eject the electron from the metal . the energy required to free the electron from a particular metal is also called the metal 's work function , which is represented by the symbol $ \phi $ ( in units of $ \text j $ ) : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ like the threshold frequency $ \nu_0 $ , the value of $ \phi $ also changes depending on the metal . we can now write the energy of the photon in terms of the light frequency using planck 's equation : $ \text { e } \text { photon } =h\nu=\text { ke } \text { electron } +\phi $ rearranging this equation in terms of the electron 's kinetic energy , we get : $ \text { ke } _\text { electron } =h\nu-\phi $ we can see that kinetic energy of the photoelectron increases linearly with $ \nu $ as long as the photon energy is greater than the work function $ \phi $ , which is exactly the relationship shown in graph ( a ) above . we can also use this equation to find the photoelectron velocity $ \text v $ , which is related to $ \text { ke } _\text { electron } $ as follows : $ \text { ke } _\text { electron } =h\nu-\phi=\dfrac { 1 } { 2 } m_e\text v^2 $ where $ m_e $ is the rest mass of an electron , $ 9.1094 \times 10^ { -31 } \ , \text { kg } $ . exploring the wave amplitude trends in terms of photons , higher amplitude light means more photons hitting the metal surface . this results in more electrons ejected over a given time period . as long as the light frequency is greater than $ \nu_0 $ , increasing the light amplitude will cause the electron current to increase proportionally as shown in graph ( a ) below . since increasing the light amplitude has no effect on the energy of the incoming photon , the photoelectron kinetic energy remains constant as the light amplitude is increased ( see graph ( b ) above ) . if we try to explain this result using our dock-and-beach-balls analogy , the relationship in graph ( b ) indicates that no matter the height of the wave hitting the dock $ - $ whether it 's a tiny swell , or a huge tsunami $ - $ the individual beach balls would be launched off the dock with the exact same speed ! thus , our intuition and analogy do n't do a very good job of explaining these particular experiments . example $ 1 $ : the photoelectric effect for copper the work function of copper metal is $ \phi=7.53\times10^ { -19 } \text { j } $ . if we shine light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ on copper metal , will the photoelectric effect be observed ? in order to eject electrons , we need the energy of the photons to be greater than the work function of copper . we can use planck 's equation to calculate the energy of the photon , $ \text { e } _ { \text { photon } } $ : $ \begin { align } \text { e } _\text { photon } & amp ; = h\nu \ & amp ; = ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) ( 3.0\times10^ { 16 } \text { hz } ) ~~~~\text { plug in values for $ h $ and $ \nu $ } \ & amp ; = 2.0\times10^ { -17 } \text { j } \end { align } $ if we compare our calculated photon energy , $ \text { e } _\text { photon } $ , to copper 's work function , we see that the photon energy is greater than $ \phi $ : $ ~2.0\times10^ { -17 } \text { j } ~ & gt ; ~7.53\times10^ { -19 } \text { j } $ $ ~~~~~~~~\text { e } _\text { photon } ~~~~~~~~~~~~~~~~~~~\phi $ thus , we would expect to see photoelectrons ejected from the copper . next , we will calculate the kinetic energy of the photoelectrons . example $ 2 $ : calculating the kinetic energy of a photoelectron what is the kinetic energy of the photoelectrons ejected from the copper by the light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ ? we can calculate the kinetic energy of the photoelectron using the equation that relates $ \text { ke } \text { electron } $ to the energy of the photon , $ \text { e } \text { photon } $ , and the work function , $ \phi $ : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ since we want to know $ \text { ke } _\text { electron } $ , we can start by rearranging the equation so that we will be solving for the kinetic energy of the electron : $ \text { ke } \text { electron } =\text { e } \text { photon } -\phi $ now we can insert our known values for $ \text { e } _\text { photon } $ and $ \phi $ from example 1 : $ \text { ke } _\text { electron } = ( 2.0\times10^ { -17 } \text { j } ) - ( 7.53\times10^ { -19 } \text { j } ) =1.9\times10^ { -17 } \text { j } $ therefore , each photoelectron has a kinetic energy of $ 1.9\times10^ { -17 } \text { j } $ . summary based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a specific metal surface . the energy of the incident photon must be equal to the sum of the work function and the kinetic energy of a photoelectron : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ try it ! when we shine light with a frequency of $ 6.20 \times 10^ { 14 } \ , \text { hz } $ on a mystery metal , we observe the ejected electrons have a kinetic energy of $ 3.28\times 10^ { -20 } \ , \text j $ . some possible candidates for the mystery metal are shown in the table below : metal | work function $ \phi $ ( joules , $ \text j $ ) : - : | : - : calcium , $ \text { ca } $ | $ 4.60\times 10^ { -19 } $ tin , $ \text { sn } $ | $ 7.08\times 10^ { -19 } $ sodium , $ \text { na } $ | $ 3.78\times 10^ { -19 } $ hafnium , $ \text { hf } $ | $ 6.25\times 10^ { -19 } $ samarium , $ \text { sm } $ | $ 4.33\times 10^ { -19 } $ based on this information , what is the most likely identity of our mystery metal ?
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we can analyze the frequency relationship using the law of conservation of energy . the total energy of the incoming photon , $ \text { e } \text { photon } $ , must be equal to the kinetic energy of the ejected electron , $ \text { ke } { \text { electron } } $ , plus the energy required to eject the electron from the metal . the energy required to free the electron from a particular metal is also called the metal 's work function , which is represented by the symbol $ \phi $ ( in units of $ \text j $ ) : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ like the threshold frequency $ \nu_0 $ , the value of $ \phi $ also changes depending on the metal .
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will the electron be pulled back in the orbit of the atom ?
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key points based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . contrary to the predictions , experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of particles called photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a metal surface , and the value of $ \phi $ depends on the metal . the energy of the incident photon must be equal to the sum of the metal 's work function and the photoelectron kinetic energy : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ introduction : what is the photoelectric effect ? when light shines on a metal , electrons can be ejected from the surface of the metal in a phenomenon known as the photoelectric effect . this process is also often referred to as photoemission , and the electrons that are ejected from the metal are called photoelectrons . in terms of their behavior and their properties , photoelectrons are no different from other electrons . the prefix , photo- , simply tells us that the electrons have been ejected from a metal surface by incident light . in this article , we will discuss how 19th century physicists attempted ( but failed ! ) to explain the photoelectric effect using classical physics . this ultimately led to the development of the modern description of electromagnetic radiation , which has both wave-like and particle-like properties . predictions based on light as a wave to explain the photoelectric effect , 19th-century physicists theorized that the oscillating electric field of the incoming light wave was heating the electrons and causing them to vibrate , eventually freeing them from the metal surface . this hypothesis was based on the assumption that light traveled purely as a wave through space . ( see this article for more information about the basic properties of light . ) scientists also believed that the energy of the light wave was proportional to its brightness , which is related to the wave 's amplitude . in order to test their hypotheses , they performed experiments to look at the effect of light amplitude and frequency on the rate of electron ejection , as well as the kinetic energy of the photoelectrons . based on the classical description of light as a wave , they made the following predictions : the kinetic energy of emitted photoelectrons should increase with the light amplitude . the rate of electron emission , which is proportional to the measured electric current , should increase as the light frequency is increased . to help us understand why they made these predictions , we can compare a light wave to a water wave . imagine some beach balls sitting on a dock that extends out into the ocean . the dock represents a metal surface , the beach balls represent electrons , and the ocean waves represent light waves . if a single large wave were to shake the dock , we would expect the energy from the big wave would send the beach balls flying off the dock with much more kinetic energy compared to a single , small wave . this is also what physicists believed would happen if the light intensity was increased . light amplitude was expected to be proportional to the light energy , so higher amplitude light was predicted to result in photoelectrons with more kinetic energy . classical physicists also predicted that increasing the frequency of light waves ( at a constant amplitude ) would increase the rate of electrons being ejected , and thus increase the measured electric current . using our beach ball analogy , we would expect waves hitting the dock more frequently would result in more beach balls being knocked off the dock compared to the same sized waves hitting the dock less often . now that we know what physicists thought would happen , let 's look at what they actually observed experimentally ! when intuition fails : photons to the rescue ! when experiments were performed to look at the effect of light amplitude and frequency , the following results were observed : the kinetic energy of photoelectrons increases with light frequency . electric current remains constant as light frequency increases . electric current increases with light amplitude . the kinetic energy of photoelectrons remains constant as light amplitude increases . these results were completely at odds with the predictions based on the classical description of light as a wave ! in order to explain what was happening , it turned out that an entirely new model of light was needed . that model was developed by albert einstein , who proposed that light sometimes behaved as particles of electromagnetic energy which we now call photons . the energy of a photon could be calculated using planck 's equation : $ \text { e } _ { \text { photon } } =h\nu $ where $ \text { e } _ { \text { photon } } $ is the energy of a photon in joules ( $ \text { j } $ ) , $ h $ is planck 's constant $ ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) $ , and $ \nu $ is the frequency of the light in $ \text { hz } $ . according to planck 's equation , the energy of a photon is proportional to the frequency of the light , $ \nu $ . the amplitude of the light is then proportional to the number of photons with a given frequency . concept check : as the wavelength of a photon increases , what happens to the photon 's energy ? light frequency and the threshold frequency $ \nu_0 $ we can think of the incident light as a stream of photons with an energy determined by the light frequency . when a photon hits the metal surface , the photon 's energy is absorbed by an electron in the metal . the graphic below illustrates the relationship between light frequency and the kinetic energy of ejected electrons . the scientists observed that if the incident light had a frequency less than a minimum frequency $ \nu_0 $ , then no electrons were ejected regardless of the light amplitude . this minimum frequency is also called the threshold frequency , and the value of $ \nu_0 $ depends on the metal . for frequencies greater than $ \nu_0 $ , electrons would be ejected from the metal . furthermore , the kinetic energy of the photoelectrons was proportional to the light frequency . the relationship between photoelectron kinetic energy and light frequency is shown in graph ( a ) below . because the light amplitude was kept constant as the light frequency increased , the number of photons being absorbed by the metal remained constant . thus , the rate at which electrons were ejected from the metal ( or the electric current ) remained constant as well . the relationship between electron current and light frequency is illustrated in graph ( b ) above . is n't there more math somewhere ? we can analyze the frequency relationship using the law of conservation of energy . the total energy of the incoming photon , $ \text { e } \text { photon } $ , must be equal to the kinetic energy of the ejected electron , $ \text { ke } { \text { electron } } $ , plus the energy required to eject the electron from the metal . the energy required to free the electron from a particular metal is also called the metal 's work function , which is represented by the symbol $ \phi $ ( in units of $ \text j $ ) : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ like the threshold frequency $ \nu_0 $ , the value of $ \phi $ also changes depending on the metal . we can now write the energy of the photon in terms of the light frequency using planck 's equation : $ \text { e } \text { photon } =h\nu=\text { ke } \text { electron } +\phi $ rearranging this equation in terms of the electron 's kinetic energy , we get : $ \text { ke } _\text { electron } =h\nu-\phi $ we can see that kinetic energy of the photoelectron increases linearly with $ \nu $ as long as the photon energy is greater than the work function $ \phi $ , which is exactly the relationship shown in graph ( a ) above . we can also use this equation to find the photoelectron velocity $ \text v $ , which is related to $ \text { ke } _\text { electron } $ as follows : $ \text { ke } _\text { electron } =h\nu-\phi=\dfrac { 1 } { 2 } m_e\text v^2 $ where $ m_e $ is the rest mass of an electron , $ 9.1094 \times 10^ { -31 } \ , \text { kg } $ . exploring the wave amplitude trends in terms of photons , higher amplitude light means more photons hitting the metal surface . this results in more electrons ejected over a given time period . as long as the light frequency is greater than $ \nu_0 $ , increasing the light amplitude will cause the electron current to increase proportionally as shown in graph ( a ) below . since increasing the light amplitude has no effect on the energy of the incoming photon , the photoelectron kinetic energy remains constant as the light amplitude is increased ( see graph ( b ) above ) . if we try to explain this result using our dock-and-beach-balls analogy , the relationship in graph ( b ) indicates that no matter the height of the wave hitting the dock $ - $ whether it 's a tiny swell , or a huge tsunami $ - $ the individual beach balls would be launched off the dock with the exact same speed ! thus , our intuition and analogy do n't do a very good job of explaining these particular experiments . example $ 1 $ : the photoelectric effect for copper the work function of copper metal is $ \phi=7.53\times10^ { -19 } \text { j } $ . if we shine light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ on copper metal , will the photoelectric effect be observed ? in order to eject electrons , we need the energy of the photons to be greater than the work function of copper . we can use planck 's equation to calculate the energy of the photon , $ \text { e } _ { \text { photon } } $ : $ \begin { align } \text { e } _\text { photon } & amp ; = h\nu \ & amp ; = ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) ( 3.0\times10^ { 16 } \text { hz } ) ~~~~\text { plug in values for $ h $ and $ \nu $ } \ & amp ; = 2.0\times10^ { -17 } \text { j } \end { align } $ if we compare our calculated photon energy , $ \text { e } _\text { photon } $ , to copper 's work function , we see that the photon energy is greater than $ \phi $ : $ ~2.0\times10^ { -17 } \text { j } ~ & gt ; ~7.53\times10^ { -19 } \text { j } $ $ ~~~~~~~~\text { e } _\text { photon } ~~~~~~~~~~~~~~~~~~~\phi $ thus , we would expect to see photoelectrons ejected from the copper . next , we will calculate the kinetic energy of the photoelectrons . example $ 2 $ : calculating the kinetic energy of a photoelectron what is the kinetic energy of the photoelectrons ejected from the copper by the light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ ? we can calculate the kinetic energy of the photoelectron using the equation that relates $ \text { ke } \text { electron } $ to the energy of the photon , $ \text { e } \text { photon } $ , and the work function , $ \phi $ : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ since we want to know $ \text { ke } _\text { electron } $ , we can start by rearranging the equation so that we will be solving for the kinetic energy of the electron : $ \text { ke } \text { electron } =\text { e } \text { photon } -\phi $ now we can insert our known values for $ \text { e } _\text { photon } $ and $ \phi $ from example 1 : $ \text { ke } _\text { electron } = ( 2.0\times10^ { -17 } \text { j } ) - ( 7.53\times10^ { -19 } \text { j } ) =1.9\times10^ { -17 } \text { j } $ therefore , each photoelectron has a kinetic energy of $ 1.9\times10^ { -17 } \text { j } $ . summary based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a specific metal surface . the energy of the incident photon must be equal to the sum of the work function and the kinetic energy of a photoelectron : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ try it ! when we shine light with a frequency of $ 6.20 \times 10^ { 14 } \ , \text { hz } $ on a mystery metal , we observe the ejected electrons have a kinetic energy of $ 3.28\times 10^ { -20 } \ , \text j $ . some possible candidates for the mystery metal are shown in the table below : metal | work function $ \phi $ ( joules , $ \text j $ ) : - : | : - : calcium , $ \text { ca } $ | $ 4.60\times 10^ { -19 } $ tin , $ \text { sn } $ | $ 7.08\times 10^ { -19 } $ sodium , $ \text { na } $ | $ 3.78\times 10^ { -19 } $ hafnium , $ \text { hf } $ | $ 6.25\times 10^ { -19 } $ samarium , $ \text { sm } $ | $ 4.33\times 10^ { -19 } $ based on this information , what is the most likely identity of our mystery metal ?
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according to planck 's equation , the energy of a photon is proportional to the frequency of the light , $ \nu $ . the amplitude of the light is then proportional to the number of photons with a given frequency . concept check : as the wavelength of a photon increases , what happens to the photon 's energy ?
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how is amplitude proportional to the number of photons with the same frequency ?
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key points based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . contrary to the predictions , experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of particles called photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a metal surface , and the value of $ \phi $ depends on the metal . the energy of the incident photon must be equal to the sum of the metal 's work function and the photoelectron kinetic energy : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ introduction : what is the photoelectric effect ? when light shines on a metal , electrons can be ejected from the surface of the metal in a phenomenon known as the photoelectric effect . this process is also often referred to as photoemission , and the electrons that are ejected from the metal are called photoelectrons . in terms of their behavior and their properties , photoelectrons are no different from other electrons . the prefix , photo- , simply tells us that the electrons have been ejected from a metal surface by incident light . in this article , we will discuss how 19th century physicists attempted ( but failed ! ) to explain the photoelectric effect using classical physics . this ultimately led to the development of the modern description of electromagnetic radiation , which has both wave-like and particle-like properties . predictions based on light as a wave to explain the photoelectric effect , 19th-century physicists theorized that the oscillating electric field of the incoming light wave was heating the electrons and causing them to vibrate , eventually freeing them from the metal surface . this hypothesis was based on the assumption that light traveled purely as a wave through space . ( see this article for more information about the basic properties of light . ) scientists also believed that the energy of the light wave was proportional to its brightness , which is related to the wave 's amplitude . in order to test their hypotheses , they performed experiments to look at the effect of light amplitude and frequency on the rate of electron ejection , as well as the kinetic energy of the photoelectrons . based on the classical description of light as a wave , they made the following predictions : the kinetic energy of emitted photoelectrons should increase with the light amplitude . the rate of electron emission , which is proportional to the measured electric current , should increase as the light frequency is increased . to help us understand why they made these predictions , we can compare a light wave to a water wave . imagine some beach balls sitting on a dock that extends out into the ocean . the dock represents a metal surface , the beach balls represent electrons , and the ocean waves represent light waves . if a single large wave were to shake the dock , we would expect the energy from the big wave would send the beach balls flying off the dock with much more kinetic energy compared to a single , small wave . this is also what physicists believed would happen if the light intensity was increased . light amplitude was expected to be proportional to the light energy , so higher amplitude light was predicted to result in photoelectrons with more kinetic energy . classical physicists also predicted that increasing the frequency of light waves ( at a constant amplitude ) would increase the rate of electrons being ejected , and thus increase the measured electric current . using our beach ball analogy , we would expect waves hitting the dock more frequently would result in more beach balls being knocked off the dock compared to the same sized waves hitting the dock less often . now that we know what physicists thought would happen , let 's look at what they actually observed experimentally ! when intuition fails : photons to the rescue ! when experiments were performed to look at the effect of light amplitude and frequency , the following results were observed : the kinetic energy of photoelectrons increases with light frequency . electric current remains constant as light frequency increases . electric current increases with light amplitude . the kinetic energy of photoelectrons remains constant as light amplitude increases . these results were completely at odds with the predictions based on the classical description of light as a wave ! in order to explain what was happening , it turned out that an entirely new model of light was needed . that model was developed by albert einstein , who proposed that light sometimes behaved as particles of electromagnetic energy which we now call photons . the energy of a photon could be calculated using planck 's equation : $ \text { e } _ { \text { photon } } =h\nu $ where $ \text { e } _ { \text { photon } } $ is the energy of a photon in joules ( $ \text { j } $ ) , $ h $ is planck 's constant $ ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) $ , and $ \nu $ is the frequency of the light in $ \text { hz } $ . according to planck 's equation , the energy of a photon is proportional to the frequency of the light , $ \nu $ . the amplitude of the light is then proportional to the number of photons with a given frequency . concept check : as the wavelength of a photon increases , what happens to the photon 's energy ? light frequency and the threshold frequency $ \nu_0 $ we can think of the incident light as a stream of photons with an energy determined by the light frequency . when a photon hits the metal surface , the photon 's energy is absorbed by an electron in the metal . the graphic below illustrates the relationship between light frequency and the kinetic energy of ejected electrons . the scientists observed that if the incident light had a frequency less than a minimum frequency $ \nu_0 $ , then no electrons were ejected regardless of the light amplitude . this minimum frequency is also called the threshold frequency , and the value of $ \nu_0 $ depends on the metal . for frequencies greater than $ \nu_0 $ , electrons would be ejected from the metal . furthermore , the kinetic energy of the photoelectrons was proportional to the light frequency . the relationship between photoelectron kinetic energy and light frequency is shown in graph ( a ) below . because the light amplitude was kept constant as the light frequency increased , the number of photons being absorbed by the metal remained constant . thus , the rate at which electrons were ejected from the metal ( or the electric current ) remained constant as well . the relationship between electron current and light frequency is illustrated in graph ( b ) above . is n't there more math somewhere ? we can analyze the frequency relationship using the law of conservation of energy . the total energy of the incoming photon , $ \text { e } \text { photon } $ , must be equal to the kinetic energy of the ejected electron , $ \text { ke } { \text { electron } } $ , plus the energy required to eject the electron from the metal . the energy required to free the electron from a particular metal is also called the metal 's work function , which is represented by the symbol $ \phi $ ( in units of $ \text j $ ) : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ like the threshold frequency $ \nu_0 $ , the value of $ \phi $ also changes depending on the metal . we can now write the energy of the photon in terms of the light frequency using planck 's equation : $ \text { e } \text { photon } =h\nu=\text { ke } \text { electron } +\phi $ rearranging this equation in terms of the electron 's kinetic energy , we get : $ \text { ke } _\text { electron } =h\nu-\phi $ we can see that kinetic energy of the photoelectron increases linearly with $ \nu $ as long as the photon energy is greater than the work function $ \phi $ , which is exactly the relationship shown in graph ( a ) above . we can also use this equation to find the photoelectron velocity $ \text v $ , which is related to $ \text { ke } _\text { electron } $ as follows : $ \text { ke } _\text { electron } =h\nu-\phi=\dfrac { 1 } { 2 } m_e\text v^2 $ where $ m_e $ is the rest mass of an electron , $ 9.1094 \times 10^ { -31 } \ , \text { kg } $ . exploring the wave amplitude trends in terms of photons , higher amplitude light means more photons hitting the metal surface . this results in more electrons ejected over a given time period . as long as the light frequency is greater than $ \nu_0 $ , increasing the light amplitude will cause the electron current to increase proportionally as shown in graph ( a ) below . since increasing the light amplitude has no effect on the energy of the incoming photon , the photoelectron kinetic energy remains constant as the light amplitude is increased ( see graph ( b ) above ) . if we try to explain this result using our dock-and-beach-balls analogy , the relationship in graph ( b ) indicates that no matter the height of the wave hitting the dock $ - $ whether it 's a tiny swell , or a huge tsunami $ - $ the individual beach balls would be launched off the dock with the exact same speed ! thus , our intuition and analogy do n't do a very good job of explaining these particular experiments . example $ 1 $ : the photoelectric effect for copper the work function of copper metal is $ \phi=7.53\times10^ { -19 } \text { j } $ . if we shine light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ on copper metal , will the photoelectric effect be observed ? in order to eject electrons , we need the energy of the photons to be greater than the work function of copper . we can use planck 's equation to calculate the energy of the photon , $ \text { e } _ { \text { photon } } $ : $ \begin { align } \text { e } _\text { photon } & amp ; = h\nu \ & amp ; = ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) ( 3.0\times10^ { 16 } \text { hz } ) ~~~~\text { plug in values for $ h $ and $ \nu $ } \ & amp ; = 2.0\times10^ { -17 } \text { j } \end { align } $ if we compare our calculated photon energy , $ \text { e } _\text { photon } $ , to copper 's work function , we see that the photon energy is greater than $ \phi $ : $ ~2.0\times10^ { -17 } \text { j } ~ & gt ; ~7.53\times10^ { -19 } \text { j } $ $ ~~~~~~~~\text { e } _\text { photon } ~~~~~~~~~~~~~~~~~~~\phi $ thus , we would expect to see photoelectrons ejected from the copper . next , we will calculate the kinetic energy of the photoelectrons . example $ 2 $ : calculating the kinetic energy of a photoelectron what is the kinetic energy of the photoelectrons ejected from the copper by the light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ ? we can calculate the kinetic energy of the photoelectron using the equation that relates $ \text { ke } \text { electron } $ to the energy of the photon , $ \text { e } \text { photon } $ , and the work function , $ \phi $ : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ since we want to know $ \text { ke } _\text { electron } $ , we can start by rearranging the equation so that we will be solving for the kinetic energy of the electron : $ \text { ke } \text { electron } =\text { e } \text { photon } -\phi $ now we can insert our known values for $ \text { e } _\text { photon } $ and $ \phi $ from example 1 : $ \text { ke } _\text { electron } = ( 2.0\times10^ { -17 } \text { j } ) - ( 7.53\times10^ { -19 } \text { j } ) =1.9\times10^ { -17 } \text { j } $ therefore , each photoelectron has a kinetic energy of $ 1.9\times10^ { -17 } \text { j } $ . summary based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a specific metal surface . the energy of the incident photon must be equal to the sum of the work function and the kinetic energy of a photoelectron : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ try it ! when we shine light with a frequency of $ 6.20 \times 10^ { 14 } \ , \text { hz } $ on a mystery metal , we observe the ejected electrons have a kinetic energy of $ 3.28\times 10^ { -20 } \ , \text j $ . some possible candidates for the mystery metal are shown in the table below : metal | work function $ \phi $ ( joules , $ \text j $ ) : - : | : - : calcium , $ \text { ca } $ | $ 4.60\times 10^ { -19 } $ tin , $ \text { sn } $ | $ 7.08\times 10^ { -19 } $ sodium , $ \text { na } $ | $ 3.78\times 10^ { -19 } $ hafnium , $ \text { hf } $ | $ 6.25\times 10^ { -19 } $ samarium , $ \text { sm } $ | $ 4.33\times 10^ { -19 } $ based on this information , what is the most likely identity of our mystery metal ?
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in this article , we will discuss how 19th century physicists attempted ( but failed ! ) to explain the photoelectric effect using classical physics . this ultimately led to the development of the modern description of electromagnetic radiation , which has both wave-like and particle-like properties .
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why do only metals exhibit photoelectric effect ?
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key points based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . contrary to the predictions , experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of particles called photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a metal surface , and the value of $ \phi $ depends on the metal . the energy of the incident photon must be equal to the sum of the metal 's work function and the photoelectron kinetic energy : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ introduction : what is the photoelectric effect ? when light shines on a metal , electrons can be ejected from the surface of the metal in a phenomenon known as the photoelectric effect . this process is also often referred to as photoemission , and the electrons that are ejected from the metal are called photoelectrons . in terms of their behavior and their properties , photoelectrons are no different from other electrons . the prefix , photo- , simply tells us that the electrons have been ejected from a metal surface by incident light . in this article , we will discuss how 19th century physicists attempted ( but failed ! ) to explain the photoelectric effect using classical physics . this ultimately led to the development of the modern description of electromagnetic radiation , which has both wave-like and particle-like properties . predictions based on light as a wave to explain the photoelectric effect , 19th-century physicists theorized that the oscillating electric field of the incoming light wave was heating the electrons and causing them to vibrate , eventually freeing them from the metal surface . this hypothesis was based on the assumption that light traveled purely as a wave through space . ( see this article for more information about the basic properties of light . ) scientists also believed that the energy of the light wave was proportional to its brightness , which is related to the wave 's amplitude . in order to test their hypotheses , they performed experiments to look at the effect of light amplitude and frequency on the rate of electron ejection , as well as the kinetic energy of the photoelectrons . based on the classical description of light as a wave , they made the following predictions : the kinetic energy of emitted photoelectrons should increase with the light amplitude . the rate of electron emission , which is proportional to the measured electric current , should increase as the light frequency is increased . to help us understand why they made these predictions , we can compare a light wave to a water wave . imagine some beach balls sitting on a dock that extends out into the ocean . the dock represents a metal surface , the beach balls represent electrons , and the ocean waves represent light waves . if a single large wave were to shake the dock , we would expect the energy from the big wave would send the beach balls flying off the dock with much more kinetic energy compared to a single , small wave . this is also what physicists believed would happen if the light intensity was increased . light amplitude was expected to be proportional to the light energy , so higher amplitude light was predicted to result in photoelectrons with more kinetic energy . classical physicists also predicted that increasing the frequency of light waves ( at a constant amplitude ) would increase the rate of electrons being ejected , and thus increase the measured electric current . using our beach ball analogy , we would expect waves hitting the dock more frequently would result in more beach balls being knocked off the dock compared to the same sized waves hitting the dock less often . now that we know what physicists thought would happen , let 's look at what they actually observed experimentally ! when intuition fails : photons to the rescue ! when experiments were performed to look at the effect of light amplitude and frequency , the following results were observed : the kinetic energy of photoelectrons increases with light frequency . electric current remains constant as light frequency increases . electric current increases with light amplitude . the kinetic energy of photoelectrons remains constant as light amplitude increases . these results were completely at odds with the predictions based on the classical description of light as a wave ! in order to explain what was happening , it turned out that an entirely new model of light was needed . that model was developed by albert einstein , who proposed that light sometimes behaved as particles of electromagnetic energy which we now call photons . the energy of a photon could be calculated using planck 's equation : $ \text { e } _ { \text { photon } } =h\nu $ where $ \text { e } _ { \text { photon } } $ is the energy of a photon in joules ( $ \text { j } $ ) , $ h $ is planck 's constant $ ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) $ , and $ \nu $ is the frequency of the light in $ \text { hz } $ . according to planck 's equation , the energy of a photon is proportional to the frequency of the light , $ \nu $ . the amplitude of the light is then proportional to the number of photons with a given frequency . concept check : as the wavelength of a photon increases , what happens to the photon 's energy ? light frequency and the threshold frequency $ \nu_0 $ we can think of the incident light as a stream of photons with an energy determined by the light frequency . when a photon hits the metal surface , the photon 's energy is absorbed by an electron in the metal . the graphic below illustrates the relationship between light frequency and the kinetic energy of ejected electrons . the scientists observed that if the incident light had a frequency less than a minimum frequency $ \nu_0 $ , then no electrons were ejected regardless of the light amplitude . this minimum frequency is also called the threshold frequency , and the value of $ \nu_0 $ depends on the metal . for frequencies greater than $ \nu_0 $ , electrons would be ejected from the metal . furthermore , the kinetic energy of the photoelectrons was proportional to the light frequency . the relationship between photoelectron kinetic energy and light frequency is shown in graph ( a ) below . because the light amplitude was kept constant as the light frequency increased , the number of photons being absorbed by the metal remained constant . thus , the rate at which electrons were ejected from the metal ( or the electric current ) remained constant as well . the relationship between electron current and light frequency is illustrated in graph ( b ) above . is n't there more math somewhere ? we can analyze the frequency relationship using the law of conservation of energy . the total energy of the incoming photon , $ \text { e } \text { photon } $ , must be equal to the kinetic energy of the ejected electron , $ \text { ke } { \text { electron } } $ , plus the energy required to eject the electron from the metal . the energy required to free the electron from a particular metal is also called the metal 's work function , which is represented by the symbol $ \phi $ ( in units of $ \text j $ ) : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ like the threshold frequency $ \nu_0 $ , the value of $ \phi $ also changes depending on the metal . we can now write the energy of the photon in terms of the light frequency using planck 's equation : $ \text { e } \text { photon } =h\nu=\text { ke } \text { electron } +\phi $ rearranging this equation in terms of the electron 's kinetic energy , we get : $ \text { ke } _\text { electron } =h\nu-\phi $ we can see that kinetic energy of the photoelectron increases linearly with $ \nu $ as long as the photon energy is greater than the work function $ \phi $ , which is exactly the relationship shown in graph ( a ) above . we can also use this equation to find the photoelectron velocity $ \text v $ , which is related to $ \text { ke } _\text { electron } $ as follows : $ \text { ke } _\text { electron } =h\nu-\phi=\dfrac { 1 } { 2 } m_e\text v^2 $ where $ m_e $ is the rest mass of an electron , $ 9.1094 \times 10^ { -31 } \ , \text { kg } $ . exploring the wave amplitude trends in terms of photons , higher amplitude light means more photons hitting the metal surface . this results in more electrons ejected over a given time period . as long as the light frequency is greater than $ \nu_0 $ , increasing the light amplitude will cause the electron current to increase proportionally as shown in graph ( a ) below . since increasing the light amplitude has no effect on the energy of the incoming photon , the photoelectron kinetic energy remains constant as the light amplitude is increased ( see graph ( b ) above ) . if we try to explain this result using our dock-and-beach-balls analogy , the relationship in graph ( b ) indicates that no matter the height of the wave hitting the dock $ - $ whether it 's a tiny swell , or a huge tsunami $ - $ the individual beach balls would be launched off the dock with the exact same speed ! thus , our intuition and analogy do n't do a very good job of explaining these particular experiments . example $ 1 $ : the photoelectric effect for copper the work function of copper metal is $ \phi=7.53\times10^ { -19 } \text { j } $ . if we shine light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ on copper metal , will the photoelectric effect be observed ? in order to eject electrons , we need the energy of the photons to be greater than the work function of copper . we can use planck 's equation to calculate the energy of the photon , $ \text { e } _ { \text { photon } } $ : $ \begin { align } \text { e } _\text { photon } & amp ; = h\nu \ & amp ; = ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) ( 3.0\times10^ { 16 } \text { hz } ) ~~~~\text { plug in values for $ h $ and $ \nu $ } \ & amp ; = 2.0\times10^ { -17 } \text { j } \end { align } $ if we compare our calculated photon energy , $ \text { e } _\text { photon } $ , to copper 's work function , we see that the photon energy is greater than $ \phi $ : $ ~2.0\times10^ { -17 } \text { j } ~ & gt ; ~7.53\times10^ { -19 } \text { j } $ $ ~~~~~~~~\text { e } _\text { photon } ~~~~~~~~~~~~~~~~~~~\phi $ thus , we would expect to see photoelectrons ejected from the copper . next , we will calculate the kinetic energy of the photoelectrons . example $ 2 $ : calculating the kinetic energy of a photoelectron what is the kinetic energy of the photoelectrons ejected from the copper by the light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ ? we can calculate the kinetic energy of the photoelectron using the equation that relates $ \text { ke } \text { electron } $ to the energy of the photon , $ \text { e } \text { photon } $ , and the work function , $ \phi $ : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ since we want to know $ \text { ke } _\text { electron } $ , we can start by rearranging the equation so that we will be solving for the kinetic energy of the electron : $ \text { ke } \text { electron } =\text { e } \text { photon } -\phi $ now we can insert our known values for $ \text { e } _\text { photon } $ and $ \phi $ from example 1 : $ \text { ke } _\text { electron } = ( 2.0\times10^ { -17 } \text { j } ) - ( 7.53\times10^ { -19 } \text { j } ) =1.9\times10^ { -17 } \text { j } $ therefore , each photoelectron has a kinetic energy of $ 1.9\times10^ { -17 } \text { j } $ . summary based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a specific metal surface . the energy of the incident photon must be equal to the sum of the work function and the kinetic energy of a photoelectron : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ try it ! when we shine light with a frequency of $ 6.20 \times 10^ { 14 } \ , \text { hz } $ on a mystery metal , we observe the ejected electrons have a kinetic energy of $ 3.28\times 10^ { -20 } \ , \text j $ . some possible candidates for the mystery metal are shown in the table below : metal | work function $ \phi $ ( joules , $ \text j $ ) : - : | : - : calcium , $ \text { ca } $ | $ 4.60\times 10^ { -19 } $ tin , $ \text { sn } $ | $ 7.08\times 10^ { -19 } $ sodium , $ \text { na } $ | $ 3.78\times 10^ { -19 } $ hafnium , $ \text { hf } $ | $ 6.25\times 10^ { -19 } $ samarium , $ \text { sm } $ | $ 4.33\times 10^ { -19 } $ based on this information , what is the most likely identity of our mystery metal ?
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we can calculate the kinetic energy of the photoelectron using the equation that relates $ \text { ke } \text { electron } $ to the energy of the photon , $ \text { e } \text { photon } $ , and the work function , $ \phi $ : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ since we want to know $ \text { ke } _\text { electron } $ , we can start by rearranging the equation so that we will be solving for the kinetic energy of the electron : $ \text { ke } \text { electron } =\text { e } \text { photon } -\phi $ now we can insert our known values for $ \text { e } _\text { photon } $ and $ \phi $ from example 1 : $ \text { ke } _\text { electron } = ( 2.0\times10^ { -17 } \text { j } ) - ( 7.53\times10^ { -19 } \text { j } ) =1.9\times10^ { -17 } \text { j } $ therefore , each photoelectron has a kinetic energy of $ 1.9\times10^ { -17 } \text { j } $ . summary based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current .
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why does the current not increase with increasing frequency ?
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key points based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . contrary to the predictions , experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of particles called photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a metal surface , and the value of $ \phi $ depends on the metal . the energy of the incident photon must be equal to the sum of the metal 's work function and the photoelectron kinetic energy : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ introduction : what is the photoelectric effect ? when light shines on a metal , electrons can be ejected from the surface of the metal in a phenomenon known as the photoelectric effect . this process is also often referred to as photoemission , and the electrons that are ejected from the metal are called photoelectrons . in terms of their behavior and their properties , photoelectrons are no different from other electrons . the prefix , photo- , simply tells us that the electrons have been ejected from a metal surface by incident light . in this article , we will discuss how 19th century physicists attempted ( but failed ! ) to explain the photoelectric effect using classical physics . this ultimately led to the development of the modern description of electromagnetic radiation , which has both wave-like and particle-like properties . predictions based on light as a wave to explain the photoelectric effect , 19th-century physicists theorized that the oscillating electric field of the incoming light wave was heating the electrons and causing them to vibrate , eventually freeing them from the metal surface . this hypothesis was based on the assumption that light traveled purely as a wave through space . ( see this article for more information about the basic properties of light . ) scientists also believed that the energy of the light wave was proportional to its brightness , which is related to the wave 's amplitude . in order to test their hypotheses , they performed experiments to look at the effect of light amplitude and frequency on the rate of electron ejection , as well as the kinetic energy of the photoelectrons . based on the classical description of light as a wave , they made the following predictions : the kinetic energy of emitted photoelectrons should increase with the light amplitude . the rate of electron emission , which is proportional to the measured electric current , should increase as the light frequency is increased . to help us understand why they made these predictions , we can compare a light wave to a water wave . imagine some beach balls sitting on a dock that extends out into the ocean . the dock represents a metal surface , the beach balls represent electrons , and the ocean waves represent light waves . if a single large wave were to shake the dock , we would expect the energy from the big wave would send the beach balls flying off the dock with much more kinetic energy compared to a single , small wave . this is also what physicists believed would happen if the light intensity was increased . light amplitude was expected to be proportional to the light energy , so higher amplitude light was predicted to result in photoelectrons with more kinetic energy . classical physicists also predicted that increasing the frequency of light waves ( at a constant amplitude ) would increase the rate of electrons being ejected , and thus increase the measured electric current . using our beach ball analogy , we would expect waves hitting the dock more frequently would result in more beach balls being knocked off the dock compared to the same sized waves hitting the dock less often . now that we know what physicists thought would happen , let 's look at what they actually observed experimentally ! when intuition fails : photons to the rescue ! when experiments were performed to look at the effect of light amplitude and frequency , the following results were observed : the kinetic energy of photoelectrons increases with light frequency . electric current remains constant as light frequency increases . electric current increases with light amplitude . the kinetic energy of photoelectrons remains constant as light amplitude increases . these results were completely at odds with the predictions based on the classical description of light as a wave ! in order to explain what was happening , it turned out that an entirely new model of light was needed . that model was developed by albert einstein , who proposed that light sometimes behaved as particles of electromagnetic energy which we now call photons . the energy of a photon could be calculated using planck 's equation : $ \text { e } _ { \text { photon } } =h\nu $ where $ \text { e } _ { \text { photon } } $ is the energy of a photon in joules ( $ \text { j } $ ) , $ h $ is planck 's constant $ ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) $ , and $ \nu $ is the frequency of the light in $ \text { hz } $ . according to planck 's equation , the energy of a photon is proportional to the frequency of the light , $ \nu $ . the amplitude of the light is then proportional to the number of photons with a given frequency . concept check : as the wavelength of a photon increases , what happens to the photon 's energy ? light frequency and the threshold frequency $ \nu_0 $ we can think of the incident light as a stream of photons with an energy determined by the light frequency . when a photon hits the metal surface , the photon 's energy is absorbed by an electron in the metal . the graphic below illustrates the relationship between light frequency and the kinetic energy of ejected electrons . the scientists observed that if the incident light had a frequency less than a minimum frequency $ \nu_0 $ , then no electrons were ejected regardless of the light amplitude . this minimum frequency is also called the threshold frequency , and the value of $ \nu_0 $ depends on the metal . for frequencies greater than $ \nu_0 $ , electrons would be ejected from the metal . furthermore , the kinetic energy of the photoelectrons was proportional to the light frequency . the relationship between photoelectron kinetic energy and light frequency is shown in graph ( a ) below . because the light amplitude was kept constant as the light frequency increased , the number of photons being absorbed by the metal remained constant . thus , the rate at which electrons were ejected from the metal ( or the electric current ) remained constant as well . the relationship between electron current and light frequency is illustrated in graph ( b ) above . is n't there more math somewhere ? we can analyze the frequency relationship using the law of conservation of energy . the total energy of the incoming photon , $ \text { e } \text { photon } $ , must be equal to the kinetic energy of the ejected electron , $ \text { ke } { \text { electron } } $ , plus the energy required to eject the electron from the metal . the energy required to free the electron from a particular metal is also called the metal 's work function , which is represented by the symbol $ \phi $ ( in units of $ \text j $ ) : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ like the threshold frequency $ \nu_0 $ , the value of $ \phi $ also changes depending on the metal . we can now write the energy of the photon in terms of the light frequency using planck 's equation : $ \text { e } \text { photon } =h\nu=\text { ke } \text { electron } +\phi $ rearranging this equation in terms of the electron 's kinetic energy , we get : $ \text { ke } _\text { electron } =h\nu-\phi $ we can see that kinetic energy of the photoelectron increases linearly with $ \nu $ as long as the photon energy is greater than the work function $ \phi $ , which is exactly the relationship shown in graph ( a ) above . we can also use this equation to find the photoelectron velocity $ \text v $ , which is related to $ \text { ke } _\text { electron } $ as follows : $ \text { ke } _\text { electron } =h\nu-\phi=\dfrac { 1 } { 2 } m_e\text v^2 $ where $ m_e $ is the rest mass of an electron , $ 9.1094 \times 10^ { -31 } \ , \text { kg } $ . exploring the wave amplitude trends in terms of photons , higher amplitude light means more photons hitting the metal surface . this results in more electrons ejected over a given time period . as long as the light frequency is greater than $ \nu_0 $ , increasing the light amplitude will cause the electron current to increase proportionally as shown in graph ( a ) below . since increasing the light amplitude has no effect on the energy of the incoming photon , the photoelectron kinetic energy remains constant as the light amplitude is increased ( see graph ( b ) above ) . if we try to explain this result using our dock-and-beach-balls analogy , the relationship in graph ( b ) indicates that no matter the height of the wave hitting the dock $ - $ whether it 's a tiny swell , or a huge tsunami $ - $ the individual beach balls would be launched off the dock with the exact same speed ! thus , our intuition and analogy do n't do a very good job of explaining these particular experiments . example $ 1 $ : the photoelectric effect for copper the work function of copper metal is $ \phi=7.53\times10^ { -19 } \text { j } $ . if we shine light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ on copper metal , will the photoelectric effect be observed ? in order to eject electrons , we need the energy of the photons to be greater than the work function of copper . we can use planck 's equation to calculate the energy of the photon , $ \text { e } _ { \text { photon } } $ : $ \begin { align } \text { e } _\text { photon } & amp ; = h\nu \ & amp ; = ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) ( 3.0\times10^ { 16 } \text { hz } ) ~~~~\text { plug in values for $ h $ and $ \nu $ } \ & amp ; = 2.0\times10^ { -17 } \text { j } \end { align } $ if we compare our calculated photon energy , $ \text { e } _\text { photon } $ , to copper 's work function , we see that the photon energy is greater than $ \phi $ : $ ~2.0\times10^ { -17 } \text { j } ~ & gt ; ~7.53\times10^ { -19 } \text { j } $ $ ~~~~~~~~\text { e } _\text { photon } ~~~~~~~~~~~~~~~~~~~\phi $ thus , we would expect to see photoelectrons ejected from the copper . next , we will calculate the kinetic energy of the photoelectrons . example $ 2 $ : calculating the kinetic energy of a photoelectron what is the kinetic energy of the photoelectrons ejected from the copper by the light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ ? we can calculate the kinetic energy of the photoelectron using the equation that relates $ \text { ke } \text { electron } $ to the energy of the photon , $ \text { e } \text { photon } $ , and the work function , $ \phi $ : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ since we want to know $ \text { ke } _\text { electron } $ , we can start by rearranging the equation so that we will be solving for the kinetic energy of the electron : $ \text { ke } \text { electron } =\text { e } \text { photon } -\phi $ now we can insert our known values for $ \text { e } _\text { photon } $ and $ \phi $ from example 1 : $ \text { ke } _\text { electron } = ( 2.0\times10^ { -17 } \text { j } ) - ( 7.53\times10^ { -19 } \text { j } ) =1.9\times10^ { -17 } \text { j } $ therefore , each photoelectron has a kinetic energy of $ 1.9\times10^ { -17 } \text { j } $ . summary based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a specific metal surface . the energy of the incident photon must be equal to the sum of the work function and the kinetic energy of a photoelectron : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ try it ! when we shine light with a frequency of $ 6.20 \times 10^ { 14 } \ , \text { hz } $ on a mystery metal , we observe the ejected electrons have a kinetic energy of $ 3.28\times 10^ { -20 } \ , \text j $ . some possible candidates for the mystery metal are shown in the table below : metal | work function $ \phi $ ( joules , $ \text j $ ) : - : | : - : calcium , $ \text { ca } $ | $ 4.60\times 10^ { -19 } $ tin , $ \text { sn } $ | $ 7.08\times 10^ { -19 } $ sodium , $ \text { na } $ | $ 3.78\times 10^ { -19 } $ hafnium , $ \text { hf } $ | $ 6.25\times 10^ { -19 } $ samarium , $ \text { sm } $ | $ 4.33\times 10^ { -19 } $ based on this information , what is the most likely identity of our mystery metal ?
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we can also use this equation to find the photoelectron velocity $ \text v $ , which is related to $ \text { ke } _\text { electron } $ as follows : $ \text { ke } _\text { electron } =h\nu-\phi=\dfrac { 1 } { 2 } m_e\text v^2 $ where $ m_e $ is the rest mass of an electron , $ 9.1094 \times 10^ { -31 } \ , \text { kg } $ . exploring the wave amplitude trends in terms of photons , higher amplitude light means more photons hitting the metal surface . this results in more electrons ejected over a given time period .
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why photons are thrown on metals only ?
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key points based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . contrary to the predictions , experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of particles called photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a metal surface , and the value of $ \phi $ depends on the metal . the energy of the incident photon must be equal to the sum of the metal 's work function and the photoelectron kinetic energy : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ introduction : what is the photoelectric effect ? when light shines on a metal , electrons can be ejected from the surface of the metal in a phenomenon known as the photoelectric effect . this process is also often referred to as photoemission , and the electrons that are ejected from the metal are called photoelectrons . in terms of their behavior and their properties , photoelectrons are no different from other electrons . the prefix , photo- , simply tells us that the electrons have been ejected from a metal surface by incident light . in this article , we will discuss how 19th century physicists attempted ( but failed ! ) to explain the photoelectric effect using classical physics . this ultimately led to the development of the modern description of electromagnetic radiation , which has both wave-like and particle-like properties . predictions based on light as a wave to explain the photoelectric effect , 19th-century physicists theorized that the oscillating electric field of the incoming light wave was heating the electrons and causing them to vibrate , eventually freeing them from the metal surface . this hypothesis was based on the assumption that light traveled purely as a wave through space . ( see this article for more information about the basic properties of light . ) scientists also believed that the energy of the light wave was proportional to its brightness , which is related to the wave 's amplitude . in order to test their hypotheses , they performed experiments to look at the effect of light amplitude and frequency on the rate of electron ejection , as well as the kinetic energy of the photoelectrons . based on the classical description of light as a wave , they made the following predictions : the kinetic energy of emitted photoelectrons should increase with the light amplitude . the rate of electron emission , which is proportional to the measured electric current , should increase as the light frequency is increased . to help us understand why they made these predictions , we can compare a light wave to a water wave . imagine some beach balls sitting on a dock that extends out into the ocean . the dock represents a metal surface , the beach balls represent electrons , and the ocean waves represent light waves . if a single large wave were to shake the dock , we would expect the energy from the big wave would send the beach balls flying off the dock with much more kinetic energy compared to a single , small wave . this is also what physicists believed would happen if the light intensity was increased . light amplitude was expected to be proportional to the light energy , so higher amplitude light was predicted to result in photoelectrons with more kinetic energy . classical physicists also predicted that increasing the frequency of light waves ( at a constant amplitude ) would increase the rate of electrons being ejected , and thus increase the measured electric current . using our beach ball analogy , we would expect waves hitting the dock more frequently would result in more beach balls being knocked off the dock compared to the same sized waves hitting the dock less often . now that we know what physicists thought would happen , let 's look at what they actually observed experimentally ! when intuition fails : photons to the rescue ! when experiments were performed to look at the effect of light amplitude and frequency , the following results were observed : the kinetic energy of photoelectrons increases with light frequency . electric current remains constant as light frequency increases . electric current increases with light amplitude . the kinetic energy of photoelectrons remains constant as light amplitude increases . these results were completely at odds with the predictions based on the classical description of light as a wave ! in order to explain what was happening , it turned out that an entirely new model of light was needed . that model was developed by albert einstein , who proposed that light sometimes behaved as particles of electromagnetic energy which we now call photons . the energy of a photon could be calculated using planck 's equation : $ \text { e } _ { \text { photon } } =h\nu $ where $ \text { e } _ { \text { photon } } $ is the energy of a photon in joules ( $ \text { j } $ ) , $ h $ is planck 's constant $ ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) $ , and $ \nu $ is the frequency of the light in $ \text { hz } $ . according to planck 's equation , the energy of a photon is proportional to the frequency of the light , $ \nu $ . the amplitude of the light is then proportional to the number of photons with a given frequency . concept check : as the wavelength of a photon increases , what happens to the photon 's energy ? light frequency and the threshold frequency $ \nu_0 $ we can think of the incident light as a stream of photons with an energy determined by the light frequency . when a photon hits the metal surface , the photon 's energy is absorbed by an electron in the metal . the graphic below illustrates the relationship between light frequency and the kinetic energy of ejected electrons . the scientists observed that if the incident light had a frequency less than a minimum frequency $ \nu_0 $ , then no electrons were ejected regardless of the light amplitude . this minimum frequency is also called the threshold frequency , and the value of $ \nu_0 $ depends on the metal . for frequencies greater than $ \nu_0 $ , electrons would be ejected from the metal . furthermore , the kinetic energy of the photoelectrons was proportional to the light frequency . the relationship between photoelectron kinetic energy and light frequency is shown in graph ( a ) below . because the light amplitude was kept constant as the light frequency increased , the number of photons being absorbed by the metal remained constant . thus , the rate at which electrons were ejected from the metal ( or the electric current ) remained constant as well . the relationship between electron current and light frequency is illustrated in graph ( b ) above . is n't there more math somewhere ? we can analyze the frequency relationship using the law of conservation of energy . the total energy of the incoming photon , $ \text { e } \text { photon } $ , must be equal to the kinetic energy of the ejected electron , $ \text { ke } { \text { electron } } $ , plus the energy required to eject the electron from the metal . the energy required to free the electron from a particular metal is also called the metal 's work function , which is represented by the symbol $ \phi $ ( in units of $ \text j $ ) : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ like the threshold frequency $ \nu_0 $ , the value of $ \phi $ also changes depending on the metal . we can now write the energy of the photon in terms of the light frequency using planck 's equation : $ \text { e } \text { photon } =h\nu=\text { ke } \text { electron } +\phi $ rearranging this equation in terms of the electron 's kinetic energy , we get : $ \text { ke } _\text { electron } =h\nu-\phi $ we can see that kinetic energy of the photoelectron increases linearly with $ \nu $ as long as the photon energy is greater than the work function $ \phi $ , which is exactly the relationship shown in graph ( a ) above . we can also use this equation to find the photoelectron velocity $ \text v $ , which is related to $ \text { ke } _\text { electron } $ as follows : $ \text { ke } _\text { electron } =h\nu-\phi=\dfrac { 1 } { 2 } m_e\text v^2 $ where $ m_e $ is the rest mass of an electron , $ 9.1094 \times 10^ { -31 } \ , \text { kg } $ . exploring the wave amplitude trends in terms of photons , higher amplitude light means more photons hitting the metal surface . this results in more electrons ejected over a given time period . as long as the light frequency is greater than $ \nu_0 $ , increasing the light amplitude will cause the electron current to increase proportionally as shown in graph ( a ) below . since increasing the light amplitude has no effect on the energy of the incoming photon , the photoelectron kinetic energy remains constant as the light amplitude is increased ( see graph ( b ) above ) . if we try to explain this result using our dock-and-beach-balls analogy , the relationship in graph ( b ) indicates that no matter the height of the wave hitting the dock $ - $ whether it 's a tiny swell , or a huge tsunami $ - $ the individual beach balls would be launched off the dock with the exact same speed ! thus , our intuition and analogy do n't do a very good job of explaining these particular experiments . example $ 1 $ : the photoelectric effect for copper the work function of copper metal is $ \phi=7.53\times10^ { -19 } \text { j } $ . if we shine light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ on copper metal , will the photoelectric effect be observed ? in order to eject electrons , we need the energy of the photons to be greater than the work function of copper . we can use planck 's equation to calculate the energy of the photon , $ \text { e } _ { \text { photon } } $ : $ \begin { align } \text { e } _\text { photon } & amp ; = h\nu \ & amp ; = ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) ( 3.0\times10^ { 16 } \text { hz } ) ~~~~\text { plug in values for $ h $ and $ \nu $ } \ & amp ; = 2.0\times10^ { -17 } \text { j } \end { align } $ if we compare our calculated photon energy , $ \text { e } _\text { photon } $ , to copper 's work function , we see that the photon energy is greater than $ \phi $ : $ ~2.0\times10^ { -17 } \text { j } ~ & gt ; ~7.53\times10^ { -19 } \text { j } $ $ ~~~~~~~~\text { e } _\text { photon } ~~~~~~~~~~~~~~~~~~~\phi $ thus , we would expect to see photoelectrons ejected from the copper . next , we will calculate the kinetic energy of the photoelectrons . example $ 2 $ : calculating the kinetic energy of a photoelectron what is the kinetic energy of the photoelectrons ejected from the copper by the light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ ? we can calculate the kinetic energy of the photoelectron using the equation that relates $ \text { ke } \text { electron } $ to the energy of the photon , $ \text { e } \text { photon } $ , and the work function , $ \phi $ : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ since we want to know $ \text { ke } _\text { electron } $ , we can start by rearranging the equation so that we will be solving for the kinetic energy of the electron : $ \text { ke } \text { electron } =\text { e } \text { photon } -\phi $ now we can insert our known values for $ \text { e } _\text { photon } $ and $ \phi $ from example 1 : $ \text { ke } _\text { electron } = ( 2.0\times10^ { -17 } \text { j } ) - ( 7.53\times10^ { -19 } \text { j } ) =1.9\times10^ { -17 } \text { j } $ therefore , each photoelectron has a kinetic energy of $ 1.9\times10^ { -17 } \text { j } $ . summary based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a specific metal surface . the energy of the incident photon must be equal to the sum of the work function and the kinetic energy of a photoelectron : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ try it ! when we shine light with a frequency of $ 6.20 \times 10^ { 14 } \ , \text { hz } $ on a mystery metal , we observe the ejected electrons have a kinetic energy of $ 3.28\times 10^ { -20 } \ , \text j $ . some possible candidates for the mystery metal are shown in the table below : metal | work function $ \phi $ ( joules , $ \text j $ ) : - : | : - : calcium , $ \text { ca } $ | $ 4.60\times 10^ { -19 } $ tin , $ \text { sn } $ | $ 7.08\times 10^ { -19 } $ sodium , $ \text { na } $ | $ 3.78\times 10^ { -19 } $ hafnium , $ \text { hf } $ | $ 6.25\times 10^ { -19 } $ samarium , $ \text { sm } $ | $ 4.33\times 10^ { -19 } $ based on this information , what is the most likely identity of our mystery metal ?
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the amplitude of the light is then proportional to the number of photons with a given frequency . concept check : as the wavelength of a photon increases , what happens to the photon 's energy ? light frequency and the threshold frequency $ \nu_0 $ we can think of the incident light as a stream of photons with an energy determined by the light frequency .
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what happens when an electron is hit by a photon of low frequency , not enough for emission or transition ?
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key points based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . contrary to the predictions , experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of particles called photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a metal surface , and the value of $ \phi $ depends on the metal . the energy of the incident photon must be equal to the sum of the metal 's work function and the photoelectron kinetic energy : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ introduction : what is the photoelectric effect ? when light shines on a metal , electrons can be ejected from the surface of the metal in a phenomenon known as the photoelectric effect . this process is also often referred to as photoemission , and the electrons that are ejected from the metal are called photoelectrons . in terms of their behavior and their properties , photoelectrons are no different from other electrons . the prefix , photo- , simply tells us that the electrons have been ejected from a metal surface by incident light . in this article , we will discuss how 19th century physicists attempted ( but failed ! ) to explain the photoelectric effect using classical physics . this ultimately led to the development of the modern description of electromagnetic radiation , which has both wave-like and particle-like properties . predictions based on light as a wave to explain the photoelectric effect , 19th-century physicists theorized that the oscillating electric field of the incoming light wave was heating the electrons and causing them to vibrate , eventually freeing them from the metal surface . this hypothesis was based on the assumption that light traveled purely as a wave through space . ( see this article for more information about the basic properties of light . ) scientists also believed that the energy of the light wave was proportional to its brightness , which is related to the wave 's amplitude . in order to test their hypotheses , they performed experiments to look at the effect of light amplitude and frequency on the rate of electron ejection , as well as the kinetic energy of the photoelectrons . based on the classical description of light as a wave , they made the following predictions : the kinetic energy of emitted photoelectrons should increase with the light amplitude . the rate of electron emission , which is proportional to the measured electric current , should increase as the light frequency is increased . to help us understand why they made these predictions , we can compare a light wave to a water wave . imagine some beach balls sitting on a dock that extends out into the ocean . the dock represents a metal surface , the beach balls represent electrons , and the ocean waves represent light waves . if a single large wave were to shake the dock , we would expect the energy from the big wave would send the beach balls flying off the dock with much more kinetic energy compared to a single , small wave . this is also what physicists believed would happen if the light intensity was increased . light amplitude was expected to be proportional to the light energy , so higher amplitude light was predicted to result in photoelectrons with more kinetic energy . classical physicists also predicted that increasing the frequency of light waves ( at a constant amplitude ) would increase the rate of electrons being ejected , and thus increase the measured electric current . using our beach ball analogy , we would expect waves hitting the dock more frequently would result in more beach balls being knocked off the dock compared to the same sized waves hitting the dock less often . now that we know what physicists thought would happen , let 's look at what they actually observed experimentally ! when intuition fails : photons to the rescue ! when experiments were performed to look at the effect of light amplitude and frequency , the following results were observed : the kinetic energy of photoelectrons increases with light frequency . electric current remains constant as light frequency increases . electric current increases with light amplitude . the kinetic energy of photoelectrons remains constant as light amplitude increases . these results were completely at odds with the predictions based on the classical description of light as a wave ! in order to explain what was happening , it turned out that an entirely new model of light was needed . that model was developed by albert einstein , who proposed that light sometimes behaved as particles of electromagnetic energy which we now call photons . the energy of a photon could be calculated using planck 's equation : $ \text { e } _ { \text { photon } } =h\nu $ where $ \text { e } _ { \text { photon } } $ is the energy of a photon in joules ( $ \text { j } $ ) , $ h $ is planck 's constant $ ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) $ , and $ \nu $ is the frequency of the light in $ \text { hz } $ . according to planck 's equation , the energy of a photon is proportional to the frequency of the light , $ \nu $ . the amplitude of the light is then proportional to the number of photons with a given frequency . concept check : as the wavelength of a photon increases , what happens to the photon 's energy ? light frequency and the threshold frequency $ \nu_0 $ we can think of the incident light as a stream of photons with an energy determined by the light frequency . when a photon hits the metal surface , the photon 's energy is absorbed by an electron in the metal . the graphic below illustrates the relationship between light frequency and the kinetic energy of ejected electrons . the scientists observed that if the incident light had a frequency less than a minimum frequency $ \nu_0 $ , then no electrons were ejected regardless of the light amplitude . this minimum frequency is also called the threshold frequency , and the value of $ \nu_0 $ depends on the metal . for frequencies greater than $ \nu_0 $ , electrons would be ejected from the metal . furthermore , the kinetic energy of the photoelectrons was proportional to the light frequency . the relationship between photoelectron kinetic energy and light frequency is shown in graph ( a ) below . because the light amplitude was kept constant as the light frequency increased , the number of photons being absorbed by the metal remained constant . thus , the rate at which electrons were ejected from the metal ( or the electric current ) remained constant as well . the relationship between electron current and light frequency is illustrated in graph ( b ) above . is n't there more math somewhere ? we can analyze the frequency relationship using the law of conservation of energy . the total energy of the incoming photon , $ \text { e } \text { photon } $ , must be equal to the kinetic energy of the ejected electron , $ \text { ke } { \text { electron } } $ , plus the energy required to eject the electron from the metal . the energy required to free the electron from a particular metal is also called the metal 's work function , which is represented by the symbol $ \phi $ ( in units of $ \text j $ ) : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ like the threshold frequency $ \nu_0 $ , the value of $ \phi $ also changes depending on the metal . we can now write the energy of the photon in terms of the light frequency using planck 's equation : $ \text { e } \text { photon } =h\nu=\text { ke } \text { electron } +\phi $ rearranging this equation in terms of the electron 's kinetic energy , we get : $ \text { ke } _\text { electron } =h\nu-\phi $ we can see that kinetic energy of the photoelectron increases linearly with $ \nu $ as long as the photon energy is greater than the work function $ \phi $ , which is exactly the relationship shown in graph ( a ) above . we can also use this equation to find the photoelectron velocity $ \text v $ , which is related to $ \text { ke } _\text { electron } $ as follows : $ \text { ke } _\text { electron } =h\nu-\phi=\dfrac { 1 } { 2 } m_e\text v^2 $ where $ m_e $ is the rest mass of an electron , $ 9.1094 \times 10^ { -31 } \ , \text { kg } $ . exploring the wave amplitude trends in terms of photons , higher amplitude light means more photons hitting the metal surface . this results in more electrons ejected over a given time period . as long as the light frequency is greater than $ \nu_0 $ , increasing the light amplitude will cause the electron current to increase proportionally as shown in graph ( a ) below . since increasing the light amplitude has no effect on the energy of the incoming photon , the photoelectron kinetic energy remains constant as the light amplitude is increased ( see graph ( b ) above ) . if we try to explain this result using our dock-and-beach-balls analogy , the relationship in graph ( b ) indicates that no matter the height of the wave hitting the dock $ - $ whether it 's a tiny swell , or a huge tsunami $ - $ the individual beach balls would be launched off the dock with the exact same speed ! thus , our intuition and analogy do n't do a very good job of explaining these particular experiments . example $ 1 $ : the photoelectric effect for copper the work function of copper metal is $ \phi=7.53\times10^ { -19 } \text { j } $ . if we shine light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ on copper metal , will the photoelectric effect be observed ? in order to eject electrons , we need the energy of the photons to be greater than the work function of copper . we can use planck 's equation to calculate the energy of the photon , $ \text { e } _ { \text { photon } } $ : $ \begin { align } \text { e } _\text { photon } & amp ; = h\nu \ & amp ; = ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) ( 3.0\times10^ { 16 } \text { hz } ) ~~~~\text { plug in values for $ h $ and $ \nu $ } \ & amp ; = 2.0\times10^ { -17 } \text { j } \end { align } $ if we compare our calculated photon energy , $ \text { e } _\text { photon } $ , to copper 's work function , we see that the photon energy is greater than $ \phi $ : $ ~2.0\times10^ { -17 } \text { j } ~ & gt ; ~7.53\times10^ { -19 } \text { j } $ $ ~~~~~~~~\text { e } _\text { photon } ~~~~~~~~~~~~~~~~~~~\phi $ thus , we would expect to see photoelectrons ejected from the copper . next , we will calculate the kinetic energy of the photoelectrons . example $ 2 $ : calculating the kinetic energy of a photoelectron what is the kinetic energy of the photoelectrons ejected from the copper by the light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ ? we can calculate the kinetic energy of the photoelectron using the equation that relates $ \text { ke } \text { electron } $ to the energy of the photon , $ \text { e } \text { photon } $ , and the work function , $ \phi $ : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ since we want to know $ \text { ke } _\text { electron } $ , we can start by rearranging the equation so that we will be solving for the kinetic energy of the electron : $ \text { ke } \text { electron } =\text { e } \text { photon } -\phi $ now we can insert our known values for $ \text { e } _\text { photon } $ and $ \phi $ from example 1 : $ \text { ke } _\text { electron } = ( 2.0\times10^ { -17 } \text { j } ) - ( 7.53\times10^ { -19 } \text { j } ) =1.9\times10^ { -17 } \text { j } $ therefore , each photoelectron has a kinetic energy of $ 1.9\times10^ { -17 } \text { j } $ . summary based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a specific metal surface . the energy of the incident photon must be equal to the sum of the work function and the kinetic energy of a photoelectron : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ try it ! when we shine light with a frequency of $ 6.20 \times 10^ { 14 } \ , \text { hz } $ on a mystery metal , we observe the ejected electrons have a kinetic energy of $ 3.28\times 10^ { -20 } \ , \text j $ . some possible candidates for the mystery metal are shown in the table below : metal | work function $ \phi $ ( joules , $ \text j $ ) : - : | : - : calcium , $ \text { ca } $ | $ 4.60\times 10^ { -19 } $ tin , $ \text { sn } $ | $ 7.08\times 10^ { -19 } $ sodium , $ \text { na } $ | $ 3.78\times 10^ { -19 } $ hafnium , $ \text { hf } $ | $ 6.25\times 10^ { -19 } $ samarium , $ \text { sm } $ | $ 4.33\times 10^ { -19 } $ based on this information , what is the most likely identity of our mystery metal ?
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when experiments were performed to look at the effect of light amplitude and frequency , the following results were observed : the kinetic energy of photoelectrons increases with light frequency . electric current remains constant as light frequency increases . electric current increases with light amplitude . the kinetic energy of photoelectrons remains constant as light amplitude increases .
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why does higher amplitude mean more current and same with frequency ?
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key points based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . contrary to the predictions , experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of particles called photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a metal surface , and the value of $ \phi $ depends on the metal . the energy of the incident photon must be equal to the sum of the metal 's work function and the photoelectron kinetic energy : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ introduction : what is the photoelectric effect ? when light shines on a metal , electrons can be ejected from the surface of the metal in a phenomenon known as the photoelectric effect . this process is also often referred to as photoemission , and the electrons that are ejected from the metal are called photoelectrons . in terms of their behavior and their properties , photoelectrons are no different from other electrons . the prefix , photo- , simply tells us that the electrons have been ejected from a metal surface by incident light . in this article , we will discuss how 19th century physicists attempted ( but failed ! ) to explain the photoelectric effect using classical physics . this ultimately led to the development of the modern description of electromagnetic radiation , which has both wave-like and particle-like properties . predictions based on light as a wave to explain the photoelectric effect , 19th-century physicists theorized that the oscillating electric field of the incoming light wave was heating the electrons and causing them to vibrate , eventually freeing them from the metal surface . this hypothesis was based on the assumption that light traveled purely as a wave through space . ( see this article for more information about the basic properties of light . ) scientists also believed that the energy of the light wave was proportional to its brightness , which is related to the wave 's amplitude . in order to test their hypotheses , they performed experiments to look at the effect of light amplitude and frequency on the rate of electron ejection , as well as the kinetic energy of the photoelectrons . based on the classical description of light as a wave , they made the following predictions : the kinetic energy of emitted photoelectrons should increase with the light amplitude . the rate of electron emission , which is proportional to the measured electric current , should increase as the light frequency is increased . to help us understand why they made these predictions , we can compare a light wave to a water wave . imagine some beach balls sitting on a dock that extends out into the ocean . the dock represents a metal surface , the beach balls represent electrons , and the ocean waves represent light waves . if a single large wave were to shake the dock , we would expect the energy from the big wave would send the beach balls flying off the dock with much more kinetic energy compared to a single , small wave . this is also what physicists believed would happen if the light intensity was increased . light amplitude was expected to be proportional to the light energy , so higher amplitude light was predicted to result in photoelectrons with more kinetic energy . classical physicists also predicted that increasing the frequency of light waves ( at a constant amplitude ) would increase the rate of electrons being ejected , and thus increase the measured electric current . using our beach ball analogy , we would expect waves hitting the dock more frequently would result in more beach balls being knocked off the dock compared to the same sized waves hitting the dock less often . now that we know what physicists thought would happen , let 's look at what they actually observed experimentally ! when intuition fails : photons to the rescue ! when experiments were performed to look at the effect of light amplitude and frequency , the following results were observed : the kinetic energy of photoelectrons increases with light frequency . electric current remains constant as light frequency increases . electric current increases with light amplitude . the kinetic energy of photoelectrons remains constant as light amplitude increases . these results were completely at odds with the predictions based on the classical description of light as a wave ! in order to explain what was happening , it turned out that an entirely new model of light was needed . that model was developed by albert einstein , who proposed that light sometimes behaved as particles of electromagnetic energy which we now call photons . the energy of a photon could be calculated using planck 's equation : $ \text { e } _ { \text { photon } } =h\nu $ where $ \text { e } _ { \text { photon } } $ is the energy of a photon in joules ( $ \text { j } $ ) , $ h $ is planck 's constant $ ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) $ , and $ \nu $ is the frequency of the light in $ \text { hz } $ . according to planck 's equation , the energy of a photon is proportional to the frequency of the light , $ \nu $ . the amplitude of the light is then proportional to the number of photons with a given frequency . concept check : as the wavelength of a photon increases , what happens to the photon 's energy ? light frequency and the threshold frequency $ \nu_0 $ we can think of the incident light as a stream of photons with an energy determined by the light frequency . when a photon hits the metal surface , the photon 's energy is absorbed by an electron in the metal . the graphic below illustrates the relationship between light frequency and the kinetic energy of ejected electrons . the scientists observed that if the incident light had a frequency less than a minimum frequency $ \nu_0 $ , then no electrons were ejected regardless of the light amplitude . this minimum frequency is also called the threshold frequency , and the value of $ \nu_0 $ depends on the metal . for frequencies greater than $ \nu_0 $ , electrons would be ejected from the metal . furthermore , the kinetic energy of the photoelectrons was proportional to the light frequency . the relationship between photoelectron kinetic energy and light frequency is shown in graph ( a ) below . because the light amplitude was kept constant as the light frequency increased , the number of photons being absorbed by the metal remained constant . thus , the rate at which electrons were ejected from the metal ( or the electric current ) remained constant as well . the relationship between electron current and light frequency is illustrated in graph ( b ) above . is n't there more math somewhere ? we can analyze the frequency relationship using the law of conservation of energy . the total energy of the incoming photon , $ \text { e } \text { photon } $ , must be equal to the kinetic energy of the ejected electron , $ \text { ke } { \text { electron } } $ , plus the energy required to eject the electron from the metal . the energy required to free the electron from a particular metal is also called the metal 's work function , which is represented by the symbol $ \phi $ ( in units of $ \text j $ ) : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ like the threshold frequency $ \nu_0 $ , the value of $ \phi $ also changes depending on the metal . we can now write the energy of the photon in terms of the light frequency using planck 's equation : $ \text { e } \text { photon } =h\nu=\text { ke } \text { electron } +\phi $ rearranging this equation in terms of the electron 's kinetic energy , we get : $ \text { ke } _\text { electron } =h\nu-\phi $ we can see that kinetic energy of the photoelectron increases linearly with $ \nu $ as long as the photon energy is greater than the work function $ \phi $ , which is exactly the relationship shown in graph ( a ) above . we can also use this equation to find the photoelectron velocity $ \text v $ , which is related to $ \text { ke } _\text { electron } $ as follows : $ \text { ke } _\text { electron } =h\nu-\phi=\dfrac { 1 } { 2 } m_e\text v^2 $ where $ m_e $ is the rest mass of an electron , $ 9.1094 \times 10^ { -31 } \ , \text { kg } $ . exploring the wave amplitude trends in terms of photons , higher amplitude light means more photons hitting the metal surface . this results in more electrons ejected over a given time period . as long as the light frequency is greater than $ \nu_0 $ , increasing the light amplitude will cause the electron current to increase proportionally as shown in graph ( a ) below . since increasing the light amplitude has no effect on the energy of the incoming photon , the photoelectron kinetic energy remains constant as the light amplitude is increased ( see graph ( b ) above ) . if we try to explain this result using our dock-and-beach-balls analogy , the relationship in graph ( b ) indicates that no matter the height of the wave hitting the dock $ - $ whether it 's a tiny swell , or a huge tsunami $ - $ the individual beach balls would be launched off the dock with the exact same speed ! thus , our intuition and analogy do n't do a very good job of explaining these particular experiments . example $ 1 $ : the photoelectric effect for copper the work function of copper metal is $ \phi=7.53\times10^ { -19 } \text { j } $ . if we shine light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ on copper metal , will the photoelectric effect be observed ? in order to eject electrons , we need the energy of the photons to be greater than the work function of copper . we can use planck 's equation to calculate the energy of the photon , $ \text { e } _ { \text { photon } } $ : $ \begin { align } \text { e } _\text { photon } & amp ; = h\nu \ & amp ; = ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) ( 3.0\times10^ { 16 } \text { hz } ) ~~~~\text { plug in values for $ h $ and $ \nu $ } \ & amp ; = 2.0\times10^ { -17 } \text { j } \end { align } $ if we compare our calculated photon energy , $ \text { e } _\text { photon } $ , to copper 's work function , we see that the photon energy is greater than $ \phi $ : $ ~2.0\times10^ { -17 } \text { j } ~ & gt ; ~7.53\times10^ { -19 } \text { j } $ $ ~~~~~~~~\text { e } _\text { photon } ~~~~~~~~~~~~~~~~~~~\phi $ thus , we would expect to see photoelectrons ejected from the copper . next , we will calculate the kinetic energy of the photoelectrons . example $ 2 $ : calculating the kinetic energy of a photoelectron what is the kinetic energy of the photoelectrons ejected from the copper by the light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ ? we can calculate the kinetic energy of the photoelectron using the equation that relates $ \text { ke } \text { electron } $ to the energy of the photon , $ \text { e } \text { photon } $ , and the work function , $ \phi $ : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ since we want to know $ \text { ke } _\text { electron } $ , we can start by rearranging the equation so that we will be solving for the kinetic energy of the electron : $ \text { ke } \text { electron } =\text { e } \text { photon } -\phi $ now we can insert our known values for $ \text { e } _\text { photon } $ and $ \phi $ from example 1 : $ \text { ke } _\text { electron } = ( 2.0\times10^ { -17 } \text { j } ) - ( 7.53\times10^ { -19 } \text { j } ) =1.9\times10^ { -17 } \text { j } $ therefore , each photoelectron has a kinetic energy of $ 1.9\times10^ { -17 } \text { j } $ . summary based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a specific metal surface . the energy of the incident photon must be equal to the sum of the work function and the kinetic energy of a photoelectron : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ try it ! when we shine light with a frequency of $ 6.20 \times 10^ { 14 } \ , \text { hz } $ on a mystery metal , we observe the ejected electrons have a kinetic energy of $ 3.28\times 10^ { -20 } \ , \text j $ . some possible candidates for the mystery metal are shown in the table below : metal | work function $ \phi $ ( joules , $ \text j $ ) : - : | : - : calcium , $ \text { ca } $ | $ 4.60\times 10^ { -19 } $ tin , $ \text { sn } $ | $ 7.08\times 10^ { -19 } $ sodium , $ \text { na } $ | $ 3.78\times 10^ { -19 } $ hafnium , $ \text { hf } $ | $ 6.25\times 10^ { -19 } $ samarium , $ \text { sm } $ | $ 4.33\times 10^ { -19 } $ based on this information , what is the most likely identity of our mystery metal ?
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electric current remains constant as light frequency increases . electric current increases with light amplitude . the kinetic energy of photoelectrons remains constant as light amplitude increases .
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does high amplitude mean the photon hits cover more area and so hitting on more electrons thus releasing more electrons for higher current ?
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key points based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . contrary to the predictions , experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of particles called photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a metal surface , and the value of $ \phi $ depends on the metal . the energy of the incident photon must be equal to the sum of the metal 's work function and the photoelectron kinetic energy : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ introduction : what is the photoelectric effect ? when light shines on a metal , electrons can be ejected from the surface of the metal in a phenomenon known as the photoelectric effect . this process is also often referred to as photoemission , and the electrons that are ejected from the metal are called photoelectrons . in terms of their behavior and their properties , photoelectrons are no different from other electrons . the prefix , photo- , simply tells us that the electrons have been ejected from a metal surface by incident light . in this article , we will discuss how 19th century physicists attempted ( but failed ! ) to explain the photoelectric effect using classical physics . this ultimately led to the development of the modern description of electromagnetic radiation , which has both wave-like and particle-like properties . predictions based on light as a wave to explain the photoelectric effect , 19th-century physicists theorized that the oscillating electric field of the incoming light wave was heating the electrons and causing them to vibrate , eventually freeing them from the metal surface . this hypothesis was based on the assumption that light traveled purely as a wave through space . ( see this article for more information about the basic properties of light . ) scientists also believed that the energy of the light wave was proportional to its brightness , which is related to the wave 's amplitude . in order to test their hypotheses , they performed experiments to look at the effect of light amplitude and frequency on the rate of electron ejection , as well as the kinetic energy of the photoelectrons . based on the classical description of light as a wave , they made the following predictions : the kinetic energy of emitted photoelectrons should increase with the light amplitude . the rate of electron emission , which is proportional to the measured electric current , should increase as the light frequency is increased . to help us understand why they made these predictions , we can compare a light wave to a water wave . imagine some beach balls sitting on a dock that extends out into the ocean . the dock represents a metal surface , the beach balls represent electrons , and the ocean waves represent light waves . if a single large wave were to shake the dock , we would expect the energy from the big wave would send the beach balls flying off the dock with much more kinetic energy compared to a single , small wave . this is also what physicists believed would happen if the light intensity was increased . light amplitude was expected to be proportional to the light energy , so higher amplitude light was predicted to result in photoelectrons with more kinetic energy . classical physicists also predicted that increasing the frequency of light waves ( at a constant amplitude ) would increase the rate of electrons being ejected , and thus increase the measured electric current . using our beach ball analogy , we would expect waves hitting the dock more frequently would result in more beach balls being knocked off the dock compared to the same sized waves hitting the dock less often . now that we know what physicists thought would happen , let 's look at what they actually observed experimentally ! when intuition fails : photons to the rescue ! when experiments were performed to look at the effect of light amplitude and frequency , the following results were observed : the kinetic energy of photoelectrons increases with light frequency . electric current remains constant as light frequency increases . electric current increases with light amplitude . the kinetic energy of photoelectrons remains constant as light amplitude increases . these results were completely at odds with the predictions based on the classical description of light as a wave ! in order to explain what was happening , it turned out that an entirely new model of light was needed . that model was developed by albert einstein , who proposed that light sometimes behaved as particles of electromagnetic energy which we now call photons . the energy of a photon could be calculated using planck 's equation : $ \text { e } _ { \text { photon } } =h\nu $ where $ \text { e } _ { \text { photon } } $ is the energy of a photon in joules ( $ \text { j } $ ) , $ h $ is planck 's constant $ ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) $ , and $ \nu $ is the frequency of the light in $ \text { hz } $ . according to planck 's equation , the energy of a photon is proportional to the frequency of the light , $ \nu $ . the amplitude of the light is then proportional to the number of photons with a given frequency . concept check : as the wavelength of a photon increases , what happens to the photon 's energy ? light frequency and the threshold frequency $ \nu_0 $ we can think of the incident light as a stream of photons with an energy determined by the light frequency . when a photon hits the metal surface , the photon 's energy is absorbed by an electron in the metal . the graphic below illustrates the relationship between light frequency and the kinetic energy of ejected electrons . the scientists observed that if the incident light had a frequency less than a minimum frequency $ \nu_0 $ , then no electrons were ejected regardless of the light amplitude . this minimum frequency is also called the threshold frequency , and the value of $ \nu_0 $ depends on the metal . for frequencies greater than $ \nu_0 $ , electrons would be ejected from the metal . furthermore , the kinetic energy of the photoelectrons was proportional to the light frequency . the relationship between photoelectron kinetic energy and light frequency is shown in graph ( a ) below . because the light amplitude was kept constant as the light frequency increased , the number of photons being absorbed by the metal remained constant . thus , the rate at which electrons were ejected from the metal ( or the electric current ) remained constant as well . the relationship between electron current and light frequency is illustrated in graph ( b ) above . is n't there more math somewhere ? we can analyze the frequency relationship using the law of conservation of energy . the total energy of the incoming photon , $ \text { e } \text { photon } $ , must be equal to the kinetic energy of the ejected electron , $ \text { ke } { \text { electron } } $ , plus the energy required to eject the electron from the metal . the energy required to free the electron from a particular metal is also called the metal 's work function , which is represented by the symbol $ \phi $ ( in units of $ \text j $ ) : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ like the threshold frequency $ \nu_0 $ , the value of $ \phi $ also changes depending on the metal . we can now write the energy of the photon in terms of the light frequency using planck 's equation : $ \text { e } \text { photon } =h\nu=\text { ke } \text { electron } +\phi $ rearranging this equation in terms of the electron 's kinetic energy , we get : $ \text { ke } _\text { electron } =h\nu-\phi $ we can see that kinetic energy of the photoelectron increases linearly with $ \nu $ as long as the photon energy is greater than the work function $ \phi $ , which is exactly the relationship shown in graph ( a ) above . we can also use this equation to find the photoelectron velocity $ \text v $ , which is related to $ \text { ke } _\text { electron } $ as follows : $ \text { ke } _\text { electron } =h\nu-\phi=\dfrac { 1 } { 2 } m_e\text v^2 $ where $ m_e $ is the rest mass of an electron , $ 9.1094 \times 10^ { -31 } \ , \text { kg } $ . exploring the wave amplitude trends in terms of photons , higher amplitude light means more photons hitting the metal surface . this results in more electrons ejected over a given time period . as long as the light frequency is greater than $ \nu_0 $ , increasing the light amplitude will cause the electron current to increase proportionally as shown in graph ( a ) below . since increasing the light amplitude has no effect on the energy of the incoming photon , the photoelectron kinetic energy remains constant as the light amplitude is increased ( see graph ( b ) above ) . if we try to explain this result using our dock-and-beach-balls analogy , the relationship in graph ( b ) indicates that no matter the height of the wave hitting the dock $ - $ whether it 's a tiny swell , or a huge tsunami $ - $ the individual beach balls would be launched off the dock with the exact same speed ! thus , our intuition and analogy do n't do a very good job of explaining these particular experiments . example $ 1 $ : the photoelectric effect for copper the work function of copper metal is $ \phi=7.53\times10^ { -19 } \text { j } $ . if we shine light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ on copper metal , will the photoelectric effect be observed ? in order to eject electrons , we need the energy of the photons to be greater than the work function of copper . we can use planck 's equation to calculate the energy of the photon , $ \text { e } _ { \text { photon } } $ : $ \begin { align } \text { e } _\text { photon } & amp ; = h\nu \ & amp ; = ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) ( 3.0\times10^ { 16 } \text { hz } ) ~~~~\text { plug in values for $ h $ and $ \nu $ } \ & amp ; = 2.0\times10^ { -17 } \text { j } \end { align } $ if we compare our calculated photon energy , $ \text { e } _\text { photon } $ , to copper 's work function , we see that the photon energy is greater than $ \phi $ : $ ~2.0\times10^ { -17 } \text { j } ~ & gt ; ~7.53\times10^ { -19 } \text { j } $ $ ~~~~~~~~\text { e } _\text { photon } ~~~~~~~~~~~~~~~~~~~\phi $ thus , we would expect to see photoelectrons ejected from the copper . next , we will calculate the kinetic energy of the photoelectrons . example $ 2 $ : calculating the kinetic energy of a photoelectron what is the kinetic energy of the photoelectrons ejected from the copper by the light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ ? we can calculate the kinetic energy of the photoelectron using the equation that relates $ \text { ke } \text { electron } $ to the energy of the photon , $ \text { e } \text { photon } $ , and the work function , $ \phi $ : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ since we want to know $ \text { ke } _\text { electron } $ , we can start by rearranging the equation so that we will be solving for the kinetic energy of the electron : $ \text { ke } \text { electron } =\text { e } \text { photon } -\phi $ now we can insert our known values for $ \text { e } _\text { photon } $ and $ \phi $ from example 1 : $ \text { ke } _\text { electron } = ( 2.0\times10^ { -17 } \text { j } ) - ( 7.53\times10^ { -19 } \text { j } ) =1.9\times10^ { -17 } \text { j } $ therefore , each photoelectron has a kinetic energy of $ 1.9\times10^ { -17 } \text { j } $ . summary based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a specific metal surface . the energy of the incident photon must be equal to the sum of the work function and the kinetic energy of a photoelectron : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ try it ! when we shine light with a frequency of $ 6.20 \times 10^ { 14 } \ , \text { hz } $ on a mystery metal , we observe the ejected electrons have a kinetic energy of $ 3.28\times 10^ { -20 } \ , \text j $ . some possible candidates for the mystery metal are shown in the table below : metal | work function $ \phi $ ( joules , $ \text j $ ) : - : | : - : calcium , $ \text { ca } $ | $ 4.60\times 10^ { -19 } $ tin , $ \text { sn } $ | $ 7.08\times 10^ { -19 } $ sodium , $ \text { na } $ | $ 3.78\times 10^ { -19 } $ hafnium , $ \text { hf } $ | $ 6.25\times 10^ { -19 } $ samarium , $ \text { sm } $ | $ 4.33\times 10^ { -19 } $ based on this information , what is the most likely identity of our mystery metal ?
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imagine some beach balls sitting on a dock that extends out into the ocean . the dock represents a metal surface , the beach balls represent electrons , and the ocean waves represent light waves . if a single large wave were to shake the dock , we would expect the energy from the big wave would send the beach balls flying off the dock with much more kinetic energy compared to a single , small wave .
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would two electromagnetic waves ( photons ) of the same frequency and same but opposite amplitude cancel each other out as sound waves and water waves do ?
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key points based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . contrary to the predictions , experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of particles called photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a metal surface , and the value of $ \phi $ depends on the metal . the energy of the incident photon must be equal to the sum of the metal 's work function and the photoelectron kinetic energy : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ introduction : what is the photoelectric effect ? when light shines on a metal , electrons can be ejected from the surface of the metal in a phenomenon known as the photoelectric effect . this process is also often referred to as photoemission , and the electrons that are ejected from the metal are called photoelectrons . in terms of their behavior and their properties , photoelectrons are no different from other electrons . the prefix , photo- , simply tells us that the electrons have been ejected from a metal surface by incident light . in this article , we will discuss how 19th century physicists attempted ( but failed ! ) to explain the photoelectric effect using classical physics . this ultimately led to the development of the modern description of electromagnetic radiation , which has both wave-like and particle-like properties . predictions based on light as a wave to explain the photoelectric effect , 19th-century physicists theorized that the oscillating electric field of the incoming light wave was heating the electrons and causing them to vibrate , eventually freeing them from the metal surface . this hypothesis was based on the assumption that light traveled purely as a wave through space . ( see this article for more information about the basic properties of light . ) scientists also believed that the energy of the light wave was proportional to its brightness , which is related to the wave 's amplitude . in order to test their hypotheses , they performed experiments to look at the effect of light amplitude and frequency on the rate of electron ejection , as well as the kinetic energy of the photoelectrons . based on the classical description of light as a wave , they made the following predictions : the kinetic energy of emitted photoelectrons should increase with the light amplitude . the rate of electron emission , which is proportional to the measured electric current , should increase as the light frequency is increased . to help us understand why they made these predictions , we can compare a light wave to a water wave . imagine some beach balls sitting on a dock that extends out into the ocean . the dock represents a metal surface , the beach balls represent electrons , and the ocean waves represent light waves . if a single large wave were to shake the dock , we would expect the energy from the big wave would send the beach balls flying off the dock with much more kinetic energy compared to a single , small wave . this is also what physicists believed would happen if the light intensity was increased . light amplitude was expected to be proportional to the light energy , so higher amplitude light was predicted to result in photoelectrons with more kinetic energy . classical physicists also predicted that increasing the frequency of light waves ( at a constant amplitude ) would increase the rate of electrons being ejected , and thus increase the measured electric current . using our beach ball analogy , we would expect waves hitting the dock more frequently would result in more beach balls being knocked off the dock compared to the same sized waves hitting the dock less often . now that we know what physicists thought would happen , let 's look at what they actually observed experimentally ! when intuition fails : photons to the rescue ! when experiments were performed to look at the effect of light amplitude and frequency , the following results were observed : the kinetic energy of photoelectrons increases with light frequency . electric current remains constant as light frequency increases . electric current increases with light amplitude . the kinetic energy of photoelectrons remains constant as light amplitude increases . these results were completely at odds with the predictions based on the classical description of light as a wave ! in order to explain what was happening , it turned out that an entirely new model of light was needed . that model was developed by albert einstein , who proposed that light sometimes behaved as particles of electromagnetic energy which we now call photons . the energy of a photon could be calculated using planck 's equation : $ \text { e } _ { \text { photon } } =h\nu $ where $ \text { e } _ { \text { photon } } $ is the energy of a photon in joules ( $ \text { j } $ ) , $ h $ is planck 's constant $ ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) $ , and $ \nu $ is the frequency of the light in $ \text { hz } $ . according to planck 's equation , the energy of a photon is proportional to the frequency of the light , $ \nu $ . the amplitude of the light is then proportional to the number of photons with a given frequency . concept check : as the wavelength of a photon increases , what happens to the photon 's energy ? light frequency and the threshold frequency $ \nu_0 $ we can think of the incident light as a stream of photons with an energy determined by the light frequency . when a photon hits the metal surface , the photon 's energy is absorbed by an electron in the metal . the graphic below illustrates the relationship between light frequency and the kinetic energy of ejected electrons . the scientists observed that if the incident light had a frequency less than a minimum frequency $ \nu_0 $ , then no electrons were ejected regardless of the light amplitude . this minimum frequency is also called the threshold frequency , and the value of $ \nu_0 $ depends on the metal . for frequencies greater than $ \nu_0 $ , electrons would be ejected from the metal . furthermore , the kinetic energy of the photoelectrons was proportional to the light frequency . the relationship between photoelectron kinetic energy and light frequency is shown in graph ( a ) below . because the light amplitude was kept constant as the light frequency increased , the number of photons being absorbed by the metal remained constant . thus , the rate at which electrons were ejected from the metal ( or the electric current ) remained constant as well . the relationship between electron current and light frequency is illustrated in graph ( b ) above . is n't there more math somewhere ? we can analyze the frequency relationship using the law of conservation of energy . the total energy of the incoming photon , $ \text { e } \text { photon } $ , must be equal to the kinetic energy of the ejected electron , $ \text { ke } { \text { electron } } $ , plus the energy required to eject the electron from the metal . the energy required to free the electron from a particular metal is also called the metal 's work function , which is represented by the symbol $ \phi $ ( in units of $ \text j $ ) : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ like the threshold frequency $ \nu_0 $ , the value of $ \phi $ also changes depending on the metal . we can now write the energy of the photon in terms of the light frequency using planck 's equation : $ \text { e } \text { photon } =h\nu=\text { ke } \text { electron } +\phi $ rearranging this equation in terms of the electron 's kinetic energy , we get : $ \text { ke } _\text { electron } =h\nu-\phi $ we can see that kinetic energy of the photoelectron increases linearly with $ \nu $ as long as the photon energy is greater than the work function $ \phi $ , which is exactly the relationship shown in graph ( a ) above . we can also use this equation to find the photoelectron velocity $ \text v $ , which is related to $ \text { ke } _\text { electron } $ as follows : $ \text { ke } _\text { electron } =h\nu-\phi=\dfrac { 1 } { 2 } m_e\text v^2 $ where $ m_e $ is the rest mass of an electron , $ 9.1094 \times 10^ { -31 } \ , \text { kg } $ . exploring the wave amplitude trends in terms of photons , higher amplitude light means more photons hitting the metal surface . this results in more electrons ejected over a given time period . as long as the light frequency is greater than $ \nu_0 $ , increasing the light amplitude will cause the electron current to increase proportionally as shown in graph ( a ) below . since increasing the light amplitude has no effect on the energy of the incoming photon , the photoelectron kinetic energy remains constant as the light amplitude is increased ( see graph ( b ) above ) . if we try to explain this result using our dock-and-beach-balls analogy , the relationship in graph ( b ) indicates that no matter the height of the wave hitting the dock $ - $ whether it 's a tiny swell , or a huge tsunami $ - $ the individual beach balls would be launched off the dock with the exact same speed ! thus , our intuition and analogy do n't do a very good job of explaining these particular experiments . example $ 1 $ : the photoelectric effect for copper the work function of copper metal is $ \phi=7.53\times10^ { -19 } \text { j } $ . if we shine light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ on copper metal , will the photoelectric effect be observed ? in order to eject electrons , we need the energy of the photons to be greater than the work function of copper . we can use planck 's equation to calculate the energy of the photon , $ \text { e } _ { \text { photon } } $ : $ \begin { align } \text { e } _\text { photon } & amp ; = h\nu \ & amp ; = ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) ( 3.0\times10^ { 16 } \text { hz } ) ~~~~\text { plug in values for $ h $ and $ \nu $ } \ & amp ; = 2.0\times10^ { -17 } \text { j } \end { align } $ if we compare our calculated photon energy , $ \text { e } _\text { photon } $ , to copper 's work function , we see that the photon energy is greater than $ \phi $ : $ ~2.0\times10^ { -17 } \text { j } ~ & gt ; ~7.53\times10^ { -19 } \text { j } $ $ ~~~~~~~~\text { e } _\text { photon } ~~~~~~~~~~~~~~~~~~~\phi $ thus , we would expect to see photoelectrons ejected from the copper . next , we will calculate the kinetic energy of the photoelectrons . example $ 2 $ : calculating the kinetic energy of a photoelectron what is the kinetic energy of the photoelectrons ejected from the copper by the light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ ? we can calculate the kinetic energy of the photoelectron using the equation that relates $ \text { ke } \text { electron } $ to the energy of the photon , $ \text { e } \text { photon } $ , and the work function , $ \phi $ : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ since we want to know $ \text { ke } _\text { electron } $ , we can start by rearranging the equation so that we will be solving for the kinetic energy of the electron : $ \text { ke } \text { electron } =\text { e } \text { photon } -\phi $ now we can insert our known values for $ \text { e } _\text { photon } $ and $ \phi $ from example 1 : $ \text { ke } _\text { electron } = ( 2.0\times10^ { -17 } \text { j } ) - ( 7.53\times10^ { -19 } \text { j } ) =1.9\times10^ { -17 } \text { j } $ therefore , each photoelectron has a kinetic energy of $ 1.9\times10^ { -17 } \text { j } $ . summary based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a specific metal surface . the energy of the incident photon must be equal to the sum of the work function and the kinetic energy of a photoelectron : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ try it ! when we shine light with a frequency of $ 6.20 \times 10^ { 14 } \ , \text { hz } $ on a mystery metal , we observe the ejected electrons have a kinetic energy of $ 3.28\times 10^ { -20 } \ , \text j $ . some possible candidates for the mystery metal are shown in the table below : metal | work function $ \phi $ ( joules , $ \text j $ ) : - : | : - : calcium , $ \text { ca } $ | $ 4.60\times 10^ { -19 } $ tin , $ \text { sn } $ | $ 7.08\times 10^ { -19 } $ sodium , $ \text { na } $ | $ 3.78\times 10^ { -19 } $ hafnium , $ \text { hf } $ | $ 6.25\times 10^ { -19 } $ samarium , $ \text { sm } $ | $ 4.33\times 10^ { -19 } $ based on this information , what is the most likely identity of our mystery metal ?
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we can also use this equation to find the photoelectron velocity $ \text v $ , which is related to $ \text { ke } _\text { electron } $ as follows : $ \text { ke } _\text { electron } =h\nu-\phi=\dfrac { 1 } { 2 } m_e\text v^2 $ where $ m_e $ is the rest mass of an electron , $ 9.1094 \times 10^ { -31 } \ , \text { kg } $ . exploring the wave amplitude trends in terms of photons , higher amplitude light means more photons hitting the metal surface . this results in more electrons ejected over a given time period .
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can photons be converted to mass ?
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key points based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . contrary to the predictions , experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of particles called photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a metal surface , and the value of $ \phi $ depends on the metal . the energy of the incident photon must be equal to the sum of the metal 's work function and the photoelectron kinetic energy : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ introduction : what is the photoelectric effect ? when light shines on a metal , electrons can be ejected from the surface of the metal in a phenomenon known as the photoelectric effect . this process is also often referred to as photoemission , and the electrons that are ejected from the metal are called photoelectrons . in terms of their behavior and their properties , photoelectrons are no different from other electrons . the prefix , photo- , simply tells us that the electrons have been ejected from a metal surface by incident light . in this article , we will discuss how 19th century physicists attempted ( but failed ! ) to explain the photoelectric effect using classical physics . this ultimately led to the development of the modern description of electromagnetic radiation , which has both wave-like and particle-like properties . predictions based on light as a wave to explain the photoelectric effect , 19th-century physicists theorized that the oscillating electric field of the incoming light wave was heating the electrons and causing them to vibrate , eventually freeing them from the metal surface . this hypothesis was based on the assumption that light traveled purely as a wave through space . ( see this article for more information about the basic properties of light . ) scientists also believed that the energy of the light wave was proportional to its brightness , which is related to the wave 's amplitude . in order to test their hypotheses , they performed experiments to look at the effect of light amplitude and frequency on the rate of electron ejection , as well as the kinetic energy of the photoelectrons . based on the classical description of light as a wave , they made the following predictions : the kinetic energy of emitted photoelectrons should increase with the light amplitude . the rate of electron emission , which is proportional to the measured electric current , should increase as the light frequency is increased . to help us understand why they made these predictions , we can compare a light wave to a water wave . imagine some beach balls sitting on a dock that extends out into the ocean . the dock represents a metal surface , the beach balls represent electrons , and the ocean waves represent light waves . if a single large wave were to shake the dock , we would expect the energy from the big wave would send the beach balls flying off the dock with much more kinetic energy compared to a single , small wave . this is also what physicists believed would happen if the light intensity was increased . light amplitude was expected to be proportional to the light energy , so higher amplitude light was predicted to result in photoelectrons with more kinetic energy . classical physicists also predicted that increasing the frequency of light waves ( at a constant amplitude ) would increase the rate of electrons being ejected , and thus increase the measured electric current . using our beach ball analogy , we would expect waves hitting the dock more frequently would result in more beach balls being knocked off the dock compared to the same sized waves hitting the dock less often . now that we know what physicists thought would happen , let 's look at what they actually observed experimentally ! when intuition fails : photons to the rescue ! when experiments were performed to look at the effect of light amplitude and frequency , the following results were observed : the kinetic energy of photoelectrons increases with light frequency . electric current remains constant as light frequency increases . electric current increases with light amplitude . the kinetic energy of photoelectrons remains constant as light amplitude increases . these results were completely at odds with the predictions based on the classical description of light as a wave ! in order to explain what was happening , it turned out that an entirely new model of light was needed . that model was developed by albert einstein , who proposed that light sometimes behaved as particles of electromagnetic energy which we now call photons . the energy of a photon could be calculated using planck 's equation : $ \text { e } _ { \text { photon } } =h\nu $ where $ \text { e } _ { \text { photon } } $ is the energy of a photon in joules ( $ \text { j } $ ) , $ h $ is planck 's constant $ ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) $ , and $ \nu $ is the frequency of the light in $ \text { hz } $ . according to planck 's equation , the energy of a photon is proportional to the frequency of the light , $ \nu $ . the amplitude of the light is then proportional to the number of photons with a given frequency . concept check : as the wavelength of a photon increases , what happens to the photon 's energy ? light frequency and the threshold frequency $ \nu_0 $ we can think of the incident light as a stream of photons with an energy determined by the light frequency . when a photon hits the metal surface , the photon 's energy is absorbed by an electron in the metal . the graphic below illustrates the relationship between light frequency and the kinetic energy of ejected electrons . the scientists observed that if the incident light had a frequency less than a minimum frequency $ \nu_0 $ , then no electrons were ejected regardless of the light amplitude . this minimum frequency is also called the threshold frequency , and the value of $ \nu_0 $ depends on the metal . for frequencies greater than $ \nu_0 $ , electrons would be ejected from the metal . furthermore , the kinetic energy of the photoelectrons was proportional to the light frequency . the relationship between photoelectron kinetic energy and light frequency is shown in graph ( a ) below . because the light amplitude was kept constant as the light frequency increased , the number of photons being absorbed by the metal remained constant . thus , the rate at which electrons were ejected from the metal ( or the electric current ) remained constant as well . the relationship between electron current and light frequency is illustrated in graph ( b ) above . is n't there more math somewhere ? we can analyze the frequency relationship using the law of conservation of energy . the total energy of the incoming photon , $ \text { e } \text { photon } $ , must be equal to the kinetic energy of the ejected electron , $ \text { ke } { \text { electron } } $ , plus the energy required to eject the electron from the metal . the energy required to free the electron from a particular metal is also called the metal 's work function , which is represented by the symbol $ \phi $ ( in units of $ \text j $ ) : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ like the threshold frequency $ \nu_0 $ , the value of $ \phi $ also changes depending on the metal . we can now write the energy of the photon in terms of the light frequency using planck 's equation : $ \text { e } \text { photon } =h\nu=\text { ke } \text { electron } +\phi $ rearranging this equation in terms of the electron 's kinetic energy , we get : $ \text { ke } _\text { electron } =h\nu-\phi $ we can see that kinetic energy of the photoelectron increases linearly with $ \nu $ as long as the photon energy is greater than the work function $ \phi $ , which is exactly the relationship shown in graph ( a ) above . we can also use this equation to find the photoelectron velocity $ \text v $ , which is related to $ \text { ke } _\text { electron } $ as follows : $ \text { ke } _\text { electron } =h\nu-\phi=\dfrac { 1 } { 2 } m_e\text v^2 $ where $ m_e $ is the rest mass of an electron , $ 9.1094 \times 10^ { -31 } \ , \text { kg } $ . exploring the wave amplitude trends in terms of photons , higher amplitude light means more photons hitting the metal surface . this results in more electrons ejected over a given time period . as long as the light frequency is greater than $ \nu_0 $ , increasing the light amplitude will cause the electron current to increase proportionally as shown in graph ( a ) below . since increasing the light amplitude has no effect on the energy of the incoming photon , the photoelectron kinetic energy remains constant as the light amplitude is increased ( see graph ( b ) above ) . if we try to explain this result using our dock-and-beach-balls analogy , the relationship in graph ( b ) indicates that no matter the height of the wave hitting the dock $ - $ whether it 's a tiny swell , or a huge tsunami $ - $ the individual beach balls would be launched off the dock with the exact same speed ! thus , our intuition and analogy do n't do a very good job of explaining these particular experiments . example $ 1 $ : the photoelectric effect for copper the work function of copper metal is $ \phi=7.53\times10^ { -19 } \text { j } $ . if we shine light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ on copper metal , will the photoelectric effect be observed ? in order to eject electrons , we need the energy of the photons to be greater than the work function of copper . we can use planck 's equation to calculate the energy of the photon , $ \text { e } _ { \text { photon } } $ : $ \begin { align } \text { e } _\text { photon } & amp ; = h\nu \ & amp ; = ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) ( 3.0\times10^ { 16 } \text { hz } ) ~~~~\text { plug in values for $ h $ and $ \nu $ } \ & amp ; = 2.0\times10^ { -17 } \text { j } \end { align } $ if we compare our calculated photon energy , $ \text { e } _\text { photon } $ , to copper 's work function , we see that the photon energy is greater than $ \phi $ : $ ~2.0\times10^ { -17 } \text { j } ~ & gt ; ~7.53\times10^ { -19 } \text { j } $ $ ~~~~~~~~\text { e } _\text { photon } ~~~~~~~~~~~~~~~~~~~\phi $ thus , we would expect to see photoelectrons ejected from the copper . next , we will calculate the kinetic energy of the photoelectrons . example $ 2 $ : calculating the kinetic energy of a photoelectron what is the kinetic energy of the photoelectrons ejected from the copper by the light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ ? we can calculate the kinetic energy of the photoelectron using the equation that relates $ \text { ke } \text { electron } $ to the energy of the photon , $ \text { e } \text { photon } $ , and the work function , $ \phi $ : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ since we want to know $ \text { ke } _\text { electron } $ , we can start by rearranging the equation so that we will be solving for the kinetic energy of the electron : $ \text { ke } \text { electron } =\text { e } \text { photon } -\phi $ now we can insert our known values for $ \text { e } _\text { photon } $ and $ \phi $ from example 1 : $ \text { ke } _\text { electron } = ( 2.0\times10^ { -17 } \text { j } ) - ( 7.53\times10^ { -19 } \text { j } ) =1.9\times10^ { -17 } \text { j } $ therefore , each photoelectron has a kinetic energy of $ 1.9\times10^ { -17 } \text { j } $ . summary based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a specific metal surface . the energy of the incident photon must be equal to the sum of the work function and the kinetic energy of a photoelectron : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ try it ! when we shine light with a frequency of $ 6.20 \times 10^ { 14 } \ , \text { hz } $ on a mystery metal , we observe the ejected electrons have a kinetic energy of $ 3.28\times 10^ { -20 } \ , \text j $ . some possible candidates for the mystery metal are shown in the table below : metal | work function $ \phi $ ( joules , $ \text j $ ) : - : | : - : calcium , $ \text { ca } $ | $ 4.60\times 10^ { -19 } $ tin , $ \text { sn } $ | $ 7.08\times 10^ { -19 } $ sodium , $ \text { na } $ | $ 3.78\times 10^ { -19 } $ hafnium , $ \text { hf } $ | $ 6.25\times 10^ { -19 } $ samarium , $ \text { sm } $ | $ 4.33\times 10^ { -19 } $ based on this information , what is the most likely identity of our mystery metal ?
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the relationship between electron current and light frequency is illustrated in graph ( b ) above . is n't there more math somewhere ? we can analyze the frequency relationship using the law of conservation of energy .
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so why these metals we does n't use for solar panels ?
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key points based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . contrary to the predictions , experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of particles called photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a metal surface , and the value of $ \phi $ depends on the metal . the energy of the incident photon must be equal to the sum of the metal 's work function and the photoelectron kinetic energy : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ introduction : what is the photoelectric effect ? when light shines on a metal , electrons can be ejected from the surface of the metal in a phenomenon known as the photoelectric effect . this process is also often referred to as photoemission , and the electrons that are ejected from the metal are called photoelectrons . in terms of their behavior and their properties , photoelectrons are no different from other electrons . the prefix , photo- , simply tells us that the electrons have been ejected from a metal surface by incident light . in this article , we will discuss how 19th century physicists attempted ( but failed ! ) to explain the photoelectric effect using classical physics . this ultimately led to the development of the modern description of electromagnetic radiation , which has both wave-like and particle-like properties . predictions based on light as a wave to explain the photoelectric effect , 19th-century physicists theorized that the oscillating electric field of the incoming light wave was heating the electrons and causing them to vibrate , eventually freeing them from the metal surface . this hypothesis was based on the assumption that light traveled purely as a wave through space . ( see this article for more information about the basic properties of light . ) scientists also believed that the energy of the light wave was proportional to its brightness , which is related to the wave 's amplitude . in order to test their hypotheses , they performed experiments to look at the effect of light amplitude and frequency on the rate of electron ejection , as well as the kinetic energy of the photoelectrons . based on the classical description of light as a wave , they made the following predictions : the kinetic energy of emitted photoelectrons should increase with the light amplitude . the rate of electron emission , which is proportional to the measured electric current , should increase as the light frequency is increased . to help us understand why they made these predictions , we can compare a light wave to a water wave . imagine some beach balls sitting on a dock that extends out into the ocean . the dock represents a metal surface , the beach balls represent electrons , and the ocean waves represent light waves . if a single large wave were to shake the dock , we would expect the energy from the big wave would send the beach balls flying off the dock with much more kinetic energy compared to a single , small wave . this is also what physicists believed would happen if the light intensity was increased . light amplitude was expected to be proportional to the light energy , so higher amplitude light was predicted to result in photoelectrons with more kinetic energy . classical physicists also predicted that increasing the frequency of light waves ( at a constant amplitude ) would increase the rate of electrons being ejected , and thus increase the measured electric current . using our beach ball analogy , we would expect waves hitting the dock more frequently would result in more beach balls being knocked off the dock compared to the same sized waves hitting the dock less often . now that we know what physicists thought would happen , let 's look at what they actually observed experimentally ! when intuition fails : photons to the rescue ! when experiments were performed to look at the effect of light amplitude and frequency , the following results were observed : the kinetic energy of photoelectrons increases with light frequency . electric current remains constant as light frequency increases . electric current increases with light amplitude . the kinetic energy of photoelectrons remains constant as light amplitude increases . these results were completely at odds with the predictions based on the classical description of light as a wave ! in order to explain what was happening , it turned out that an entirely new model of light was needed . that model was developed by albert einstein , who proposed that light sometimes behaved as particles of electromagnetic energy which we now call photons . the energy of a photon could be calculated using planck 's equation : $ \text { e } _ { \text { photon } } =h\nu $ where $ \text { e } _ { \text { photon } } $ is the energy of a photon in joules ( $ \text { j } $ ) , $ h $ is planck 's constant $ ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) $ , and $ \nu $ is the frequency of the light in $ \text { hz } $ . according to planck 's equation , the energy of a photon is proportional to the frequency of the light , $ \nu $ . the amplitude of the light is then proportional to the number of photons with a given frequency . concept check : as the wavelength of a photon increases , what happens to the photon 's energy ? light frequency and the threshold frequency $ \nu_0 $ we can think of the incident light as a stream of photons with an energy determined by the light frequency . when a photon hits the metal surface , the photon 's energy is absorbed by an electron in the metal . the graphic below illustrates the relationship between light frequency and the kinetic energy of ejected electrons . the scientists observed that if the incident light had a frequency less than a minimum frequency $ \nu_0 $ , then no electrons were ejected regardless of the light amplitude . this minimum frequency is also called the threshold frequency , and the value of $ \nu_0 $ depends on the metal . for frequencies greater than $ \nu_0 $ , electrons would be ejected from the metal . furthermore , the kinetic energy of the photoelectrons was proportional to the light frequency . the relationship between photoelectron kinetic energy and light frequency is shown in graph ( a ) below . because the light amplitude was kept constant as the light frequency increased , the number of photons being absorbed by the metal remained constant . thus , the rate at which electrons were ejected from the metal ( or the electric current ) remained constant as well . the relationship between electron current and light frequency is illustrated in graph ( b ) above . is n't there more math somewhere ? we can analyze the frequency relationship using the law of conservation of energy . the total energy of the incoming photon , $ \text { e } \text { photon } $ , must be equal to the kinetic energy of the ejected electron , $ \text { ke } { \text { electron } } $ , plus the energy required to eject the electron from the metal . the energy required to free the electron from a particular metal is also called the metal 's work function , which is represented by the symbol $ \phi $ ( in units of $ \text j $ ) : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ like the threshold frequency $ \nu_0 $ , the value of $ \phi $ also changes depending on the metal . we can now write the energy of the photon in terms of the light frequency using planck 's equation : $ \text { e } \text { photon } =h\nu=\text { ke } \text { electron } +\phi $ rearranging this equation in terms of the electron 's kinetic energy , we get : $ \text { ke } _\text { electron } =h\nu-\phi $ we can see that kinetic energy of the photoelectron increases linearly with $ \nu $ as long as the photon energy is greater than the work function $ \phi $ , which is exactly the relationship shown in graph ( a ) above . we can also use this equation to find the photoelectron velocity $ \text v $ , which is related to $ \text { ke } _\text { electron } $ as follows : $ \text { ke } _\text { electron } =h\nu-\phi=\dfrac { 1 } { 2 } m_e\text v^2 $ where $ m_e $ is the rest mass of an electron , $ 9.1094 \times 10^ { -31 } \ , \text { kg } $ . exploring the wave amplitude trends in terms of photons , higher amplitude light means more photons hitting the metal surface . this results in more electrons ejected over a given time period . as long as the light frequency is greater than $ \nu_0 $ , increasing the light amplitude will cause the electron current to increase proportionally as shown in graph ( a ) below . since increasing the light amplitude has no effect on the energy of the incoming photon , the photoelectron kinetic energy remains constant as the light amplitude is increased ( see graph ( b ) above ) . if we try to explain this result using our dock-and-beach-balls analogy , the relationship in graph ( b ) indicates that no matter the height of the wave hitting the dock $ - $ whether it 's a tiny swell , or a huge tsunami $ - $ the individual beach balls would be launched off the dock with the exact same speed ! thus , our intuition and analogy do n't do a very good job of explaining these particular experiments . example $ 1 $ : the photoelectric effect for copper the work function of copper metal is $ \phi=7.53\times10^ { -19 } \text { j } $ . if we shine light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ on copper metal , will the photoelectric effect be observed ? in order to eject electrons , we need the energy of the photons to be greater than the work function of copper . we can use planck 's equation to calculate the energy of the photon , $ \text { e } _ { \text { photon } } $ : $ \begin { align } \text { e } _\text { photon } & amp ; = h\nu \ & amp ; = ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) ( 3.0\times10^ { 16 } \text { hz } ) ~~~~\text { plug in values for $ h $ and $ \nu $ } \ & amp ; = 2.0\times10^ { -17 } \text { j } \end { align } $ if we compare our calculated photon energy , $ \text { e } _\text { photon } $ , to copper 's work function , we see that the photon energy is greater than $ \phi $ : $ ~2.0\times10^ { -17 } \text { j } ~ & gt ; ~7.53\times10^ { -19 } \text { j } $ $ ~~~~~~~~\text { e } _\text { photon } ~~~~~~~~~~~~~~~~~~~\phi $ thus , we would expect to see photoelectrons ejected from the copper . next , we will calculate the kinetic energy of the photoelectrons . example $ 2 $ : calculating the kinetic energy of a photoelectron what is the kinetic energy of the photoelectrons ejected from the copper by the light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ ? we can calculate the kinetic energy of the photoelectron using the equation that relates $ \text { ke } \text { electron } $ to the energy of the photon , $ \text { e } \text { photon } $ , and the work function , $ \phi $ : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ since we want to know $ \text { ke } _\text { electron } $ , we can start by rearranging the equation so that we will be solving for the kinetic energy of the electron : $ \text { ke } \text { electron } =\text { e } \text { photon } -\phi $ now we can insert our known values for $ \text { e } _\text { photon } $ and $ \phi $ from example 1 : $ \text { ke } _\text { electron } = ( 2.0\times10^ { -17 } \text { j } ) - ( 7.53\times10^ { -19 } \text { j } ) =1.9\times10^ { -17 } \text { j } $ therefore , each photoelectron has a kinetic energy of $ 1.9\times10^ { -17 } \text { j } $ . summary based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a specific metal surface . the energy of the incident photon must be equal to the sum of the work function and the kinetic energy of a photoelectron : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ try it ! when we shine light with a frequency of $ 6.20 \times 10^ { 14 } \ , \text { hz } $ on a mystery metal , we observe the ejected electrons have a kinetic energy of $ 3.28\times 10^ { -20 } \ , \text j $ . some possible candidates for the mystery metal are shown in the table below : metal | work function $ \phi $ ( joules , $ \text j $ ) : - : | : - : calcium , $ \text { ca } $ | $ 4.60\times 10^ { -19 } $ tin , $ \text { sn } $ | $ 7.08\times 10^ { -19 } $ sodium , $ \text { na } $ | $ 3.78\times 10^ { -19 } $ hafnium , $ \text { hf } $ | $ 6.25\times 10^ { -19 } $ samarium , $ \text { sm } $ | $ 4.33\times 10^ { -19 } $ based on this information , what is the most likely identity of our mystery metal ?
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the energy of the incident photon must be equal to the sum of the metal 's work function and the photoelectron kinetic energy : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ introduction : what is the photoelectric effect ? when light shines on a metal , electrons can be ejected from the surface of the metal in a phenomenon known as the photoelectric effect . this process is also often referred to as photoemission , and the electrons that are ejected from the metal are called photoelectrons .
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is metal the only element that has the potential to release electrons from photoelectric effect ?
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key points based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . contrary to the predictions , experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of particles called photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a metal surface , and the value of $ \phi $ depends on the metal . the energy of the incident photon must be equal to the sum of the metal 's work function and the photoelectron kinetic energy : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ introduction : what is the photoelectric effect ? when light shines on a metal , electrons can be ejected from the surface of the metal in a phenomenon known as the photoelectric effect . this process is also often referred to as photoemission , and the electrons that are ejected from the metal are called photoelectrons . in terms of their behavior and their properties , photoelectrons are no different from other electrons . the prefix , photo- , simply tells us that the electrons have been ejected from a metal surface by incident light . in this article , we will discuss how 19th century physicists attempted ( but failed ! ) to explain the photoelectric effect using classical physics . this ultimately led to the development of the modern description of electromagnetic radiation , which has both wave-like and particle-like properties . predictions based on light as a wave to explain the photoelectric effect , 19th-century physicists theorized that the oscillating electric field of the incoming light wave was heating the electrons and causing them to vibrate , eventually freeing them from the metal surface . this hypothesis was based on the assumption that light traveled purely as a wave through space . ( see this article for more information about the basic properties of light . ) scientists also believed that the energy of the light wave was proportional to its brightness , which is related to the wave 's amplitude . in order to test their hypotheses , they performed experiments to look at the effect of light amplitude and frequency on the rate of electron ejection , as well as the kinetic energy of the photoelectrons . based on the classical description of light as a wave , they made the following predictions : the kinetic energy of emitted photoelectrons should increase with the light amplitude . the rate of electron emission , which is proportional to the measured electric current , should increase as the light frequency is increased . to help us understand why they made these predictions , we can compare a light wave to a water wave . imagine some beach balls sitting on a dock that extends out into the ocean . the dock represents a metal surface , the beach balls represent electrons , and the ocean waves represent light waves . if a single large wave were to shake the dock , we would expect the energy from the big wave would send the beach balls flying off the dock with much more kinetic energy compared to a single , small wave . this is also what physicists believed would happen if the light intensity was increased . light amplitude was expected to be proportional to the light energy , so higher amplitude light was predicted to result in photoelectrons with more kinetic energy . classical physicists also predicted that increasing the frequency of light waves ( at a constant amplitude ) would increase the rate of electrons being ejected , and thus increase the measured electric current . using our beach ball analogy , we would expect waves hitting the dock more frequently would result in more beach balls being knocked off the dock compared to the same sized waves hitting the dock less often . now that we know what physicists thought would happen , let 's look at what they actually observed experimentally ! when intuition fails : photons to the rescue ! when experiments were performed to look at the effect of light amplitude and frequency , the following results were observed : the kinetic energy of photoelectrons increases with light frequency . electric current remains constant as light frequency increases . electric current increases with light amplitude . the kinetic energy of photoelectrons remains constant as light amplitude increases . these results were completely at odds with the predictions based on the classical description of light as a wave ! in order to explain what was happening , it turned out that an entirely new model of light was needed . that model was developed by albert einstein , who proposed that light sometimes behaved as particles of electromagnetic energy which we now call photons . the energy of a photon could be calculated using planck 's equation : $ \text { e } _ { \text { photon } } =h\nu $ where $ \text { e } _ { \text { photon } } $ is the energy of a photon in joules ( $ \text { j } $ ) , $ h $ is planck 's constant $ ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) $ , and $ \nu $ is the frequency of the light in $ \text { hz } $ . according to planck 's equation , the energy of a photon is proportional to the frequency of the light , $ \nu $ . the amplitude of the light is then proportional to the number of photons with a given frequency . concept check : as the wavelength of a photon increases , what happens to the photon 's energy ? light frequency and the threshold frequency $ \nu_0 $ we can think of the incident light as a stream of photons with an energy determined by the light frequency . when a photon hits the metal surface , the photon 's energy is absorbed by an electron in the metal . the graphic below illustrates the relationship between light frequency and the kinetic energy of ejected electrons . the scientists observed that if the incident light had a frequency less than a minimum frequency $ \nu_0 $ , then no electrons were ejected regardless of the light amplitude . this minimum frequency is also called the threshold frequency , and the value of $ \nu_0 $ depends on the metal . for frequencies greater than $ \nu_0 $ , electrons would be ejected from the metal . furthermore , the kinetic energy of the photoelectrons was proportional to the light frequency . the relationship between photoelectron kinetic energy and light frequency is shown in graph ( a ) below . because the light amplitude was kept constant as the light frequency increased , the number of photons being absorbed by the metal remained constant . thus , the rate at which electrons were ejected from the metal ( or the electric current ) remained constant as well . the relationship between electron current and light frequency is illustrated in graph ( b ) above . is n't there more math somewhere ? we can analyze the frequency relationship using the law of conservation of energy . the total energy of the incoming photon , $ \text { e } \text { photon } $ , must be equal to the kinetic energy of the ejected electron , $ \text { ke } { \text { electron } } $ , plus the energy required to eject the electron from the metal . the energy required to free the electron from a particular metal is also called the metal 's work function , which is represented by the symbol $ \phi $ ( in units of $ \text j $ ) : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ like the threshold frequency $ \nu_0 $ , the value of $ \phi $ also changes depending on the metal . we can now write the energy of the photon in terms of the light frequency using planck 's equation : $ \text { e } \text { photon } =h\nu=\text { ke } \text { electron } +\phi $ rearranging this equation in terms of the electron 's kinetic energy , we get : $ \text { ke } _\text { electron } =h\nu-\phi $ we can see that kinetic energy of the photoelectron increases linearly with $ \nu $ as long as the photon energy is greater than the work function $ \phi $ , which is exactly the relationship shown in graph ( a ) above . we can also use this equation to find the photoelectron velocity $ \text v $ , which is related to $ \text { ke } _\text { electron } $ as follows : $ \text { ke } _\text { electron } =h\nu-\phi=\dfrac { 1 } { 2 } m_e\text v^2 $ where $ m_e $ is the rest mass of an electron , $ 9.1094 \times 10^ { -31 } \ , \text { kg } $ . exploring the wave amplitude trends in terms of photons , higher amplitude light means more photons hitting the metal surface . this results in more electrons ejected over a given time period . as long as the light frequency is greater than $ \nu_0 $ , increasing the light amplitude will cause the electron current to increase proportionally as shown in graph ( a ) below . since increasing the light amplitude has no effect on the energy of the incoming photon , the photoelectron kinetic energy remains constant as the light amplitude is increased ( see graph ( b ) above ) . if we try to explain this result using our dock-and-beach-balls analogy , the relationship in graph ( b ) indicates that no matter the height of the wave hitting the dock $ - $ whether it 's a tiny swell , or a huge tsunami $ - $ the individual beach balls would be launched off the dock with the exact same speed ! thus , our intuition and analogy do n't do a very good job of explaining these particular experiments . example $ 1 $ : the photoelectric effect for copper the work function of copper metal is $ \phi=7.53\times10^ { -19 } \text { j } $ . if we shine light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ on copper metal , will the photoelectric effect be observed ? in order to eject electrons , we need the energy of the photons to be greater than the work function of copper . we can use planck 's equation to calculate the energy of the photon , $ \text { e } _ { \text { photon } } $ : $ \begin { align } \text { e } _\text { photon } & amp ; = h\nu \ & amp ; = ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) ( 3.0\times10^ { 16 } \text { hz } ) ~~~~\text { plug in values for $ h $ and $ \nu $ } \ & amp ; = 2.0\times10^ { -17 } \text { j } \end { align } $ if we compare our calculated photon energy , $ \text { e } _\text { photon } $ , to copper 's work function , we see that the photon energy is greater than $ \phi $ : $ ~2.0\times10^ { -17 } \text { j } ~ & gt ; ~7.53\times10^ { -19 } \text { j } $ $ ~~~~~~~~\text { e } _\text { photon } ~~~~~~~~~~~~~~~~~~~\phi $ thus , we would expect to see photoelectrons ejected from the copper . next , we will calculate the kinetic energy of the photoelectrons . example $ 2 $ : calculating the kinetic energy of a photoelectron what is the kinetic energy of the photoelectrons ejected from the copper by the light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ ? we can calculate the kinetic energy of the photoelectron using the equation that relates $ \text { ke } \text { electron } $ to the energy of the photon , $ \text { e } \text { photon } $ , and the work function , $ \phi $ : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ since we want to know $ \text { ke } _\text { electron } $ , we can start by rearranging the equation so that we will be solving for the kinetic energy of the electron : $ \text { ke } \text { electron } =\text { e } \text { photon } -\phi $ now we can insert our known values for $ \text { e } _\text { photon } $ and $ \phi $ from example 1 : $ \text { ke } _\text { electron } = ( 2.0\times10^ { -17 } \text { j } ) - ( 7.53\times10^ { -19 } \text { j } ) =1.9\times10^ { -17 } \text { j } $ therefore , each photoelectron has a kinetic energy of $ 1.9\times10^ { -17 } \text { j } $ . summary based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a specific metal surface . the energy of the incident photon must be equal to the sum of the work function and the kinetic energy of a photoelectron : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ try it ! when we shine light with a frequency of $ 6.20 \times 10^ { 14 } \ , \text { hz } $ on a mystery metal , we observe the ejected electrons have a kinetic energy of $ 3.28\times 10^ { -20 } \ , \text j $ . some possible candidates for the mystery metal are shown in the table below : metal | work function $ \phi $ ( joules , $ \text j $ ) : - : | : - : calcium , $ \text { ca } $ | $ 4.60\times 10^ { -19 } $ tin , $ \text { sn } $ | $ 7.08\times 10^ { -19 } $ sodium , $ \text { na } $ | $ 3.78\times 10^ { -19 } $ hafnium , $ \text { hf } $ | $ 6.25\times 10^ { -19 } $ samarium , $ \text { sm } $ | $ 4.33\times 10^ { -19 } $ based on this information , what is the most likely identity of our mystery metal ?
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electric current remains constant as light frequency increases . electric current increases with light amplitude . the kinetic energy of photoelectrons remains constant as light amplitude increases .
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how do you measure amplitude ?
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key points based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . contrary to the predictions , experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of particles called photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a metal surface , and the value of $ \phi $ depends on the metal . the energy of the incident photon must be equal to the sum of the metal 's work function and the photoelectron kinetic energy : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ introduction : what is the photoelectric effect ? when light shines on a metal , electrons can be ejected from the surface of the metal in a phenomenon known as the photoelectric effect . this process is also often referred to as photoemission , and the electrons that are ejected from the metal are called photoelectrons . in terms of their behavior and their properties , photoelectrons are no different from other electrons . the prefix , photo- , simply tells us that the electrons have been ejected from a metal surface by incident light . in this article , we will discuss how 19th century physicists attempted ( but failed ! ) to explain the photoelectric effect using classical physics . this ultimately led to the development of the modern description of electromagnetic radiation , which has both wave-like and particle-like properties . predictions based on light as a wave to explain the photoelectric effect , 19th-century physicists theorized that the oscillating electric field of the incoming light wave was heating the electrons and causing them to vibrate , eventually freeing them from the metal surface . this hypothesis was based on the assumption that light traveled purely as a wave through space . ( see this article for more information about the basic properties of light . ) scientists also believed that the energy of the light wave was proportional to its brightness , which is related to the wave 's amplitude . in order to test their hypotheses , they performed experiments to look at the effect of light amplitude and frequency on the rate of electron ejection , as well as the kinetic energy of the photoelectrons . based on the classical description of light as a wave , they made the following predictions : the kinetic energy of emitted photoelectrons should increase with the light amplitude . the rate of electron emission , which is proportional to the measured electric current , should increase as the light frequency is increased . to help us understand why they made these predictions , we can compare a light wave to a water wave . imagine some beach balls sitting on a dock that extends out into the ocean . the dock represents a metal surface , the beach balls represent electrons , and the ocean waves represent light waves . if a single large wave were to shake the dock , we would expect the energy from the big wave would send the beach balls flying off the dock with much more kinetic energy compared to a single , small wave . this is also what physicists believed would happen if the light intensity was increased . light amplitude was expected to be proportional to the light energy , so higher amplitude light was predicted to result in photoelectrons with more kinetic energy . classical physicists also predicted that increasing the frequency of light waves ( at a constant amplitude ) would increase the rate of electrons being ejected , and thus increase the measured electric current . using our beach ball analogy , we would expect waves hitting the dock more frequently would result in more beach balls being knocked off the dock compared to the same sized waves hitting the dock less often . now that we know what physicists thought would happen , let 's look at what they actually observed experimentally ! when intuition fails : photons to the rescue ! when experiments were performed to look at the effect of light amplitude and frequency , the following results were observed : the kinetic energy of photoelectrons increases with light frequency . electric current remains constant as light frequency increases . electric current increases with light amplitude . the kinetic energy of photoelectrons remains constant as light amplitude increases . these results were completely at odds with the predictions based on the classical description of light as a wave ! in order to explain what was happening , it turned out that an entirely new model of light was needed . that model was developed by albert einstein , who proposed that light sometimes behaved as particles of electromagnetic energy which we now call photons . the energy of a photon could be calculated using planck 's equation : $ \text { e } _ { \text { photon } } =h\nu $ where $ \text { e } _ { \text { photon } } $ is the energy of a photon in joules ( $ \text { j } $ ) , $ h $ is planck 's constant $ ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) $ , and $ \nu $ is the frequency of the light in $ \text { hz } $ . according to planck 's equation , the energy of a photon is proportional to the frequency of the light , $ \nu $ . the amplitude of the light is then proportional to the number of photons with a given frequency . concept check : as the wavelength of a photon increases , what happens to the photon 's energy ? light frequency and the threshold frequency $ \nu_0 $ we can think of the incident light as a stream of photons with an energy determined by the light frequency . when a photon hits the metal surface , the photon 's energy is absorbed by an electron in the metal . the graphic below illustrates the relationship between light frequency and the kinetic energy of ejected electrons . the scientists observed that if the incident light had a frequency less than a minimum frequency $ \nu_0 $ , then no electrons were ejected regardless of the light amplitude . this minimum frequency is also called the threshold frequency , and the value of $ \nu_0 $ depends on the metal . for frequencies greater than $ \nu_0 $ , electrons would be ejected from the metal . furthermore , the kinetic energy of the photoelectrons was proportional to the light frequency . the relationship between photoelectron kinetic energy and light frequency is shown in graph ( a ) below . because the light amplitude was kept constant as the light frequency increased , the number of photons being absorbed by the metal remained constant . thus , the rate at which electrons were ejected from the metal ( or the electric current ) remained constant as well . the relationship between electron current and light frequency is illustrated in graph ( b ) above . is n't there more math somewhere ? we can analyze the frequency relationship using the law of conservation of energy . the total energy of the incoming photon , $ \text { e } \text { photon } $ , must be equal to the kinetic energy of the ejected electron , $ \text { ke } { \text { electron } } $ , plus the energy required to eject the electron from the metal . the energy required to free the electron from a particular metal is also called the metal 's work function , which is represented by the symbol $ \phi $ ( in units of $ \text j $ ) : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ like the threshold frequency $ \nu_0 $ , the value of $ \phi $ also changes depending on the metal . we can now write the energy of the photon in terms of the light frequency using planck 's equation : $ \text { e } \text { photon } =h\nu=\text { ke } \text { electron } +\phi $ rearranging this equation in terms of the electron 's kinetic energy , we get : $ \text { ke } _\text { electron } =h\nu-\phi $ we can see that kinetic energy of the photoelectron increases linearly with $ \nu $ as long as the photon energy is greater than the work function $ \phi $ , which is exactly the relationship shown in graph ( a ) above . we can also use this equation to find the photoelectron velocity $ \text v $ , which is related to $ \text { ke } _\text { electron } $ as follows : $ \text { ke } _\text { electron } =h\nu-\phi=\dfrac { 1 } { 2 } m_e\text v^2 $ where $ m_e $ is the rest mass of an electron , $ 9.1094 \times 10^ { -31 } \ , \text { kg } $ . exploring the wave amplitude trends in terms of photons , higher amplitude light means more photons hitting the metal surface . this results in more electrons ejected over a given time period . as long as the light frequency is greater than $ \nu_0 $ , increasing the light amplitude will cause the electron current to increase proportionally as shown in graph ( a ) below . since increasing the light amplitude has no effect on the energy of the incoming photon , the photoelectron kinetic energy remains constant as the light amplitude is increased ( see graph ( b ) above ) . if we try to explain this result using our dock-and-beach-balls analogy , the relationship in graph ( b ) indicates that no matter the height of the wave hitting the dock $ - $ whether it 's a tiny swell , or a huge tsunami $ - $ the individual beach balls would be launched off the dock with the exact same speed ! thus , our intuition and analogy do n't do a very good job of explaining these particular experiments . example $ 1 $ : the photoelectric effect for copper the work function of copper metal is $ \phi=7.53\times10^ { -19 } \text { j } $ . if we shine light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ on copper metal , will the photoelectric effect be observed ? in order to eject electrons , we need the energy of the photons to be greater than the work function of copper . we can use planck 's equation to calculate the energy of the photon , $ \text { e } _ { \text { photon } } $ : $ \begin { align } \text { e } _\text { photon } & amp ; = h\nu \ & amp ; = ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) ( 3.0\times10^ { 16 } \text { hz } ) ~~~~\text { plug in values for $ h $ and $ \nu $ } \ & amp ; = 2.0\times10^ { -17 } \text { j } \end { align } $ if we compare our calculated photon energy , $ \text { e } _\text { photon } $ , to copper 's work function , we see that the photon energy is greater than $ \phi $ : $ ~2.0\times10^ { -17 } \text { j } ~ & gt ; ~7.53\times10^ { -19 } \text { j } $ $ ~~~~~~~~\text { e } _\text { photon } ~~~~~~~~~~~~~~~~~~~\phi $ thus , we would expect to see photoelectrons ejected from the copper . next , we will calculate the kinetic energy of the photoelectrons . example $ 2 $ : calculating the kinetic energy of a photoelectron what is the kinetic energy of the photoelectrons ejected from the copper by the light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ ? we can calculate the kinetic energy of the photoelectron using the equation that relates $ \text { ke } \text { electron } $ to the energy of the photon , $ \text { e } \text { photon } $ , and the work function , $ \phi $ : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ since we want to know $ \text { ke } _\text { electron } $ , we can start by rearranging the equation so that we will be solving for the kinetic energy of the electron : $ \text { ke } \text { electron } =\text { e } \text { photon } -\phi $ now we can insert our known values for $ \text { e } _\text { photon } $ and $ \phi $ from example 1 : $ \text { ke } _\text { electron } = ( 2.0\times10^ { -17 } \text { j } ) - ( 7.53\times10^ { -19 } \text { j } ) =1.9\times10^ { -17 } \text { j } $ therefore , each photoelectron has a kinetic energy of $ 1.9\times10^ { -17 } \text { j } $ . summary based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a specific metal surface . the energy of the incident photon must be equal to the sum of the work function and the kinetic energy of a photoelectron : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ try it ! when we shine light with a frequency of $ 6.20 \times 10^ { 14 } \ , \text { hz } $ on a mystery metal , we observe the ejected electrons have a kinetic energy of $ 3.28\times 10^ { -20 } \ , \text j $ . some possible candidates for the mystery metal are shown in the table below : metal | work function $ \phi $ ( joules , $ \text j $ ) : - : | : - : calcium , $ \text { ca } $ | $ 4.60\times 10^ { -19 } $ tin , $ \text { sn } $ | $ 7.08\times 10^ { -19 } $ sodium , $ \text { na } $ | $ 3.78\times 10^ { -19 } $ hafnium , $ \text { hf } $ | $ 6.25\times 10^ { -19 } $ samarium , $ \text { sm } $ | $ 4.33\times 10^ { -19 } $ based on this information , what is the most likely identity of our mystery metal ?
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the rate of electron emission , which is proportional to the measured electric current , should increase as the light frequency is increased . to help us understand why they made these predictions , we can compare a light wave to a water wave . imagine some beach balls sitting on a dock that extends out into the ocean .
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i know it is the distance from the top of a wave to the bottom of a wave , but how can you know that in any of these problems ?
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key points based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . contrary to the predictions , experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of particles called photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a metal surface , and the value of $ \phi $ depends on the metal . the energy of the incident photon must be equal to the sum of the metal 's work function and the photoelectron kinetic energy : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ introduction : what is the photoelectric effect ? when light shines on a metal , electrons can be ejected from the surface of the metal in a phenomenon known as the photoelectric effect . this process is also often referred to as photoemission , and the electrons that are ejected from the metal are called photoelectrons . in terms of their behavior and their properties , photoelectrons are no different from other electrons . the prefix , photo- , simply tells us that the electrons have been ejected from a metal surface by incident light . in this article , we will discuss how 19th century physicists attempted ( but failed ! ) to explain the photoelectric effect using classical physics . this ultimately led to the development of the modern description of electromagnetic radiation , which has both wave-like and particle-like properties . predictions based on light as a wave to explain the photoelectric effect , 19th-century physicists theorized that the oscillating electric field of the incoming light wave was heating the electrons and causing them to vibrate , eventually freeing them from the metal surface . this hypothesis was based on the assumption that light traveled purely as a wave through space . ( see this article for more information about the basic properties of light . ) scientists also believed that the energy of the light wave was proportional to its brightness , which is related to the wave 's amplitude . in order to test their hypotheses , they performed experiments to look at the effect of light amplitude and frequency on the rate of electron ejection , as well as the kinetic energy of the photoelectrons . based on the classical description of light as a wave , they made the following predictions : the kinetic energy of emitted photoelectrons should increase with the light amplitude . the rate of electron emission , which is proportional to the measured electric current , should increase as the light frequency is increased . to help us understand why they made these predictions , we can compare a light wave to a water wave . imagine some beach balls sitting on a dock that extends out into the ocean . the dock represents a metal surface , the beach balls represent electrons , and the ocean waves represent light waves . if a single large wave were to shake the dock , we would expect the energy from the big wave would send the beach balls flying off the dock with much more kinetic energy compared to a single , small wave . this is also what physicists believed would happen if the light intensity was increased . light amplitude was expected to be proportional to the light energy , so higher amplitude light was predicted to result in photoelectrons with more kinetic energy . classical physicists also predicted that increasing the frequency of light waves ( at a constant amplitude ) would increase the rate of electrons being ejected , and thus increase the measured electric current . using our beach ball analogy , we would expect waves hitting the dock more frequently would result in more beach balls being knocked off the dock compared to the same sized waves hitting the dock less often . now that we know what physicists thought would happen , let 's look at what they actually observed experimentally ! when intuition fails : photons to the rescue ! when experiments were performed to look at the effect of light amplitude and frequency , the following results were observed : the kinetic energy of photoelectrons increases with light frequency . electric current remains constant as light frequency increases . electric current increases with light amplitude . the kinetic energy of photoelectrons remains constant as light amplitude increases . these results were completely at odds with the predictions based on the classical description of light as a wave ! in order to explain what was happening , it turned out that an entirely new model of light was needed . that model was developed by albert einstein , who proposed that light sometimes behaved as particles of electromagnetic energy which we now call photons . the energy of a photon could be calculated using planck 's equation : $ \text { e } _ { \text { photon } } =h\nu $ where $ \text { e } _ { \text { photon } } $ is the energy of a photon in joules ( $ \text { j } $ ) , $ h $ is planck 's constant $ ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) $ , and $ \nu $ is the frequency of the light in $ \text { hz } $ . according to planck 's equation , the energy of a photon is proportional to the frequency of the light , $ \nu $ . the amplitude of the light is then proportional to the number of photons with a given frequency . concept check : as the wavelength of a photon increases , what happens to the photon 's energy ? light frequency and the threshold frequency $ \nu_0 $ we can think of the incident light as a stream of photons with an energy determined by the light frequency . when a photon hits the metal surface , the photon 's energy is absorbed by an electron in the metal . the graphic below illustrates the relationship between light frequency and the kinetic energy of ejected electrons . the scientists observed that if the incident light had a frequency less than a minimum frequency $ \nu_0 $ , then no electrons were ejected regardless of the light amplitude . this minimum frequency is also called the threshold frequency , and the value of $ \nu_0 $ depends on the metal . for frequencies greater than $ \nu_0 $ , electrons would be ejected from the metal . furthermore , the kinetic energy of the photoelectrons was proportional to the light frequency . the relationship between photoelectron kinetic energy and light frequency is shown in graph ( a ) below . because the light amplitude was kept constant as the light frequency increased , the number of photons being absorbed by the metal remained constant . thus , the rate at which electrons were ejected from the metal ( or the electric current ) remained constant as well . the relationship between electron current and light frequency is illustrated in graph ( b ) above . is n't there more math somewhere ? we can analyze the frequency relationship using the law of conservation of energy . the total energy of the incoming photon , $ \text { e } \text { photon } $ , must be equal to the kinetic energy of the ejected electron , $ \text { ke } { \text { electron } } $ , plus the energy required to eject the electron from the metal . the energy required to free the electron from a particular metal is also called the metal 's work function , which is represented by the symbol $ \phi $ ( in units of $ \text j $ ) : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ like the threshold frequency $ \nu_0 $ , the value of $ \phi $ also changes depending on the metal . we can now write the energy of the photon in terms of the light frequency using planck 's equation : $ \text { e } \text { photon } =h\nu=\text { ke } \text { electron } +\phi $ rearranging this equation in terms of the electron 's kinetic energy , we get : $ \text { ke } _\text { electron } =h\nu-\phi $ we can see that kinetic energy of the photoelectron increases linearly with $ \nu $ as long as the photon energy is greater than the work function $ \phi $ , which is exactly the relationship shown in graph ( a ) above . we can also use this equation to find the photoelectron velocity $ \text v $ , which is related to $ \text { ke } _\text { electron } $ as follows : $ \text { ke } _\text { electron } =h\nu-\phi=\dfrac { 1 } { 2 } m_e\text v^2 $ where $ m_e $ is the rest mass of an electron , $ 9.1094 \times 10^ { -31 } \ , \text { kg } $ . exploring the wave amplitude trends in terms of photons , higher amplitude light means more photons hitting the metal surface . this results in more electrons ejected over a given time period . as long as the light frequency is greater than $ \nu_0 $ , increasing the light amplitude will cause the electron current to increase proportionally as shown in graph ( a ) below . since increasing the light amplitude has no effect on the energy of the incoming photon , the photoelectron kinetic energy remains constant as the light amplitude is increased ( see graph ( b ) above ) . if we try to explain this result using our dock-and-beach-balls analogy , the relationship in graph ( b ) indicates that no matter the height of the wave hitting the dock $ - $ whether it 's a tiny swell , or a huge tsunami $ - $ the individual beach balls would be launched off the dock with the exact same speed ! thus , our intuition and analogy do n't do a very good job of explaining these particular experiments . example $ 1 $ : the photoelectric effect for copper the work function of copper metal is $ \phi=7.53\times10^ { -19 } \text { j } $ . if we shine light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ on copper metal , will the photoelectric effect be observed ? in order to eject electrons , we need the energy of the photons to be greater than the work function of copper . we can use planck 's equation to calculate the energy of the photon , $ \text { e } _ { \text { photon } } $ : $ \begin { align } \text { e } _\text { photon } & amp ; = h\nu \ & amp ; = ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) ( 3.0\times10^ { 16 } \text { hz } ) ~~~~\text { plug in values for $ h $ and $ \nu $ } \ & amp ; = 2.0\times10^ { -17 } \text { j } \end { align } $ if we compare our calculated photon energy , $ \text { e } _\text { photon } $ , to copper 's work function , we see that the photon energy is greater than $ \phi $ : $ ~2.0\times10^ { -17 } \text { j } ~ & gt ; ~7.53\times10^ { -19 } \text { j } $ $ ~~~~~~~~\text { e } _\text { photon } ~~~~~~~~~~~~~~~~~~~\phi $ thus , we would expect to see photoelectrons ejected from the copper . next , we will calculate the kinetic energy of the photoelectrons . example $ 2 $ : calculating the kinetic energy of a photoelectron what is the kinetic energy of the photoelectrons ejected from the copper by the light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ ? we can calculate the kinetic energy of the photoelectron using the equation that relates $ \text { ke } \text { electron } $ to the energy of the photon , $ \text { e } \text { photon } $ , and the work function , $ \phi $ : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ since we want to know $ \text { ke } _\text { electron } $ , we can start by rearranging the equation so that we will be solving for the kinetic energy of the electron : $ \text { ke } \text { electron } =\text { e } \text { photon } -\phi $ now we can insert our known values for $ \text { e } _\text { photon } $ and $ \phi $ from example 1 : $ \text { ke } _\text { electron } = ( 2.0\times10^ { -17 } \text { j } ) - ( 7.53\times10^ { -19 } \text { j } ) =1.9\times10^ { -17 } \text { j } $ therefore , each photoelectron has a kinetic energy of $ 1.9\times10^ { -17 } \text { j } $ . summary based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a specific metal surface . the energy of the incident photon must be equal to the sum of the work function and the kinetic energy of a photoelectron : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ try it ! when we shine light with a frequency of $ 6.20 \times 10^ { 14 } \ , \text { hz } $ on a mystery metal , we observe the ejected electrons have a kinetic energy of $ 3.28\times 10^ { -20 } \ , \text j $ . some possible candidates for the mystery metal are shown in the table below : metal | work function $ \phi $ ( joules , $ \text j $ ) : - : | : - : calcium , $ \text { ca } $ | $ 4.60\times 10^ { -19 } $ tin , $ \text { sn } $ | $ 7.08\times 10^ { -19 } $ sodium , $ \text { na } $ | $ 3.78\times 10^ { -19 } $ hafnium , $ \text { hf } $ | $ 6.25\times 10^ { -19 } $ samarium , $ \text { sm } $ | $ 4.33\times 10^ { -19 } $ based on this information , what is the most likely identity of our mystery metal ?
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light frequency and the threshold frequency $ \nu_0 $ we can think of the incident light as a stream of photons with an energy determined by the light frequency . when a photon hits the metal surface , the photon 's energy is absorbed by an electron in the metal . the graphic below illustrates the relationship between light frequency and the kinetic energy of ejected electrons .
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what happens to the surface of the metal , does photon replace the electron ?
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key points based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . contrary to the predictions , experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of particles called photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a metal surface , and the value of $ \phi $ depends on the metal . the energy of the incident photon must be equal to the sum of the metal 's work function and the photoelectron kinetic energy : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ introduction : what is the photoelectric effect ? when light shines on a metal , electrons can be ejected from the surface of the metal in a phenomenon known as the photoelectric effect . this process is also often referred to as photoemission , and the electrons that are ejected from the metal are called photoelectrons . in terms of their behavior and their properties , photoelectrons are no different from other electrons . the prefix , photo- , simply tells us that the electrons have been ejected from a metal surface by incident light . in this article , we will discuss how 19th century physicists attempted ( but failed ! ) to explain the photoelectric effect using classical physics . this ultimately led to the development of the modern description of electromagnetic radiation , which has both wave-like and particle-like properties . predictions based on light as a wave to explain the photoelectric effect , 19th-century physicists theorized that the oscillating electric field of the incoming light wave was heating the electrons and causing them to vibrate , eventually freeing them from the metal surface . this hypothesis was based on the assumption that light traveled purely as a wave through space . ( see this article for more information about the basic properties of light . ) scientists also believed that the energy of the light wave was proportional to its brightness , which is related to the wave 's amplitude . in order to test their hypotheses , they performed experiments to look at the effect of light amplitude and frequency on the rate of electron ejection , as well as the kinetic energy of the photoelectrons . based on the classical description of light as a wave , they made the following predictions : the kinetic energy of emitted photoelectrons should increase with the light amplitude . the rate of electron emission , which is proportional to the measured electric current , should increase as the light frequency is increased . to help us understand why they made these predictions , we can compare a light wave to a water wave . imagine some beach balls sitting on a dock that extends out into the ocean . the dock represents a metal surface , the beach balls represent electrons , and the ocean waves represent light waves . if a single large wave were to shake the dock , we would expect the energy from the big wave would send the beach balls flying off the dock with much more kinetic energy compared to a single , small wave . this is also what physicists believed would happen if the light intensity was increased . light amplitude was expected to be proportional to the light energy , so higher amplitude light was predicted to result in photoelectrons with more kinetic energy . classical physicists also predicted that increasing the frequency of light waves ( at a constant amplitude ) would increase the rate of electrons being ejected , and thus increase the measured electric current . using our beach ball analogy , we would expect waves hitting the dock more frequently would result in more beach balls being knocked off the dock compared to the same sized waves hitting the dock less often . now that we know what physicists thought would happen , let 's look at what they actually observed experimentally ! when intuition fails : photons to the rescue ! when experiments were performed to look at the effect of light amplitude and frequency , the following results were observed : the kinetic energy of photoelectrons increases with light frequency . electric current remains constant as light frequency increases . electric current increases with light amplitude . the kinetic energy of photoelectrons remains constant as light amplitude increases . these results were completely at odds with the predictions based on the classical description of light as a wave ! in order to explain what was happening , it turned out that an entirely new model of light was needed . that model was developed by albert einstein , who proposed that light sometimes behaved as particles of electromagnetic energy which we now call photons . the energy of a photon could be calculated using planck 's equation : $ \text { e } _ { \text { photon } } =h\nu $ where $ \text { e } _ { \text { photon } } $ is the energy of a photon in joules ( $ \text { j } $ ) , $ h $ is planck 's constant $ ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) $ , and $ \nu $ is the frequency of the light in $ \text { hz } $ . according to planck 's equation , the energy of a photon is proportional to the frequency of the light , $ \nu $ . the amplitude of the light is then proportional to the number of photons with a given frequency . concept check : as the wavelength of a photon increases , what happens to the photon 's energy ? light frequency and the threshold frequency $ \nu_0 $ we can think of the incident light as a stream of photons with an energy determined by the light frequency . when a photon hits the metal surface , the photon 's energy is absorbed by an electron in the metal . the graphic below illustrates the relationship between light frequency and the kinetic energy of ejected electrons . the scientists observed that if the incident light had a frequency less than a minimum frequency $ \nu_0 $ , then no electrons were ejected regardless of the light amplitude . this minimum frequency is also called the threshold frequency , and the value of $ \nu_0 $ depends on the metal . for frequencies greater than $ \nu_0 $ , electrons would be ejected from the metal . furthermore , the kinetic energy of the photoelectrons was proportional to the light frequency . the relationship between photoelectron kinetic energy and light frequency is shown in graph ( a ) below . because the light amplitude was kept constant as the light frequency increased , the number of photons being absorbed by the metal remained constant . thus , the rate at which electrons were ejected from the metal ( or the electric current ) remained constant as well . the relationship between electron current and light frequency is illustrated in graph ( b ) above . is n't there more math somewhere ? we can analyze the frequency relationship using the law of conservation of energy . the total energy of the incoming photon , $ \text { e } \text { photon } $ , must be equal to the kinetic energy of the ejected electron , $ \text { ke } { \text { electron } } $ , plus the energy required to eject the electron from the metal . the energy required to free the electron from a particular metal is also called the metal 's work function , which is represented by the symbol $ \phi $ ( in units of $ \text j $ ) : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ like the threshold frequency $ \nu_0 $ , the value of $ \phi $ also changes depending on the metal . we can now write the energy of the photon in terms of the light frequency using planck 's equation : $ \text { e } \text { photon } =h\nu=\text { ke } \text { electron } +\phi $ rearranging this equation in terms of the electron 's kinetic energy , we get : $ \text { ke } _\text { electron } =h\nu-\phi $ we can see that kinetic energy of the photoelectron increases linearly with $ \nu $ as long as the photon energy is greater than the work function $ \phi $ , which is exactly the relationship shown in graph ( a ) above . we can also use this equation to find the photoelectron velocity $ \text v $ , which is related to $ \text { ke } _\text { electron } $ as follows : $ \text { ke } _\text { electron } =h\nu-\phi=\dfrac { 1 } { 2 } m_e\text v^2 $ where $ m_e $ is the rest mass of an electron , $ 9.1094 \times 10^ { -31 } \ , \text { kg } $ . exploring the wave amplitude trends in terms of photons , higher amplitude light means more photons hitting the metal surface . this results in more electrons ejected over a given time period . as long as the light frequency is greater than $ \nu_0 $ , increasing the light amplitude will cause the electron current to increase proportionally as shown in graph ( a ) below . since increasing the light amplitude has no effect on the energy of the incoming photon , the photoelectron kinetic energy remains constant as the light amplitude is increased ( see graph ( b ) above ) . if we try to explain this result using our dock-and-beach-balls analogy , the relationship in graph ( b ) indicates that no matter the height of the wave hitting the dock $ - $ whether it 's a tiny swell , or a huge tsunami $ - $ the individual beach balls would be launched off the dock with the exact same speed ! thus , our intuition and analogy do n't do a very good job of explaining these particular experiments . example $ 1 $ : the photoelectric effect for copper the work function of copper metal is $ \phi=7.53\times10^ { -19 } \text { j } $ . if we shine light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ on copper metal , will the photoelectric effect be observed ? in order to eject electrons , we need the energy of the photons to be greater than the work function of copper . we can use planck 's equation to calculate the energy of the photon , $ \text { e } _ { \text { photon } } $ : $ \begin { align } \text { e } _\text { photon } & amp ; = h\nu \ & amp ; = ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) ( 3.0\times10^ { 16 } \text { hz } ) ~~~~\text { plug in values for $ h $ and $ \nu $ } \ & amp ; = 2.0\times10^ { -17 } \text { j } \end { align } $ if we compare our calculated photon energy , $ \text { e } _\text { photon } $ , to copper 's work function , we see that the photon energy is greater than $ \phi $ : $ ~2.0\times10^ { -17 } \text { j } ~ & gt ; ~7.53\times10^ { -19 } \text { j } $ $ ~~~~~~~~\text { e } _\text { photon } ~~~~~~~~~~~~~~~~~~~\phi $ thus , we would expect to see photoelectrons ejected from the copper . next , we will calculate the kinetic energy of the photoelectrons . example $ 2 $ : calculating the kinetic energy of a photoelectron what is the kinetic energy of the photoelectrons ejected from the copper by the light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ ? we can calculate the kinetic energy of the photoelectron using the equation that relates $ \text { ke } \text { electron } $ to the energy of the photon , $ \text { e } \text { photon } $ , and the work function , $ \phi $ : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ since we want to know $ \text { ke } _\text { electron } $ , we can start by rearranging the equation so that we will be solving for the kinetic energy of the electron : $ \text { ke } \text { electron } =\text { e } \text { photon } -\phi $ now we can insert our known values for $ \text { e } _\text { photon } $ and $ \phi $ from example 1 : $ \text { ke } _\text { electron } = ( 2.0\times10^ { -17 } \text { j } ) - ( 7.53\times10^ { -19 } \text { j } ) =1.9\times10^ { -17 } \text { j } $ therefore , each photoelectron has a kinetic energy of $ 1.9\times10^ { -17 } \text { j } $ . summary based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a specific metal surface . the energy of the incident photon must be equal to the sum of the work function and the kinetic energy of a photoelectron : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ try it ! when we shine light with a frequency of $ 6.20 \times 10^ { 14 } \ , \text { hz } $ on a mystery metal , we observe the ejected electrons have a kinetic energy of $ 3.28\times 10^ { -20 } \ , \text j $ . some possible candidates for the mystery metal are shown in the table below : metal | work function $ \phi $ ( joules , $ \text j $ ) : - : | : - : calcium , $ \text { ca } $ | $ 4.60\times 10^ { -19 } $ tin , $ \text { sn } $ | $ 7.08\times 10^ { -19 } $ sodium , $ \text { na } $ | $ 3.78\times 10^ { -19 } $ hafnium , $ \text { hf } $ | $ 6.25\times 10^ { -19 } $ samarium , $ \text { sm } $ | $ 4.33\times 10^ { -19 } $ based on this information , what is the most likely identity of our mystery metal ?
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experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a specific metal surface .
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is the only reason for 'e- ' being loosely held by metals that they are located on left of periodic table i.e they have low ionisation energy or even loose helding of 'e- ' due distance from nucleus and screaning effect add to the reason ?
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key points based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . contrary to the predictions , experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of particles called photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a metal surface , and the value of $ \phi $ depends on the metal . the energy of the incident photon must be equal to the sum of the metal 's work function and the photoelectron kinetic energy : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ introduction : what is the photoelectric effect ? when light shines on a metal , electrons can be ejected from the surface of the metal in a phenomenon known as the photoelectric effect . this process is also often referred to as photoemission , and the electrons that are ejected from the metal are called photoelectrons . in terms of their behavior and their properties , photoelectrons are no different from other electrons . the prefix , photo- , simply tells us that the electrons have been ejected from a metal surface by incident light . in this article , we will discuss how 19th century physicists attempted ( but failed ! ) to explain the photoelectric effect using classical physics . this ultimately led to the development of the modern description of electromagnetic radiation , which has both wave-like and particle-like properties . predictions based on light as a wave to explain the photoelectric effect , 19th-century physicists theorized that the oscillating electric field of the incoming light wave was heating the electrons and causing them to vibrate , eventually freeing them from the metal surface . this hypothesis was based on the assumption that light traveled purely as a wave through space . ( see this article for more information about the basic properties of light . ) scientists also believed that the energy of the light wave was proportional to its brightness , which is related to the wave 's amplitude . in order to test their hypotheses , they performed experiments to look at the effect of light amplitude and frequency on the rate of electron ejection , as well as the kinetic energy of the photoelectrons . based on the classical description of light as a wave , they made the following predictions : the kinetic energy of emitted photoelectrons should increase with the light amplitude . the rate of electron emission , which is proportional to the measured electric current , should increase as the light frequency is increased . to help us understand why they made these predictions , we can compare a light wave to a water wave . imagine some beach balls sitting on a dock that extends out into the ocean . the dock represents a metal surface , the beach balls represent electrons , and the ocean waves represent light waves . if a single large wave were to shake the dock , we would expect the energy from the big wave would send the beach balls flying off the dock with much more kinetic energy compared to a single , small wave . this is also what physicists believed would happen if the light intensity was increased . light amplitude was expected to be proportional to the light energy , so higher amplitude light was predicted to result in photoelectrons with more kinetic energy . classical physicists also predicted that increasing the frequency of light waves ( at a constant amplitude ) would increase the rate of electrons being ejected , and thus increase the measured electric current . using our beach ball analogy , we would expect waves hitting the dock more frequently would result in more beach balls being knocked off the dock compared to the same sized waves hitting the dock less often . now that we know what physicists thought would happen , let 's look at what they actually observed experimentally ! when intuition fails : photons to the rescue ! when experiments were performed to look at the effect of light amplitude and frequency , the following results were observed : the kinetic energy of photoelectrons increases with light frequency . electric current remains constant as light frequency increases . electric current increases with light amplitude . the kinetic energy of photoelectrons remains constant as light amplitude increases . these results were completely at odds with the predictions based on the classical description of light as a wave ! in order to explain what was happening , it turned out that an entirely new model of light was needed . that model was developed by albert einstein , who proposed that light sometimes behaved as particles of electromagnetic energy which we now call photons . the energy of a photon could be calculated using planck 's equation : $ \text { e } _ { \text { photon } } =h\nu $ where $ \text { e } _ { \text { photon } } $ is the energy of a photon in joules ( $ \text { j } $ ) , $ h $ is planck 's constant $ ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) $ , and $ \nu $ is the frequency of the light in $ \text { hz } $ . according to planck 's equation , the energy of a photon is proportional to the frequency of the light , $ \nu $ . the amplitude of the light is then proportional to the number of photons with a given frequency . concept check : as the wavelength of a photon increases , what happens to the photon 's energy ? light frequency and the threshold frequency $ \nu_0 $ we can think of the incident light as a stream of photons with an energy determined by the light frequency . when a photon hits the metal surface , the photon 's energy is absorbed by an electron in the metal . the graphic below illustrates the relationship between light frequency and the kinetic energy of ejected electrons . the scientists observed that if the incident light had a frequency less than a minimum frequency $ \nu_0 $ , then no electrons were ejected regardless of the light amplitude . this minimum frequency is also called the threshold frequency , and the value of $ \nu_0 $ depends on the metal . for frequencies greater than $ \nu_0 $ , electrons would be ejected from the metal . furthermore , the kinetic energy of the photoelectrons was proportional to the light frequency . the relationship between photoelectron kinetic energy and light frequency is shown in graph ( a ) below . because the light amplitude was kept constant as the light frequency increased , the number of photons being absorbed by the metal remained constant . thus , the rate at which electrons were ejected from the metal ( or the electric current ) remained constant as well . the relationship between electron current and light frequency is illustrated in graph ( b ) above . is n't there more math somewhere ? we can analyze the frequency relationship using the law of conservation of energy . the total energy of the incoming photon , $ \text { e } \text { photon } $ , must be equal to the kinetic energy of the ejected electron , $ \text { ke } { \text { electron } } $ , plus the energy required to eject the electron from the metal . the energy required to free the electron from a particular metal is also called the metal 's work function , which is represented by the symbol $ \phi $ ( in units of $ \text j $ ) : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ like the threshold frequency $ \nu_0 $ , the value of $ \phi $ also changes depending on the metal . we can now write the energy of the photon in terms of the light frequency using planck 's equation : $ \text { e } \text { photon } =h\nu=\text { ke } \text { electron } +\phi $ rearranging this equation in terms of the electron 's kinetic energy , we get : $ \text { ke } _\text { electron } =h\nu-\phi $ we can see that kinetic energy of the photoelectron increases linearly with $ \nu $ as long as the photon energy is greater than the work function $ \phi $ , which is exactly the relationship shown in graph ( a ) above . we can also use this equation to find the photoelectron velocity $ \text v $ , which is related to $ \text { ke } _\text { electron } $ as follows : $ \text { ke } _\text { electron } =h\nu-\phi=\dfrac { 1 } { 2 } m_e\text v^2 $ where $ m_e $ is the rest mass of an electron , $ 9.1094 \times 10^ { -31 } \ , \text { kg } $ . exploring the wave amplitude trends in terms of photons , higher amplitude light means more photons hitting the metal surface . this results in more electrons ejected over a given time period . as long as the light frequency is greater than $ \nu_0 $ , increasing the light amplitude will cause the electron current to increase proportionally as shown in graph ( a ) below . since increasing the light amplitude has no effect on the energy of the incoming photon , the photoelectron kinetic energy remains constant as the light amplitude is increased ( see graph ( b ) above ) . if we try to explain this result using our dock-and-beach-balls analogy , the relationship in graph ( b ) indicates that no matter the height of the wave hitting the dock $ - $ whether it 's a tiny swell , or a huge tsunami $ - $ the individual beach balls would be launched off the dock with the exact same speed ! thus , our intuition and analogy do n't do a very good job of explaining these particular experiments . example $ 1 $ : the photoelectric effect for copper the work function of copper metal is $ \phi=7.53\times10^ { -19 } \text { j } $ . if we shine light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ on copper metal , will the photoelectric effect be observed ? in order to eject electrons , we need the energy of the photons to be greater than the work function of copper . we can use planck 's equation to calculate the energy of the photon , $ \text { e } _ { \text { photon } } $ : $ \begin { align } \text { e } _\text { photon } & amp ; = h\nu \ & amp ; = ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) ( 3.0\times10^ { 16 } \text { hz } ) ~~~~\text { plug in values for $ h $ and $ \nu $ } \ & amp ; = 2.0\times10^ { -17 } \text { j } \end { align } $ if we compare our calculated photon energy , $ \text { e } _\text { photon } $ , to copper 's work function , we see that the photon energy is greater than $ \phi $ : $ ~2.0\times10^ { -17 } \text { j } ~ & gt ; ~7.53\times10^ { -19 } \text { j } $ $ ~~~~~~~~\text { e } _\text { photon } ~~~~~~~~~~~~~~~~~~~\phi $ thus , we would expect to see photoelectrons ejected from the copper . next , we will calculate the kinetic energy of the photoelectrons . example $ 2 $ : calculating the kinetic energy of a photoelectron what is the kinetic energy of the photoelectrons ejected from the copper by the light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ ? we can calculate the kinetic energy of the photoelectron using the equation that relates $ \text { ke } \text { electron } $ to the energy of the photon , $ \text { e } \text { photon } $ , and the work function , $ \phi $ : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ since we want to know $ \text { ke } _\text { electron } $ , we can start by rearranging the equation so that we will be solving for the kinetic energy of the electron : $ \text { ke } \text { electron } =\text { e } \text { photon } -\phi $ now we can insert our known values for $ \text { e } _\text { photon } $ and $ \phi $ from example 1 : $ \text { ke } _\text { electron } = ( 2.0\times10^ { -17 } \text { j } ) - ( 7.53\times10^ { -19 } \text { j } ) =1.9\times10^ { -17 } \text { j } $ therefore , each photoelectron has a kinetic energy of $ 1.9\times10^ { -17 } \text { j } $ . summary based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a specific metal surface . the energy of the incident photon must be equal to the sum of the work function and the kinetic energy of a photoelectron : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ try it ! when we shine light with a frequency of $ 6.20 \times 10^ { 14 } \ , \text { hz } $ on a mystery metal , we observe the ejected electrons have a kinetic energy of $ 3.28\times 10^ { -20 } \ , \text j $ . some possible candidates for the mystery metal are shown in the table below : metal | work function $ \phi $ ( joules , $ \text j $ ) : - : | : - : calcium , $ \text { ca } $ | $ 4.60\times 10^ { -19 } $ tin , $ \text { sn } $ | $ 7.08\times 10^ { -19 } $ sodium , $ \text { na } $ | $ 3.78\times 10^ { -19 } $ hafnium , $ \text { hf } $ | $ 6.25\times 10^ { -19 } $ samarium , $ \text { sm } $ | $ 4.33\times 10^ { -19 } $ based on this information , what is the most likely identity of our mystery metal ?
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light frequency and the threshold frequency $ \nu_0 $ we can think of the incident light as a stream of photons with an energy determined by the light frequency . when a photon hits the metal surface , the photon 's energy is absorbed by an electron in the metal . the graphic below illustrates the relationship between light frequency and the kinetic energy of ejected electrons .
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and do we get em radiation back when we throw 'e- ' on metal or any other substance with same energy ?
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key points based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . contrary to the predictions , experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of particles called photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a metal surface , and the value of $ \phi $ depends on the metal . the energy of the incident photon must be equal to the sum of the metal 's work function and the photoelectron kinetic energy : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ introduction : what is the photoelectric effect ? when light shines on a metal , electrons can be ejected from the surface of the metal in a phenomenon known as the photoelectric effect . this process is also often referred to as photoemission , and the electrons that are ejected from the metal are called photoelectrons . in terms of their behavior and their properties , photoelectrons are no different from other electrons . the prefix , photo- , simply tells us that the electrons have been ejected from a metal surface by incident light . in this article , we will discuss how 19th century physicists attempted ( but failed ! ) to explain the photoelectric effect using classical physics . this ultimately led to the development of the modern description of electromagnetic radiation , which has both wave-like and particle-like properties . predictions based on light as a wave to explain the photoelectric effect , 19th-century physicists theorized that the oscillating electric field of the incoming light wave was heating the electrons and causing them to vibrate , eventually freeing them from the metal surface . this hypothesis was based on the assumption that light traveled purely as a wave through space . ( see this article for more information about the basic properties of light . ) scientists also believed that the energy of the light wave was proportional to its brightness , which is related to the wave 's amplitude . in order to test their hypotheses , they performed experiments to look at the effect of light amplitude and frequency on the rate of electron ejection , as well as the kinetic energy of the photoelectrons . based on the classical description of light as a wave , they made the following predictions : the kinetic energy of emitted photoelectrons should increase with the light amplitude . the rate of electron emission , which is proportional to the measured electric current , should increase as the light frequency is increased . to help us understand why they made these predictions , we can compare a light wave to a water wave . imagine some beach balls sitting on a dock that extends out into the ocean . the dock represents a metal surface , the beach balls represent electrons , and the ocean waves represent light waves . if a single large wave were to shake the dock , we would expect the energy from the big wave would send the beach balls flying off the dock with much more kinetic energy compared to a single , small wave . this is also what physicists believed would happen if the light intensity was increased . light amplitude was expected to be proportional to the light energy , so higher amplitude light was predicted to result in photoelectrons with more kinetic energy . classical physicists also predicted that increasing the frequency of light waves ( at a constant amplitude ) would increase the rate of electrons being ejected , and thus increase the measured electric current . using our beach ball analogy , we would expect waves hitting the dock more frequently would result in more beach balls being knocked off the dock compared to the same sized waves hitting the dock less often . now that we know what physicists thought would happen , let 's look at what they actually observed experimentally ! when intuition fails : photons to the rescue ! when experiments were performed to look at the effect of light amplitude and frequency , the following results were observed : the kinetic energy of photoelectrons increases with light frequency . electric current remains constant as light frequency increases . electric current increases with light amplitude . the kinetic energy of photoelectrons remains constant as light amplitude increases . these results were completely at odds with the predictions based on the classical description of light as a wave ! in order to explain what was happening , it turned out that an entirely new model of light was needed . that model was developed by albert einstein , who proposed that light sometimes behaved as particles of electromagnetic energy which we now call photons . the energy of a photon could be calculated using planck 's equation : $ \text { e } _ { \text { photon } } =h\nu $ where $ \text { e } _ { \text { photon } } $ is the energy of a photon in joules ( $ \text { j } $ ) , $ h $ is planck 's constant $ ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) $ , and $ \nu $ is the frequency of the light in $ \text { hz } $ . according to planck 's equation , the energy of a photon is proportional to the frequency of the light , $ \nu $ . the amplitude of the light is then proportional to the number of photons with a given frequency . concept check : as the wavelength of a photon increases , what happens to the photon 's energy ? light frequency and the threshold frequency $ \nu_0 $ we can think of the incident light as a stream of photons with an energy determined by the light frequency . when a photon hits the metal surface , the photon 's energy is absorbed by an electron in the metal . the graphic below illustrates the relationship between light frequency and the kinetic energy of ejected electrons . the scientists observed that if the incident light had a frequency less than a minimum frequency $ \nu_0 $ , then no electrons were ejected regardless of the light amplitude . this minimum frequency is also called the threshold frequency , and the value of $ \nu_0 $ depends on the metal . for frequencies greater than $ \nu_0 $ , electrons would be ejected from the metal . furthermore , the kinetic energy of the photoelectrons was proportional to the light frequency . the relationship between photoelectron kinetic energy and light frequency is shown in graph ( a ) below . because the light amplitude was kept constant as the light frequency increased , the number of photons being absorbed by the metal remained constant . thus , the rate at which electrons were ejected from the metal ( or the electric current ) remained constant as well . the relationship between electron current and light frequency is illustrated in graph ( b ) above . is n't there more math somewhere ? we can analyze the frequency relationship using the law of conservation of energy . the total energy of the incoming photon , $ \text { e } \text { photon } $ , must be equal to the kinetic energy of the ejected electron , $ \text { ke } { \text { electron } } $ , plus the energy required to eject the electron from the metal . the energy required to free the electron from a particular metal is also called the metal 's work function , which is represented by the symbol $ \phi $ ( in units of $ \text j $ ) : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ like the threshold frequency $ \nu_0 $ , the value of $ \phi $ also changes depending on the metal . we can now write the energy of the photon in terms of the light frequency using planck 's equation : $ \text { e } \text { photon } =h\nu=\text { ke } \text { electron } +\phi $ rearranging this equation in terms of the electron 's kinetic energy , we get : $ \text { ke } _\text { electron } =h\nu-\phi $ we can see that kinetic energy of the photoelectron increases linearly with $ \nu $ as long as the photon energy is greater than the work function $ \phi $ , which is exactly the relationship shown in graph ( a ) above . we can also use this equation to find the photoelectron velocity $ \text v $ , which is related to $ \text { ke } _\text { electron } $ as follows : $ \text { ke } _\text { electron } =h\nu-\phi=\dfrac { 1 } { 2 } m_e\text v^2 $ where $ m_e $ is the rest mass of an electron , $ 9.1094 \times 10^ { -31 } \ , \text { kg } $ . exploring the wave amplitude trends in terms of photons , higher amplitude light means more photons hitting the metal surface . this results in more electrons ejected over a given time period . as long as the light frequency is greater than $ \nu_0 $ , increasing the light amplitude will cause the electron current to increase proportionally as shown in graph ( a ) below . since increasing the light amplitude has no effect on the energy of the incoming photon , the photoelectron kinetic energy remains constant as the light amplitude is increased ( see graph ( b ) above ) . if we try to explain this result using our dock-and-beach-balls analogy , the relationship in graph ( b ) indicates that no matter the height of the wave hitting the dock $ - $ whether it 's a tiny swell , or a huge tsunami $ - $ the individual beach balls would be launched off the dock with the exact same speed ! thus , our intuition and analogy do n't do a very good job of explaining these particular experiments . example $ 1 $ : the photoelectric effect for copper the work function of copper metal is $ \phi=7.53\times10^ { -19 } \text { j } $ . if we shine light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ on copper metal , will the photoelectric effect be observed ? in order to eject electrons , we need the energy of the photons to be greater than the work function of copper . we can use planck 's equation to calculate the energy of the photon , $ \text { e } _ { \text { photon } } $ : $ \begin { align } \text { e } _\text { photon } & amp ; = h\nu \ & amp ; = ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) ( 3.0\times10^ { 16 } \text { hz } ) ~~~~\text { plug in values for $ h $ and $ \nu $ } \ & amp ; = 2.0\times10^ { -17 } \text { j } \end { align } $ if we compare our calculated photon energy , $ \text { e } _\text { photon } $ , to copper 's work function , we see that the photon energy is greater than $ \phi $ : $ ~2.0\times10^ { -17 } \text { j } ~ & gt ; ~7.53\times10^ { -19 } \text { j } $ $ ~~~~~~~~\text { e } _\text { photon } ~~~~~~~~~~~~~~~~~~~\phi $ thus , we would expect to see photoelectrons ejected from the copper . next , we will calculate the kinetic energy of the photoelectrons . example $ 2 $ : calculating the kinetic energy of a photoelectron what is the kinetic energy of the photoelectrons ejected from the copper by the light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ ? we can calculate the kinetic energy of the photoelectron using the equation that relates $ \text { ke } \text { electron } $ to the energy of the photon , $ \text { e } \text { photon } $ , and the work function , $ \phi $ : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ since we want to know $ \text { ke } _\text { electron } $ , we can start by rearranging the equation so that we will be solving for the kinetic energy of the electron : $ \text { ke } \text { electron } =\text { e } \text { photon } -\phi $ now we can insert our known values for $ \text { e } _\text { photon } $ and $ \phi $ from example 1 : $ \text { ke } _\text { electron } = ( 2.0\times10^ { -17 } \text { j } ) - ( 7.53\times10^ { -19 } \text { j } ) =1.9\times10^ { -17 } \text { j } $ therefore , each photoelectron has a kinetic energy of $ 1.9\times10^ { -17 } \text { j } $ . summary based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a specific metal surface . the energy of the incident photon must be equal to the sum of the work function and the kinetic energy of a photoelectron : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ try it ! when we shine light with a frequency of $ 6.20 \times 10^ { 14 } \ , \text { hz } $ on a mystery metal , we observe the ejected electrons have a kinetic energy of $ 3.28\times 10^ { -20 } \ , \text j $ . some possible candidates for the mystery metal are shown in the table below : metal | work function $ \phi $ ( joules , $ \text j $ ) : - : | : - : calcium , $ \text { ca } $ | $ 4.60\times 10^ { -19 } $ tin , $ \text { sn } $ | $ 7.08\times 10^ { -19 } $ sodium , $ \text { na } $ | $ 3.78\times 10^ { -19 } $ hafnium , $ \text { hf } $ | $ 6.25\times 10^ { -19 } $ samarium , $ \text { sm } $ | $ 4.33\times 10^ { -19 } $ based on this information , what is the most likely identity of our mystery metal ?
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this is also what physicists believed would happen if the light intensity was increased . light amplitude was expected to be proportional to the light energy , so higher amplitude light was predicted to result in photoelectrons with more kinetic energy . classical physicists also predicted that increasing the frequency of light waves ( at a constant amplitude ) would increase the rate of electrons being ejected , and thus increase the measured electric current .
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what happens to the electrons if there is large kinetic energy light ?
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key points based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . contrary to the predictions , experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of particles called photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a metal surface , and the value of $ \phi $ depends on the metal . the energy of the incident photon must be equal to the sum of the metal 's work function and the photoelectron kinetic energy : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ introduction : what is the photoelectric effect ? when light shines on a metal , electrons can be ejected from the surface of the metal in a phenomenon known as the photoelectric effect . this process is also often referred to as photoemission , and the electrons that are ejected from the metal are called photoelectrons . in terms of their behavior and their properties , photoelectrons are no different from other electrons . the prefix , photo- , simply tells us that the electrons have been ejected from a metal surface by incident light . in this article , we will discuss how 19th century physicists attempted ( but failed ! ) to explain the photoelectric effect using classical physics . this ultimately led to the development of the modern description of electromagnetic radiation , which has both wave-like and particle-like properties . predictions based on light as a wave to explain the photoelectric effect , 19th-century physicists theorized that the oscillating electric field of the incoming light wave was heating the electrons and causing them to vibrate , eventually freeing them from the metal surface . this hypothesis was based on the assumption that light traveled purely as a wave through space . ( see this article for more information about the basic properties of light . ) scientists also believed that the energy of the light wave was proportional to its brightness , which is related to the wave 's amplitude . in order to test their hypotheses , they performed experiments to look at the effect of light amplitude and frequency on the rate of electron ejection , as well as the kinetic energy of the photoelectrons . based on the classical description of light as a wave , they made the following predictions : the kinetic energy of emitted photoelectrons should increase with the light amplitude . the rate of electron emission , which is proportional to the measured electric current , should increase as the light frequency is increased . to help us understand why they made these predictions , we can compare a light wave to a water wave . imagine some beach balls sitting on a dock that extends out into the ocean . the dock represents a metal surface , the beach balls represent electrons , and the ocean waves represent light waves . if a single large wave were to shake the dock , we would expect the energy from the big wave would send the beach balls flying off the dock with much more kinetic energy compared to a single , small wave . this is also what physicists believed would happen if the light intensity was increased . light amplitude was expected to be proportional to the light energy , so higher amplitude light was predicted to result in photoelectrons with more kinetic energy . classical physicists also predicted that increasing the frequency of light waves ( at a constant amplitude ) would increase the rate of electrons being ejected , and thus increase the measured electric current . using our beach ball analogy , we would expect waves hitting the dock more frequently would result in more beach balls being knocked off the dock compared to the same sized waves hitting the dock less often . now that we know what physicists thought would happen , let 's look at what they actually observed experimentally ! when intuition fails : photons to the rescue ! when experiments were performed to look at the effect of light amplitude and frequency , the following results were observed : the kinetic energy of photoelectrons increases with light frequency . electric current remains constant as light frequency increases . electric current increases with light amplitude . the kinetic energy of photoelectrons remains constant as light amplitude increases . these results were completely at odds with the predictions based on the classical description of light as a wave ! in order to explain what was happening , it turned out that an entirely new model of light was needed . that model was developed by albert einstein , who proposed that light sometimes behaved as particles of electromagnetic energy which we now call photons . the energy of a photon could be calculated using planck 's equation : $ \text { e } _ { \text { photon } } =h\nu $ where $ \text { e } _ { \text { photon } } $ is the energy of a photon in joules ( $ \text { j } $ ) , $ h $ is planck 's constant $ ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) $ , and $ \nu $ is the frequency of the light in $ \text { hz } $ . according to planck 's equation , the energy of a photon is proportional to the frequency of the light , $ \nu $ . the amplitude of the light is then proportional to the number of photons with a given frequency . concept check : as the wavelength of a photon increases , what happens to the photon 's energy ? light frequency and the threshold frequency $ \nu_0 $ we can think of the incident light as a stream of photons with an energy determined by the light frequency . when a photon hits the metal surface , the photon 's energy is absorbed by an electron in the metal . the graphic below illustrates the relationship between light frequency and the kinetic energy of ejected electrons . the scientists observed that if the incident light had a frequency less than a minimum frequency $ \nu_0 $ , then no electrons were ejected regardless of the light amplitude . this minimum frequency is also called the threshold frequency , and the value of $ \nu_0 $ depends on the metal . for frequencies greater than $ \nu_0 $ , electrons would be ejected from the metal . furthermore , the kinetic energy of the photoelectrons was proportional to the light frequency . the relationship between photoelectron kinetic energy and light frequency is shown in graph ( a ) below . because the light amplitude was kept constant as the light frequency increased , the number of photons being absorbed by the metal remained constant . thus , the rate at which electrons were ejected from the metal ( or the electric current ) remained constant as well . the relationship between electron current and light frequency is illustrated in graph ( b ) above . is n't there more math somewhere ? we can analyze the frequency relationship using the law of conservation of energy . the total energy of the incoming photon , $ \text { e } \text { photon } $ , must be equal to the kinetic energy of the ejected electron , $ \text { ke } { \text { electron } } $ , plus the energy required to eject the electron from the metal . the energy required to free the electron from a particular metal is also called the metal 's work function , which is represented by the symbol $ \phi $ ( in units of $ \text j $ ) : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ like the threshold frequency $ \nu_0 $ , the value of $ \phi $ also changes depending on the metal . we can now write the energy of the photon in terms of the light frequency using planck 's equation : $ \text { e } \text { photon } =h\nu=\text { ke } \text { electron } +\phi $ rearranging this equation in terms of the electron 's kinetic energy , we get : $ \text { ke } _\text { electron } =h\nu-\phi $ we can see that kinetic energy of the photoelectron increases linearly with $ \nu $ as long as the photon energy is greater than the work function $ \phi $ , which is exactly the relationship shown in graph ( a ) above . we can also use this equation to find the photoelectron velocity $ \text v $ , which is related to $ \text { ke } _\text { electron } $ as follows : $ \text { ke } _\text { electron } =h\nu-\phi=\dfrac { 1 } { 2 } m_e\text v^2 $ where $ m_e $ is the rest mass of an electron , $ 9.1094 \times 10^ { -31 } \ , \text { kg } $ . exploring the wave amplitude trends in terms of photons , higher amplitude light means more photons hitting the metal surface . this results in more electrons ejected over a given time period . as long as the light frequency is greater than $ \nu_0 $ , increasing the light amplitude will cause the electron current to increase proportionally as shown in graph ( a ) below . since increasing the light amplitude has no effect on the energy of the incoming photon , the photoelectron kinetic energy remains constant as the light amplitude is increased ( see graph ( b ) above ) . if we try to explain this result using our dock-and-beach-balls analogy , the relationship in graph ( b ) indicates that no matter the height of the wave hitting the dock $ - $ whether it 's a tiny swell , or a huge tsunami $ - $ the individual beach balls would be launched off the dock with the exact same speed ! thus , our intuition and analogy do n't do a very good job of explaining these particular experiments . example $ 1 $ : the photoelectric effect for copper the work function of copper metal is $ \phi=7.53\times10^ { -19 } \text { j } $ . if we shine light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ on copper metal , will the photoelectric effect be observed ? in order to eject electrons , we need the energy of the photons to be greater than the work function of copper . we can use planck 's equation to calculate the energy of the photon , $ \text { e } _ { \text { photon } } $ : $ \begin { align } \text { e } _\text { photon } & amp ; = h\nu \ & amp ; = ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) ( 3.0\times10^ { 16 } \text { hz } ) ~~~~\text { plug in values for $ h $ and $ \nu $ } \ & amp ; = 2.0\times10^ { -17 } \text { j } \end { align } $ if we compare our calculated photon energy , $ \text { e } _\text { photon } $ , to copper 's work function , we see that the photon energy is greater than $ \phi $ : $ ~2.0\times10^ { -17 } \text { j } ~ & gt ; ~7.53\times10^ { -19 } \text { j } $ $ ~~~~~~~~\text { e } _\text { photon } ~~~~~~~~~~~~~~~~~~~\phi $ thus , we would expect to see photoelectrons ejected from the copper . next , we will calculate the kinetic energy of the photoelectrons . example $ 2 $ : calculating the kinetic energy of a photoelectron what is the kinetic energy of the photoelectrons ejected from the copper by the light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ ? we can calculate the kinetic energy of the photoelectron using the equation that relates $ \text { ke } \text { electron } $ to the energy of the photon , $ \text { e } \text { photon } $ , and the work function , $ \phi $ : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ since we want to know $ \text { ke } _\text { electron } $ , we can start by rearranging the equation so that we will be solving for the kinetic energy of the electron : $ \text { ke } \text { electron } =\text { e } \text { photon } -\phi $ now we can insert our known values for $ \text { e } _\text { photon } $ and $ \phi $ from example 1 : $ \text { ke } _\text { electron } = ( 2.0\times10^ { -17 } \text { j } ) - ( 7.53\times10^ { -19 } \text { j } ) =1.9\times10^ { -17 } \text { j } $ therefore , each photoelectron has a kinetic energy of $ 1.9\times10^ { -17 } \text { j } $ . summary based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a specific metal surface . the energy of the incident photon must be equal to the sum of the work function and the kinetic energy of a photoelectron : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ try it ! when we shine light with a frequency of $ 6.20 \times 10^ { 14 } \ , \text { hz } $ on a mystery metal , we observe the ejected electrons have a kinetic energy of $ 3.28\times 10^ { -20 } \ , \text j $ . some possible candidates for the mystery metal are shown in the table below : metal | work function $ \phi $ ( joules , $ \text j $ ) : - : | : - : calcium , $ \text { ca } $ | $ 4.60\times 10^ { -19 } $ tin , $ \text { sn } $ | $ 7.08\times 10^ { -19 } $ sodium , $ \text { na } $ | $ 3.78\times 10^ { -19 } $ hafnium , $ \text { hf } $ | $ 6.25\times 10^ { -19 } $ samarium , $ \text { sm } $ | $ 4.33\times 10^ { -19 } $ based on this information , what is the most likely identity of our mystery metal ?
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concept check : as the wavelength of a photon increases , what happens to the photon 's energy ? light frequency and the threshold frequency $ \nu_0 $ we can think of the incident light as a stream of photons with an energy determined by the light frequency . when a photon hits the metal surface , the photon 's energy is absorbed by an electron in the metal .
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i know that work function is the energy required to free electrons whereas threshold frequency is the frequency of the light necessary for the photoelectric effect to occur.other than this can somebody please tell me if is there any other difference between them ?
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key points based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . contrary to the predictions , experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of particles called photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a metal surface , and the value of $ \phi $ depends on the metal . the energy of the incident photon must be equal to the sum of the metal 's work function and the photoelectron kinetic energy : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ introduction : what is the photoelectric effect ? when light shines on a metal , electrons can be ejected from the surface of the metal in a phenomenon known as the photoelectric effect . this process is also often referred to as photoemission , and the electrons that are ejected from the metal are called photoelectrons . in terms of their behavior and their properties , photoelectrons are no different from other electrons . the prefix , photo- , simply tells us that the electrons have been ejected from a metal surface by incident light . in this article , we will discuss how 19th century physicists attempted ( but failed ! ) to explain the photoelectric effect using classical physics . this ultimately led to the development of the modern description of electromagnetic radiation , which has both wave-like and particle-like properties . predictions based on light as a wave to explain the photoelectric effect , 19th-century physicists theorized that the oscillating electric field of the incoming light wave was heating the electrons and causing them to vibrate , eventually freeing them from the metal surface . this hypothesis was based on the assumption that light traveled purely as a wave through space . ( see this article for more information about the basic properties of light . ) scientists also believed that the energy of the light wave was proportional to its brightness , which is related to the wave 's amplitude . in order to test their hypotheses , they performed experiments to look at the effect of light amplitude and frequency on the rate of electron ejection , as well as the kinetic energy of the photoelectrons . based on the classical description of light as a wave , they made the following predictions : the kinetic energy of emitted photoelectrons should increase with the light amplitude . the rate of electron emission , which is proportional to the measured electric current , should increase as the light frequency is increased . to help us understand why they made these predictions , we can compare a light wave to a water wave . imagine some beach balls sitting on a dock that extends out into the ocean . the dock represents a metal surface , the beach balls represent electrons , and the ocean waves represent light waves . if a single large wave were to shake the dock , we would expect the energy from the big wave would send the beach balls flying off the dock with much more kinetic energy compared to a single , small wave . this is also what physicists believed would happen if the light intensity was increased . light amplitude was expected to be proportional to the light energy , so higher amplitude light was predicted to result in photoelectrons with more kinetic energy . classical physicists also predicted that increasing the frequency of light waves ( at a constant amplitude ) would increase the rate of electrons being ejected , and thus increase the measured electric current . using our beach ball analogy , we would expect waves hitting the dock more frequently would result in more beach balls being knocked off the dock compared to the same sized waves hitting the dock less often . now that we know what physicists thought would happen , let 's look at what they actually observed experimentally ! when intuition fails : photons to the rescue ! when experiments were performed to look at the effect of light amplitude and frequency , the following results were observed : the kinetic energy of photoelectrons increases with light frequency . electric current remains constant as light frequency increases . electric current increases with light amplitude . the kinetic energy of photoelectrons remains constant as light amplitude increases . these results were completely at odds with the predictions based on the classical description of light as a wave ! in order to explain what was happening , it turned out that an entirely new model of light was needed . that model was developed by albert einstein , who proposed that light sometimes behaved as particles of electromagnetic energy which we now call photons . the energy of a photon could be calculated using planck 's equation : $ \text { e } _ { \text { photon } } =h\nu $ where $ \text { e } _ { \text { photon } } $ is the energy of a photon in joules ( $ \text { j } $ ) , $ h $ is planck 's constant $ ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) $ , and $ \nu $ is the frequency of the light in $ \text { hz } $ . according to planck 's equation , the energy of a photon is proportional to the frequency of the light , $ \nu $ . the amplitude of the light is then proportional to the number of photons with a given frequency . concept check : as the wavelength of a photon increases , what happens to the photon 's energy ? light frequency and the threshold frequency $ \nu_0 $ we can think of the incident light as a stream of photons with an energy determined by the light frequency . when a photon hits the metal surface , the photon 's energy is absorbed by an electron in the metal . the graphic below illustrates the relationship between light frequency and the kinetic energy of ejected electrons . the scientists observed that if the incident light had a frequency less than a minimum frequency $ \nu_0 $ , then no electrons were ejected regardless of the light amplitude . this minimum frequency is also called the threshold frequency , and the value of $ \nu_0 $ depends on the metal . for frequencies greater than $ \nu_0 $ , electrons would be ejected from the metal . furthermore , the kinetic energy of the photoelectrons was proportional to the light frequency . the relationship between photoelectron kinetic energy and light frequency is shown in graph ( a ) below . because the light amplitude was kept constant as the light frequency increased , the number of photons being absorbed by the metal remained constant . thus , the rate at which electrons were ejected from the metal ( or the electric current ) remained constant as well . the relationship between electron current and light frequency is illustrated in graph ( b ) above . is n't there more math somewhere ? we can analyze the frequency relationship using the law of conservation of energy . the total energy of the incoming photon , $ \text { e } \text { photon } $ , must be equal to the kinetic energy of the ejected electron , $ \text { ke } { \text { electron } } $ , plus the energy required to eject the electron from the metal . the energy required to free the electron from a particular metal is also called the metal 's work function , which is represented by the symbol $ \phi $ ( in units of $ \text j $ ) : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ like the threshold frequency $ \nu_0 $ , the value of $ \phi $ also changes depending on the metal . we can now write the energy of the photon in terms of the light frequency using planck 's equation : $ \text { e } \text { photon } =h\nu=\text { ke } \text { electron } +\phi $ rearranging this equation in terms of the electron 's kinetic energy , we get : $ \text { ke } _\text { electron } =h\nu-\phi $ we can see that kinetic energy of the photoelectron increases linearly with $ \nu $ as long as the photon energy is greater than the work function $ \phi $ , which is exactly the relationship shown in graph ( a ) above . we can also use this equation to find the photoelectron velocity $ \text v $ , which is related to $ \text { ke } _\text { electron } $ as follows : $ \text { ke } _\text { electron } =h\nu-\phi=\dfrac { 1 } { 2 } m_e\text v^2 $ where $ m_e $ is the rest mass of an electron , $ 9.1094 \times 10^ { -31 } \ , \text { kg } $ . exploring the wave amplitude trends in terms of photons , higher amplitude light means more photons hitting the metal surface . this results in more electrons ejected over a given time period . as long as the light frequency is greater than $ \nu_0 $ , increasing the light amplitude will cause the electron current to increase proportionally as shown in graph ( a ) below . since increasing the light amplitude has no effect on the energy of the incoming photon , the photoelectron kinetic energy remains constant as the light amplitude is increased ( see graph ( b ) above ) . if we try to explain this result using our dock-and-beach-balls analogy , the relationship in graph ( b ) indicates that no matter the height of the wave hitting the dock $ - $ whether it 's a tiny swell , or a huge tsunami $ - $ the individual beach balls would be launched off the dock with the exact same speed ! thus , our intuition and analogy do n't do a very good job of explaining these particular experiments . example $ 1 $ : the photoelectric effect for copper the work function of copper metal is $ \phi=7.53\times10^ { -19 } \text { j } $ . if we shine light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ on copper metal , will the photoelectric effect be observed ? in order to eject electrons , we need the energy of the photons to be greater than the work function of copper . we can use planck 's equation to calculate the energy of the photon , $ \text { e } _ { \text { photon } } $ : $ \begin { align } \text { e } _\text { photon } & amp ; = h\nu \ & amp ; = ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) ( 3.0\times10^ { 16 } \text { hz } ) ~~~~\text { plug in values for $ h $ and $ \nu $ } \ & amp ; = 2.0\times10^ { -17 } \text { j } \end { align } $ if we compare our calculated photon energy , $ \text { e } _\text { photon } $ , to copper 's work function , we see that the photon energy is greater than $ \phi $ : $ ~2.0\times10^ { -17 } \text { j } ~ & gt ; ~7.53\times10^ { -19 } \text { j } $ $ ~~~~~~~~\text { e } _\text { photon } ~~~~~~~~~~~~~~~~~~~\phi $ thus , we would expect to see photoelectrons ejected from the copper . next , we will calculate the kinetic energy of the photoelectrons . example $ 2 $ : calculating the kinetic energy of a photoelectron what is the kinetic energy of the photoelectrons ejected from the copper by the light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ ? we can calculate the kinetic energy of the photoelectron using the equation that relates $ \text { ke } \text { electron } $ to the energy of the photon , $ \text { e } \text { photon } $ , and the work function , $ \phi $ : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ since we want to know $ \text { ke } _\text { electron } $ , we can start by rearranging the equation so that we will be solving for the kinetic energy of the electron : $ \text { ke } \text { electron } =\text { e } \text { photon } -\phi $ now we can insert our known values for $ \text { e } _\text { photon } $ and $ \phi $ from example 1 : $ \text { ke } _\text { electron } = ( 2.0\times10^ { -17 } \text { j } ) - ( 7.53\times10^ { -19 } \text { j } ) =1.9\times10^ { -17 } \text { j } $ therefore , each photoelectron has a kinetic energy of $ 1.9\times10^ { -17 } \text { j } $ . summary based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a specific metal surface . the energy of the incident photon must be equal to the sum of the work function and the kinetic energy of a photoelectron : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ try it ! when we shine light with a frequency of $ 6.20 \times 10^ { 14 } \ , \text { hz } $ on a mystery metal , we observe the ejected electrons have a kinetic energy of $ 3.28\times 10^ { -20 } \ , \text j $ . some possible candidates for the mystery metal are shown in the table below : metal | work function $ \phi $ ( joules , $ \text j $ ) : - : | : - : calcium , $ \text { ca } $ | $ 4.60\times 10^ { -19 } $ tin , $ \text { sn } $ | $ 7.08\times 10^ { -19 } $ sodium , $ \text { na } $ | $ 3.78\times 10^ { -19 } $ hafnium , $ \text { hf } $ | $ 6.25\times 10^ { -19 } $ samarium , $ \text { sm } $ | $ 4.33\times 10^ { -19 } $ based on this information , what is the most likely identity of our mystery metal ?
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when experiments were performed to look at the effect of light amplitude and frequency , the following results were observed : the kinetic energy of photoelectrons increases with light frequency . electric current remains constant as light frequency increases . electric current increases with light amplitude .
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what is derivation of planck 's constant ?
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key points based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . contrary to the predictions , experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of particles called photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a metal surface , and the value of $ \phi $ depends on the metal . the energy of the incident photon must be equal to the sum of the metal 's work function and the photoelectron kinetic energy : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ introduction : what is the photoelectric effect ? when light shines on a metal , electrons can be ejected from the surface of the metal in a phenomenon known as the photoelectric effect . this process is also often referred to as photoemission , and the electrons that are ejected from the metal are called photoelectrons . in terms of their behavior and their properties , photoelectrons are no different from other electrons . the prefix , photo- , simply tells us that the electrons have been ejected from a metal surface by incident light . in this article , we will discuss how 19th century physicists attempted ( but failed ! ) to explain the photoelectric effect using classical physics . this ultimately led to the development of the modern description of electromagnetic radiation , which has both wave-like and particle-like properties . predictions based on light as a wave to explain the photoelectric effect , 19th-century physicists theorized that the oscillating electric field of the incoming light wave was heating the electrons and causing them to vibrate , eventually freeing them from the metal surface . this hypothesis was based on the assumption that light traveled purely as a wave through space . ( see this article for more information about the basic properties of light . ) scientists also believed that the energy of the light wave was proportional to its brightness , which is related to the wave 's amplitude . in order to test their hypotheses , they performed experiments to look at the effect of light amplitude and frequency on the rate of electron ejection , as well as the kinetic energy of the photoelectrons . based on the classical description of light as a wave , they made the following predictions : the kinetic energy of emitted photoelectrons should increase with the light amplitude . the rate of electron emission , which is proportional to the measured electric current , should increase as the light frequency is increased . to help us understand why they made these predictions , we can compare a light wave to a water wave . imagine some beach balls sitting on a dock that extends out into the ocean . the dock represents a metal surface , the beach balls represent electrons , and the ocean waves represent light waves . if a single large wave were to shake the dock , we would expect the energy from the big wave would send the beach balls flying off the dock with much more kinetic energy compared to a single , small wave . this is also what physicists believed would happen if the light intensity was increased . light amplitude was expected to be proportional to the light energy , so higher amplitude light was predicted to result in photoelectrons with more kinetic energy . classical physicists also predicted that increasing the frequency of light waves ( at a constant amplitude ) would increase the rate of electrons being ejected , and thus increase the measured electric current . using our beach ball analogy , we would expect waves hitting the dock more frequently would result in more beach balls being knocked off the dock compared to the same sized waves hitting the dock less often . now that we know what physicists thought would happen , let 's look at what they actually observed experimentally ! when intuition fails : photons to the rescue ! when experiments were performed to look at the effect of light amplitude and frequency , the following results were observed : the kinetic energy of photoelectrons increases with light frequency . electric current remains constant as light frequency increases . electric current increases with light amplitude . the kinetic energy of photoelectrons remains constant as light amplitude increases . these results were completely at odds with the predictions based on the classical description of light as a wave ! in order to explain what was happening , it turned out that an entirely new model of light was needed . that model was developed by albert einstein , who proposed that light sometimes behaved as particles of electromagnetic energy which we now call photons . the energy of a photon could be calculated using planck 's equation : $ \text { e } _ { \text { photon } } =h\nu $ where $ \text { e } _ { \text { photon } } $ is the energy of a photon in joules ( $ \text { j } $ ) , $ h $ is planck 's constant $ ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) $ , and $ \nu $ is the frequency of the light in $ \text { hz } $ . according to planck 's equation , the energy of a photon is proportional to the frequency of the light , $ \nu $ . the amplitude of the light is then proportional to the number of photons with a given frequency . concept check : as the wavelength of a photon increases , what happens to the photon 's energy ? light frequency and the threshold frequency $ \nu_0 $ we can think of the incident light as a stream of photons with an energy determined by the light frequency . when a photon hits the metal surface , the photon 's energy is absorbed by an electron in the metal . the graphic below illustrates the relationship between light frequency and the kinetic energy of ejected electrons . the scientists observed that if the incident light had a frequency less than a minimum frequency $ \nu_0 $ , then no electrons were ejected regardless of the light amplitude . this minimum frequency is also called the threshold frequency , and the value of $ \nu_0 $ depends on the metal . for frequencies greater than $ \nu_0 $ , electrons would be ejected from the metal . furthermore , the kinetic energy of the photoelectrons was proportional to the light frequency . the relationship between photoelectron kinetic energy and light frequency is shown in graph ( a ) below . because the light amplitude was kept constant as the light frequency increased , the number of photons being absorbed by the metal remained constant . thus , the rate at which electrons were ejected from the metal ( or the electric current ) remained constant as well . the relationship between electron current and light frequency is illustrated in graph ( b ) above . is n't there more math somewhere ? we can analyze the frequency relationship using the law of conservation of energy . the total energy of the incoming photon , $ \text { e } \text { photon } $ , must be equal to the kinetic energy of the ejected electron , $ \text { ke } { \text { electron } } $ , plus the energy required to eject the electron from the metal . the energy required to free the electron from a particular metal is also called the metal 's work function , which is represented by the symbol $ \phi $ ( in units of $ \text j $ ) : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ like the threshold frequency $ \nu_0 $ , the value of $ \phi $ also changes depending on the metal . we can now write the energy of the photon in terms of the light frequency using planck 's equation : $ \text { e } \text { photon } =h\nu=\text { ke } \text { electron } +\phi $ rearranging this equation in terms of the electron 's kinetic energy , we get : $ \text { ke } _\text { electron } =h\nu-\phi $ we can see that kinetic energy of the photoelectron increases linearly with $ \nu $ as long as the photon energy is greater than the work function $ \phi $ , which is exactly the relationship shown in graph ( a ) above . we can also use this equation to find the photoelectron velocity $ \text v $ , which is related to $ \text { ke } _\text { electron } $ as follows : $ \text { ke } _\text { electron } =h\nu-\phi=\dfrac { 1 } { 2 } m_e\text v^2 $ where $ m_e $ is the rest mass of an electron , $ 9.1094 \times 10^ { -31 } \ , \text { kg } $ . exploring the wave amplitude trends in terms of photons , higher amplitude light means more photons hitting the metal surface . this results in more electrons ejected over a given time period . as long as the light frequency is greater than $ \nu_0 $ , increasing the light amplitude will cause the electron current to increase proportionally as shown in graph ( a ) below . since increasing the light amplitude has no effect on the energy of the incoming photon , the photoelectron kinetic energy remains constant as the light amplitude is increased ( see graph ( b ) above ) . if we try to explain this result using our dock-and-beach-balls analogy , the relationship in graph ( b ) indicates that no matter the height of the wave hitting the dock $ - $ whether it 's a tiny swell , or a huge tsunami $ - $ the individual beach balls would be launched off the dock with the exact same speed ! thus , our intuition and analogy do n't do a very good job of explaining these particular experiments . example $ 1 $ : the photoelectric effect for copper the work function of copper metal is $ \phi=7.53\times10^ { -19 } \text { j } $ . if we shine light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ on copper metal , will the photoelectric effect be observed ? in order to eject electrons , we need the energy of the photons to be greater than the work function of copper . we can use planck 's equation to calculate the energy of the photon , $ \text { e } _ { \text { photon } } $ : $ \begin { align } \text { e } _\text { photon } & amp ; = h\nu \ & amp ; = ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) ( 3.0\times10^ { 16 } \text { hz } ) ~~~~\text { plug in values for $ h $ and $ \nu $ } \ & amp ; = 2.0\times10^ { -17 } \text { j } \end { align } $ if we compare our calculated photon energy , $ \text { e } _\text { photon } $ , to copper 's work function , we see that the photon energy is greater than $ \phi $ : $ ~2.0\times10^ { -17 } \text { j } ~ & gt ; ~7.53\times10^ { -19 } \text { j } $ $ ~~~~~~~~\text { e } _\text { photon } ~~~~~~~~~~~~~~~~~~~\phi $ thus , we would expect to see photoelectrons ejected from the copper . next , we will calculate the kinetic energy of the photoelectrons . example $ 2 $ : calculating the kinetic energy of a photoelectron what is the kinetic energy of the photoelectrons ejected from the copper by the light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ ? we can calculate the kinetic energy of the photoelectron using the equation that relates $ \text { ke } \text { electron } $ to the energy of the photon , $ \text { e } \text { photon } $ , and the work function , $ \phi $ : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ since we want to know $ \text { ke } _\text { electron } $ , we can start by rearranging the equation so that we will be solving for the kinetic energy of the electron : $ \text { ke } \text { electron } =\text { e } \text { photon } -\phi $ now we can insert our known values for $ \text { e } _\text { photon } $ and $ \phi $ from example 1 : $ \text { ke } _\text { electron } = ( 2.0\times10^ { -17 } \text { j } ) - ( 7.53\times10^ { -19 } \text { j } ) =1.9\times10^ { -17 } \text { j } $ therefore , each photoelectron has a kinetic energy of $ 1.9\times10^ { -17 } \text { j } $ . summary based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a specific metal surface . the energy of the incident photon must be equal to the sum of the work function and the kinetic energy of a photoelectron : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ try it ! when we shine light with a frequency of $ 6.20 \times 10^ { 14 } \ , \text { hz } $ on a mystery metal , we observe the ejected electrons have a kinetic energy of $ 3.28\times 10^ { -20 } \ , \text j $ . some possible candidates for the mystery metal are shown in the table below : metal | work function $ \phi $ ( joules , $ \text j $ ) : - : | : - : calcium , $ \text { ca } $ | $ 4.60\times 10^ { -19 } $ tin , $ \text { sn } $ | $ 7.08\times 10^ { -19 } $ sodium , $ \text { na } $ | $ 3.78\times 10^ { -19 } $ hafnium , $ \text { hf } $ | $ 6.25\times 10^ { -19 } $ samarium , $ \text { sm } $ | $ 4.33\times 10^ { -19 } $ based on this information , what is the most likely identity of our mystery metal ?
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concept check : as the wavelength of a photon increases , what happens to the photon 's energy ? light frequency and the threshold frequency $ \nu_0 $ we can think of the incident light as a stream of photons with an energy determined by the light frequency . when a photon hits the metal surface , the photon 's energy is absorbed by an electron in the metal .
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what would happen if the frequency of light would be equal to the threshold frequency ?
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key points based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . contrary to the predictions , experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of particles called photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a metal surface , and the value of $ \phi $ depends on the metal . the energy of the incident photon must be equal to the sum of the metal 's work function and the photoelectron kinetic energy : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ introduction : what is the photoelectric effect ? when light shines on a metal , electrons can be ejected from the surface of the metal in a phenomenon known as the photoelectric effect . this process is also often referred to as photoemission , and the electrons that are ejected from the metal are called photoelectrons . in terms of their behavior and their properties , photoelectrons are no different from other electrons . the prefix , photo- , simply tells us that the electrons have been ejected from a metal surface by incident light . in this article , we will discuss how 19th century physicists attempted ( but failed ! ) to explain the photoelectric effect using classical physics . this ultimately led to the development of the modern description of electromagnetic radiation , which has both wave-like and particle-like properties . predictions based on light as a wave to explain the photoelectric effect , 19th-century physicists theorized that the oscillating electric field of the incoming light wave was heating the electrons and causing them to vibrate , eventually freeing them from the metal surface . this hypothesis was based on the assumption that light traveled purely as a wave through space . ( see this article for more information about the basic properties of light . ) scientists also believed that the energy of the light wave was proportional to its brightness , which is related to the wave 's amplitude . in order to test their hypotheses , they performed experiments to look at the effect of light amplitude and frequency on the rate of electron ejection , as well as the kinetic energy of the photoelectrons . based on the classical description of light as a wave , they made the following predictions : the kinetic energy of emitted photoelectrons should increase with the light amplitude . the rate of electron emission , which is proportional to the measured electric current , should increase as the light frequency is increased . to help us understand why they made these predictions , we can compare a light wave to a water wave . imagine some beach balls sitting on a dock that extends out into the ocean . the dock represents a metal surface , the beach balls represent electrons , and the ocean waves represent light waves . if a single large wave were to shake the dock , we would expect the energy from the big wave would send the beach balls flying off the dock with much more kinetic energy compared to a single , small wave . this is also what physicists believed would happen if the light intensity was increased . light amplitude was expected to be proportional to the light energy , so higher amplitude light was predicted to result in photoelectrons with more kinetic energy . classical physicists also predicted that increasing the frequency of light waves ( at a constant amplitude ) would increase the rate of electrons being ejected , and thus increase the measured electric current . using our beach ball analogy , we would expect waves hitting the dock more frequently would result in more beach balls being knocked off the dock compared to the same sized waves hitting the dock less often . now that we know what physicists thought would happen , let 's look at what they actually observed experimentally ! when intuition fails : photons to the rescue ! when experiments were performed to look at the effect of light amplitude and frequency , the following results were observed : the kinetic energy of photoelectrons increases with light frequency . electric current remains constant as light frequency increases . electric current increases with light amplitude . the kinetic energy of photoelectrons remains constant as light amplitude increases . these results were completely at odds with the predictions based on the classical description of light as a wave ! in order to explain what was happening , it turned out that an entirely new model of light was needed . that model was developed by albert einstein , who proposed that light sometimes behaved as particles of electromagnetic energy which we now call photons . the energy of a photon could be calculated using planck 's equation : $ \text { e } _ { \text { photon } } =h\nu $ where $ \text { e } _ { \text { photon } } $ is the energy of a photon in joules ( $ \text { j } $ ) , $ h $ is planck 's constant $ ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) $ , and $ \nu $ is the frequency of the light in $ \text { hz } $ . according to planck 's equation , the energy of a photon is proportional to the frequency of the light , $ \nu $ . the amplitude of the light is then proportional to the number of photons with a given frequency . concept check : as the wavelength of a photon increases , what happens to the photon 's energy ? light frequency and the threshold frequency $ \nu_0 $ we can think of the incident light as a stream of photons with an energy determined by the light frequency . when a photon hits the metal surface , the photon 's energy is absorbed by an electron in the metal . the graphic below illustrates the relationship between light frequency and the kinetic energy of ejected electrons . the scientists observed that if the incident light had a frequency less than a minimum frequency $ \nu_0 $ , then no electrons were ejected regardless of the light amplitude . this minimum frequency is also called the threshold frequency , and the value of $ \nu_0 $ depends on the metal . for frequencies greater than $ \nu_0 $ , electrons would be ejected from the metal . furthermore , the kinetic energy of the photoelectrons was proportional to the light frequency . the relationship between photoelectron kinetic energy and light frequency is shown in graph ( a ) below . because the light amplitude was kept constant as the light frequency increased , the number of photons being absorbed by the metal remained constant . thus , the rate at which electrons were ejected from the metal ( or the electric current ) remained constant as well . the relationship between electron current and light frequency is illustrated in graph ( b ) above . is n't there more math somewhere ? we can analyze the frequency relationship using the law of conservation of energy . the total energy of the incoming photon , $ \text { e } \text { photon } $ , must be equal to the kinetic energy of the ejected electron , $ \text { ke } { \text { electron } } $ , plus the energy required to eject the electron from the metal . the energy required to free the electron from a particular metal is also called the metal 's work function , which is represented by the symbol $ \phi $ ( in units of $ \text j $ ) : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ like the threshold frequency $ \nu_0 $ , the value of $ \phi $ also changes depending on the metal . we can now write the energy of the photon in terms of the light frequency using planck 's equation : $ \text { e } \text { photon } =h\nu=\text { ke } \text { electron } +\phi $ rearranging this equation in terms of the electron 's kinetic energy , we get : $ \text { ke } _\text { electron } =h\nu-\phi $ we can see that kinetic energy of the photoelectron increases linearly with $ \nu $ as long as the photon energy is greater than the work function $ \phi $ , which is exactly the relationship shown in graph ( a ) above . we can also use this equation to find the photoelectron velocity $ \text v $ , which is related to $ \text { ke } _\text { electron } $ as follows : $ \text { ke } _\text { electron } =h\nu-\phi=\dfrac { 1 } { 2 } m_e\text v^2 $ where $ m_e $ is the rest mass of an electron , $ 9.1094 \times 10^ { -31 } \ , \text { kg } $ . exploring the wave amplitude trends in terms of photons , higher amplitude light means more photons hitting the metal surface . this results in more electrons ejected over a given time period . as long as the light frequency is greater than $ \nu_0 $ , increasing the light amplitude will cause the electron current to increase proportionally as shown in graph ( a ) below . since increasing the light amplitude has no effect on the energy of the incoming photon , the photoelectron kinetic energy remains constant as the light amplitude is increased ( see graph ( b ) above ) . if we try to explain this result using our dock-and-beach-balls analogy , the relationship in graph ( b ) indicates that no matter the height of the wave hitting the dock $ - $ whether it 's a tiny swell , or a huge tsunami $ - $ the individual beach balls would be launched off the dock with the exact same speed ! thus , our intuition and analogy do n't do a very good job of explaining these particular experiments . example $ 1 $ : the photoelectric effect for copper the work function of copper metal is $ \phi=7.53\times10^ { -19 } \text { j } $ . if we shine light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ on copper metal , will the photoelectric effect be observed ? in order to eject electrons , we need the energy of the photons to be greater than the work function of copper . we can use planck 's equation to calculate the energy of the photon , $ \text { e } _ { \text { photon } } $ : $ \begin { align } \text { e } _\text { photon } & amp ; = h\nu \ & amp ; = ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) ( 3.0\times10^ { 16 } \text { hz } ) ~~~~\text { plug in values for $ h $ and $ \nu $ } \ & amp ; = 2.0\times10^ { -17 } \text { j } \end { align } $ if we compare our calculated photon energy , $ \text { e } _\text { photon } $ , to copper 's work function , we see that the photon energy is greater than $ \phi $ : $ ~2.0\times10^ { -17 } \text { j } ~ & gt ; ~7.53\times10^ { -19 } \text { j } $ $ ~~~~~~~~\text { e } _\text { photon } ~~~~~~~~~~~~~~~~~~~\phi $ thus , we would expect to see photoelectrons ejected from the copper . next , we will calculate the kinetic energy of the photoelectrons . example $ 2 $ : calculating the kinetic energy of a photoelectron what is the kinetic energy of the photoelectrons ejected from the copper by the light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ ? we can calculate the kinetic energy of the photoelectron using the equation that relates $ \text { ke } \text { electron } $ to the energy of the photon , $ \text { e } \text { photon } $ , and the work function , $ \phi $ : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ since we want to know $ \text { ke } _\text { electron } $ , we can start by rearranging the equation so that we will be solving for the kinetic energy of the electron : $ \text { ke } \text { electron } =\text { e } \text { photon } -\phi $ now we can insert our known values for $ \text { e } _\text { photon } $ and $ \phi $ from example 1 : $ \text { ke } _\text { electron } = ( 2.0\times10^ { -17 } \text { j } ) - ( 7.53\times10^ { -19 } \text { j } ) =1.9\times10^ { -17 } \text { j } $ therefore , each photoelectron has a kinetic energy of $ 1.9\times10^ { -17 } \text { j } $ . summary based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a specific metal surface . the energy of the incident photon must be equal to the sum of the work function and the kinetic energy of a photoelectron : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ try it ! when we shine light with a frequency of $ 6.20 \times 10^ { 14 } \ , \text { hz } $ on a mystery metal , we observe the ejected electrons have a kinetic energy of $ 3.28\times 10^ { -20 } \ , \text j $ . some possible candidates for the mystery metal are shown in the table below : metal | work function $ \phi $ ( joules , $ \text j $ ) : - : | : - : calcium , $ \text { ca } $ | $ 4.60\times 10^ { -19 } $ tin , $ \text { sn } $ | $ 7.08\times 10^ { -19 } $ sodium , $ \text { na } $ | $ 3.78\times 10^ { -19 } $ hafnium , $ \text { hf } $ | $ 6.25\times 10^ { -19 } $ samarium , $ \text { sm } $ | $ 4.33\times 10^ { -19 } $ based on this information , what is the most likely identity of our mystery metal ?
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based on the classical description of light as a wave , they made the following predictions : the kinetic energy of emitted photoelectrons should increase with the light amplitude . the rate of electron emission , which is proportional to the measured electric current , should increase as the light frequency is increased . to help us understand why they made these predictions , we can compare a light wave to a water wave .
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will there be a change in the rate of electron emission ?
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key points based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . contrary to the predictions , experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of particles called photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a metal surface , and the value of $ \phi $ depends on the metal . the energy of the incident photon must be equal to the sum of the metal 's work function and the photoelectron kinetic energy : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ introduction : what is the photoelectric effect ? when light shines on a metal , electrons can be ejected from the surface of the metal in a phenomenon known as the photoelectric effect . this process is also often referred to as photoemission , and the electrons that are ejected from the metal are called photoelectrons . in terms of their behavior and their properties , photoelectrons are no different from other electrons . the prefix , photo- , simply tells us that the electrons have been ejected from a metal surface by incident light . in this article , we will discuss how 19th century physicists attempted ( but failed ! ) to explain the photoelectric effect using classical physics . this ultimately led to the development of the modern description of electromagnetic radiation , which has both wave-like and particle-like properties . predictions based on light as a wave to explain the photoelectric effect , 19th-century physicists theorized that the oscillating electric field of the incoming light wave was heating the electrons and causing them to vibrate , eventually freeing them from the metal surface . this hypothesis was based on the assumption that light traveled purely as a wave through space . ( see this article for more information about the basic properties of light . ) scientists also believed that the energy of the light wave was proportional to its brightness , which is related to the wave 's amplitude . in order to test their hypotheses , they performed experiments to look at the effect of light amplitude and frequency on the rate of electron ejection , as well as the kinetic energy of the photoelectrons . based on the classical description of light as a wave , they made the following predictions : the kinetic energy of emitted photoelectrons should increase with the light amplitude . the rate of electron emission , which is proportional to the measured electric current , should increase as the light frequency is increased . to help us understand why they made these predictions , we can compare a light wave to a water wave . imagine some beach balls sitting on a dock that extends out into the ocean . the dock represents a metal surface , the beach balls represent electrons , and the ocean waves represent light waves . if a single large wave were to shake the dock , we would expect the energy from the big wave would send the beach balls flying off the dock with much more kinetic energy compared to a single , small wave . this is also what physicists believed would happen if the light intensity was increased . light amplitude was expected to be proportional to the light energy , so higher amplitude light was predicted to result in photoelectrons with more kinetic energy . classical physicists also predicted that increasing the frequency of light waves ( at a constant amplitude ) would increase the rate of electrons being ejected , and thus increase the measured electric current . using our beach ball analogy , we would expect waves hitting the dock more frequently would result in more beach balls being knocked off the dock compared to the same sized waves hitting the dock less often . now that we know what physicists thought would happen , let 's look at what they actually observed experimentally ! when intuition fails : photons to the rescue ! when experiments were performed to look at the effect of light amplitude and frequency , the following results were observed : the kinetic energy of photoelectrons increases with light frequency . electric current remains constant as light frequency increases . electric current increases with light amplitude . the kinetic energy of photoelectrons remains constant as light amplitude increases . these results were completely at odds with the predictions based on the classical description of light as a wave ! in order to explain what was happening , it turned out that an entirely new model of light was needed . that model was developed by albert einstein , who proposed that light sometimes behaved as particles of electromagnetic energy which we now call photons . the energy of a photon could be calculated using planck 's equation : $ \text { e } _ { \text { photon } } =h\nu $ where $ \text { e } _ { \text { photon } } $ is the energy of a photon in joules ( $ \text { j } $ ) , $ h $ is planck 's constant $ ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) $ , and $ \nu $ is the frequency of the light in $ \text { hz } $ . according to planck 's equation , the energy of a photon is proportional to the frequency of the light , $ \nu $ . the amplitude of the light is then proportional to the number of photons with a given frequency . concept check : as the wavelength of a photon increases , what happens to the photon 's energy ? light frequency and the threshold frequency $ \nu_0 $ we can think of the incident light as a stream of photons with an energy determined by the light frequency . when a photon hits the metal surface , the photon 's energy is absorbed by an electron in the metal . the graphic below illustrates the relationship between light frequency and the kinetic energy of ejected electrons . the scientists observed that if the incident light had a frequency less than a minimum frequency $ \nu_0 $ , then no electrons were ejected regardless of the light amplitude . this minimum frequency is also called the threshold frequency , and the value of $ \nu_0 $ depends on the metal . for frequencies greater than $ \nu_0 $ , electrons would be ejected from the metal . furthermore , the kinetic energy of the photoelectrons was proportional to the light frequency . the relationship between photoelectron kinetic energy and light frequency is shown in graph ( a ) below . because the light amplitude was kept constant as the light frequency increased , the number of photons being absorbed by the metal remained constant . thus , the rate at which electrons were ejected from the metal ( or the electric current ) remained constant as well . the relationship between electron current and light frequency is illustrated in graph ( b ) above . is n't there more math somewhere ? we can analyze the frequency relationship using the law of conservation of energy . the total energy of the incoming photon , $ \text { e } \text { photon } $ , must be equal to the kinetic energy of the ejected electron , $ \text { ke } { \text { electron } } $ , plus the energy required to eject the electron from the metal . the energy required to free the electron from a particular metal is also called the metal 's work function , which is represented by the symbol $ \phi $ ( in units of $ \text j $ ) : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ like the threshold frequency $ \nu_0 $ , the value of $ \phi $ also changes depending on the metal . we can now write the energy of the photon in terms of the light frequency using planck 's equation : $ \text { e } \text { photon } =h\nu=\text { ke } \text { electron } +\phi $ rearranging this equation in terms of the electron 's kinetic energy , we get : $ \text { ke } _\text { electron } =h\nu-\phi $ we can see that kinetic energy of the photoelectron increases linearly with $ \nu $ as long as the photon energy is greater than the work function $ \phi $ , which is exactly the relationship shown in graph ( a ) above . we can also use this equation to find the photoelectron velocity $ \text v $ , which is related to $ \text { ke } _\text { electron } $ as follows : $ \text { ke } _\text { electron } =h\nu-\phi=\dfrac { 1 } { 2 } m_e\text v^2 $ where $ m_e $ is the rest mass of an electron , $ 9.1094 \times 10^ { -31 } \ , \text { kg } $ . exploring the wave amplitude trends in terms of photons , higher amplitude light means more photons hitting the metal surface . this results in more electrons ejected over a given time period . as long as the light frequency is greater than $ \nu_0 $ , increasing the light amplitude will cause the electron current to increase proportionally as shown in graph ( a ) below . since increasing the light amplitude has no effect on the energy of the incoming photon , the photoelectron kinetic energy remains constant as the light amplitude is increased ( see graph ( b ) above ) . if we try to explain this result using our dock-and-beach-balls analogy , the relationship in graph ( b ) indicates that no matter the height of the wave hitting the dock $ - $ whether it 's a tiny swell , or a huge tsunami $ - $ the individual beach balls would be launched off the dock with the exact same speed ! thus , our intuition and analogy do n't do a very good job of explaining these particular experiments . example $ 1 $ : the photoelectric effect for copper the work function of copper metal is $ \phi=7.53\times10^ { -19 } \text { j } $ . if we shine light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ on copper metal , will the photoelectric effect be observed ? in order to eject electrons , we need the energy of the photons to be greater than the work function of copper . we can use planck 's equation to calculate the energy of the photon , $ \text { e } _ { \text { photon } } $ : $ \begin { align } \text { e } _\text { photon } & amp ; = h\nu \ & amp ; = ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) ( 3.0\times10^ { 16 } \text { hz } ) ~~~~\text { plug in values for $ h $ and $ \nu $ } \ & amp ; = 2.0\times10^ { -17 } \text { j } \end { align } $ if we compare our calculated photon energy , $ \text { e } _\text { photon } $ , to copper 's work function , we see that the photon energy is greater than $ \phi $ : $ ~2.0\times10^ { -17 } \text { j } ~ & gt ; ~7.53\times10^ { -19 } \text { j } $ $ ~~~~~~~~\text { e } _\text { photon } ~~~~~~~~~~~~~~~~~~~\phi $ thus , we would expect to see photoelectrons ejected from the copper . next , we will calculate the kinetic energy of the photoelectrons . example $ 2 $ : calculating the kinetic energy of a photoelectron what is the kinetic energy of the photoelectrons ejected from the copper by the light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ ? we can calculate the kinetic energy of the photoelectron using the equation that relates $ \text { ke } \text { electron } $ to the energy of the photon , $ \text { e } \text { photon } $ , and the work function , $ \phi $ : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ since we want to know $ \text { ke } _\text { electron } $ , we can start by rearranging the equation so that we will be solving for the kinetic energy of the electron : $ \text { ke } \text { electron } =\text { e } \text { photon } -\phi $ now we can insert our known values for $ \text { e } _\text { photon } $ and $ \phi $ from example 1 : $ \text { ke } _\text { electron } = ( 2.0\times10^ { -17 } \text { j } ) - ( 7.53\times10^ { -19 } \text { j } ) =1.9\times10^ { -17 } \text { j } $ therefore , each photoelectron has a kinetic energy of $ 1.9\times10^ { -17 } \text { j } $ . summary based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a specific metal surface . the energy of the incident photon must be equal to the sum of the work function and the kinetic energy of a photoelectron : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ try it ! when we shine light with a frequency of $ 6.20 \times 10^ { 14 } \ , \text { hz } $ on a mystery metal , we observe the ejected electrons have a kinetic energy of $ 3.28\times 10^ { -20 } \ , \text j $ . some possible candidates for the mystery metal are shown in the table below : metal | work function $ \phi $ ( joules , $ \text j $ ) : - : | : - : calcium , $ \text { ca } $ | $ 4.60\times 10^ { -19 } $ tin , $ \text { sn } $ | $ 7.08\times 10^ { -19 } $ sodium , $ \text { na } $ | $ 3.78\times 10^ { -19 } $ hafnium , $ \text { hf } $ | $ 6.25\times 10^ { -19 } $ samarium , $ \text { sm } $ | $ 4.33\times 10^ { -19 } $ based on this information , what is the most likely identity of our mystery metal ?
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we can calculate the kinetic energy of the photoelectron using the equation that relates $ \text { ke } \text { electron } $ to the energy of the photon , $ \text { e } \text { photon } $ , and the work function , $ \phi $ : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ since we want to know $ \text { ke } _\text { electron } $ , we can start by rearranging the equation so that we will be solving for the kinetic energy of the electron : $ \text { ke } \text { electron } =\text { e } \text { photon } -\phi $ now we can insert our known values for $ \text { e } _\text { photon } $ and $ \phi $ from example 1 : $ \text { ke } _\text { electron } = ( 2.0\times10^ { -17 } \text { j } ) - ( 7.53\times10^ { -19 } \text { j } ) =1.9\times10^ { -17 } \text { j } $ therefore , each photoelectron has a kinetic energy of $ 1.9\times10^ { -17 } \text { j } $ . summary based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current .
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the increase in the kinetic energy of electron will not lead to increase in the electric current ?
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key points based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . contrary to the predictions , experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of particles called photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a metal surface , and the value of $ \phi $ depends on the metal . the energy of the incident photon must be equal to the sum of the metal 's work function and the photoelectron kinetic energy : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ introduction : what is the photoelectric effect ? when light shines on a metal , electrons can be ejected from the surface of the metal in a phenomenon known as the photoelectric effect . this process is also often referred to as photoemission , and the electrons that are ejected from the metal are called photoelectrons . in terms of their behavior and their properties , photoelectrons are no different from other electrons . the prefix , photo- , simply tells us that the electrons have been ejected from a metal surface by incident light . in this article , we will discuss how 19th century physicists attempted ( but failed ! ) to explain the photoelectric effect using classical physics . this ultimately led to the development of the modern description of electromagnetic radiation , which has both wave-like and particle-like properties . predictions based on light as a wave to explain the photoelectric effect , 19th-century physicists theorized that the oscillating electric field of the incoming light wave was heating the electrons and causing them to vibrate , eventually freeing them from the metal surface . this hypothesis was based on the assumption that light traveled purely as a wave through space . ( see this article for more information about the basic properties of light . ) scientists also believed that the energy of the light wave was proportional to its brightness , which is related to the wave 's amplitude . in order to test their hypotheses , they performed experiments to look at the effect of light amplitude and frequency on the rate of electron ejection , as well as the kinetic energy of the photoelectrons . based on the classical description of light as a wave , they made the following predictions : the kinetic energy of emitted photoelectrons should increase with the light amplitude . the rate of electron emission , which is proportional to the measured electric current , should increase as the light frequency is increased . to help us understand why they made these predictions , we can compare a light wave to a water wave . imagine some beach balls sitting on a dock that extends out into the ocean . the dock represents a metal surface , the beach balls represent electrons , and the ocean waves represent light waves . if a single large wave were to shake the dock , we would expect the energy from the big wave would send the beach balls flying off the dock with much more kinetic energy compared to a single , small wave . this is also what physicists believed would happen if the light intensity was increased . light amplitude was expected to be proportional to the light energy , so higher amplitude light was predicted to result in photoelectrons with more kinetic energy . classical physicists also predicted that increasing the frequency of light waves ( at a constant amplitude ) would increase the rate of electrons being ejected , and thus increase the measured electric current . using our beach ball analogy , we would expect waves hitting the dock more frequently would result in more beach balls being knocked off the dock compared to the same sized waves hitting the dock less often . now that we know what physicists thought would happen , let 's look at what they actually observed experimentally ! when intuition fails : photons to the rescue ! when experiments were performed to look at the effect of light amplitude and frequency , the following results were observed : the kinetic energy of photoelectrons increases with light frequency . electric current remains constant as light frequency increases . electric current increases with light amplitude . the kinetic energy of photoelectrons remains constant as light amplitude increases . these results were completely at odds with the predictions based on the classical description of light as a wave ! in order to explain what was happening , it turned out that an entirely new model of light was needed . that model was developed by albert einstein , who proposed that light sometimes behaved as particles of electromagnetic energy which we now call photons . the energy of a photon could be calculated using planck 's equation : $ \text { e } _ { \text { photon } } =h\nu $ where $ \text { e } _ { \text { photon } } $ is the energy of a photon in joules ( $ \text { j } $ ) , $ h $ is planck 's constant $ ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) $ , and $ \nu $ is the frequency of the light in $ \text { hz } $ . according to planck 's equation , the energy of a photon is proportional to the frequency of the light , $ \nu $ . the amplitude of the light is then proportional to the number of photons with a given frequency . concept check : as the wavelength of a photon increases , what happens to the photon 's energy ? light frequency and the threshold frequency $ \nu_0 $ we can think of the incident light as a stream of photons with an energy determined by the light frequency . when a photon hits the metal surface , the photon 's energy is absorbed by an electron in the metal . the graphic below illustrates the relationship between light frequency and the kinetic energy of ejected electrons . the scientists observed that if the incident light had a frequency less than a minimum frequency $ \nu_0 $ , then no electrons were ejected regardless of the light amplitude . this minimum frequency is also called the threshold frequency , and the value of $ \nu_0 $ depends on the metal . for frequencies greater than $ \nu_0 $ , electrons would be ejected from the metal . furthermore , the kinetic energy of the photoelectrons was proportional to the light frequency . the relationship between photoelectron kinetic energy and light frequency is shown in graph ( a ) below . because the light amplitude was kept constant as the light frequency increased , the number of photons being absorbed by the metal remained constant . thus , the rate at which electrons were ejected from the metal ( or the electric current ) remained constant as well . the relationship between electron current and light frequency is illustrated in graph ( b ) above . is n't there more math somewhere ? we can analyze the frequency relationship using the law of conservation of energy . the total energy of the incoming photon , $ \text { e } \text { photon } $ , must be equal to the kinetic energy of the ejected electron , $ \text { ke } { \text { electron } } $ , plus the energy required to eject the electron from the metal . the energy required to free the electron from a particular metal is also called the metal 's work function , which is represented by the symbol $ \phi $ ( in units of $ \text j $ ) : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ like the threshold frequency $ \nu_0 $ , the value of $ \phi $ also changes depending on the metal . we can now write the energy of the photon in terms of the light frequency using planck 's equation : $ \text { e } \text { photon } =h\nu=\text { ke } \text { electron } +\phi $ rearranging this equation in terms of the electron 's kinetic energy , we get : $ \text { ke } _\text { electron } =h\nu-\phi $ we can see that kinetic energy of the photoelectron increases linearly with $ \nu $ as long as the photon energy is greater than the work function $ \phi $ , which is exactly the relationship shown in graph ( a ) above . we can also use this equation to find the photoelectron velocity $ \text v $ , which is related to $ \text { ke } _\text { electron } $ as follows : $ \text { ke } _\text { electron } =h\nu-\phi=\dfrac { 1 } { 2 } m_e\text v^2 $ where $ m_e $ is the rest mass of an electron , $ 9.1094 \times 10^ { -31 } \ , \text { kg } $ . exploring the wave amplitude trends in terms of photons , higher amplitude light means more photons hitting the metal surface . this results in more electrons ejected over a given time period . as long as the light frequency is greater than $ \nu_0 $ , increasing the light amplitude will cause the electron current to increase proportionally as shown in graph ( a ) below . since increasing the light amplitude has no effect on the energy of the incoming photon , the photoelectron kinetic energy remains constant as the light amplitude is increased ( see graph ( b ) above ) . if we try to explain this result using our dock-and-beach-balls analogy , the relationship in graph ( b ) indicates that no matter the height of the wave hitting the dock $ - $ whether it 's a tiny swell , or a huge tsunami $ - $ the individual beach balls would be launched off the dock with the exact same speed ! thus , our intuition and analogy do n't do a very good job of explaining these particular experiments . example $ 1 $ : the photoelectric effect for copper the work function of copper metal is $ \phi=7.53\times10^ { -19 } \text { j } $ . if we shine light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ on copper metal , will the photoelectric effect be observed ? in order to eject electrons , we need the energy of the photons to be greater than the work function of copper . we can use planck 's equation to calculate the energy of the photon , $ \text { e } _ { \text { photon } } $ : $ \begin { align } \text { e } _\text { photon } & amp ; = h\nu \ & amp ; = ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) ( 3.0\times10^ { 16 } \text { hz } ) ~~~~\text { plug in values for $ h $ and $ \nu $ } \ & amp ; = 2.0\times10^ { -17 } \text { j } \end { align } $ if we compare our calculated photon energy , $ \text { e } _\text { photon } $ , to copper 's work function , we see that the photon energy is greater than $ \phi $ : $ ~2.0\times10^ { -17 } \text { j } ~ & gt ; ~7.53\times10^ { -19 } \text { j } $ $ ~~~~~~~~\text { e } _\text { photon } ~~~~~~~~~~~~~~~~~~~\phi $ thus , we would expect to see photoelectrons ejected from the copper . next , we will calculate the kinetic energy of the photoelectrons . example $ 2 $ : calculating the kinetic energy of a photoelectron what is the kinetic energy of the photoelectrons ejected from the copper by the light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ ? we can calculate the kinetic energy of the photoelectron using the equation that relates $ \text { ke } \text { electron } $ to the energy of the photon , $ \text { e } \text { photon } $ , and the work function , $ \phi $ : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ since we want to know $ \text { ke } _\text { electron } $ , we can start by rearranging the equation so that we will be solving for the kinetic energy of the electron : $ \text { ke } \text { electron } =\text { e } \text { photon } -\phi $ now we can insert our known values for $ \text { e } _\text { photon } $ and $ \phi $ from example 1 : $ \text { ke } _\text { electron } = ( 2.0\times10^ { -17 } \text { j } ) - ( 7.53\times10^ { -19 } \text { j } ) =1.9\times10^ { -17 } \text { j } $ therefore , each photoelectron has a kinetic energy of $ 1.9\times10^ { -17 } \text { j } $ . summary based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a specific metal surface . the energy of the incident photon must be equal to the sum of the work function and the kinetic energy of a photoelectron : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ try it ! when we shine light with a frequency of $ 6.20 \times 10^ { 14 } \ , \text { hz } $ on a mystery metal , we observe the ejected electrons have a kinetic energy of $ 3.28\times 10^ { -20 } \ , \text j $ . some possible candidates for the mystery metal are shown in the table below : metal | work function $ \phi $ ( joules , $ \text j $ ) : - : | : - : calcium , $ \text { ca } $ | $ 4.60\times 10^ { -19 } $ tin , $ \text { sn } $ | $ 7.08\times 10^ { -19 } $ sodium , $ \text { na } $ | $ 3.78\times 10^ { -19 } $ hafnium , $ \text { hf } $ | $ 6.25\times 10^ { -19 } $ samarium , $ \text { sm } $ | $ 4.33\times 10^ { -19 } $ based on this information , what is the most likely identity of our mystery metal ?
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if a single large wave were to shake the dock , we would expect the energy from the big wave would send the beach balls flying off the dock with much more kinetic energy compared to a single , small wave . this is also what physicists believed would happen if the light intensity was increased . light amplitude was expected to be proportional to the light energy , so higher amplitude light was predicted to result in photoelectrons with more kinetic energy . classical physicists also predicted that increasing the frequency of light waves ( at a constant amplitude ) would increase the rate of electrons being ejected , and thus increase the measured electric current .
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what is light if it is not matter ?
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key points based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . contrary to the predictions , experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of particles called photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a metal surface , and the value of $ \phi $ depends on the metal . the energy of the incident photon must be equal to the sum of the metal 's work function and the photoelectron kinetic energy : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ introduction : what is the photoelectric effect ? when light shines on a metal , electrons can be ejected from the surface of the metal in a phenomenon known as the photoelectric effect . this process is also often referred to as photoemission , and the electrons that are ejected from the metal are called photoelectrons . in terms of their behavior and their properties , photoelectrons are no different from other electrons . the prefix , photo- , simply tells us that the electrons have been ejected from a metal surface by incident light . in this article , we will discuss how 19th century physicists attempted ( but failed ! ) to explain the photoelectric effect using classical physics . this ultimately led to the development of the modern description of electromagnetic radiation , which has both wave-like and particle-like properties . predictions based on light as a wave to explain the photoelectric effect , 19th-century physicists theorized that the oscillating electric field of the incoming light wave was heating the electrons and causing them to vibrate , eventually freeing them from the metal surface . this hypothesis was based on the assumption that light traveled purely as a wave through space . ( see this article for more information about the basic properties of light . ) scientists also believed that the energy of the light wave was proportional to its brightness , which is related to the wave 's amplitude . in order to test their hypotheses , they performed experiments to look at the effect of light amplitude and frequency on the rate of electron ejection , as well as the kinetic energy of the photoelectrons . based on the classical description of light as a wave , they made the following predictions : the kinetic energy of emitted photoelectrons should increase with the light amplitude . the rate of electron emission , which is proportional to the measured electric current , should increase as the light frequency is increased . to help us understand why they made these predictions , we can compare a light wave to a water wave . imagine some beach balls sitting on a dock that extends out into the ocean . the dock represents a metal surface , the beach balls represent electrons , and the ocean waves represent light waves . if a single large wave were to shake the dock , we would expect the energy from the big wave would send the beach balls flying off the dock with much more kinetic energy compared to a single , small wave . this is also what physicists believed would happen if the light intensity was increased . light amplitude was expected to be proportional to the light energy , so higher amplitude light was predicted to result in photoelectrons with more kinetic energy . classical physicists also predicted that increasing the frequency of light waves ( at a constant amplitude ) would increase the rate of electrons being ejected , and thus increase the measured electric current . using our beach ball analogy , we would expect waves hitting the dock more frequently would result in more beach balls being knocked off the dock compared to the same sized waves hitting the dock less often . now that we know what physicists thought would happen , let 's look at what they actually observed experimentally ! when intuition fails : photons to the rescue ! when experiments were performed to look at the effect of light amplitude and frequency , the following results were observed : the kinetic energy of photoelectrons increases with light frequency . electric current remains constant as light frequency increases . electric current increases with light amplitude . the kinetic energy of photoelectrons remains constant as light amplitude increases . these results were completely at odds with the predictions based on the classical description of light as a wave ! in order to explain what was happening , it turned out that an entirely new model of light was needed . that model was developed by albert einstein , who proposed that light sometimes behaved as particles of electromagnetic energy which we now call photons . the energy of a photon could be calculated using planck 's equation : $ \text { e } _ { \text { photon } } =h\nu $ where $ \text { e } _ { \text { photon } } $ is the energy of a photon in joules ( $ \text { j } $ ) , $ h $ is planck 's constant $ ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) $ , and $ \nu $ is the frequency of the light in $ \text { hz } $ . according to planck 's equation , the energy of a photon is proportional to the frequency of the light , $ \nu $ . the amplitude of the light is then proportional to the number of photons with a given frequency . concept check : as the wavelength of a photon increases , what happens to the photon 's energy ? light frequency and the threshold frequency $ \nu_0 $ we can think of the incident light as a stream of photons with an energy determined by the light frequency . when a photon hits the metal surface , the photon 's energy is absorbed by an electron in the metal . the graphic below illustrates the relationship between light frequency and the kinetic energy of ejected electrons . the scientists observed that if the incident light had a frequency less than a minimum frequency $ \nu_0 $ , then no electrons were ejected regardless of the light amplitude . this minimum frequency is also called the threshold frequency , and the value of $ \nu_0 $ depends on the metal . for frequencies greater than $ \nu_0 $ , electrons would be ejected from the metal . furthermore , the kinetic energy of the photoelectrons was proportional to the light frequency . the relationship between photoelectron kinetic energy and light frequency is shown in graph ( a ) below . because the light amplitude was kept constant as the light frequency increased , the number of photons being absorbed by the metal remained constant . thus , the rate at which electrons were ejected from the metal ( or the electric current ) remained constant as well . the relationship between electron current and light frequency is illustrated in graph ( b ) above . is n't there more math somewhere ? we can analyze the frequency relationship using the law of conservation of energy . the total energy of the incoming photon , $ \text { e } \text { photon } $ , must be equal to the kinetic energy of the ejected electron , $ \text { ke } { \text { electron } } $ , plus the energy required to eject the electron from the metal . the energy required to free the electron from a particular metal is also called the metal 's work function , which is represented by the symbol $ \phi $ ( in units of $ \text j $ ) : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ like the threshold frequency $ \nu_0 $ , the value of $ \phi $ also changes depending on the metal . we can now write the energy of the photon in terms of the light frequency using planck 's equation : $ \text { e } \text { photon } =h\nu=\text { ke } \text { electron } +\phi $ rearranging this equation in terms of the electron 's kinetic energy , we get : $ \text { ke } _\text { electron } =h\nu-\phi $ we can see that kinetic energy of the photoelectron increases linearly with $ \nu $ as long as the photon energy is greater than the work function $ \phi $ , which is exactly the relationship shown in graph ( a ) above . we can also use this equation to find the photoelectron velocity $ \text v $ , which is related to $ \text { ke } _\text { electron } $ as follows : $ \text { ke } _\text { electron } =h\nu-\phi=\dfrac { 1 } { 2 } m_e\text v^2 $ where $ m_e $ is the rest mass of an electron , $ 9.1094 \times 10^ { -31 } \ , \text { kg } $ . exploring the wave amplitude trends in terms of photons , higher amplitude light means more photons hitting the metal surface . this results in more electrons ejected over a given time period . as long as the light frequency is greater than $ \nu_0 $ , increasing the light amplitude will cause the electron current to increase proportionally as shown in graph ( a ) below . since increasing the light amplitude has no effect on the energy of the incoming photon , the photoelectron kinetic energy remains constant as the light amplitude is increased ( see graph ( b ) above ) . if we try to explain this result using our dock-and-beach-balls analogy , the relationship in graph ( b ) indicates that no matter the height of the wave hitting the dock $ - $ whether it 's a tiny swell , or a huge tsunami $ - $ the individual beach balls would be launched off the dock with the exact same speed ! thus , our intuition and analogy do n't do a very good job of explaining these particular experiments . example $ 1 $ : the photoelectric effect for copper the work function of copper metal is $ \phi=7.53\times10^ { -19 } \text { j } $ . if we shine light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ on copper metal , will the photoelectric effect be observed ? in order to eject electrons , we need the energy of the photons to be greater than the work function of copper . we can use planck 's equation to calculate the energy of the photon , $ \text { e } _ { \text { photon } } $ : $ \begin { align } \text { e } _\text { photon } & amp ; = h\nu \ & amp ; = ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) ( 3.0\times10^ { 16 } \text { hz } ) ~~~~\text { plug in values for $ h $ and $ \nu $ } \ & amp ; = 2.0\times10^ { -17 } \text { j } \end { align } $ if we compare our calculated photon energy , $ \text { e } _\text { photon } $ , to copper 's work function , we see that the photon energy is greater than $ \phi $ : $ ~2.0\times10^ { -17 } \text { j } ~ & gt ; ~7.53\times10^ { -19 } \text { j } $ $ ~~~~~~~~\text { e } _\text { photon } ~~~~~~~~~~~~~~~~~~~\phi $ thus , we would expect to see photoelectrons ejected from the copper . next , we will calculate the kinetic energy of the photoelectrons . example $ 2 $ : calculating the kinetic energy of a photoelectron what is the kinetic energy of the photoelectrons ejected from the copper by the light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ ? we can calculate the kinetic energy of the photoelectron using the equation that relates $ \text { ke } \text { electron } $ to the energy of the photon , $ \text { e } \text { photon } $ , and the work function , $ \phi $ : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ since we want to know $ \text { ke } _\text { electron } $ , we can start by rearranging the equation so that we will be solving for the kinetic energy of the electron : $ \text { ke } \text { electron } =\text { e } \text { photon } -\phi $ now we can insert our known values for $ \text { e } _\text { photon } $ and $ \phi $ from example 1 : $ \text { ke } _\text { electron } = ( 2.0\times10^ { -17 } \text { j } ) - ( 7.53\times10^ { -19 } \text { j } ) =1.9\times10^ { -17 } \text { j } $ therefore , each photoelectron has a kinetic energy of $ 1.9\times10^ { -17 } \text { j } $ . summary based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a specific metal surface . the energy of the incident photon must be equal to the sum of the work function and the kinetic energy of a photoelectron : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ try it ! when we shine light with a frequency of $ 6.20 \times 10^ { 14 } \ , \text { hz } $ on a mystery metal , we observe the ejected electrons have a kinetic energy of $ 3.28\times 10^ { -20 } \ , \text j $ . some possible candidates for the mystery metal are shown in the table below : metal | work function $ \phi $ ( joules , $ \text j $ ) : - : | : - : calcium , $ \text { ca } $ | $ 4.60\times 10^ { -19 } $ tin , $ \text { sn } $ | $ 7.08\times 10^ { -19 } $ sodium , $ \text { na } $ | $ 3.78\times 10^ { -19 } $ hafnium , $ \text { hf } $ | $ 6.25\times 10^ { -19 } $ samarium , $ \text { sm } $ | $ 4.33\times 10^ { -19 } $ based on this information , what is the most likely identity of our mystery metal ?
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the relationship between electron current and light frequency is illustrated in graph ( b ) above . is n't there more math somewhere ? we can analyze the frequency relationship using the law of conservation of energy .
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in the portion `` is n't there more math somewhere '' , will the choice of metal have an effect on the generated photoemission current ?
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key points based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . contrary to the predictions , experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of particles called photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a metal surface , and the value of $ \phi $ depends on the metal . the energy of the incident photon must be equal to the sum of the metal 's work function and the photoelectron kinetic energy : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ introduction : what is the photoelectric effect ? when light shines on a metal , electrons can be ejected from the surface of the metal in a phenomenon known as the photoelectric effect . this process is also often referred to as photoemission , and the electrons that are ejected from the metal are called photoelectrons . in terms of their behavior and their properties , photoelectrons are no different from other electrons . the prefix , photo- , simply tells us that the electrons have been ejected from a metal surface by incident light . in this article , we will discuss how 19th century physicists attempted ( but failed ! ) to explain the photoelectric effect using classical physics . this ultimately led to the development of the modern description of electromagnetic radiation , which has both wave-like and particle-like properties . predictions based on light as a wave to explain the photoelectric effect , 19th-century physicists theorized that the oscillating electric field of the incoming light wave was heating the electrons and causing them to vibrate , eventually freeing them from the metal surface . this hypothesis was based on the assumption that light traveled purely as a wave through space . ( see this article for more information about the basic properties of light . ) scientists also believed that the energy of the light wave was proportional to its brightness , which is related to the wave 's amplitude . in order to test their hypotheses , they performed experiments to look at the effect of light amplitude and frequency on the rate of electron ejection , as well as the kinetic energy of the photoelectrons . based on the classical description of light as a wave , they made the following predictions : the kinetic energy of emitted photoelectrons should increase with the light amplitude . the rate of electron emission , which is proportional to the measured electric current , should increase as the light frequency is increased . to help us understand why they made these predictions , we can compare a light wave to a water wave . imagine some beach balls sitting on a dock that extends out into the ocean . the dock represents a metal surface , the beach balls represent electrons , and the ocean waves represent light waves . if a single large wave were to shake the dock , we would expect the energy from the big wave would send the beach balls flying off the dock with much more kinetic energy compared to a single , small wave . this is also what physicists believed would happen if the light intensity was increased . light amplitude was expected to be proportional to the light energy , so higher amplitude light was predicted to result in photoelectrons with more kinetic energy . classical physicists also predicted that increasing the frequency of light waves ( at a constant amplitude ) would increase the rate of electrons being ejected , and thus increase the measured electric current . using our beach ball analogy , we would expect waves hitting the dock more frequently would result in more beach balls being knocked off the dock compared to the same sized waves hitting the dock less often . now that we know what physicists thought would happen , let 's look at what they actually observed experimentally ! when intuition fails : photons to the rescue ! when experiments were performed to look at the effect of light amplitude and frequency , the following results were observed : the kinetic energy of photoelectrons increases with light frequency . electric current remains constant as light frequency increases . electric current increases with light amplitude . the kinetic energy of photoelectrons remains constant as light amplitude increases . these results were completely at odds with the predictions based on the classical description of light as a wave ! in order to explain what was happening , it turned out that an entirely new model of light was needed . that model was developed by albert einstein , who proposed that light sometimes behaved as particles of electromagnetic energy which we now call photons . the energy of a photon could be calculated using planck 's equation : $ \text { e } _ { \text { photon } } =h\nu $ where $ \text { e } _ { \text { photon } } $ is the energy of a photon in joules ( $ \text { j } $ ) , $ h $ is planck 's constant $ ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) $ , and $ \nu $ is the frequency of the light in $ \text { hz } $ . according to planck 's equation , the energy of a photon is proportional to the frequency of the light , $ \nu $ . the amplitude of the light is then proportional to the number of photons with a given frequency . concept check : as the wavelength of a photon increases , what happens to the photon 's energy ? light frequency and the threshold frequency $ \nu_0 $ we can think of the incident light as a stream of photons with an energy determined by the light frequency . when a photon hits the metal surface , the photon 's energy is absorbed by an electron in the metal . the graphic below illustrates the relationship between light frequency and the kinetic energy of ejected electrons . the scientists observed that if the incident light had a frequency less than a minimum frequency $ \nu_0 $ , then no electrons were ejected regardless of the light amplitude . this minimum frequency is also called the threshold frequency , and the value of $ \nu_0 $ depends on the metal . for frequencies greater than $ \nu_0 $ , electrons would be ejected from the metal . furthermore , the kinetic energy of the photoelectrons was proportional to the light frequency . the relationship between photoelectron kinetic energy and light frequency is shown in graph ( a ) below . because the light amplitude was kept constant as the light frequency increased , the number of photons being absorbed by the metal remained constant . thus , the rate at which electrons were ejected from the metal ( or the electric current ) remained constant as well . the relationship between electron current and light frequency is illustrated in graph ( b ) above . is n't there more math somewhere ? we can analyze the frequency relationship using the law of conservation of energy . the total energy of the incoming photon , $ \text { e } \text { photon } $ , must be equal to the kinetic energy of the ejected electron , $ \text { ke } { \text { electron } } $ , plus the energy required to eject the electron from the metal . the energy required to free the electron from a particular metal is also called the metal 's work function , which is represented by the symbol $ \phi $ ( in units of $ \text j $ ) : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ like the threshold frequency $ \nu_0 $ , the value of $ \phi $ also changes depending on the metal . we can now write the energy of the photon in terms of the light frequency using planck 's equation : $ \text { e } \text { photon } =h\nu=\text { ke } \text { electron } +\phi $ rearranging this equation in terms of the electron 's kinetic energy , we get : $ \text { ke } _\text { electron } =h\nu-\phi $ we can see that kinetic energy of the photoelectron increases linearly with $ \nu $ as long as the photon energy is greater than the work function $ \phi $ , which is exactly the relationship shown in graph ( a ) above . we can also use this equation to find the photoelectron velocity $ \text v $ , which is related to $ \text { ke } _\text { electron } $ as follows : $ \text { ke } _\text { electron } =h\nu-\phi=\dfrac { 1 } { 2 } m_e\text v^2 $ where $ m_e $ is the rest mass of an electron , $ 9.1094 \times 10^ { -31 } \ , \text { kg } $ . exploring the wave amplitude trends in terms of photons , higher amplitude light means more photons hitting the metal surface . this results in more electrons ejected over a given time period . as long as the light frequency is greater than $ \nu_0 $ , increasing the light amplitude will cause the electron current to increase proportionally as shown in graph ( a ) below . since increasing the light amplitude has no effect on the energy of the incoming photon , the photoelectron kinetic energy remains constant as the light amplitude is increased ( see graph ( b ) above ) . if we try to explain this result using our dock-and-beach-balls analogy , the relationship in graph ( b ) indicates that no matter the height of the wave hitting the dock $ - $ whether it 's a tiny swell , or a huge tsunami $ - $ the individual beach balls would be launched off the dock with the exact same speed ! thus , our intuition and analogy do n't do a very good job of explaining these particular experiments . example $ 1 $ : the photoelectric effect for copper the work function of copper metal is $ \phi=7.53\times10^ { -19 } \text { j } $ . if we shine light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ on copper metal , will the photoelectric effect be observed ? in order to eject electrons , we need the energy of the photons to be greater than the work function of copper . we can use planck 's equation to calculate the energy of the photon , $ \text { e } _ { \text { photon } } $ : $ \begin { align } \text { e } _\text { photon } & amp ; = h\nu \ & amp ; = ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) ( 3.0\times10^ { 16 } \text { hz } ) ~~~~\text { plug in values for $ h $ and $ \nu $ } \ & amp ; = 2.0\times10^ { -17 } \text { j } \end { align } $ if we compare our calculated photon energy , $ \text { e } _\text { photon } $ , to copper 's work function , we see that the photon energy is greater than $ \phi $ : $ ~2.0\times10^ { -17 } \text { j } ~ & gt ; ~7.53\times10^ { -19 } \text { j } $ $ ~~~~~~~~\text { e } _\text { photon } ~~~~~~~~~~~~~~~~~~~\phi $ thus , we would expect to see photoelectrons ejected from the copper . next , we will calculate the kinetic energy of the photoelectrons . example $ 2 $ : calculating the kinetic energy of a photoelectron what is the kinetic energy of the photoelectrons ejected from the copper by the light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ ? we can calculate the kinetic energy of the photoelectron using the equation that relates $ \text { ke } \text { electron } $ to the energy of the photon , $ \text { e } \text { photon } $ , and the work function , $ \phi $ : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ since we want to know $ \text { ke } _\text { electron } $ , we can start by rearranging the equation so that we will be solving for the kinetic energy of the electron : $ \text { ke } \text { electron } =\text { e } \text { photon } -\phi $ now we can insert our known values for $ \text { e } _\text { photon } $ and $ \phi $ from example 1 : $ \text { ke } _\text { electron } = ( 2.0\times10^ { -17 } \text { j } ) - ( 7.53\times10^ { -19 } \text { j } ) =1.9\times10^ { -17 } \text { j } $ therefore , each photoelectron has a kinetic energy of $ 1.9\times10^ { -17 } \text { j } $ . summary based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a specific metal surface . the energy of the incident photon must be equal to the sum of the work function and the kinetic energy of a photoelectron : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ try it ! when we shine light with a frequency of $ 6.20 \times 10^ { 14 } \ , \text { hz } $ on a mystery metal , we observe the ejected electrons have a kinetic energy of $ 3.28\times 10^ { -20 } \ , \text j $ . some possible candidates for the mystery metal are shown in the table below : metal | work function $ \phi $ ( joules , $ \text j $ ) : - : | : - : calcium , $ \text { ca } $ | $ 4.60\times 10^ { -19 } $ tin , $ \text { sn } $ | $ 7.08\times 10^ { -19 } $ sodium , $ \text { na } $ | $ 3.78\times 10^ { -19 } $ hafnium , $ \text { hf } $ | $ 6.25\times 10^ { -19 } $ samarium , $ \text { sm } $ | $ 4.33\times 10^ { -19 } $ based on this information , what is the most likely identity of our mystery metal ?
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the amplitude of the light is then proportional to the number of photons with a given frequency . concept check : as the wavelength of a photon increases , what happens to the photon 's energy ? light frequency and the threshold frequency $ \nu_0 $ we can think of the incident light as a stream of photons with an energy determined by the light frequency .
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if photon does not have any mass how it is structured as a quanta < packet of energy > , does it has any structure ?
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key points based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . contrary to the predictions , experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of particles called photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a metal surface , and the value of $ \phi $ depends on the metal . the energy of the incident photon must be equal to the sum of the metal 's work function and the photoelectron kinetic energy : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ introduction : what is the photoelectric effect ? when light shines on a metal , electrons can be ejected from the surface of the metal in a phenomenon known as the photoelectric effect . this process is also often referred to as photoemission , and the electrons that are ejected from the metal are called photoelectrons . in terms of their behavior and their properties , photoelectrons are no different from other electrons . the prefix , photo- , simply tells us that the electrons have been ejected from a metal surface by incident light . in this article , we will discuss how 19th century physicists attempted ( but failed ! ) to explain the photoelectric effect using classical physics . this ultimately led to the development of the modern description of electromagnetic radiation , which has both wave-like and particle-like properties . predictions based on light as a wave to explain the photoelectric effect , 19th-century physicists theorized that the oscillating electric field of the incoming light wave was heating the electrons and causing them to vibrate , eventually freeing them from the metal surface . this hypothesis was based on the assumption that light traveled purely as a wave through space . ( see this article for more information about the basic properties of light . ) scientists also believed that the energy of the light wave was proportional to its brightness , which is related to the wave 's amplitude . in order to test their hypotheses , they performed experiments to look at the effect of light amplitude and frequency on the rate of electron ejection , as well as the kinetic energy of the photoelectrons . based on the classical description of light as a wave , they made the following predictions : the kinetic energy of emitted photoelectrons should increase with the light amplitude . the rate of electron emission , which is proportional to the measured electric current , should increase as the light frequency is increased . to help us understand why they made these predictions , we can compare a light wave to a water wave . imagine some beach balls sitting on a dock that extends out into the ocean . the dock represents a metal surface , the beach balls represent electrons , and the ocean waves represent light waves . if a single large wave were to shake the dock , we would expect the energy from the big wave would send the beach balls flying off the dock with much more kinetic energy compared to a single , small wave . this is also what physicists believed would happen if the light intensity was increased . light amplitude was expected to be proportional to the light energy , so higher amplitude light was predicted to result in photoelectrons with more kinetic energy . classical physicists also predicted that increasing the frequency of light waves ( at a constant amplitude ) would increase the rate of electrons being ejected , and thus increase the measured electric current . using our beach ball analogy , we would expect waves hitting the dock more frequently would result in more beach balls being knocked off the dock compared to the same sized waves hitting the dock less often . now that we know what physicists thought would happen , let 's look at what they actually observed experimentally ! when intuition fails : photons to the rescue ! when experiments were performed to look at the effect of light amplitude and frequency , the following results were observed : the kinetic energy of photoelectrons increases with light frequency . electric current remains constant as light frequency increases . electric current increases with light amplitude . the kinetic energy of photoelectrons remains constant as light amplitude increases . these results were completely at odds with the predictions based on the classical description of light as a wave ! in order to explain what was happening , it turned out that an entirely new model of light was needed . that model was developed by albert einstein , who proposed that light sometimes behaved as particles of electromagnetic energy which we now call photons . the energy of a photon could be calculated using planck 's equation : $ \text { e } _ { \text { photon } } =h\nu $ where $ \text { e } _ { \text { photon } } $ is the energy of a photon in joules ( $ \text { j } $ ) , $ h $ is planck 's constant $ ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) $ , and $ \nu $ is the frequency of the light in $ \text { hz } $ . according to planck 's equation , the energy of a photon is proportional to the frequency of the light , $ \nu $ . the amplitude of the light is then proportional to the number of photons with a given frequency . concept check : as the wavelength of a photon increases , what happens to the photon 's energy ? light frequency and the threshold frequency $ \nu_0 $ we can think of the incident light as a stream of photons with an energy determined by the light frequency . when a photon hits the metal surface , the photon 's energy is absorbed by an electron in the metal . the graphic below illustrates the relationship between light frequency and the kinetic energy of ejected electrons . the scientists observed that if the incident light had a frequency less than a minimum frequency $ \nu_0 $ , then no electrons were ejected regardless of the light amplitude . this minimum frequency is also called the threshold frequency , and the value of $ \nu_0 $ depends on the metal . for frequencies greater than $ \nu_0 $ , electrons would be ejected from the metal . furthermore , the kinetic energy of the photoelectrons was proportional to the light frequency . the relationship between photoelectron kinetic energy and light frequency is shown in graph ( a ) below . because the light amplitude was kept constant as the light frequency increased , the number of photons being absorbed by the metal remained constant . thus , the rate at which electrons were ejected from the metal ( or the electric current ) remained constant as well . the relationship between electron current and light frequency is illustrated in graph ( b ) above . is n't there more math somewhere ? we can analyze the frequency relationship using the law of conservation of energy . the total energy of the incoming photon , $ \text { e } \text { photon } $ , must be equal to the kinetic energy of the ejected electron , $ \text { ke } { \text { electron } } $ , plus the energy required to eject the electron from the metal . the energy required to free the electron from a particular metal is also called the metal 's work function , which is represented by the symbol $ \phi $ ( in units of $ \text j $ ) : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ like the threshold frequency $ \nu_0 $ , the value of $ \phi $ also changes depending on the metal . we can now write the energy of the photon in terms of the light frequency using planck 's equation : $ \text { e } \text { photon } =h\nu=\text { ke } \text { electron } +\phi $ rearranging this equation in terms of the electron 's kinetic energy , we get : $ \text { ke } _\text { electron } =h\nu-\phi $ we can see that kinetic energy of the photoelectron increases linearly with $ \nu $ as long as the photon energy is greater than the work function $ \phi $ , which is exactly the relationship shown in graph ( a ) above . we can also use this equation to find the photoelectron velocity $ \text v $ , which is related to $ \text { ke } _\text { electron } $ as follows : $ \text { ke } _\text { electron } =h\nu-\phi=\dfrac { 1 } { 2 } m_e\text v^2 $ where $ m_e $ is the rest mass of an electron , $ 9.1094 \times 10^ { -31 } \ , \text { kg } $ . exploring the wave amplitude trends in terms of photons , higher amplitude light means more photons hitting the metal surface . this results in more electrons ejected over a given time period . as long as the light frequency is greater than $ \nu_0 $ , increasing the light amplitude will cause the electron current to increase proportionally as shown in graph ( a ) below . since increasing the light amplitude has no effect on the energy of the incoming photon , the photoelectron kinetic energy remains constant as the light amplitude is increased ( see graph ( b ) above ) . if we try to explain this result using our dock-and-beach-balls analogy , the relationship in graph ( b ) indicates that no matter the height of the wave hitting the dock $ - $ whether it 's a tiny swell , or a huge tsunami $ - $ the individual beach balls would be launched off the dock with the exact same speed ! thus , our intuition and analogy do n't do a very good job of explaining these particular experiments . example $ 1 $ : the photoelectric effect for copper the work function of copper metal is $ \phi=7.53\times10^ { -19 } \text { j } $ . if we shine light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ on copper metal , will the photoelectric effect be observed ? in order to eject electrons , we need the energy of the photons to be greater than the work function of copper . we can use planck 's equation to calculate the energy of the photon , $ \text { e } _ { \text { photon } } $ : $ \begin { align } \text { e } _\text { photon } & amp ; = h\nu \ & amp ; = ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) ( 3.0\times10^ { 16 } \text { hz } ) ~~~~\text { plug in values for $ h $ and $ \nu $ } \ & amp ; = 2.0\times10^ { -17 } \text { j } \end { align } $ if we compare our calculated photon energy , $ \text { e } _\text { photon } $ , to copper 's work function , we see that the photon energy is greater than $ \phi $ : $ ~2.0\times10^ { -17 } \text { j } ~ & gt ; ~7.53\times10^ { -19 } \text { j } $ $ ~~~~~~~~\text { e } _\text { photon } ~~~~~~~~~~~~~~~~~~~\phi $ thus , we would expect to see photoelectrons ejected from the copper . next , we will calculate the kinetic energy of the photoelectrons . example $ 2 $ : calculating the kinetic energy of a photoelectron what is the kinetic energy of the photoelectrons ejected from the copper by the light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ ? we can calculate the kinetic energy of the photoelectron using the equation that relates $ \text { ke } \text { electron } $ to the energy of the photon , $ \text { e } \text { photon } $ , and the work function , $ \phi $ : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ since we want to know $ \text { ke } _\text { electron } $ , we can start by rearranging the equation so that we will be solving for the kinetic energy of the electron : $ \text { ke } \text { electron } =\text { e } \text { photon } -\phi $ now we can insert our known values for $ \text { e } _\text { photon } $ and $ \phi $ from example 1 : $ \text { ke } _\text { electron } = ( 2.0\times10^ { -17 } \text { j } ) - ( 7.53\times10^ { -19 } \text { j } ) =1.9\times10^ { -17 } \text { j } $ therefore , each photoelectron has a kinetic energy of $ 1.9\times10^ { -17 } \text { j } $ . summary based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a specific metal surface . the energy of the incident photon must be equal to the sum of the work function and the kinetic energy of a photoelectron : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ try it ! when we shine light with a frequency of $ 6.20 \times 10^ { 14 } \ , \text { hz } $ on a mystery metal , we observe the ejected electrons have a kinetic energy of $ 3.28\times 10^ { -20 } \ , \text j $ . some possible candidates for the mystery metal are shown in the table below : metal | work function $ \phi $ ( joules , $ \text j $ ) : - : | : - : calcium , $ \text { ca } $ | $ 4.60\times 10^ { -19 } $ tin , $ \text { sn } $ | $ 7.08\times 10^ { -19 } $ sodium , $ \text { na } $ | $ 3.78\times 10^ { -19 } $ hafnium , $ \text { hf } $ | $ 6.25\times 10^ { -19 } $ samarium , $ \text { sm } $ | $ 4.33\times 10^ { -19 } $ based on this information , what is the most likely identity of our mystery metal ?
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if a single large wave were to shake the dock , we would expect the energy from the big wave would send the beach balls flying off the dock with much more kinetic energy compared to a single , small wave . this is also what physicists believed would happen if the light intensity was increased . light amplitude was expected to be proportional to the light energy , so higher amplitude light was predicted to result in photoelectrons with more kinetic energy . classical physicists also predicted that increasing the frequency of light waves ( at a constant amplitude ) would increase the rate of electrons being ejected , and thus increase the measured electric current . using our beach ball analogy , we would expect waves hitting the dock more frequently would result in more beach balls being knocked off the dock compared to the same sized waves hitting the dock less often .
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would n't the amplitude also be a factor or the energy ?
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key points based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . contrary to the predictions , experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of particles called photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a metal surface , and the value of $ \phi $ depends on the metal . the energy of the incident photon must be equal to the sum of the metal 's work function and the photoelectron kinetic energy : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ introduction : what is the photoelectric effect ? when light shines on a metal , electrons can be ejected from the surface of the metal in a phenomenon known as the photoelectric effect . this process is also often referred to as photoemission , and the electrons that are ejected from the metal are called photoelectrons . in terms of their behavior and their properties , photoelectrons are no different from other electrons . the prefix , photo- , simply tells us that the electrons have been ejected from a metal surface by incident light . in this article , we will discuss how 19th century physicists attempted ( but failed ! ) to explain the photoelectric effect using classical physics . this ultimately led to the development of the modern description of electromagnetic radiation , which has both wave-like and particle-like properties . predictions based on light as a wave to explain the photoelectric effect , 19th-century physicists theorized that the oscillating electric field of the incoming light wave was heating the electrons and causing them to vibrate , eventually freeing them from the metal surface . this hypothesis was based on the assumption that light traveled purely as a wave through space . ( see this article for more information about the basic properties of light . ) scientists also believed that the energy of the light wave was proportional to its brightness , which is related to the wave 's amplitude . in order to test their hypotheses , they performed experiments to look at the effect of light amplitude and frequency on the rate of electron ejection , as well as the kinetic energy of the photoelectrons . based on the classical description of light as a wave , they made the following predictions : the kinetic energy of emitted photoelectrons should increase with the light amplitude . the rate of electron emission , which is proportional to the measured electric current , should increase as the light frequency is increased . to help us understand why they made these predictions , we can compare a light wave to a water wave . imagine some beach balls sitting on a dock that extends out into the ocean . the dock represents a metal surface , the beach balls represent electrons , and the ocean waves represent light waves . if a single large wave were to shake the dock , we would expect the energy from the big wave would send the beach balls flying off the dock with much more kinetic energy compared to a single , small wave . this is also what physicists believed would happen if the light intensity was increased . light amplitude was expected to be proportional to the light energy , so higher amplitude light was predicted to result in photoelectrons with more kinetic energy . classical physicists also predicted that increasing the frequency of light waves ( at a constant amplitude ) would increase the rate of electrons being ejected , and thus increase the measured electric current . using our beach ball analogy , we would expect waves hitting the dock more frequently would result in more beach balls being knocked off the dock compared to the same sized waves hitting the dock less often . now that we know what physicists thought would happen , let 's look at what they actually observed experimentally ! when intuition fails : photons to the rescue ! when experiments were performed to look at the effect of light amplitude and frequency , the following results were observed : the kinetic energy of photoelectrons increases with light frequency . electric current remains constant as light frequency increases . electric current increases with light amplitude . the kinetic energy of photoelectrons remains constant as light amplitude increases . these results were completely at odds with the predictions based on the classical description of light as a wave ! in order to explain what was happening , it turned out that an entirely new model of light was needed . that model was developed by albert einstein , who proposed that light sometimes behaved as particles of electromagnetic energy which we now call photons . the energy of a photon could be calculated using planck 's equation : $ \text { e } _ { \text { photon } } =h\nu $ where $ \text { e } _ { \text { photon } } $ is the energy of a photon in joules ( $ \text { j } $ ) , $ h $ is planck 's constant $ ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) $ , and $ \nu $ is the frequency of the light in $ \text { hz } $ . according to planck 's equation , the energy of a photon is proportional to the frequency of the light , $ \nu $ . the amplitude of the light is then proportional to the number of photons with a given frequency . concept check : as the wavelength of a photon increases , what happens to the photon 's energy ? light frequency and the threshold frequency $ \nu_0 $ we can think of the incident light as a stream of photons with an energy determined by the light frequency . when a photon hits the metal surface , the photon 's energy is absorbed by an electron in the metal . the graphic below illustrates the relationship between light frequency and the kinetic energy of ejected electrons . the scientists observed that if the incident light had a frequency less than a minimum frequency $ \nu_0 $ , then no electrons were ejected regardless of the light amplitude . this minimum frequency is also called the threshold frequency , and the value of $ \nu_0 $ depends on the metal . for frequencies greater than $ \nu_0 $ , electrons would be ejected from the metal . furthermore , the kinetic energy of the photoelectrons was proportional to the light frequency . the relationship between photoelectron kinetic energy and light frequency is shown in graph ( a ) below . because the light amplitude was kept constant as the light frequency increased , the number of photons being absorbed by the metal remained constant . thus , the rate at which electrons were ejected from the metal ( or the electric current ) remained constant as well . the relationship between electron current and light frequency is illustrated in graph ( b ) above . is n't there more math somewhere ? we can analyze the frequency relationship using the law of conservation of energy . the total energy of the incoming photon , $ \text { e } \text { photon } $ , must be equal to the kinetic energy of the ejected electron , $ \text { ke } { \text { electron } } $ , plus the energy required to eject the electron from the metal . the energy required to free the electron from a particular metal is also called the metal 's work function , which is represented by the symbol $ \phi $ ( in units of $ \text j $ ) : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ like the threshold frequency $ \nu_0 $ , the value of $ \phi $ also changes depending on the metal . we can now write the energy of the photon in terms of the light frequency using planck 's equation : $ \text { e } \text { photon } =h\nu=\text { ke } \text { electron } +\phi $ rearranging this equation in terms of the electron 's kinetic energy , we get : $ \text { ke } _\text { electron } =h\nu-\phi $ we can see that kinetic energy of the photoelectron increases linearly with $ \nu $ as long as the photon energy is greater than the work function $ \phi $ , which is exactly the relationship shown in graph ( a ) above . we can also use this equation to find the photoelectron velocity $ \text v $ , which is related to $ \text { ke } _\text { electron } $ as follows : $ \text { ke } _\text { electron } =h\nu-\phi=\dfrac { 1 } { 2 } m_e\text v^2 $ where $ m_e $ is the rest mass of an electron , $ 9.1094 \times 10^ { -31 } \ , \text { kg } $ . exploring the wave amplitude trends in terms of photons , higher amplitude light means more photons hitting the metal surface . this results in more electrons ejected over a given time period . as long as the light frequency is greater than $ \nu_0 $ , increasing the light amplitude will cause the electron current to increase proportionally as shown in graph ( a ) below . since increasing the light amplitude has no effect on the energy of the incoming photon , the photoelectron kinetic energy remains constant as the light amplitude is increased ( see graph ( b ) above ) . if we try to explain this result using our dock-and-beach-balls analogy , the relationship in graph ( b ) indicates that no matter the height of the wave hitting the dock $ - $ whether it 's a tiny swell , or a huge tsunami $ - $ the individual beach balls would be launched off the dock with the exact same speed ! thus , our intuition and analogy do n't do a very good job of explaining these particular experiments . example $ 1 $ : the photoelectric effect for copper the work function of copper metal is $ \phi=7.53\times10^ { -19 } \text { j } $ . if we shine light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ on copper metal , will the photoelectric effect be observed ? in order to eject electrons , we need the energy of the photons to be greater than the work function of copper . we can use planck 's equation to calculate the energy of the photon , $ \text { e } _ { \text { photon } } $ : $ \begin { align } \text { e } _\text { photon } & amp ; = h\nu \ & amp ; = ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) ( 3.0\times10^ { 16 } \text { hz } ) ~~~~\text { plug in values for $ h $ and $ \nu $ } \ & amp ; = 2.0\times10^ { -17 } \text { j } \end { align } $ if we compare our calculated photon energy , $ \text { e } _\text { photon } $ , to copper 's work function , we see that the photon energy is greater than $ \phi $ : $ ~2.0\times10^ { -17 } \text { j } ~ & gt ; ~7.53\times10^ { -19 } \text { j } $ $ ~~~~~~~~\text { e } _\text { photon } ~~~~~~~~~~~~~~~~~~~\phi $ thus , we would expect to see photoelectrons ejected from the copper . next , we will calculate the kinetic energy of the photoelectrons . example $ 2 $ : calculating the kinetic energy of a photoelectron what is the kinetic energy of the photoelectrons ejected from the copper by the light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ ? we can calculate the kinetic energy of the photoelectron using the equation that relates $ \text { ke } \text { electron } $ to the energy of the photon , $ \text { e } \text { photon } $ , and the work function , $ \phi $ : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ since we want to know $ \text { ke } _\text { electron } $ , we can start by rearranging the equation so that we will be solving for the kinetic energy of the electron : $ \text { ke } \text { electron } =\text { e } \text { photon } -\phi $ now we can insert our known values for $ \text { e } _\text { photon } $ and $ \phi $ from example 1 : $ \text { ke } _\text { electron } = ( 2.0\times10^ { -17 } \text { j } ) - ( 7.53\times10^ { -19 } \text { j } ) =1.9\times10^ { -17 } \text { j } $ therefore , each photoelectron has a kinetic energy of $ 1.9\times10^ { -17 } \text { j } $ . summary based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a specific metal surface . the energy of the incident photon must be equal to the sum of the work function and the kinetic energy of a photoelectron : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ try it ! when we shine light with a frequency of $ 6.20 \times 10^ { 14 } \ , \text { hz } $ on a mystery metal , we observe the ejected electrons have a kinetic energy of $ 3.28\times 10^ { -20 } \ , \text j $ . some possible candidates for the mystery metal are shown in the table below : metal | work function $ \phi $ ( joules , $ \text j $ ) : - : | : - : calcium , $ \text { ca } $ | $ 4.60\times 10^ { -19 } $ tin , $ \text { sn } $ | $ 7.08\times 10^ { -19 } $ sodium , $ \text { na } $ | $ 3.78\times 10^ { -19 } $ hafnium , $ \text { hf } $ | $ 6.25\times 10^ { -19 } $ samarium , $ \text { sm } $ | $ 4.33\times 10^ { -19 } $ based on this information , what is the most likely identity of our mystery metal ?
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concept check : as the wavelength of a photon increases , what happens to the photon 's energy ? light frequency and the threshold frequency $ \nu_0 $ we can think of the incident light as a stream of photons with an energy determined by the light frequency . when a photon hits the metal surface , the photon 's energy is absorbed by an electron in the metal .
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what if the frequency of the light striking the metal surface is just equal to threshold frequency ?
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key points based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . contrary to the predictions , experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of particles called photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a metal surface , and the value of $ \phi $ depends on the metal . the energy of the incident photon must be equal to the sum of the metal 's work function and the photoelectron kinetic energy : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ introduction : what is the photoelectric effect ? when light shines on a metal , electrons can be ejected from the surface of the metal in a phenomenon known as the photoelectric effect . this process is also often referred to as photoemission , and the electrons that are ejected from the metal are called photoelectrons . in terms of their behavior and their properties , photoelectrons are no different from other electrons . the prefix , photo- , simply tells us that the electrons have been ejected from a metal surface by incident light . in this article , we will discuss how 19th century physicists attempted ( but failed ! ) to explain the photoelectric effect using classical physics . this ultimately led to the development of the modern description of electromagnetic radiation , which has both wave-like and particle-like properties . predictions based on light as a wave to explain the photoelectric effect , 19th-century physicists theorized that the oscillating electric field of the incoming light wave was heating the electrons and causing them to vibrate , eventually freeing them from the metal surface . this hypothesis was based on the assumption that light traveled purely as a wave through space . ( see this article for more information about the basic properties of light . ) scientists also believed that the energy of the light wave was proportional to its brightness , which is related to the wave 's amplitude . in order to test their hypotheses , they performed experiments to look at the effect of light amplitude and frequency on the rate of electron ejection , as well as the kinetic energy of the photoelectrons . based on the classical description of light as a wave , they made the following predictions : the kinetic energy of emitted photoelectrons should increase with the light amplitude . the rate of electron emission , which is proportional to the measured electric current , should increase as the light frequency is increased . to help us understand why they made these predictions , we can compare a light wave to a water wave . imagine some beach balls sitting on a dock that extends out into the ocean . the dock represents a metal surface , the beach balls represent electrons , and the ocean waves represent light waves . if a single large wave were to shake the dock , we would expect the energy from the big wave would send the beach balls flying off the dock with much more kinetic energy compared to a single , small wave . this is also what physicists believed would happen if the light intensity was increased . light amplitude was expected to be proportional to the light energy , so higher amplitude light was predicted to result in photoelectrons with more kinetic energy . classical physicists also predicted that increasing the frequency of light waves ( at a constant amplitude ) would increase the rate of electrons being ejected , and thus increase the measured electric current . using our beach ball analogy , we would expect waves hitting the dock more frequently would result in more beach balls being knocked off the dock compared to the same sized waves hitting the dock less often . now that we know what physicists thought would happen , let 's look at what they actually observed experimentally ! when intuition fails : photons to the rescue ! when experiments were performed to look at the effect of light amplitude and frequency , the following results were observed : the kinetic energy of photoelectrons increases with light frequency . electric current remains constant as light frequency increases . electric current increases with light amplitude . the kinetic energy of photoelectrons remains constant as light amplitude increases . these results were completely at odds with the predictions based on the classical description of light as a wave ! in order to explain what was happening , it turned out that an entirely new model of light was needed . that model was developed by albert einstein , who proposed that light sometimes behaved as particles of electromagnetic energy which we now call photons . the energy of a photon could be calculated using planck 's equation : $ \text { e } _ { \text { photon } } =h\nu $ where $ \text { e } _ { \text { photon } } $ is the energy of a photon in joules ( $ \text { j } $ ) , $ h $ is planck 's constant $ ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) $ , and $ \nu $ is the frequency of the light in $ \text { hz } $ . according to planck 's equation , the energy of a photon is proportional to the frequency of the light , $ \nu $ . the amplitude of the light is then proportional to the number of photons with a given frequency . concept check : as the wavelength of a photon increases , what happens to the photon 's energy ? light frequency and the threshold frequency $ \nu_0 $ we can think of the incident light as a stream of photons with an energy determined by the light frequency . when a photon hits the metal surface , the photon 's energy is absorbed by an electron in the metal . the graphic below illustrates the relationship between light frequency and the kinetic energy of ejected electrons . the scientists observed that if the incident light had a frequency less than a minimum frequency $ \nu_0 $ , then no electrons were ejected regardless of the light amplitude . this minimum frequency is also called the threshold frequency , and the value of $ \nu_0 $ depends on the metal . for frequencies greater than $ \nu_0 $ , electrons would be ejected from the metal . furthermore , the kinetic energy of the photoelectrons was proportional to the light frequency . the relationship between photoelectron kinetic energy and light frequency is shown in graph ( a ) below . because the light amplitude was kept constant as the light frequency increased , the number of photons being absorbed by the metal remained constant . thus , the rate at which electrons were ejected from the metal ( or the electric current ) remained constant as well . the relationship between electron current and light frequency is illustrated in graph ( b ) above . is n't there more math somewhere ? we can analyze the frequency relationship using the law of conservation of energy . the total energy of the incoming photon , $ \text { e } \text { photon } $ , must be equal to the kinetic energy of the ejected electron , $ \text { ke } { \text { electron } } $ , plus the energy required to eject the electron from the metal . the energy required to free the electron from a particular metal is also called the metal 's work function , which is represented by the symbol $ \phi $ ( in units of $ \text j $ ) : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ like the threshold frequency $ \nu_0 $ , the value of $ \phi $ also changes depending on the metal . we can now write the energy of the photon in terms of the light frequency using planck 's equation : $ \text { e } \text { photon } =h\nu=\text { ke } \text { electron } +\phi $ rearranging this equation in terms of the electron 's kinetic energy , we get : $ \text { ke } _\text { electron } =h\nu-\phi $ we can see that kinetic energy of the photoelectron increases linearly with $ \nu $ as long as the photon energy is greater than the work function $ \phi $ , which is exactly the relationship shown in graph ( a ) above . we can also use this equation to find the photoelectron velocity $ \text v $ , which is related to $ \text { ke } _\text { electron } $ as follows : $ \text { ke } _\text { electron } =h\nu-\phi=\dfrac { 1 } { 2 } m_e\text v^2 $ where $ m_e $ is the rest mass of an electron , $ 9.1094 \times 10^ { -31 } \ , \text { kg } $ . exploring the wave amplitude trends in terms of photons , higher amplitude light means more photons hitting the metal surface . this results in more electrons ejected over a given time period . as long as the light frequency is greater than $ \nu_0 $ , increasing the light amplitude will cause the electron current to increase proportionally as shown in graph ( a ) below . since increasing the light amplitude has no effect on the energy of the incoming photon , the photoelectron kinetic energy remains constant as the light amplitude is increased ( see graph ( b ) above ) . if we try to explain this result using our dock-and-beach-balls analogy , the relationship in graph ( b ) indicates that no matter the height of the wave hitting the dock $ - $ whether it 's a tiny swell , or a huge tsunami $ - $ the individual beach balls would be launched off the dock with the exact same speed ! thus , our intuition and analogy do n't do a very good job of explaining these particular experiments . example $ 1 $ : the photoelectric effect for copper the work function of copper metal is $ \phi=7.53\times10^ { -19 } \text { j } $ . if we shine light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ on copper metal , will the photoelectric effect be observed ? in order to eject electrons , we need the energy of the photons to be greater than the work function of copper . we can use planck 's equation to calculate the energy of the photon , $ \text { e } _ { \text { photon } } $ : $ \begin { align } \text { e } _\text { photon } & amp ; = h\nu \ & amp ; = ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) ( 3.0\times10^ { 16 } \text { hz } ) ~~~~\text { plug in values for $ h $ and $ \nu $ } \ & amp ; = 2.0\times10^ { -17 } \text { j } \end { align } $ if we compare our calculated photon energy , $ \text { e } _\text { photon } $ , to copper 's work function , we see that the photon energy is greater than $ \phi $ : $ ~2.0\times10^ { -17 } \text { j } ~ & gt ; ~7.53\times10^ { -19 } \text { j } $ $ ~~~~~~~~\text { e } _\text { photon } ~~~~~~~~~~~~~~~~~~~\phi $ thus , we would expect to see photoelectrons ejected from the copper . next , we will calculate the kinetic energy of the photoelectrons . example $ 2 $ : calculating the kinetic energy of a photoelectron what is the kinetic energy of the photoelectrons ejected from the copper by the light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ ? we can calculate the kinetic energy of the photoelectron using the equation that relates $ \text { ke } \text { electron } $ to the energy of the photon , $ \text { e } \text { photon } $ , and the work function , $ \phi $ : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ since we want to know $ \text { ke } _\text { electron } $ , we can start by rearranging the equation so that we will be solving for the kinetic energy of the electron : $ \text { ke } \text { electron } =\text { e } \text { photon } -\phi $ now we can insert our known values for $ \text { e } _\text { photon } $ and $ \phi $ from example 1 : $ \text { ke } _\text { electron } = ( 2.0\times10^ { -17 } \text { j } ) - ( 7.53\times10^ { -19 } \text { j } ) =1.9\times10^ { -17 } \text { j } $ therefore , each photoelectron has a kinetic energy of $ 1.9\times10^ { -17 } \text { j } $ . summary based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a specific metal surface . the energy of the incident photon must be equal to the sum of the work function and the kinetic energy of a photoelectron : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ try it ! when we shine light with a frequency of $ 6.20 \times 10^ { 14 } \ , \text { hz } $ on a mystery metal , we observe the ejected electrons have a kinetic energy of $ 3.28\times 10^ { -20 } \ , \text j $ . some possible candidates for the mystery metal are shown in the table below : metal | work function $ \phi $ ( joules , $ \text j $ ) : - : | : - : calcium , $ \text { ca } $ | $ 4.60\times 10^ { -19 } $ tin , $ \text { sn } $ | $ 7.08\times 10^ { -19 } $ sodium , $ \text { na } $ | $ 3.78\times 10^ { -19 } $ hafnium , $ \text { hf } $ | $ 6.25\times 10^ { -19 } $ samarium , $ \text { sm } $ | $ 4.33\times 10^ { -19 } $ based on this information , what is the most likely identity of our mystery metal ?
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thus , our intuition and analogy do n't do a very good job of explaining these particular experiments . example $ 1 $ : the photoelectric effect for copper the work function of copper metal is $ \phi=7.53\times10^ { -19 } \text { j } $ . if we shine light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ on copper metal , will the photoelectric effect be observed ?
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what is psi 's , the work function , relationship to the schrodinger equation ?
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key points based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . contrary to the predictions , experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of particles called photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a metal surface , and the value of $ \phi $ depends on the metal . the energy of the incident photon must be equal to the sum of the metal 's work function and the photoelectron kinetic energy : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ introduction : what is the photoelectric effect ? when light shines on a metal , electrons can be ejected from the surface of the metal in a phenomenon known as the photoelectric effect . this process is also often referred to as photoemission , and the electrons that are ejected from the metal are called photoelectrons . in terms of their behavior and their properties , photoelectrons are no different from other electrons . the prefix , photo- , simply tells us that the electrons have been ejected from a metal surface by incident light . in this article , we will discuss how 19th century physicists attempted ( but failed ! ) to explain the photoelectric effect using classical physics . this ultimately led to the development of the modern description of electromagnetic radiation , which has both wave-like and particle-like properties . predictions based on light as a wave to explain the photoelectric effect , 19th-century physicists theorized that the oscillating electric field of the incoming light wave was heating the electrons and causing them to vibrate , eventually freeing them from the metal surface . this hypothesis was based on the assumption that light traveled purely as a wave through space . ( see this article for more information about the basic properties of light . ) scientists also believed that the energy of the light wave was proportional to its brightness , which is related to the wave 's amplitude . in order to test their hypotheses , they performed experiments to look at the effect of light amplitude and frequency on the rate of electron ejection , as well as the kinetic energy of the photoelectrons . based on the classical description of light as a wave , they made the following predictions : the kinetic energy of emitted photoelectrons should increase with the light amplitude . the rate of electron emission , which is proportional to the measured electric current , should increase as the light frequency is increased . to help us understand why they made these predictions , we can compare a light wave to a water wave . imagine some beach balls sitting on a dock that extends out into the ocean . the dock represents a metal surface , the beach balls represent electrons , and the ocean waves represent light waves . if a single large wave were to shake the dock , we would expect the energy from the big wave would send the beach balls flying off the dock with much more kinetic energy compared to a single , small wave . this is also what physicists believed would happen if the light intensity was increased . light amplitude was expected to be proportional to the light energy , so higher amplitude light was predicted to result in photoelectrons with more kinetic energy . classical physicists also predicted that increasing the frequency of light waves ( at a constant amplitude ) would increase the rate of electrons being ejected , and thus increase the measured electric current . using our beach ball analogy , we would expect waves hitting the dock more frequently would result in more beach balls being knocked off the dock compared to the same sized waves hitting the dock less often . now that we know what physicists thought would happen , let 's look at what they actually observed experimentally ! when intuition fails : photons to the rescue ! when experiments were performed to look at the effect of light amplitude and frequency , the following results were observed : the kinetic energy of photoelectrons increases with light frequency . electric current remains constant as light frequency increases . electric current increases with light amplitude . the kinetic energy of photoelectrons remains constant as light amplitude increases . these results were completely at odds with the predictions based on the classical description of light as a wave ! in order to explain what was happening , it turned out that an entirely new model of light was needed . that model was developed by albert einstein , who proposed that light sometimes behaved as particles of electromagnetic energy which we now call photons . the energy of a photon could be calculated using planck 's equation : $ \text { e } _ { \text { photon } } =h\nu $ where $ \text { e } _ { \text { photon } } $ is the energy of a photon in joules ( $ \text { j } $ ) , $ h $ is planck 's constant $ ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) $ , and $ \nu $ is the frequency of the light in $ \text { hz } $ . according to planck 's equation , the energy of a photon is proportional to the frequency of the light , $ \nu $ . the amplitude of the light is then proportional to the number of photons with a given frequency . concept check : as the wavelength of a photon increases , what happens to the photon 's energy ? light frequency and the threshold frequency $ \nu_0 $ we can think of the incident light as a stream of photons with an energy determined by the light frequency . when a photon hits the metal surface , the photon 's energy is absorbed by an electron in the metal . the graphic below illustrates the relationship between light frequency and the kinetic energy of ejected electrons . the scientists observed that if the incident light had a frequency less than a minimum frequency $ \nu_0 $ , then no electrons were ejected regardless of the light amplitude . this minimum frequency is also called the threshold frequency , and the value of $ \nu_0 $ depends on the metal . for frequencies greater than $ \nu_0 $ , electrons would be ejected from the metal . furthermore , the kinetic energy of the photoelectrons was proportional to the light frequency . the relationship between photoelectron kinetic energy and light frequency is shown in graph ( a ) below . because the light amplitude was kept constant as the light frequency increased , the number of photons being absorbed by the metal remained constant . thus , the rate at which electrons were ejected from the metal ( or the electric current ) remained constant as well . the relationship between electron current and light frequency is illustrated in graph ( b ) above . is n't there more math somewhere ? we can analyze the frequency relationship using the law of conservation of energy . the total energy of the incoming photon , $ \text { e } \text { photon } $ , must be equal to the kinetic energy of the ejected electron , $ \text { ke } { \text { electron } } $ , plus the energy required to eject the electron from the metal . the energy required to free the electron from a particular metal is also called the metal 's work function , which is represented by the symbol $ \phi $ ( in units of $ \text j $ ) : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ like the threshold frequency $ \nu_0 $ , the value of $ \phi $ also changes depending on the metal . we can now write the energy of the photon in terms of the light frequency using planck 's equation : $ \text { e } \text { photon } =h\nu=\text { ke } \text { electron } +\phi $ rearranging this equation in terms of the electron 's kinetic energy , we get : $ \text { ke } _\text { electron } =h\nu-\phi $ we can see that kinetic energy of the photoelectron increases linearly with $ \nu $ as long as the photon energy is greater than the work function $ \phi $ , which is exactly the relationship shown in graph ( a ) above . we can also use this equation to find the photoelectron velocity $ \text v $ , which is related to $ \text { ke } _\text { electron } $ as follows : $ \text { ke } _\text { electron } =h\nu-\phi=\dfrac { 1 } { 2 } m_e\text v^2 $ where $ m_e $ is the rest mass of an electron , $ 9.1094 \times 10^ { -31 } \ , \text { kg } $ . exploring the wave amplitude trends in terms of photons , higher amplitude light means more photons hitting the metal surface . this results in more electrons ejected over a given time period . as long as the light frequency is greater than $ \nu_0 $ , increasing the light amplitude will cause the electron current to increase proportionally as shown in graph ( a ) below . since increasing the light amplitude has no effect on the energy of the incoming photon , the photoelectron kinetic energy remains constant as the light amplitude is increased ( see graph ( b ) above ) . if we try to explain this result using our dock-and-beach-balls analogy , the relationship in graph ( b ) indicates that no matter the height of the wave hitting the dock $ - $ whether it 's a tiny swell , or a huge tsunami $ - $ the individual beach balls would be launched off the dock with the exact same speed ! thus , our intuition and analogy do n't do a very good job of explaining these particular experiments . example $ 1 $ : the photoelectric effect for copper the work function of copper metal is $ \phi=7.53\times10^ { -19 } \text { j } $ . if we shine light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ on copper metal , will the photoelectric effect be observed ? in order to eject electrons , we need the energy of the photons to be greater than the work function of copper . we can use planck 's equation to calculate the energy of the photon , $ \text { e } _ { \text { photon } } $ : $ \begin { align } \text { e } _\text { photon } & amp ; = h\nu \ & amp ; = ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) ( 3.0\times10^ { 16 } \text { hz } ) ~~~~\text { plug in values for $ h $ and $ \nu $ } \ & amp ; = 2.0\times10^ { -17 } \text { j } \end { align } $ if we compare our calculated photon energy , $ \text { e } _\text { photon } $ , to copper 's work function , we see that the photon energy is greater than $ \phi $ : $ ~2.0\times10^ { -17 } \text { j } ~ & gt ; ~7.53\times10^ { -19 } \text { j } $ $ ~~~~~~~~\text { e } _\text { photon } ~~~~~~~~~~~~~~~~~~~\phi $ thus , we would expect to see photoelectrons ejected from the copper . next , we will calculate the kinetic energy of the photoelectrons . example $ 2 $ : calculating the kinetic energy of a photoelectron what is the kinetic energy of the photoelectrons ejected from the copper by the light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ ? we can calculate the kinetic energy of the photoelectron using the equation that relates $ \text { ke } \text { electron } $ to the energy of the photon , $ \text { e } \text { photon } $ , and the work function , $ \phi $ : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ since we want to know $ \text { ke } _\text { electron } $ , we can start by rearranging the equation so that we will be solving for the kinetic energy of the electron : $ \text { ke } \text { electron } =\text { e } \text { photon } -\phi $ now we can insert our known values for $ \text { e } _\text { photon } $ and $ \phi $ from example 1 : $ \text { ke } _\text { electron } = ( 2.0\times10^ { -17 } \text { j } ) - ( 7.53\times10^ { -19 } \text { j } ) =1.9\times10^ { -17 } \text { j } $ therefore , each photoelectron has a kinetic energy of $ 1.9\times10^ { -17 } \text { j } $ . summary based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a specific metal surface . the energy of the incident photon must be equal to the sum of the work function and the kinetic energy of a photoelectron : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ try it ! when we shine light with a frequency of $ 6.20 \times 10^ { 14 } \ , \text { hz } $ on a mystery metal , we observe the ejected electrons have a kinetic energy of $ 3.28\times 10^ { -20 } \ , \text j $ . some possible candidates for the mystery metal are shown in the table below : metal | work function $ \phi $ ( joules , $ \text j $ ) : - : | : - : calcium , $ \text { ca } $ | $ 4.60\times 10^ { -19 } $ tin , $ \text { sn } $ | $ 7.08\times 10^ { -19 } $ sodium , $ \text { na } $ | $ 3.78\times 10^ { -19 } $ hafnium , $ \text { hf } $ | $ 6.25\times 10^ { -19 } $ samarium , $ \text { sm } $ | $ 4.33\times 10^ { -19 } $ based on this information , what is the most likely identity of our mystery metal ?
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we can also use this equation to find the photoelectron velocity $ \text v $ , which is related to $ \text { ke } _\text { electron } $ as follows : $ \text { ke } _\text { electron } =h\nu-\phi=\dfrac { 1 } { 2 } m_e\text v^2 $ where $ m_e $ is the rest mass of an electron , $ 9.1094 \times 10^ { -31 } \ , \text { kg } $ . exploring the wave amplitude trends in terms of photons , higher amplitude light means more photons hitting the metal surface . this results in more electrons ejected over a given time period .
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is the wave amplitude a measure of the individual electron or the total combined brightness/intensity of all the photons ?
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key points based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . contrary to the predictions , experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of particles called photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a metal surface , and the value of $ \phi $ depends on the metal . the energy of the incident photon must be equal to the sum of the metal 's work function and the photoelectron kinetic energy : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ introduction : what is the photoelectric effect ? when light shines on a metal , electrons can be ejected from the surface of the metal in a phenomenon known as the photoelectric effect . this process is also often referred to as photoemission , and the electrons that are ejected from the metal are called photoelectrons . in terms of their behavior and their properties , photoelectrons are no different from other electrons . the prefix , photo- , simply tells us that the electrons have been ejected from a metal surface by incident light . in this article , we will discuss how 19th century physicists attempted ( but failed ! ) to explain the photoelectric effect using classical physics . this ultimately led to the development of the modern description of electromagnetic radiation , which has both wave-like and particle-like properties . predictions based on light as a wave to explain the photoelectric effect , 19th-century physicists theorized that the oscillating electric field of the incoming light wave was heating the electrons and causing them to vibrate , eventually freeing them from the metal surface . this hypothesis was based on the assumption that light traveled purely as a wave through space . ( see this article for more information about the basic properties of light . ) scientists also believed that the energy of the light wave was proportional to its brightness , which is related to the wave 's amplitude . in order to test their hypotheses , they performed experiments to look at the effect of light amplitude and frequency on the rate of electron ejection , as well as the kinetic energy of the photoelectrons . based on the classical description of light as a wave , they made the following predictions : the kinetic energy of emitted photoelectrons should increase with the light amplitude . the rate of electron emission , which is proportional to the measured electric current , should increase as the light frequency is increased . to help us understand why they made these predictions , we can compare a light wave to a water wave . imagine some beach balls sitting on a dock that extends out into the ocean . the dock represents a metal surface , the beach balls represent electrons , and the ocean waves represent light waves . if a single large wave were to shake the dock , we would expect the energy from the big wave would send the beach balls flying off the dock with much more kinetic energy compared to a single , small wave . this is also what physicists believed would happen if the light intensity was increased . light amplitude was expected to be proportional to the light energy , so higher amplitude light was predicted to result in photoelectrons with more kinetic energy . classical physicists also predicted that increasing the frequency of light waves ( at a constant amplitude ) would increase the rate of electrons being ejected , and thus increase the measured electric current . using our beach ball analogy , we would expect waves hitting the dock more frequently would result in more beach balls being knocked off the dock compared to the same sized waves hitting the dock less often . now that we know what physicists thought would happen , let 's look at what they actually observed experimentally ! when intuition fails : photons to the rescue ! when experiments were performed to look at the effect of light amplitude and frequency , the following results were observed : the kinetic energy of photoelectrons increases with light frequency . electric current remains constant as light frequency increases . electric current increases with light amplitude . the kinetic energy of photoelectrons remains constant as light amplitude increases . these results were completely at odds with the predictions based on the classical description of light as a wave ! in order to explain what was happening , it turned out that an entirely new model of light was needed . that model was developed by albert einstein , who proposed that light sometimes behaved as particles of electromagnetic energy which we now call photons . the energy of a photon could be calculated using planck 's equation : $ \text { e } _ { \text { photon } } =h\nu $ where $ \text { e } _ { \text { photon } } $ is the energy of a photon in joules ( $ \text { j } $ ) , $ h $ is planck 's constant $ ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) $ , and $ \nu $ is the frequency of the light in $ \text { hz } $ . according to planck 's equation , the energy of a photon is proportional to the frequency of the light , $ \nu $ . the amplitude of the light is then proportional to the number of photons with a given frequency . concept check : as the wavelength of a photon increases , what happens to the photon 's energy ? light frequency and the threshold frequency $ \nu_0 $ we can think of the incident light as a stream of photons with an energy determined by the light frequency . when a photon hits the metal surface , the photon 's energy is absorbed by an electron in the metal . the graphic below illustrates the relationship between light frequency and the kinetic energy of ejected electrons . the scientists observed that if the incident light had a frequency less than a minimum frequency $ \nu_0 $ , then no electrons were ejected regardless of the light amplitude . this minimum frequency is also called the threshold frequency , and the value of $ \nu_0 $ depends on the metal . for frequencies greater than $ \nu_0 $ , electrons would be ejected from the metal . furthermore , the kinetic energy of the photoelectrons was proportional to the light frequency . the relationship between photoelectron kinetic energy and light frequency is shown in graph ( a ) below . because the light amplitude was kept constant as the light frequency increased , the number of photons being absorbed by the metal remained constant . thus , the rate at which electrons were ejected from the metal ( or the electric current ) remained constant as well . the relationship between electron current and light frequency is illustrated in graph ( b ) above . is n't there more math somewhere ? we can analyze the frequency relationship using the law of conservation of energy . the total energy of the incoming photon , $ \text { e } \text { photon } $ , must be equal to the kinetic energy of the ejected electron , $ \text { ke } { \text { electron } } $ , plus the energy required to eject the electron from the metal . the energy required to free the electron from a particular metal is also called the metal 's work function , which is represented by the symbol $ \phi $ ( in units of $ \text j $ ) : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ like the threshold frequency $ \nu_0 $ , the value of $ \phi $ also changes depending on the metal . we can now write the energy of the photon in terms of the light frequency using planck 's equation : $ \text { e } \text { photon } =h\nu=\text { ke } \text { electron } +\phi $ rearranging this equation in terms of the electron 's kinetic energy , we get : $ \text { ke } _\text { electron } =h\nu-\phi $ we can see that kinetic energy of the photoelectron increases linearly with $ \nu $ as long as the photon energy is greater than the work function $ \phi $ , which is exactly the relationship shown in graph ( a ) above . we can also use this equation to find the photoelectron velocity $ \text v $ , which is related to $ \text { ke } _\text { electron } $ as follows : $ \text { ke } _\text { electron } =h\nu-\phi=\dfrac { 1 } { 2 } m_e\text v^2 $ where $ m_e $ is the rest mass of an electron , $ 9.1094 \times 10^ { -31 } \ , \text { kg } $ . exploring the wave amplitude trends in terms of photons , higher amplitude light means more photons hitting the metal surface . this results in more electrons ejected over a given time period . as long as the light frequency is greater than $ \nu_0 $ , increasing the light amplitude will cause the electron current to increase proportionally as shown in graph ( a ) below . since increasing the light amplitude has no effect on the energy of the incoming photon , the photoelectron kinetic energy remains constant as the light amplitude is increased ( see graph ( b ) above ) . if we try to explain this result using our dock-and-beach-balls analogy , the relationship in graph ( b ) indicates that no matter the height of the wave hitting the dock $ - $ whether it 's a tiny swell , or a huge tsunami $ - $ the individual beach balls would be launched off the dock with the exact same speed ! thus , our intuition and analogy do n't do a very good job of explaining these particular experiments . example $ 1 $ : the photoelectric effect for copper the work function of copper metal is $ \phi=7.53\times10^ { -19 } \text { j } $ . if we shine light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ on copper metal , will the photoelectric effect be observed ? in order to eject electrons , we need the energy of the photons to be greater than the work function of copper . we can use planck 's equation to calculate the energy of the photon , $ \text { e } _ { \text { photon } } $ : $ \begin { align } \text { e } _\text { photon } & amp ; = h\nu \ & amp ; = ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) ( 3.0\times10^ { 16 } \text { hz } ) ~~~~\text { plug in values for $ h $ and $ \nu $ } \ & amp ; = 2.0\times10^ { -17 } \text { j } \end { align } $ if we compare our calculated photon energy , $ \text { e } _\text { photon } $ , to copper 's work function , we see that the photon energy is greater than $ \phi $ : $ ~2.0\times10^ { -17 } \text { j } ~ & gt ; ~7.53\times10^ { -19 } \text { j } $ $ ~~~~~~~~\text { e } _\text { photon } ~~~~~~~~~~~~~~~~~~~\phi $ thus , we would expect to see photoelectrons ejected from the copper . next , we will calculate the kinetic energy of the photoelectrons . example $ 2 $ : calculating the kinetic energy of a photoelectron what is the kinetic energy of the photoelectrons ejected from the copper by the light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ ? we can calculate the kinetic energy of the photoelectron using the equation that relates $ \text { ke } \text { electron } $ to the energy of the photon , $ \text { e } \text { photon } $ , and the work function , $ \phi $ : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ since we want to know $ \text { ke } _\text { electron } $ , we can start by rearranging the equation so that we will be solving for the kinetic energy of the electron : $ \text { ke } \text { electron } =\text { e } \text { photon } -\phi $ now we can insert our known values for $ \text { e } _\text { photon } $ and $ \phi $ from example 1 : $ \text { ke } _\text { electron } = ( 2.0\times10^ { -17 } \text { j } ) - ( 7.53\times10^ { -19 } \text { j } ) =1.9\times10^ { -17 } \text { j } $ therefore , each photoelectron has a kinetic energy of $ 1.9\times10^ { -17 } \text { j } $ . summary based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a specific metal surface . the energy of the incident photon must be equal to the sum of the work function and the kinetic energy of a photoelectron : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ try it ! when we shine light with a frequency of $ 6.20 \times 10^ { 14 } \ , \text { hz } $ on a mystery metal , we observe the ejected electrons have a kinetic energy of $ 3.28\times 10^ { -20 } \ , \text j $ . some possible candidates for the mystery metal are shown in the table below : metal | work function $ \phi $ ( joules , $ \text j $ ) : - : | : - : calcium , $ \text { ca } $ | $ 4.60\times 10^ { -19 } $ tin , $ \text { sn } $ | $ 7.08\times 10^ { -19 } $ sodium , $ \text { na } $ | $ 3.78\times 10^ { -19 } $ hafnium , $ \text { hf } $ | $ 6.25\times 10^ { -19 } $ samarium , $ \text { sm } $ | $ 4.33\times 10^ { -19 } $ based on this information , what is the most likely identity of our mystery metal ?
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we can analyze the frequency relationship using the law of conservation of energy . the total energy of the incoming photon , $ \text { e } \text { photon } $ , must be equal to the kinetic energy of the ejected electron , $ \text { ke } { \text { electron } } $ , plus the energy required to eject the electron from the metal . the energy required to free the electron from a particular metal is also called the metal 's work function , which is represented by the symbol $ \phi $ ( in units of $ \text j $ ) : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ like the threshold frequency $ \nu_0 $ , the value of $ \phi $ also changes depending on the metal .
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if the photons energy is exactly equal to the work function , can an electron be released with zero kinetic energy ?
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key points based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . contrary to the predictions , experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of particles called photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a metal surface , and the value of $ \phi $ depends on the metal . the energy of the incident photon must be equal to the sum of the metal 's work function and the photoelectron kinetic energy : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ introduction : what is the photoelectric effect ? when light shines on a metal , electrons can be ejected from the surface of the metal in a phenomenon known as the photoelectric effect . this process is also often referred to as photoemission , and the electrons that are ejected from the metal are called photoelectrons . in terms of their behavior and their properties , photoelectrons are no different from other electrons . the prefix , photo- , simply tells us that the electrons have been ejected from a metal surface by incident light . in this article , we will discuss how 19th century physicists attempted ( but failed ! ) to explain the photoelectric effect using classical physics . this ultimately led to the development of the modern description of electromagnetic radiation , which has both wave-like and particle-like properties . predictions based on light as a wave to explain the photoelectric effect , 19th-century physicists theorized that the oscillating electric field of the incoming light wave was heating the electrons and causing them to vibrate , eventually freeing them from the metal surface . this hypothesis was based on the assumption that light traveled purely as a wave through space . ( see this article for more information about the basic properties of light . ) scientists also believed that the energy of the light wave was proportional to its brightness , which is related to the wave 's amplitude . in order to test their hypotheses , they performed experiments to look at the effect of light amplitude and frequency on the rate of electron ejection , as well as the kinetic energy of the photoelectrons . based on the classical description of light as a wave , they made the following predictions : the kinetic energy of emitted photoelectrons should increase with the light amplitude . the rate of electron emission , which is proportional to the measured electric current , should increase as the light frequency is increased . to help us understand why they made these predictions , we can compare a light wave to a water wave . imagine some beach balls sitting on a dock that extends out into the ocean . the dock represents a metal surface , the beach balls represent electrons , and the ocean waves represent light waves . if a single large wave were to shake the dock , we would expect the energy from the big wave would send the beach balls flying off the dock with much more kinetic energy compared to a single , small wave . this is also what physicists believed would happen if the light intensity was increased . light amplitude was expected to be proportional to the light energy , so higher amplitude light was predicted to result in photoelectrons with more kinetic energy . classical physicists also predicted that increasing the frequency of light waves ( at a constant amplitude ) would increase the rate of electrons being ejected , and thus increase the measured electric current . using our beach ball analogy , we would expect waves hitting the dock more frequently would result in more beach balls being knocked off the dock compared to the same sized waves hitting the dock less often . now that we know what physicists thought would happen , let 's look at what they actually observed experimentally ! when intuition fails : photons to the rescue ! when experiments were performed to look at the effect of light amplitude and frequency , the following results were observed : the kinetic energy of photoelectrons increases with light frequency . electric current remains constant as light frequency increases . electric current increases with light amplitude . the kinetic energy of photoelectrons remains constant as light amplitude increases . these results were completely at odds with the predictions based on the classical description of light as a wave ! in order to explain what was happening , it turned out that an entirely new model of light was needed . that model was developed by albert einstein , who proposed that light sometimes behaved as particles of electromagnetic energy which we now call photons . the energy of a photon could be calculated using planck 's equation : $ \text { e } _ { \text { photon } } =h\nu $ where $ \text { e } _ { \text { photon } } $ is the energy of a photon in joules ( $ \text { j } $ ) , $ h $ is planck 's constant $ ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) $ , and $ \nu $ is the frequency of the light in $ \text { hz } $ . according to planck 's equation , the energy of a photon is proportional to the frequency of the light , $ \nu $ . the amplitude of the light is then proportional to the number of photons with a given frequency . concept check : as the wavelength of a photon increases , what happens to the photon 's energy ? light frequency and the threshold frequency $ \nu_0 $ we can think of the incident light as a stream of photons with an energy determined by the light frequency . when a photon hits the metal surface , the photon 's energy is absorbed by an electron in the metal . the graphic below illustrates the relationship between light frequency and the kinetic energy of ejected electrons . the scientists observed that if the incident light had a frequency less than a minimum frequency $ \nu_0 $ , then no electrons were ejected regardless of the light amplitude . this minimum frequency is also called the threshold frequency , and the value of $ \nu_0 $ depends on the metal . for frequencies greater than $ \nu_0 $ , electrons would be ejected from the metal . furthermore , the kinetic energy of the photoelectrons was proportional to the light frequency . the relationship between photoelectron kinetic energy and light frequency is shown in graph ( a ) below . because the light amplitude was kept constant as the light frequency increased , the number of photons being absorbed by the metal remained constant . thus , the rate at which electrons were ejected from the metal ( or the electric current ) remained constant as well . the relationship between electron current and light frequency is illustrated in graph ( b ) above . is n't there more math somewhere ? we can analyze the frequency relationship using the law of conservation of energy . the total energy of the incoming photon , $ \text { e } \text { photon } $ , must be equal to the kinetic energy of the ejected electron , $ \text { ke } { \text { electron } } $ , plus the energy required to eject the electron from the metal . the energy required to free the electron from a particular metal is also called the metal 's work function , which is represented by the symbol $ \phi $ ( in units of $ \text j $ ) : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ like the threshold frequency $ \nu_0 $ , the value of $ \phi $ also changes depending on the metal . we can now write the energy of the photon in terms of the light frequency using planck 's equation : $ \text { e } \text { photon } =h\nu=\text { ke } \text { electron } +\phi $ rearranging this equation in terms of the electron 's kinetic energy , we get : $ \text { ke } _\text { electron } =h\nu-\phi $ we can see that kinetic energy of the photoelectron increases linearly with $ \nu $ as long as the photon energy is greater than the work function $ \phi $ , which is exactly the relationship shown in graph ( a ) above . we can also use this equation to find the photoelectron velocity $ \text v $ , which is related to $ \text { ke } _\text { electron } $ as follows : $ \text { ke } _\text { electron } =h\nu-\phi=\dfrac { 1 } { 2 } m_e\text v^2 $ where $ m_e $ is the rest mass of an electron , $ 9.1094 \times 10^ { -31 } \ , \text { kg } $ . exploring the wave amplitude trends in terms of photons , higher amplitude light means more photons hitting the metal surface . this results in more electrons ejected over a given time period . as long as the light frequency is greater than $ \nu_0 $ , increasing the light amplitude will cause the electron current to increase proportionally as shown in graph ( a ) below . since increasing the light amplitude has no effect on the energy of the incoming photon , the photoelectron kinetic energy remains constant as the light amplitude is increased ( see graph ( b ) above ) . if we try to explain this result using our dock-and-beach-balls analogy , the relationship in graph ( b ) indicates that no matter the height of the wave hitting the dock $ - $ whether it 's a tiny swell , or a huge tsunami $ - $ the individual beach balls would be launched off the dock with the exact same speed ! thus , our intuition and analogy do n't do a very good job of explaining these particular experiments . example $ 1 $ : the photoelectric effect for copper the work function of copper metal is $ \phi=7.53\times10^ { -19 } \text { j } $ . if we shine light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ on copper metal , will the photoelectric effect be observed ? in order to eject electrons , we need the energy of the photons to be greater than the work function of copper . we can use planck 's equation to calculate the energy of the photon , $ \text { e } _ { \text { photon } } $ : $ \begin { align } \text { e } _\text { photon } & amp ; = h\nu \ & amp ; = ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) ( 3.0\times10^ { 16 } \text { hz } ) ~~~~\text { plug in values for $ h $ and $ \nu $ } \ & amp ; = 2.0\times10^ { -17 } \text { j } \end { align } $ if we compare our calculated photon energy , $ \text { e } _\text { photon } $ , to copper 's work function , we see that the photon energy is greater than $ \phi $ : $ ~2.0\times10^ { -17 } \text { j } ~ & gt ; ~7.53\times10^ { -19 } \text { j } $ $ ~~~~~~~~\text { e } _\text { photon } ~~~~~~~~~~~~~~~~~~~\phi $ thus , we would expect to see photoelectrons ejected from the copper . next , we will calculate the kinetic energy of the photoelectrons . example $ 2 $ : calculating the kinetic energy of a photoelectron what is the kinetic energy of the photoelectrons ejected from the copper by the light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ ? we can calculate the kinetic energy of the photoelectron using the equation that relates $ \text { ke } \text { electron } $ to the energy of the photon , $ \text { e } \text { photon } $ , and the work function , $ \phi $ : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ since we want to know $ \text { ke } _\text { electron } $ , we can start by rearranging the equation so that we will be solving for the kinetic energy of the electron : $ \text { ke } \text { electron } =\text { e } \text { photon } -\phi $ now we can insert our known values for $ \text { e } _\text { photon } $ and $ \phi $ from example 1 : $ \text { ke } _\text { electron } = ( 2.0\times10^ { -17 } \text { j } ) - ( 7.53\times10^ { -19 } \text { j } ) =1.9\times10^ { -17 } \text { j } $ therefore , each photoelectron has a kinetic energy of $ 1.9\times10^ { -17 } \text { j } $ . summary based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a specific metal surface . the energy of the incident photon must be equal to the sum of the work function and the kinetic energy of a photoelectron : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ try it ! when we shine light with a frequency of $ 6.20 \times 10^ { 14 } \ , \text { hz } $ on a mystery metal , we observe the ejected electrons have a kinetic energy of $ 3.28\times 10^ { -20 } \ , \text j $ . some possible candidates for the mystery metal are shown in the table below : metal | work function $ \phi $ ( joules , $ \text j $ ) : - : | : - : calcium , $ \text { ca } $ | $ 4.60\times 10^ { -19 } $ tin , $ \text { sn } $ | $ 7.08\times 10^ { -19 } $ sodium , $ \text { na } $ | $ 3.78\times 10^ { -19 } $ hafnium , $ \text { hf } $ | $ 6.25\times 10^ { -19 } $ samarium , $ \text { sm } $ | $ 4.33\times 10^ { -19 } $ based on this information , what is the most likely identity of our mystery metal ?
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we can also use this equation to find the photoelectron velocity $ \text v $ , which is related to $ \text { ke } _\text { electron } $ as follows : $ \text { ke } _\text { electron } =h\nu-\phi=\dfrac { 1 } { 2 } m_e\text v^2 $ where $ m_e $ is the rest mass of an electron , $ 9.1094 \times 10^ { -31 } \ , \text { kg } $ . exploring the wave amplitude trends in terms of photons , higher amplitude light means more photons hitting the metal surface . this results in more electrons ejected over a given time period .
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how does an increase in amplitude of the wave lead to more photons hitting the metal surface ?
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key points based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . contrary to the predictions , experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of particles called photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a metal surface , and the value of $ \phi $ depends on the metal . the energy of the incident photon must be equal to the sum of the metal 's work function and the photoelectron kinetic energy : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ introduction : what is the photoelectric effect ? when light shines on a metal , electrons can be ejected from the surface of the metal in a phenomenon known as the photoelectric effect . this process is also often referred to as photoemission , and the electrons that are ejected from the metal are called photoelectrons . in terms of their behavior and their properties , photoelectrons are no different from other electrons . the prefix , photo- , simply tells us that the electrons have been ejected from a metal surface by incident light . in this article , we will discuss how 19th century physicists attempted ( but failed ! ) to explain the photoelectric effect using classical physics . this ultimately led to the development of the modern description of electromagnetic radiation , which has both wave-like and particle-like properties . predictions based on light as a wave to explain the photoelectric effect , 19th-century physicists theorized that the oscillating electric field of the incoming light wave was heating the electrons and causing them to vibrate , eventually freeing them from the metal surface . this hypothesis was based on the assumption that light traveled purely as a wave through space . ( see this article for more information about the basic properties of light . ) scientists also believed that the energy of the light wave was proportional to its brightness , which is related to the wave 's amplitude . in order to test their hypotheses , they performed experiments to look at the effect of light amplitude and frequency on the rate of electron ejection , as well as the kinetic energy of the photoelectrons . based on the classical description of light as a wave , they made the following predictions : the kinetic energy of emitted photoelectrons should increase with the light amplitude . the rate of electron emission , which is proportional to the measured electric current , should increase as the light frequency is increased . to help us understand why they made these predictions , we can compare a light wave to a water wave . imagine some beach balls sitting on a dock that extends out into the ocean . the dock represents a metal surface , the beach balls represent electrons , and the ocean waves represent light waves . if a single large wave were to shake the dock , we would expect the energy from the big wave would send the beach balls flying off the dock with much more kinetic energy compared to a single , small wave . this is also what physicists believed would happen if the light intensity was increased . light amplitude was expected to be proportional to the light energy , so higher amplitude light was predicted to result in photoelectrons with more kinetic energy . classical physicists also predicted that increasing the frequency of light waves ( at a constant amplitude ) would increase the rate of electrons being ejected , and thus increase the measured electric current . using our beach ball analogy , we would expect waves hitting the dock more frequently would result in more beach balls being knocked off the dock compared to the same sized waves hitting the dock less often . now that we know what physicists thought would happen , let 's look at what they actually observed experimentally ! when intuition fails : photons to the rescue ! when experiments were performed to look at the effect of light amplitude and frequency , the following results were observed : the kinetic energy of photoelectrons increases with light frequency . electric current remains constant as light frequency increases . electric current increases with light amplitude . the kinetic energy of photoelectrons remains constant as light amplitude increases . these results were completely at odds with the predictions based on the classical description of light as a wave ! in order to explain what was happening , it turned out that an entirely new model of light was needed . that model was developed by albert einstein , who proposed that light sometimes behaved as particles of electromagnetic energy which we now call photons . the energy of a photon could be calculated using planck 's equation : $ \text { e } _ { \text { photon } } =h\nu $ where $ \text { e } _ { \text { photon } } $ is the energy of a photon in joules ( $ \text { j } $ ) , $ h $ is planck 's constant $ ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) $ , and $ \nu $ is the frequency of the light in $ \text { hz } $ . according to planck 's equation , the energy of a photon is proportional to the frequency of the light , $ \nu $ . the amplitude of the light is then proportional to the number of photons with a given frequency . concept check : as the wavelength of a photon increases , what happens to the photon 's energy ? light frequency and the threshold frequency $ \nu_0 $ we can think of the incident light as a stream of photons with an energy determined by the light frequency . when a photon hits the metal surface , the photon 's energy is absorbed by an electron in the metal . the graphic below illustrates the relationship between light frequency and the kinetic energy of ejected electrons . the scientists observed that if the incident light had a frequency less than a minimum frequency $ \nu_0 $ , then no electrons were ejected regardless of the light amplitude . this minimum frequency is also called the threshold frequency , and the value of $ \nu_0 $ depends on the metal . for frequencies greater than $ \nu_0 $ , electrons would be ejected from the metal . furthermore , the kinetic energy of the photoelectrons was proportional to the light frequency . the relationship between photoelectron kinetic energy and light frequency is shown in graph ( a ) below . because the light amplitude was kept constant as the light frequency increased , the number of photons being absorbed by the metal remained constant . thus , the rate at which electrons were ejected from the metal ( or the electric current ) remained constant as well . the relationship between electron current and light frequency is illustrated in graph ( b ) above . is n't there more math somewhere ? we can analyze the frequency relationship using the law of conservation of energy . the total energy of the incoming photon , $ \text { e } \text { photon } $ , must be equal to the kinetic energy of the ejected electron , $ \text { ke } { \text { electron } } $ , plus the energy required to eject the electron from the metal . the energy required to free the electron from a particular metal is also called the metal 's work function , which is represented by the symbol $ \phi $ ( in units of $ \text j $ ) : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ like the threshold frequency $ \nu_0 $ , the value of $ \phi $ also changes depending on the metal . we can now write the energy of the photon in terms of the light frequency using planck 's equation : $ \text { e } \text { photon } =h\nu=\text { ke } \text { electron } +\phi $ rearranging this equation in terms of the electron 's kinetic energy , we get : $ \text { ke } _\text { electron } =h\nu-\phi $ we can see that kinetic energy of the photoelectron increases linearly with $ \nu $ as long as the photon energy is greater than the work function $ \phi $ , which is exactly the relationship shown in graph ( a ) above . we can also use this equation to find the photoelectron velocity $ \text v $ , which is related to $ \text { ke } _\text { electron } $ as follows : $ \text { ke } _\text { electron } =h\nu-\phi=\dfrac { 1 } { 2 } m_e\text v^2 $ where $ m_e $ is the rest mass of an electron , $ 9.1094 \times 10^ { -31 } \ , \text { kg } $ . exploring the wave amplitude trends in terms of photons , higher amplitude light means more photons hitting the metal surface . this results in more electrons ejected over a given time period . as long as the light frequency is greater than $ \nu_0 $ , increasing the light amplitude will cause the electron current to increase proportionally as shown in graph ( a ) below . since increasing the light amplitude has no effect on the energy of the incoming photon , the photoelectron kinetic energy remains constant as the light amplitude is increased ( see graph ( b ) above ) . if we try to explain this result using our dock-and-beach-balls analogy , the relationship in graph ( b ) indicates that no matter the height of the wave hitting the dock $ - $ whether it 's a tiny swell , or a huge tsunami $ - $ the individual beach balls would be launched off the dock with the exact same speed ! thus , our intuition and analogy do n't do a very good job of explaining these particular experiments . example $ 1 $ : the photoelectric effect for copper the work function of copper metal is $ \phi=7.53\times10^ { -19 } \text { j } $ . if we shine light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ on copper metal , will the photoelectric effect be observed ? in order to eject electrons , we need the energy of the photons to be greater than the work function of copper . we can use planck 's equation to calculate the energy of the photon , $ \text { e } _ { \text { photon } } $ : $ \begin { align } \text { e } _\text { photon } & amp ; = h\nu \ & amp ; = ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) ( 3.0\times10^ { 16 } \text { hz } ) ~~~~\text { plug in values for $ h $ and $ \nu $ } \ & amp ; = 2.0\times10^ { -17 } \text { j } \end { align } $ if we compare our calculated photon energy , $ \text { e } _\text { photon } $ , to copper 's work function , we see that the photon energy is greater than $ \phi $ : $ ~2.0\times10^ { -17 } \text { j } ~ & gt ; ~7.53\times10^ { -19 } \text { j } $ $ ~~~~~~~~\text { e } _\text { photon } ~~~~~~~~~~~~~~~~~~~\phi $ thus , we would expect to see photoelectrons ejected from the copper . next , we will calculate the kinetic energy of the photoelectrons . example $ 2 $ : calculating the kinetic energy of a photoelectron what is the kinetic energy of the photoelectrons ejected from the copper by the light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ ? we can calculate the kinetic energy of the photoelectron using the equation that relates $ \text { ke } \text { electron } $ to the energy of the photon , $ \text { e } \text { photon } $ , and the work function , $ \phi $ : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ since we want to know $ \text { ke } _\text { electron } $ , we can start by rearranging the equation so that we will be solving for the kinetic energy of the electron : $ \text { ke } \text { electron } =\text { e } \text { photon } -\phi $ now we can insert our known values for $ \text { e } _\text { photon } $ and $ \phi $ from example 1 : $ \text { ke } _\text { electron } = ( 2.0\times10^ { -17 } \text { j } ) - ( 7.53\times10^ { -19 } \text { j } ) =1.9\times10^ { -17 } \text { j } $ therefore , each photoelectron has a kinetic energy of $ 1.9\times10^ { -17 } \text { j } $ . summary based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a specific metal surface . the energy of the incident photon must be equal to the sum of the work function and the kinetic energy of a photoelectron : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ try it ! when we shine light with a frequency of $ 6.20 \times 10^ { 14 } \ , \text { hz } $ on a mystery metal , we observe the ejected electrons have a kinetic energy of $ 3.28\times 10^ { -20 } \ , \text j $ . some possible candidates for the mystery metal are shown in the table below : metal | work function $ \phi $ ( joules , $ \text j $ ) : - : | : - : calcium , $ \text { ca } $ | $ 4.60\times 10^ { -19 } $ tin , $ \text { sn } $ | $ 7.08\times 10^ { -19 } $ sodium , $ \text { na } $ | $ 3.78\times 10^ { -19 } $ hafnium , $ \text { hf } $ | $ 6.25\times 10^ { -19 } $ samarium , $ \text { sm } $ | $ 4.33\times 10^ { -19 } $ based on this information , what is the most likely identity of our mystery metal ?
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thus , our intuition and analogy do n't do a very good job of explaining these particular experiments . example $ 1 $ : the photoelectric effect for copper the work function of copper metal is $ \phi=7.53\times10^ { -19 } \text { j } $ . if we shine light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ on copper metal , will the photoelectric effect be observed ?
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is there any connection between work function and electronegativity ?
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key points based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . contrary to the predictions , experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of particles called photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a metal surface , and the value of $ \phi $ depends on the metal . the energy of the incident photon must be equal to the sum of the metal 's work function and the photoelectron kinetic energy : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ introduction : what is the photoelectric effect ? when light shines on a metal , electrons can be ejected from the surface of the metal in a phenomenon known as the photoelectric effect . this process is also often referred to as photoemission , and the electrons that are ejected from the metal are called photoelectrons . in terms of their behavior and their properties , photoelectrons are no different from other electrons . the prefix , photo- , simply tells us that the electrons have been ejected from a metal surface by incident light . in this article , we will discuss how 19th century physicists attempted ( but failed ! ) to explain the photoelectric effect using classical physics . this ultimately led to the development of the modern description of electromagnetic radiation , which has both wave-like and particle-like properties . predictions based on light as a wave to explain the photoelectric effect , 19th-century physicists theorized that the oscillating electric field of the incoming light wave was heating the electrons and causing them to vibrate , eventually freeing them from the metal surface . this hypothesis was based on the assumption that light traveled purely as a wave through space . ( see this article for more information about the basic properties of light . ) scientists also believed that the energy of the light wave was proportional to its brightness , which is related to the wave 's amplitude . in order to test their hypotheses , they performed experiments to look at the effect of light amplitude and frequency on the rate of electron ejection , as well as the kinetic energy of the photoelectrons . based on the classical description of light as a wave , they made the following predictions : the kinetic energy of emitted photoelectrons should increase with the light amplitude . the rate of electron emission , which is proportional to the measured electric current , should increase as the light frequency is increased . to help us understand why they made these predictions , we can compare a light wave to a water wave . imagine some beach balls sitting on a dock that extends out into the ocean . the dock represents a metal surface , the beach balls represent electrons , and the ocean waves represent light waves . if a single large wave were to shake the dock , we would expect the energy from the big wave would send the beach balls flying off the dock with much more kinetic energy compared to a single , small wave . this is also what physicists believed would happen if the light intensity was increased . light amplitude was expected to be proportional to the light energy , so higher amplitude light was predicted to result in photoelectrons with more kinetic energy . classical physicists also predicted that increasing the frequency of light waves ( at a constant amplitude ) would increase the rate of electrons being ejected , and thus increase the measured electric current . using our beach ball analogy , we would expect waves hitting the dock more frequently would result in more beach balls being knocked off the dock compared to the same sized waves hitting the dock less often . now that we know what physicists thought would happen , let 's look at what they actually observed experimentally ! when intuition fails : photons to the rescue ! when experiments were performed to look at the effect of light amplitude and frequency , the following results were observed : the kinetic energy of photoelectrons increases with light frequency . electric current remains constant as light frequency increases . electric current increases with light amplitude . the kinetic energy of photoelectrons remains constant as light amplitude increases . these results were completely at odds with the predictions based on the classical description of light as a wave ! in order to explain what was happening , it turned out that an entirely new model of light was needed . that model was developed by albert einstein , who proposed that light sometimes behaved as particles of electromagnetic energy which we now call photons . the energy of a photon could be calculated using planck 's equation : $ \text { e } _ { \text { photon } } =h\nu $ where $ \text { e } _ { \text { photon } } $ is the energy of a photon in joules ( $ \text { j } $ ) , $ h $ is planck 's constant $ ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) $ , and $ \nu $ is the frequency of the light in $ \text { hz } $ . according to planck 's equation , the energy of a photon is proportional to the frequency of the light , $ \nu $ . the amplitude of the light is then proportional to the number of photons with a given frequency . concept check : as the wavelength of a photon increases , what happens to the photon 's energy ? light frequency and the threshold frequency $ \nu_0 $ we can think of the incident light as a stream of photons with an energy determined by the light frequency . when a photon hits the metal surface , the photon 's energy is absorbed by an electron in the metal . the graphic below illustrates the relationship between light frequency and the kinetic energy of ejected electrons . the scientists observed that if the incident light had a frequency less than a minimum frequency $ \nu_0 $ , then no electrons were ejected regardless of the light amplitude . this minimum frequency is also called the threshold frequency , and the value of $ \nu_0 $ depends on the metal . for frequencies greater than $ \nu_0 $ , electrons would be ejected from the metal . furthermore , the kinetic energy of the photoelectrons was proportional to the light frequency . the relationship between photoelectron kinetic energy and light frequency is shown in graph ( a ) below . because the light amplitude was kept constant as the light frequency increased , the number of photons being absorbed by the metal remained constant . thus , the rate at which electrons were ejected from the metal ( or the electric current ) remained constant as well . the relationship between electron current and light frequency is illustrated in graph ( b ) above . is n't there more math somewhere ? we can analyze the frequency relationship using the law of conservation of energy . the total energy of the incoming photon , $ \text { e } \text { photon } $ , must be equal to the kinetic energy of the ejected electron , $ \text { ke } { \text { electron } } $ , plus the energy required to eject the electron from the metal . the energy required to free the electron from a particular metal is also called the metal 's work function , which is represented by the symbol $ \phi $ ( in units of $ \text j $ ) : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ like the threshold frequency $ \nu_0 $ , the value of $ \phi $ also changes depending on the metal . we can now write the energy of the photon in terms of the light frequency using planck 's equation : $ \text { e } \text { photon } =h\nu=\text { ke } \text { electron } +\phi $ rearranging this equation in terms of the electron 's kinetic energy , we get : $ \text { ke } _\text { electron } =h\nu-\phi $ we can see that kinetic energy of the photoelectron increases linearly with $ \nu $ as long as the photon energy is greater than the work function $ \phi $ , which is exactly the relationship shown in graph ( a ) above . we can also use this equation to find the photoelectron velocity $ \text v $ , which is related to $ \text { ke } _\text { electron } $ as follows : $ \text { ke } _\text { electron } =h\nu-\phi=\dfrac { 1 } { 2 } m_e\text v^2 $ where $ m_e $ is the rest mass of an electron , $ 9.1094 \times 10^ { -31 } \ , \text { kg } $ . exploring the wave amplitude trends in terms of photons , higher amplitude light means more photons hitting the metal surface . this results in more electrons ejected over a given time period . as long as the light frequency is greater than $ \nu_0 $ , increasing the light amplitude will cause the electron current to increase proportionally as shown in graph ( a ) below . since increasing the light amplitude has no effect on the energy of the incoming photon , the photoelectron kinetic energy remains constant as the light amplitude is increased ( see graph ( b ) above ) . if we try to explain this result using our dock-and-beach-balls analogy , the relationship in graph ( b ) indicates that no matter the height of the wave hitting the dock $ - $ whether it 's a tiny swell , or a huge tsunami $ - $ the individual beach balls would be launched off the dock with the exact same speed ! thus , our intuition and analogy do n't do a very good job of explaining these particular experiments . example $ 1 $ : the photoelectric effect for copper the work function of copper metal is $ \phi=7.53\times10^ { -19 } \text { j } $ . if we shine light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ on copper metal , will the photoelectric effect be observed ? in order to eject electrons , we need the energy of the photons to be greater than the work function of copper . we can use planck 's equation to calculate the energy of the photon , $ \text { e } _ { \text { photon } } $ : $ \begin { align } \text { e } _\text { photon } & amp ; = h\nu \ & amp ; = ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) ( 3.0\times10^ { 16 } \text { hz } ) ~~~~\text { plug in values for $ h $ and $ \nu $ } \ & amp ; = 2.0\times10^ { -17 } \text { j } \end { align } $ if we compare our calculated photon energy , $ \text { e } _\text { photon } $ , to copper 's work function , we see that the photon energy is greater than $ \phi $ : $ ~2.0\times10^ { -17 } \text { j } ~ & gt ; ~7.53\times10^ { -19 } \text { j } $ $ ~~~~~~~~\text { e } _\text { photon } ~~~~~~~~~~~~~~~~~~~\phi $ thus , we would expect to see photoelectrons ejected from the copper . next , we will calculate the kinetic energy of the photoelectrons . example $ 2 $ : calculating the kinetic energy of a photoelectron what is the kinetic energy of the photoelectrons ejected from the copper by the light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ ? we can calculate the kinetic energy of the photoelectron using the equation that relates $ \text { ke } \text { electron } $ to the energy of the photon , $ \text { e } \text { photon } $ , and the work function , $ \phi $ : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ since we want to know $ \text { ke } _\text { electron } $ , we can start by rearranging the equation so that we will be solving for the kinetic energy of the electron : $ \text { ke } \text { electron } =\text { e } \text { photon } -\phi $ now we can insert our known values for $ \text { e } _\text { photon } $ and $ \phi $ from example 1 : $ \text { ke } _\text { electron } = ( 2.0\times10^ { -17 } \text { j } ) - ( 7.53\times10^ { -19 } \text { j } ) =1.9\times10^ { -17 } \text { j } $ therefore , each photoelectron has a kinetic energy of $ 1.9\times10^ { -17 } \text { j } $ . summary based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a specific metal surface . the energy of the incident photon must be equal to the sum of the work function and the kinetic energy of a photoelectron : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ try it ! when we shine light with a frequency of $ 6.20 \times 10^ { 14 } \ , \text { hz } $ on a mystery metal , we observe the ejected electrons have a kinetic energy of $ 3.28\times 10^ { -20 } \ , \text j $ . some possible candidates for the mystery metal are shown in the table below : metal | work function $ \phi $ ( joules , $ \text j $ ) : - : | : - : calcium , $ \text { ca } $ | $ 4.60\times 10^ { -19 } $ tin , $ \text { sn } $ | $ 7.08\times 10^ { -19 } $ sodium , $ \text { na } $ | $ 3.78\times 10^ { -19 } $ hafnium , $ \text { hf } $ | $ 6.25\times 10^ { -19 } $ samarium , $ \text { sm } $ | $ 4.33\times 10^ { -19 } $ based on this information , what is the most likely identity of our mystery metal ?
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concept check : as the wavelength of a photon increases , what happens to the photon 's energy ? light frequency and the threshold frequency $ \nu_0 $ we can think of the incident light as a stream of photons with an energy determined by the light frequency . when a photon hits the metal surface , the photon 's energy is absorbed by an electron in the metal .
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i have seen graphs that show the photocurrent from higher frequency light , less than the photocurrent from lower frequency , why is that happening ?
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key points based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . contrary to the predictions , experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of particles called photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a metal surface , and the value of $ \phi $ depends on the metal . the energy of the incident photon must be equal to the sum of the metal 's work function and the photoelectron kinetic energy : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ introduction : what is the photoelectric effect ? when light shines on a metal , electrons can be ejected from the surface of the metal in a phenomenon known as the photoelectric effect . this process is also often referred to as photoemission , and the electrons that are ejected from the metal are called photoelectrons . in terms of their behavior and their properties , photoelectrons are no different from other electrons . the prefix , photo- , simply tells us that the electrons have been ejected from a metal surface by incident light . in this article , we will discuss how 19th century physicists attempted ( but failed ! ) to explain the photoelectric effect using classical physics . this ultimately led to the development of the modern description of electromagnetic radiation , which has both wave-like and particle-like properties . predictions based on light as a wave to explain the photoelectric effect , 19th-century physicists theorized that the oscillating electric field of the incoming light wave was heating the electrons and causing them to vibrate , eventually freeing them from the metal surface . this hypothesis was based on the assumption that light traveled purely as a wave through space . ( see this article for more information about the basic properties of light . ) scientists also believed that the energy of the light wave was proportional to its brightness , which is related to the wave 's amplitude . in order to test their hypotheses , they performed experiments to look at the effect of light amplitude and frequency on the rate of electron ejection , as well as the kinetic energy of the photoelectrons . based on the classical description of light as a wave , they made the following predictions : the kinetic energy of emitted photoelectrons should increase with the light amplitude . the rate of electron emission , which is proportional to the measured electric current , should increase as the light frequency is increased . to help us understand why they made these predictions , we can compare a light wave to a water wave . imagine some beach balls sitting on a dock that extends out into the ocean . the dock represents a metal surface , the beach balls represent electrons , and the ocean waves represent light waves . if a single large wave were to shake the dock , we would expect the energy from the big wave would send the beach balls flying off the dock with much more kinetic energy compared to a single , small wave . this is also what physicists believed would happen if the light intensity was increased . light amplitude was expected to be proportional to the light energy , so higher amplitude light was predicted to result in photoelectrons with more kinetic energy . classical physicists also predicted that increasing the frequency of light waves ( at a constant amplitude ) would increase the rate of electrons being ejected , and thus increase the measured electric current . using our beach ball analogy , we would expect waves hitting the dock more frequently would result in more beach balls being knocked off the dock compared to the same sized waves hitting the dock less often . now that we know what physicists thought would happen , let 's look at what they actually observed experimentally ! when intuition fails : photons to the rescue ! when experiments were performed to look at the effect of light amplitude and frequency , the following results were observed : the kinetic energy of photoelectrons increases with light frequency . electric current remains constant as light frequency increases . electric current increases with light amplitude . the kinetic energy of photoelectrons remains constant as light amplitude increases . these results were completely at odds with the predictions based on the classical description of light as a wave ! in order to explain what was happening , it turned out that an entirely new model of light was needed . that model was developed by albert einstein , who proposed that light sometimes behaved as particles of electromagnetic energy which we now call photons . the energy of a photon could be calculated using planck 's equation : $ \text { e } _ { \text { photon } } =h\nu $ where $ \text { e } _ { \text { photon } } $ is the energy of a photon in joules ( $ \text { j } $ ) , $ h $ is planck 's constant $ ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) $ , and $ \nu $ is the frequency of the light in $ \text { hz } $ . according to planck 's equation , the energy of a photon is proportional to the frequency of the light , $ \nu $ . the amplitude of the light is then proportional to the number of photons with a given frequency . concept check : as the wavelength of a photon increases , what happens to the photon 's energy ? light frequency and the threshold frequency $ \nu_0 $ we can think of the incident light as a stream of photons with an energy determined by the light frequency . when a photon hits the metal surface , the photon 's energy is absorbed by an electron in the metal . the graphic below illustrates the relationship between light frequency and the kinetic energy of ejected electrons . the scientists observed that if the incident light had a frequency less than a minimum frequency $ \nu_0 $ , then no electrons were ejected regardless of the light amplitude . this minimum frequency is also called the threshold frequency , and the value of $ \nu_0 $ depends on the metal . for frequencies greater than $ \nu_0 $ , electrons would be ejected from the metal . furthermore , the kinetic energy of the photoelectrons was proportional to the light frequency . the relationship between photoelectron kinetic energy and light frequency is shown in graph ( a ) below . because the light amplitude was kept constant as the light frequency increased , the number of photons being absorbed by the metal remained constant . thus , the rate at which electrons were ejected from the metal ( or the electric current ) remained constant as well . the relationship between electron current and light frequency is illustrated in graph ( b ) above . is n't there more math somewhere ? we can analyze the frequency relationship using the law of conservation of energy . the total energy of the incoming photon , $ \text { e } \text { photon } $ , must be equal to the kinetic energy of the ejected electron , $ \text { ke } { \text { electron } } $ , plus the energy required to eject the electron from the metal . the energy required to free the electron from a particular metal is also called the metal 's work function , which is represented by the symbol $ \phi $ ( in units of $ \text j $ ) : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ like the threshold frequency $ \nu_0 $ , the value of $ \phi $ also changes depending on the metal . we can now write the energy of the photon in terms of the light frequency using planck 's equation : $ \text { e } \text { photon } =h\nu=\text { ke } \text { electron } +\phi $ rearranging this equation in terms of the electron 's kinetic energy , we get : $ \text { ke } _\text { electron } =h\nu-\phi $ we can see that kinetic energy of the photoelectron increases linearly with $ \nu $ as long as the photon energy is greater than the work function $ \phi $ , which is exactly the relationship shown in graph ( a ) above . we can also use this equation to find the photoelectron velocity $ \text v $ , which is related to $ \text { ke } _\text { electron } $ as follows : $ \text { ke } _\text { electron } =h\nu-\phi=\dfrac { 1 } { 2 } m_e\text v^2 $ where $ m_e $ is the rest mass of an electron , $ 9.1094 \times 10^ { -31 } \ , \text { kg } $ . exploring the wave amplitude trends in terms of photons , higher amplitude light means more photons hitting the metal surface . this results in more electrons ejected over a given time period . as long as the light frequency is greater than $ \nu_0 $ , increasing the light amplitude will cause the electron current to increase proportionally as shown in graph ( a ) below . since increasing the light amplitude has no effect on the energy of the incoming photon , the photoelectron kinetic energy remains constant as the light amplitude is increased ( see graph ( b ) above ) . if we try to explain this result using our dock-and-beach-balls analogy , the relationship in graph ( b ) indicates that no matter the height of the wave hitting the dock $ - $ whether it 's a tiny swell , or a huge tsunami $ - $ the individual beach balls would be launched off the dock with the exact same speed ! thus , our intuition and analogy do n't do a very good job of explaining these particular experiments . example $ 1 $ : the photoelectric effect for copper the work function of copper metal is $ \phi=7.53\times10^ { -19 } \text { j } $ . if we shine light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ on copper metal , will the photoelectric effect be observed ? in order to eject electrons , we need the energy of the photons to be greater than the work function of copper . we can use planck 's equation to calculate the energy of the photon , $ \text { e } _ { \text { photon } } $ : $ \begin { align } \text { e } _\text { photon } & amp ; = h\nu \ & amp ; = ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) ( 3.0\times10^ { 16 } \text { hz } ) ~~~~\text { plug in values for $ h $ and $ \nu $ } \ & amp ; = 2.0\times10^ { -17 } \text { j } \end { align } $ if we compare our calculated photon energy , $ \text { e } _\text { photon } $ , to copper 's work function , we see that the photon energy is greater than $ \phi $ : $ ~2.0\times10^ { -17 } \text { j } ~ & gt ; ~7.53\times10^ { -19 } \text { j } $ $ ~~~~~~~~\text { e } _\text { photon } ~~~~~~~~~~~~~~~~~~~\phi $ thus , we would expect to see photoelectrons ejected from the copper . next , we will calculate the kinetic energy of the photoelectrons . example $ 2 $ : calculating the kinetic energy of a photoelectron what is the kinetic energy of the photoelectrons ejected from the copper by the light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ ? we can calculate the kinetic energy of the photoelectron using the equation that relates $ \text { ke } \text { electron } $ to the energy of the photon , $ \text { e } \text { photon } $ , and the work function , $ \phi $ : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ since we want to know $ \text { ke } _\text { electron } $ , we can start by rearranging the equation so that we will be solving for the kinetic energy of the electron : $ \text { ke } \text { electron } =\text { e } \text { photon } -\phi $ now we can insert our known values for $ \text { e } _\text { photon } $ and $ \phi $ from example 1 : $ \text { ke } _\text { electron } = ( 2.0\times10^ { -17 } \text { j } ) - ( 7.53\times10^ { -19 } \text { j } ) =1.9\times10^ { -17 } \text { j } $ therefore , each photoelectron has a kinetic energy of $ 1.9\times10^ { -17 } \text { j } $ . summary based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a specific metal surface . the energy of the incident photon must be equal to the sum of the work function and the kinetic energy of a photoelectron : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ try it ! when we shine light with a frequency of $ 6.20 \times 10^ { 14 } \ , \text { hz } $ on a mystery metal , we observe the ejected electrons have a kinetic energy of $ 3.28\times 10^ { -20 } \ , \text j $ . some possible candidates for the mystery metal are shown in the table below : metal | work function $ \phi $ ( joules , $ \text j $ ) : - : | : - : calcium , $ \text { ca } $ | $ 4.60\times 10^ { -19 } $ tin , $ \text { sn } $ | $ 7.08\times 10^ { -19 } $ sodium , $ \text { na } $ | $ 3.78\times 10^ { -19 } $ hafnium , $ \text { hf } $ | $ 6.25\times 10^ { -19 } $ samarium , $ \text { sm } $ | $ 4.33\times 10^ { -19 } $ based on this information , what is the most likely identity of our mystery metal ?
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the amplitude of the light is then proportional to the number of photons with a given frequency . concept check : as the wavelength of a photon increases , what happens to the photon 's energy ? light frequency and the threshold frequency $ \nu_0 $ we can think of the incident light as a stream of photons with an energy determined by the light frequency .
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what is the size of a photon ?
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key points based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . contrary to the predictions , experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of particles called photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a metal surface , and the value of $ \phi $ depends on the metal . the energy of the incident photon must be equal to the sum of the metal 's work function and the photoelectron kinetic energy : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ introduction : what is the photoelectric effect ? when light shines on a metal , electrons can be ejected from the surface of the metal in a phenomenon known as the photoelectric effect . this process is also often referred to as photoemission , and the electrons that are ejected from the metal are called photoelectrons . in terms of their behavior and their properties , photoelectrons are no different from other electrons . the prefix , photo- , simply tells us that the electrons have been ejected from a metal surface by incident light . in this article , we will discuss how 19th century physicists attempted ( but failed ! ) to explain the photoelectric effect using classical physics . this ultimately led to the development of the modern description of electromagnetic radiation , which has both wave-like and particle-like properties . predictions based on light as a wave to explain the photoelectric effect , 19th-century physicists theorized that the oscillating electric field of the incoming light wave was heating the electrons and causing them to vibrate , eventually freeing them from the metal surface . this hypothesis was based on the assumption that light traveled purely as a wave through space . ( see this article for more information about the basic properties of light . ) scientists also believed that the energy of the light wave was proportional to its brightness , which is related to the wave 's amplitude . in order to test their hypotheses , they performed experiments to look at the effect of light amplitude and frequency on the rate of electron ejection , as well as the kinetic energy of the photoelectrons . based on the classical description of light as a wave , they made the following predictions : the kinetic energy of emitted photoelectrons should increase with the light amplitude . the rate of electron emission , which is proportional to the measured electric current , should increase as the light frequency is increased . to help us understand why they made these predictions , we can compare a light wave to a water wave . imagine some beach balls sitting on a dock that extends out into the ocean . the dock represents a metal surface , the beach balls represent electrons , and the ocean waves represent light waves . if a single large wave were to shake the dock , we would expect the energy from the big wave would send the beach balls flying off the dock with much more kinetic energy compared to a single , small wave . this is also what physicists believed would happen if the light intensity was increased . light amplitude was expected to be proportional to the light energy , so higher amplitude light was predicted to result in photoelectrons with more kinetic energy . classical physicists also predicted that increasing the frequency of light waves ( at a constant amplitude ) would increase the rate of electrons being ejected , and thus increase the measured electric current . using our beach ball analogy , we would expect waves hitting the dock more frequently would result in more beach balls being knocked off the dock compared to the same sized waves hitting the dock less often . now that we know what physicists thought would happen , let 's look at what they actually observed experimentally ! when intuition fails : photons to the rescue ! when experiments were performed to look at the effect of light amplitude and frequency , the following results were observed : the kinetic energy of photoelectrons increases with light frequency . electric current remains constant as light frequency increases . electric current increases with light amplitude . the kinetic energy of photoelectrons remains constant as light amplitude increases . these results were completely at odds with the predictions based on the classical description of light as a wave ! in order to explain what was happening , it turned out that an entirely new model of light was needed . that model was developed by albert einstein , who proposed that light sometimes behaved as particles of electromagnetic energy which we now call photons . the energy of a photon could be calculated using planck 's equation : $ \text { e } _ { \text { photon } } =h\nu $ where $ \text { e } _ { \text { photon } } $ is the energy of a photon in joules ( $ \text { j } $ ) , $ h $ is planck 's constant $ ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) $ , and $ \nu $ is the frequency of the light in $ \text { hz } $ . according to planck 's equation , the energy of a photon is proportional to the frequency of the light , $ \nu $ . the amplitude of the light is then proportional to the number of photons with a given frequency . concept check : as the wavelength of a photon increases , what happens to the photon 's energy ? light frequency and the threshold frequency $ \nu_0 $ we can think of the incident light as a stream of photons with an energy determined by the light frequency . when a photon hits the metal surface , the photon 's energy is absorbed by an electron in the metal . the graphic below illustrates the relationship between light frequency and the kinetic energy of ejected electrons . the scientists observed that if the incident light had a frequency less than a minimum frequency $ \nu_0 $ , then no electrons were ejected regardless of the light amplitude . this minimum frequency is also called the threshold frequency , and the value of $ \nu_0 $ depends on the metal . for frequencies greater than $ \nu_0 $ , electrons would be ejected from the metal . furthermore , the kinetic energy of the photoelectrons was proportional to the light frequency . the relationship between photoelectron kinetic energy and light frequency is shown in graph ( a ) below . because the light amplitude was kept constant as the light frequency increased , the number of photons being absorbed by the metal remained constant . thus , the rate at which electrons were ejected from the metal ( or the electric current ) remained constant as well . the relationship between electron current and light frequency is illustrated in graph ( b ) above . is n't there more math somewhere ? we can analyze the frequency relationship using the law of conservation of energy . the total energy of the incoming photon , $ \text { e } \text { photon } $ , must be equal to the kinetic energy of the ejected electron , $ \text { ke } { \text { electron } } $ , plus the energy required to eject the electron from the metal . the energy required to free the electron from a particular metal is also called the metal 's work function , which is represented by the symbol $ \phi $ ( in units of $ \text j $ ) : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ like the threshold frequency $ \nu_0 $ , the value of $ \phi $ also changes depending on the metal . we can now write the energy of the photon in terms of the light frequency using planck 's equation : $ \text { e } \text { photon } =h\nu=\text { ke } \text { electron } +\phi $ rearranging this equation in terms of the electron 's kinetic energy , we get : $ \text { ke } _\text { electron } =h\nu-\phi $ we can see that kinetic energy of the photoelectron increases linearly with $ \nu $ as long as the photon energy is greater than the work function $ \phi $ , which is exactly the relationship shown in graph ( a ) above . we can also use this equation to find the photoelectron velocity $ \text v $ , which is related to $ \text { ke } _\text { electron } $ as follows : $ \text { ke } _\text { electron } =h\nu-\phi=\dfrac { 1 } { 2 } m_e\text v^2 $ where $ m_e $ is the rest mass of an electron , $ 9.1094 \times 10^ { -31 } \ , \text { kg } $ . exploring the wave amplitude trends in terms of photons , higher amplitude light means more photons hitting the metal surface . this results in more electrons ejected over a given time period . as long as the light frequency is greater than $ \nu_0 $ , increasing the light amplitude will cause the electron current to increase proportionally as shown in graph ( a ) below . since increasing the light amplitude has no effect on the energy of the incoming photon , the photoelectron kinetic energy remains constant as the light amplitude is increased ( see graph ( b ) above ) . if we try to explain this result using our dock-and-beach-balls analogy , the relationship in graph ( b ) indicates that no matter the height of the wave hitting the dock $ - $ whether it 's a tiny swell , or a huge tsunami $ - $ the individual beach balls would be launched off the dock with the exact same speed ! thus , our intuition and analogy do n't do a very good job of explaining these particular experiments . example $ 1 $ : the photoelectric effect for copper the work function of copper metal is $ \phi=7.53\times10^ { -19 } \text { j } $ . if we shine light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ on copper metal , will the photoelectric effect be observed ? in order to eject electrons , we need the energy of the photons to be greater than the work function of copper . we can use planck 's equation to calculate the energy of the photon , $ \text { e } _ { \text { photon } } $ : $ \begin { align } \text { e } _\text { photon } & amp ; = h\nu \ & amp ; = ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) ( 3.0\times10^ { 16 } \text { hz } ) ~~~~\text { plug in values for $ h $ and $ \nu $ } \ & amp ; = 2.0\times10^ { -17 } \text { j } \end { align } $ if we compare our calculated photon energy , $ \text { e } _\text { photon } $ , to copper 's work function , we see that the photon energy is greater than $ \phi $ : $ ~2.0\times10^ { -17 } \text { j } ~ & gt ; ~7.53\times10^ { -19 } \text { j } $ $ ~~~~~~~~\text { e } _\text { photon } ~~~~~~~~~~~~~~~~~~~\phi $ thus , we would expect to see photoelectrons ejected from the copper . next , we will calculate the kinetic energy of the photoelectrons . example $ 2 $ : calculating the kinetic energy of a photoelectron what is the kinetic energy of the photoelectrons ejected from the copper by the light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ ? we can calculate the kinetic energy of the photoelectron using the equation that relates $ \text { ke } \text { electron } $ to the energy of the photon , $ \text { e } \text { photon } $ , and the work function , $ \phi $ : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ since we want to know $ \text { ke } _\text { electron } $ , we can start by rearranging the equation so that we will be solving for the kinetic energy of the electron : $ \text { ke } \text { electron } =\text { e } \text { photon } -\phi $ now we can insert our known values for $ \text { e } _\text { photon } $ and $ \phi $ from example 1 : $ \text { ke } _\text { electron } = ( 2.0\times10^ { -17 } \text { j } ) - ( 7.53\times10^ { -19 } \text { j } ) =1.9\times10^ { -17 } \text { j } $ therefore , each photoelectron has a kinetic energy of $ 1.9\times10^ { -17 } \text { j } $ . summary based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a specific metal surface . the energy of the incident photon must be equal to the sum of the work function and the kinetic energy of a photoelectron : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ try it ! when we shine light with a frequency of $ 6.20 \times 10^ { 14 } \ , \text { hz } $ on a mystery metal , we observe the ejected electrons have a kinetic energy of $ 3.28\times 10^ { -20 } \ , \text j $ . some possible candidates for the mystery metal are shown in the table below : metal | work function $ \phi $ ( joules , $ \text j $ ) : - : | : - : calcium , $ \text { ca } $ | $ 4.60\times 10^ { -19 } $ tin , $ \text { sn } $ | $ 7.08\times 10^ { -19 } $ sodium , $ \text { na } $ | $ 3.78\times 10^ { -19 } $ hafnium , $ \text { hf } $ | $ 6.25\times 10^ { -19 } $ samarium , $ \text { sm } $ | $ 4.33\times 10^ { -19 } $ based on this information , what is the most likely identity of our mystery metal ?
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we can also use this equation to find the photoelectron velocity $ \text v $ , which is related to $ \text { ke } _\text { electron } $ as follows : $ \text { ke } _\text { electron } =h\nu-\phi=\dfrac { 1 } { 2 } m_e\text v^2 $ where $ m_e $ is the rest mass of an electron , $ 9.1094 \times 10^ { -31 } \ , \text { kg } $ . exploring the wave amplitude trends in terms of photons , higher amplitude light means more photons hitting the metal surface . this results in more electrons ejected over a given time period .
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what is the relation between photons , frequency and amplitude ?
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key points based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . contrary to the predictions , experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of particles called photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a metal surface , and the value of $ \phi $ depends on the metal . the energy of the incident photon must be equal to the sum of the metal 's work function and the photoelectron kinetic energy : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ introduction : what is the photoelectric effect ? when light shines on a metal , electrons can be ejected from the surface of the metal in a phenomenon known as the photoelectric effect . this process is also often referred to as photoemission , and the electrons that are ejected from the metal are called photoelectrons . in terms of their behavior and their properties , photoelectrons are no different from other electrons . the prefix , photo- , simply tells us that the electrons have been ejected from a metal surface by incident light . in this article , we will discuss how 19th century physicists attempted ( but failed ! ) to explain the photoelectric effect using classical physics . this ultimately led to the development of the modern description of electromagnetic radiation , which has both wave-like and particle-like properties . predictions based on light as a wave to explain the photoelectric effect , 19th-century physicists theorized that the oscillating electric field of the incoming light wave was heating the electrons and causing them to vibrate , eventually freeing them from the metal surface . this hypothesis was based on the assumption that light traveled purely as a wave through space . ( see this article for more information about the basic properties of light . ) scientists also believed that the energy of the light wave was proportional to its brightness , which is related to the wave 's amplitude . in order to test their hypotheses , they performed experiments to look at the effect of light amplitude and frequency on the rate of electron ejection , as well as the kinetic energy of the photoelectrons . based on the classical description of light as a wave , they made the following predictions : the kinetic energy of emitted photoelectrons should increase with the light amplitude . the rate of electron emission , which is proportional to the measured electric current , should increase as the light frequency is increased . to help us understand why they made these predictions , we can compare a light wave to a water wave . imagine some beach balls sitting on a dock that extends out into the ocean . the dock represents a metal surface , the beach balls represent electrons , and the ocean waves represent light waves . if a single large wave were to shake the dock , we would expect the energy from the big wave would send the beach balls flying off the dock with much more kinetic energy compared to a single , small wave . this is also what physicists believed would happen if the light intensity was increased . light amplitude was expected to be proportional to the light energy , so higher amplitude light was predicted to result in photoelectrons with more kinetic energy . classical physicists also predicted that increasing the frequency of light waves ( at a constant amplitude ) would increase the rate of electrons being ejected , and thus increase the measured electric current . using our beach ball analogy , we would expect waves hitting the dock more frequently would result in more beach balls being knocked off the dock compared to the same sized waves hitting the dock less often . now that we know what physicists thought would happen , let 's look at what they actually observed experimentally ! when intuition fails : photons to the rescue ! when experiments were performed to look at the effect of light amplitude and frequency , the following results were observed : the kinetic energy of photoelectrons increases with light frequency . electric current remains constant as light frequency increases . electric current increases with light amplitude . the kinetic energy of photoelectrons remains constant as light amplitude increases . these results were completely at odds with the predictions based on the classical description of light as a wave ! in order to explain what was happening , it turned out that an entirely new model of light was needed . that model was developed by albert einstein , who proposed that light sometimes behaved as particles of electromagnetic energy which we now call photons . the energy of a photon could be calculated using planck 's equation : $ \text { e } _ { \text { photon } } =h\nu $ where $ \text { e } _ { \text { photon } } $ is the energy of a photon in joules ( $ \text { j } $ ) , $ h $ is planck 's constant $ ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) $ , and $ \nu $ is the frequency of the light in $ \text { hz } $ . according to planck 's equation , the energy of a photon is proportional to the frequency of the light , $ \nu $ . the amplitude of the light is then proportional to the number of photons with a given frequency . concept check : as the wavelength of a photon increases , what happens to the photon 's energy ? light frequency and the threshold frequency $ \nu_0 $ we can think of the incident light as a stream of photons with an energy determined by the light frequency . when a photon hits the metal surface , the photon 's energy is absorbed by an electron in the metal . the graphic below illustrates the relationship between light frequency and the kinetic energy of ejected electrons . the scientists observed that if the incident light had a frequency less than a minimum frequency $ \nu_0 $ , then no electrons were ejected regardless of the light amplitude . this minimum frequency is also called the threshold frequency , and the value of $ \nu_0 $ depends on the metal . for frequencies greater than $ \nu_0 $ , electrons would be ejected from the metal . furthermore , the kinetic energy of the photoelectrons was proportional to the light frequency . the relationship between photoelectron kinetic energy and light frequency is shown in graph ( a ) below . because the light amplitude was kept constant as the light frequency increased , the number of photons being absorbed by the metal remained constant . thus , the rate at which electrons were ejected from the metal ( or the electric current ) remained constant as well . the relationship between electron current and light frequency is illustrated in graph ( b ) above . is n't there more math somewhere ? we can analyze the frequency relationship using the law of conservation of energy . the total energy of the incoming photon , $ \text { e } \text { photon } $ , must be equal to the kinetic energy of the ejected electron , $ \text { ke } { \text { electron } } $ , plus the energy required to eject the electron from the metal . the energy required to free the electron from a particular metal is also called the metal 's work function , which is represented by the symbol $ \phi $ ( in units of $ \text j $ ) : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ like the threshold frequency $ \nu_0 $ , the value of $ \phi $ also changes depending on the metal . we can now write the energy of the photon in terms of the light frequency using planck 's equation : $ \text { e } \text { photon } =h\nu=\text { ke } \text { electron } +\phi $ rearranging this equation in terms of the electron 's kinetic energy , we get : $ \text { ke } _\text { electron } =h\nu-\phi $ we can see that kinetic energy of the photoelectron increases linearly with $ \nu $ as long as the photon energy is greater than the work function $ \phi $ , which is exactly the relationship shown in graph ( a ) above . we can also use this equation to find the photoelectron velocity $ \text v $ , which is related to $ \text { ke } _\text { electron } $ as follows : $ \text { ke } _\text { electron } =h\nu-\phi=\dfrac { 1 } { 2 } m_e\text v^2 $ where $ m_e $ is the rest mass of an electron , $ 9.1094 \times 10^ { -31 } \ , \text { kg } $ . exploring the wave amplitude trends in terms of photons , higher amplitude light means more photons hitting the metal surface . this results in more electrons ejected over a given time period . as long as the light frequency is greater than $ \nu_0 $ , increasing the light amplitude will cause the electron current to increase proportionally as shown in graph ( a ) below . since increasing the light amplitude has no effect on the energy of the incoming photon , the photoelectron kinetic energy remains constant as the light amplitude is increased ( see graph ( b ) above ) . if we try to explain this result using our dock-and-beach-balls analogy , the relationship in graph ( b ) indicates that no matter the height of the wave hitting the dock $ - $ whether it 's a tiny swell , or a huge tsunami $ - $ the individual beach balls would be launched off the dock with the exact same speed ! thus , our intuition and analogy do n't do a very good job of explaining these particular experiments . example $ 1 $ : the photoelectric effect for copper the work function of copper metal is $ \phi=7.53\times10^ { -19 } \text { j } $ . if we shine light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ on copper metal , will the photoelectric effect be observed ? in order to eject electrons , we need the energy of the photons to be greater than the work function of copper . we can use planck 's equation to calculate the energy of the photon , $ \text { e } _ { \text { photon } } $ : $ \begin { align } \text { e } _\text { photon } & amp ; = h\nu \ & amp ; = ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) ( 3.0\times10^ { 16 } \text { hz } ) ~~~~\text { plug in values for $ h $ and $ \nu $ } \ & amp ; = 2.0\times10^ { -17 } \text { j } \end { align } $ if we compare our calculated photon energy , $ \text { e } _\text { photon } $ , to copper 's work function , we see that the photon energy is greater than $ \phi $ : $ ~2.0\times10^ { -17 } \text { j } ~ & gt ; ~7.53\times10^ { -19 } \text { j } $ $ ~~~~~~~~\text { e } _\text { photon } ~~~~~~~~~~~~~~~~~~~\phi $ thus , we would expect to see photoelectrons ejected from the copper . next , we will calculate the kinetic energy of the photoelectrons . example $ 2 $ : calculating the kinetic energy of a photoelectron what is the kinetic energy of the photoelectrons ejected from the copper by the light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ ? we can calculate the kinetic energy of the photoelectron using the equation that relates $ \text { ke } \text { electron } $ to the energy of the photon , $ \text { e } \text { photon } $ , and the work function , $ \phi $ : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ since we want to know $ \text { ke } _\text { electron } $ , we can start by rearranging the equation so that we will be solving for the kinetic energy of the electron : $ \text { ke } \text { electron } =\text { e } \text { photon } -\phi $ now we can insert our known values for $ \text { e } _\text { photon } $ and $ \phi $ from example 1 : $ \text { ke } _\text { electron } = ( 2.0\times10^ { -17 } \text { j } ) - ( 7.53\times10^ { -19 } \text { j } ) =1.9\times10^ { -17 } \text { j } $ therefore , each photoelectron has a kinetic energy of $ 1.9\times10^ { -17 } \text { j } $ . summary based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a specific metal surface . the energy of the incident photon must be equal to the sum of the work function and the kinetic energy of a photoelectron : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ try it ! when we shine light with a frequency of $ 6.20 \times 10^ { 14 } \ , \text { hz } $ on a mystery metal , we observe the ejected electrons have a kinetic energy of $ 3.28\times 10^ { -20 } \ , \text j $ . some possible candidates for the mystery metal are shown in the table below : metal | work function $ \phi $ ( joules , $ \text j $ ) : - : | : - : calcium , $ \text { ca } $ | $ 4.60\times 10^ { -19 } $ tin , $ \text { sn } $ | $ 7.08\times 10^ { -19 } $ sodium , $ \text { na } $ | $ 3.78\times 10^ { -19 } $ hafnium , $ \text { hf } $ | $ 6.25\times 10^ { -19 } $ samarium , $ \text { sm } $ | $ 4.33\times 10^ { -19 } $ based on this information , what is the most likely identity of our mystery metal ?
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the amplitude of the light is then proportional to the number of photons with a given frequency . concept check : as the wavelength of a photon increases , what happens to the photon 's energy ? light frequency and the threshold frequency $ \nu_0 $ we can think of the incident light as a stream of photons with an energy determined by the light frequency .
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does a photon has mass ?
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key points based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . contrary to the predictions , experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of particles called photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a metal surface , and the value of $ \phi $ depends on the metal . the energy of the incident photon must be equal to the sum of the metal 's work function and the photoelectron kinetic energy : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ introduction : what is the photoelectric effect ? when light shines on a metal , electrons can be ejected from the surface of the metal in a phenomenon known as the photoelectric effect . this process is also often referred to as photoemission , and the electrons that are ejected from the metal are called photoelectrons . in terms of their behavior and their properties , photoelectrons are no different from other electrons . the prefix , photo- , simply tells us that the electrons have been ejected from a metal surface by incident light . in this article , we will discuss how 19th century physicists attempted ( but failed ! ) to explain the photoelectric effect using classical physics . this ultimately led to the development of the modern description of electromagnetic radiation , which has both wave-like and particle-like properties . predictions based on light as a wave to explain the photoelectric effect , 19th-century physicists theorized that the oscillating electric field of the incoming light wave was heating the electrons and causing them to vibrate , eventually freeing them from the metal surface . this hypothesis was based on the assumption that light traveled purely as a wave through space . ( see this article for more information about the basic properties of light . ) scientists also believed that the energy of the light wave was proportional to its brightness , which is related to the wave 's amplitude . in order to test their hypotheses , they performed experiments to look at the effect of light amplitude and frequency on the rate of electron ejection , as well as the kinetic energy of the photoelectrons . based on the classical description of light as a wave , they made the following predictions : the kinetic energy of emitted photoelectrons should increase with the light amplitude . the rate of electron emission , which is proportional to the measured electric current , should increase as the light frequency is increased . to help us understand why they made these predictions , we can compare a light wave to a water wave . imagine some beach balls sitting on a dock that extends out into the ocean . the dock represents a metal surface , the beach balls represent electrons , and the ocean waves represent light waves . if a single large wave were to shake the dock , we would expect the energy from the big wave would send the beach balls flying off the dock with much more kinetic energy compared to a single , small wave . this is also what physicists believed would happen if the light intensity was increased . light amplitude was expected to be proportional to the light energy , so higher amplitude light was predicted to result in photoelectrons with more kinetic energy . classical physicists also predicted that increasing the frequency of light waves ( at a constant amplitude ) would increase the rate of electrons being ejected , and thus increase the measured electric current . using our beach ball analogy , we would expect waves hitting the dock more frequently would result in more beach balls being knocked off the dock compared to the same sized waves hitting the dock less often . now that we know what physicists thought would happen , let 's look at what they actually observed experimentally ! when intuition fails : photons to the rescue ! when experiments were performed to look at the effect of light amplitude and frequency , the following results were observed : the kinetic energy of photoelectrons increases with light frequency . electric current remains constant as light frequency increases . electric current increases with light amplitude . the kinetic energy of photoelectrons remains constant as light amplitude increases . these results were completely at odds with the predictions based on the classical description of light as a wave ! in order to explain what was happening , it turned out that an entirely new model of light was needed . that model was developed by albert einstein , who proposed that light sometimes behaved as particles of electromagnetic energy which we now call photons . the energy of a photon could be calculated using planck 's equation : $ \text { e } _ { \text { photon } } =h\nu $ where $ \text { e } _ { \text { photon } } $ is the energy of a photon in joules ( $ \text { j } $ ) , $ h $ is planck 's constant $ ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) $ , and $ \nu $ is the frequency of the light in $ \text { hz } $ . according to planck 's equation , the energy of a photon is proportional to the frequency of the light , $ \nu $ . the amplitude of the light is then proportional to the number of photons with a given frequency . concept check : as the wavelength of a photon increases , what happens to the photon 's energy ? light frequency and the threshold frequency $ \nu_0 $ we can think of the incident light as a stream of photons with an energy determined by the light frequency . when a photon hits the metal surface , the photon 's energy is absorbed by an electron in the metal . the graphic below illustrates the relationship between light frequency and the kinetic energy of ejected electrons . the scientists observed that if the incident light had a frequency less than a minimum frequency $ \nu_0 $ , then no electrons were ejected regardless of the light amplitude . this minimum frequency is also called the threshold frequency , and the value of $ \nu_0 $ depends on the metal . for frequencies greater than $ \nu_0 $ , electrons would be ejected from the metal . furthermore , the kinetic energy of the photoelectrons was proportional to the light frequency . the relationship between photoelectron kinetic energy and light frequency is shown in graph ( a ) below . because the light amplitude was kept constant as the light frequency increased , the number of photons being absorbed by the metal remained constant . thus , the rate at which electrons were ejected from the metal ( or the electric current ) remained constant as well . the relationship between electron current and light frequency is illustrated in graph ( b ) above . is n't there more math somewhere ? we can analyze the frequency relationship using the law of conservation of energy . the total energy of the incoming photon , $ \text { e } \text { photon } $ , must be equal to the kinetic energy of the ejected electron , $ \text { ke } { \text { electron } } $ , plus the energy required to eject the electron from the metal . the energy required to free the electron from a particular metal is also called the metal 's work function , which is represented by the symbol $ \phi $ ( in units of $ \text j $ ) : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ like the threshold frequency $ \nu_0 $ , the value of $ \phi $ also changes depending on the metal . we can now write the energy of the photon in terms of the light frequency using planck 's equation : $ \text { e } \text { photon } =h\nu=\text { ke } \text { electron } +\phi $ rearranging this equation in terms of the electron 's kinetic energy , we get : $ \text { ke } _\text { electron } =h\nu-\phi $ we can see that kinetic energy of the photoelectron increases linearly with $ \nu $ as long as the photon energy is greater than the work function $ \phi $ , which is exactly the relationship shown in graph ( a ) above . we can also use this equation to find the photoelectron velocity $ \text v $ , which is related to $ \text { ke } _\text { electron } $ as follows : $ \text { ke } _\text { electron } =h\nu-\phi=\dfrac { 1 } { 2 } m_e\text v^2 $ where $ m_e $ is the rest mass of an electron , $ 9.1094 \times 10^ { -31 } \ , \text { kg } $ . exploring the wave amplitude trends in terms of photons , higher amplitude light means more photons hitting the metal surface . this results in more electrons ejected over a given time period . as long as the light frequency is greater than $ \nu_0 $ , increasing the light amplitude will cause the electron current to increase proportionally as shown in graph ( a ) below . since increasing the light amplitude has no effect on the energy of the incoming photon , the photoelectron kinetic energy remains constant as the light amplitude is increased ( see graph ( b ) above ) . if we try to explain this result using our dock-and-beach-balls analogy , the relationship in graph ( b ) indicates that no matter the height of the wave hitting the dock $ - $ whether it 's a tiny swell , or a huge tsunami $ - $ the individual beach balls would be launched off the dock with the exact same speed ! thus , our intuition and analogy do n't do a very good job of explaining these particular experiments . example $ 1 $ : the photoelectric effect for copper the work function of copper metal is $ \phi=7.53\times10^ { -19 } \text { j } $ . if we shine light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ on copper metal , will the photoelectric effect be observed ? in order to eject electrons , we need the energy of the photons to be greater than the work function of copper . we can use planck 's equation to calculate the energy of the photon , $ \text { e } _ { \text { photon } } $ : $ \begin { align } \text { e } _\text { photon } & amp ; = h\nu \ & amp ; = ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) ( 3.0\times10^ { 16 } \text { hz } ) ~~~~\text { plug in values for $ h $ and $ \nu $ } \ & amp ; = 2.0\times10^ { -17 } \text { j } \end { align } $ if we compare our calculated photon energy , $ \text { e } _\text { photon } $ , to copper 's work function , we see that the photon energy is greater than $ \phi $ : $ ~2.0\times10^ { -17 } \text { j } ~ & gt ; ~7.53\times10^ { -19 } \text { j } $ $ ~~~~~~~~\text { e } _\text { photon } ~~~~~~~~~~~~~~~~~~~\phi $ thus , we would expect to see photoelectrons ejected from the copper . next , we will calculate the kinetic energy of the photoelectrons . example $ 2 $ : calculating the kinetic energy of a photoelectron what is the kinetic energy of the photoelectrons ejected from the copper by the light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ ? we can calculate the kinetic energy of the photoelectron using the equation that relates $ \text { ke } \text { electron } $ to the energy of the photon , $ \text { e } \text { photon } $ , and the work function , $ \phi $ : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ since we want to know $ \text { ke } _\text { electron } $ , we can start by rearranging the equation so that we will be solving for the kinetic energy of the electron : $ \text { ke } \text { electron } =\text { e } \text { photon } -\phi $ now we can insert our known values for $ \text { e } _\text { photon } $ and $ \phi $ from example 1 : $ \text { ke } _\text { electron } = ( 2.0\times10^ { -17 } \text { j } ) - ( 7.53\times10^ { -19 } \text { j } ) =1.9\times10^ { -17 } \text { j } $ therefore , each photoelectron has a kinetic energy of $ 1.9\times10^ { -17 } \text { j } $ . summary based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a specific metal surface . the energy of the incident photon must be equal to the sum of the work function and the kinetic energy of a photoelectron : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ try it ! when we shine light with a frequency of $ 6.20 \times 10^ { 14 } \ , \text { hz } $ on a mystery metal , we observe the ejected electrons have a kinetic energy of $ 3.28\times 10^ { -20 } \ , \text j $ . some possible candidates for the mystery metal are shown in the table below : metal | work function $ \phi $ ( joules , $ \text j $ ) : - : | : - : calcium , $ \text { ca } $ | $ 4.60\times 10^ { -19 } $ tin , $ \text { sn } $ | $ 7.08\times 10^ { -19 } $ sodium , $ \text { na } $ | $ 3.78\times 10^ { -19 } $ hafnium , $ \text { hf } $ | $ 6.25\times 10^ { -19 } $ samarium , $ \text { sm } $ | $ 4.33\times 10^ { -19 } $ based on this information , what is the most likely identity of our mystery metal ?
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light frequency and the threshold frequency $ \nu_0 $ we can think of the incident light as a stream of photons with an energy determined by the light frequency . when a photon hits the metal surface , the photon 's energy is absorbed by an electron in the metal . the graphic below illustrates the relationship between light frequency and the kinetic energy of ejected electrons .
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and how can a photon with no mass knock out an electron , which has a mass ?
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key points based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . contrary to the predictions , experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of particles called photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a metal surface , and the value of $ \phi $ depends on the metal . the energy of the incident photon must be equal to the sum of the metal 's work function and the photoelectron kinetic energy : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ introduction : what is the photoelectric effect ? when light shines on a metal , electrons can be ejected from the surface of the metal in a phenomenon known as the photoelectric effect . this process is also often referred to as photoemission , and the electrons that are ejected from the metal are called photoelectrons . in terms of their behavior and their properties , photoelectrons are no different from other electrons . the prefix , photo- , simply tells us that the electrons have been ejected from a metal surface by incident light . in this article , we will discuss how 19th century physicists attempted ( but failed ! ) to explain the photoelectric effect using classical physics . this ultimately led to the development of the modern description of electromagnetic radiation , which has both wave-like and particle-like properties . predictions based on light as a wave to explain the photoelectric effect , 19th-century physicists theorized that the oscillating electric field of the incoming light wave was heating the electrons and causing them to vibrate , eventually freeing them from the metal surface . this hypothesis was based on the assumption that light traveled purely as a wave through space . ( see this article for more information about the basic properties of light . ) scientists also believed that the energy of the light wave was proportional to its brightness , which is related to the wave 's amplitude . in order to test their hypotheses , they performed experiments to look at the effect of light amplitude and frequency on the rate of electron ejection , as well as the kinetic energy of the photoelectrons . based on the classical description of light as a wave , they made the following predictions : the kinetic energy of emitted photoelectrons should increase with the light amplitude . the rate of electron emission , which is proportional to the measured electric current , should increase as the light frequency is increased . to help us understand why they made these predictions , we can compare a light wave to a water wave . imagine some beach balls sitting on a dock that extends out into the ocean . the dock represents a metal surface , the beach balls represent electrons , and the ocean waves represent light waves . if a single large wave were to shake the dock , we would expect the energy from the big wave would send the beach balls flying off the dock with much more kinetic energy compared to a single , small wave . this is also what physicists believed would happen if the light intensity was increased . light amplitude was expected to be proportional to the light energy , so higher amplitude light was predicted to result in photoelectrons with more kinetic energy . classical physicists also predicted that increasing the frequency of light waves ( at a constant amplitude ) would increase the rate of electrons being ejected , and thus increase the measured electric current . using our beach ball analogy , we would expect waves hitting the dock more frequently would result in more beach balls being knocked off the dock compared to the same sized waves hitting the dock less often . now that we know what physicists thought would happen , let 's look at what they actually observed experimentally ! when intuition fails : photons to the rescue ! when experiments were performed to look at the effect of light amplitude and frequency , the following results were observed : the kinetic energy of photoelectrons increases with light frequency . electric current remains constant as light frequency increases . electric current increases with light amplitude . the kinetic energy of photoelectrons remains constant as light amplitude increases . these results were completely at odds with the predictions based on the classical description of light as a wave ! in order to explain what was happening , it turned out that an entirely new model of light was needed . that model was developed by albert einstein , who proposed that light sometimes behaved as particles of electromagnetic energy which we now call photons . the energy of a photon could be calculated using planck 's equation : $ \text { e } _ { \text { photon } } =h\nu $ where $ \text { e } _ { \text { photon } } $ is the energy of a photon in joules ( $ \text { j } $ ) , $ h $ is planck 's constant $ ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) $ , and $ \nu $ is the frequency of the light in $ \text { hz } $ . according to planck 's equation , the energy of a photon is proportional to the frequency of the light , $ \nu $ . the amplitude of the light is then proportional to the number of photons with a given frequency . concept check : as the wavelength of a photon increases , what happens to the photon 's energy ? light frequency and the threshold frequency $ \nu_0 $ we can think of the incident light as a stream of photons with an energy determined by the light frequency . when a photon hits the metal surface , the photon 's energy is absorbed by an electron in the metal . the graphic below illustrates the relationship between light frequency and the kinetic energy of ejected electrons . the scientists observed that if the incident light had a frequency less than a minimum frequency $ \nu_0 $ , then no electrons were ejected regardless of the light amplitude . this minimum frequency is also called the threshold frequency , and the value of $ \nu_0 $ depends on the metal . for frequencies greater than $ \nu_0 $ , electrons would be ejected from the metal . furthermore , the kinetic energy of the photoelectrons was proportional to the light frequency . the relationship between photoelectron kinetic energy and light frequency is shown in graph ( a ) below . because the light amplitude was kept constant as the light frequency increased , the number of photons being absorbed by the metal remained constant . thus , the rate at which electrons were ejected from the metal ( or the electric current ) remained constant as well . the relationship between electron current and light frequency is illustrated in graph ( b ) above . is n't there more math somewhere ? we can analyze the frequency relationship using the law of conservation of energy . the total energy of the incoming photon , $ \text { e } \text { photon } $ , must be equal to the kinetic energy of the ejected electron , $ \text { ke } { \text { electron } } $ , plus the energy required to eject the electron from the metal . the energy required to free the electron from a particular metal is also called the metal 's work function , which is represented by the symbol $ \phi $ ( in units of $ \text j $ ) : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ like the threshold frequency $ \nu_0 $ , the value of $ \phi $ also changes depending on the metal . we can now write the energy of the photon in terms of the light frequency using planck 's equation : $ \text { e } \text { photon } =h\nu=\text { ke } \text { electron } +\phi $ rearranging this equation in terms of the electron 's kinetic energy , we get : $ \text { ke } _\text { electron } =h\nu-\phi $ we can see that kinetic energy of the photoelectron increases linearly with $ \nu $ as long as the photon energy is greater than the work function $ \phi $ , which is exactly the relationship shown in graph ( a ) above . we can also use this equation to find the photoelectron velocity $ \text v $ , which is related to $ \text { ke } _\text { electron } $ as follows : $ \text { ke } _\text { electron } =h\nu-\phi=\dfrac { 1 } { 2 } m_e\text v^2 $ where $ m_e $ is the rest mass of an electron , $ 9.1094 \times 10^ { -31 } \ , \text { kg } $ . exploring the wave amplitude trends in terms of photons , higher amplitude light means more photons hitting the metal surface . this results in more electrons ejected over a given time period . as long as the light frequency is greater than $ \nu_0 $ , increasing the light amplitude will cause the electron current to increase proportionally as shown in graph ( a ) below . since increasing the light amplitude has no effect on the energy of the incoming photon , the photoelectron kinetic energy remains constant as the light amplitude is increased ( see graph ( b ) above ) . if we try to explain this result using our dock-and-beach-balls analogy , the relationship in graph ( b ) indicates that no matter the height of the wave hitting the dock $ - $ whether it 's a tiny swell , or a huge tsunami $ - $ the individual beach balls would be launched off the dock with the exact same speed ! thus , our intuition and analogy do n't do a very good job of explaining these particular experiments . example $ 1 $ : the photoelectric effect for copper the work function of copper metal is $ \phi=7.53\times10^ { -19 } \text { j } $ . if we shine light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ on copper metal , will the photoelectric effect be observed ? in order to eject electrons , we need the energy of the photons to be greater than the work function of copper . we can use planck 's equation to calculate the energy of the photon , $ \text { e } _ { \text { photon } } $ : $ \begin { align } \text { e } _\text { photon } & amp ; = h\nu \ & amp ; = ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) ( 3.0\times10^ { 16 } \text { hz } ) ~~~~\text { plug in values for $ h $ and $ \nu $ } \ & amp ; = 2.0\times10^ { -17 } \text { j } \end { align } $ if we compare our calculated photon energy , $ \text { e } _\text { photon } $ , to copper 's work function , we see that the photon energy is greater than $ \phi $ : $ ~2.0\times10^ { -17 } \text { j } ~ & gt ; ~7.53\times10^ { -19 } \text { j } $ $ ~~~~~~~~\text { e } _\text { photon } ~~~~~~~~~~~~~~~~~~~\phi $ thus , we would expect to see photoelectrons ejected from the copper . next , we will calculate the kinetic energy of the photoelectrons . example $ 2 $ : calculating the kinetic energy of a photoelectron what is the kinetic energy of the photoelectrons ejected from the copper by the light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ ? we can calculate the kinetic energy of the photoelectron using the equation that relates $ \text { ke } \text { electron } $ to the energy of the photon , $ \text { e } \text { photon } $ , and the work function , $ \phi $ : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ since we want to know $ \text { ke } _\text { electron } $ , we can start by rearranging the equation so that we will be solving for the kinetic energy of the electron : $ \text { ke } \text { electron } =\text { e } \text { photon } -\phi $ now we can insert our known values for $ \text { e } _\text { photon } $ and $ \phi $ from example 1 : $ \text { ke } _\text { electron } = ( 2.0\times10^ { -17 } \text { j } ) - ( 7.53\times10^ { -19 } \text { j } ) =1.9\times10^ { -17 } \text { j } $ therefore , each photoelectron has a kinetic energy of $ 1.9\times10^ { -17 } \text { j } $ . summary based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a specific metal surface . the energy of the incident photon must be equal to the sum of the work function and the kinetic energy of a photoelectron : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ try it ! when we shine light with a frequency of $ 6.20 \times 10^ { 14 } \ , \text { hz } $ on a mystery metal , we observe the ejected electrons have a kinetic energy of $ 3.28\times 10^ { -20 } \ , \text j $ . some possible candidates for the mystery metal are shown in the table below : metal | work function $ \phi $ ( joules , $ \text j $ ) : - : | : - : calcium , $ \text { ca } $ | $ 4.60\times 10^ { -19 } $ tin , $ \text { sn } $ | $ 7.08\times 10^ { -19 } $ sodium , $ \text { na } $ | $ 3.78\times 10^ { -19 } $ hafnium , $ \text { hf } $ | $ 6.25\times 10^ { -19 } $ samarium , $ \text { sm } $ | $ 4.33\times 10^ { -19 } $ based on this information , what is the most likely identity of our mystery metal ?
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the amplitude of the light is then proportional to the number of photons with a given frequency . concept check : as the wavelength of a photon increases , what happens to the photon 's energy ? light frequency and the threshold frequency $ \nu_0 $ we can think of the incident light as a stream of photons with an energy determined by the light frequency . when a photon hits the metal surface , the photon 's energy is absorbed by an electron in the metal .
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if photons with high energy ( high frequency ) have high penetrating power , does a photon have a lower penetrating power ( and thus lower energy and frequency ) after penetrating a substance ?
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key points based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . contrary to the predictions , experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of particles called photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a metal surface , and the value of $ \phi $ depends on the metal . the energy of the incident photon must be equal to the sum of the metal 's work function and the photoelectron kinetic energy : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ introduction : what is the photoelectric effect ? when light shines on a metal , electrons can be ejected from the surface of the metal in a phenomenon known as the photoelectric effect . this process is also often referred to as photoemission , and the electrons that are ejected from the metal are called photoelectrons . in terms of their behavior and their properties , photoelectrons are no different from other electrons . the prefix , photo- , simply tells us that the electrons have been ejected from a metal surface by incident light . in this article , we will discuss how 19th century physicists attempted ( but failed ! ) to explain the photoelectric effect using classical physics . this ultimately led to the development of the modern description of electromagnetic radiation , which has both wave-like and particle-like properties . predictions based on light as a wave to explain the photoelectric effect , 19th-century physicists theorized that the oscillating electric field of the incoming light wave was heating the electrons and causing them to vibrate , eventually freeing them from the metal surface . this hypothesis was based on the assumption that light traveled purely as a wave through space . ( see this article for more information about the basic properties of light . ) scientists also believed that the energy of the light wave was proportional to its brightness , which is related to the wave 's amplitude . in order to test their hypotheses , they performed experiments to look at the effect of light amplitude and frequency on the rate of electron ejection , as well as the kinetic energy of the photoelectrons . based on the classical description of light as a wave , they made the following predictions : the kinetic energy of emitted photoelectrons should increase with the light amplitude . the rate of electron emission , which is proportional to the measured electric current , should increase as the light frequency is increased . to help us understand why they made these predictions , we can compare a light wave to a water wave . imagine some beach balls sitting on a dock that extends out into the ocean . the dock represents a metal surface , the beach balls represent electrons , and the ocean waves represent light waves . if a single large wave were to shake the dock , we would expect the energy from the big wave would send the beach balls flying off the dock with much more kinetic energy compared to a single , small wave . this is also what physicists believed would happen if the light intensity was increased . light amplitude was expected to be proportional to the light energy , so higher amplitude light was predicted to result in photoelectrons with more kinetic energy . classical physicists also predicted that increasing the frequency of light waves ( at a constant amplitude ) would increase the rate of electrons being ejected , and thus increase the measured electric current . using our beach ball analogy , we would expect waves hitting the dock more frequently would result in more beach balls being knocked off the dock compared to the same sized waves hitting the dock less often . now that we know what physicists thought would happen , let 's look at what they actually observed experimentally ! when intuition fails : photons to the rescue ! when experiments were performed to look at the effect of light amplitude and frequency , the following results were observed : the kinetic energy of photoelectrons increases with light frequency . electric current remains constant as light frequency increases . electric current increases with light amplitude . the kinetic energy of photoelectrons remains constant as light amplitude increases . these results were completely at odds with the predictions based on the classical description of light as a wave ! in order to explain what was happening , it turned out that an entirely new model of light was needed . that model was developed by albert einstein , who proposed that light sometimes behaved as particles of electromagnetic energy which we now call photons . the energy of a photon could be calculated using planck 's equation : $ \text { e } _ { \text { photon } } =h\nu $ where $ \text { e } _ { \text { photon } } $ is the energy of a photon in joules ( $ \text { j } $ ) , $ h $ is planck 's constant $ ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) $ , and $ \nu $ is the frequency of the light in $ \text { hz } $ . according to planck 's equation , the energy of a photon is proportional to the frequency of the light , $ \nu $ . the amplitude of the light is then proportional to the number of photons with a given frequency . concept check : as the wavelength of a photon increases , what happens to the photon 's energy ? light frequency and the threshold frequency $ \nu_0 $ we can think of the incident light as a stream of photons with an energy determined by the light frequency . when a photon hits the metal surface , the photon 's energy is absorbed by an electron in the metal . the graphic below illustrates the relationship between light frequency and the kinetic energy of ejected electrons . the scientists observed that if the incident light had a frequency less than a minimum frequency $ \nu_0 $ , then no electrons were ejected regardless of the light amplitude . this minimum frequency is also called the threshold frequency , and the value of $ \nu_0 $ depends on the metal . for frequencies greater than $ \nu_0 $ , electrons would be ejected from the metal . furthermore , the kinetic energy of the photoelectrons was proportional to the light frequency . the relationship between photoelectron kinetic energy and light frequency is shown in graph ( a ) below . because the light amplitude was kept constant as the light frequency increased , the number of photons being absorbed by the metal remained constant . thus , the rate at which electrons were ejected from the metal ( or the electric current ) remained constant as well . the relationship between electron current and light frequency is illustrated in graph ( b ) above . is n't there more math somewhere ? we can analyze the frequency relationship using the law of conservation of energy . the total energy of the incoming photon , $ \text { e } \text { photon } $ , must be equal to the kinetic energy of the ejected electron , $ \text { ke } { \text { electron } } $ , plus the energy required to eject the electron from the metal . the energy required to free the electron from a particular metal is also called the metal 's work function , which is represented by the symbol $ \phi $ ( in units of $ \text j $ ) : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ like the threshold frequency $ \nu_0 $ , the value of $ \phi $ also changes depending on the metal . we can now write the energy of the photon in terms of the light frequency using planck 's equation : $ \text { e } \text { photon } =h\nu=\text { ke } \text { electron } +\phi $ rearranging this equation in terms of the electron 's kinetic energy , we get : $ \text { ke } _\text { electron } =h\nu-\phi $ we can see that kinetic energy of the photoelectron increases linearly with $ \nu $ as long as the photon energy is greater than the work function $ \phi $ , which is exactly the relationship shown in graph ( a ) above . we can also use this equation to find the photoelectron velocity $ \text v $ , which is related to $ \text { ke } _\text { electron } $ as follows : $ \text { ke } _\text { electron } =h\nu-\phi=\dfrac { 1 } { 2 } m_e\text v^2 $ where $ m_e $ is the rest mass of an electron , $ 9.1094 \times 10^ { -31 } \ , \text { kg } $ . exploring the wave amplitude trends in terms of photons , higher amplitude light means more photons hitting the metal surface . this results in more electrons ejected over a given time period . as long as the light frequency is greater than $ \nu_0 $ , increasing the light amplitude will cause the electron current to increase proportionally as shown in graph ( a ) below . since increasing the light amplitude has no effect on the energy of the incoming photon , the photoelectron kinetic energy remains constant as the light amplitude is increased ( see graph ( b ) above ) . if we try to explain this result using our dock-and-beach-balls analogy , the relationship in graph ( b ) indicates that no matter the height of the wave hitting the dock $ - $ whether it 's a tiny swell , or a huge tsunami $ - $ the individual beach balls would be launched off the dock with the exact same speed ! thus , our intuition and analogy do n't do a very good job of explaining these particular experiments . example $ 1 $ : the photoelectric effect for copper the work function of copper metal is $ \phi=7.53\times10^ { -19 } \text { j } $ . if we shine light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ on copper metal , will the photoelectric effect be observed ? in order to eject electrons , we need the energy of the photons to be greater than the work function of copper . we can use planck 's equation to calculate the energy of the photon , $ \text { e } _ { \text { photon } } $ : $ \begin { align } \text { e } _\text { photon } & amp ; = h\nu \ & amp ; = ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) ( 3.0\times10^ { 16 } \text { hz } ) ~~~~\text { plug in values for $ h $ and $ \nu $ } \ & amp ; = 2.0\times10^ { -17 } \text { j } \end { align } $ if we compare our calculated photon energy , $ \text { e } _\text { photon } $ , to copper 's work function , we see that the photon energy is greater than $ \phi $ : $ ~2.0\times10^ { -17 } \text { j } ~ & gt ; ~7.53\times10^ { -19 } \text { j } $ $ ~~~~~~~~\text { e } _\text { photon } ~~~~~~~~~~~~~~~~~~~\phi $ thus , we would expect to see photoelectrons ejected from the copper . next , we will calculate the kinetic energy of the photoelectrons . example $ 2 $ : calculating the kinetic energy of a photoelectron what is the kinetic energy of the photoelectrons ejected from the copper by the light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ ? we can calculate the kinetic energy of the photoelectron using the equation that relates $ \text { ke } \text { electron } $ to the energy of the photon , $ \text { e } \text { photon } $ , and the work function , $ \phi $ : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ since we want to know $ \text { ke } _\text { electron } $ , we can start by rearranging the equation so that we will be solving for the kinetic energy of the electron : $ \text { ke } \text { electron } =\text { e } \text { photon } -\phi $ now we can insert our known values for $ \text { e } _\text { photon } $ and $ \phi $ from example 1 : $ \text { ke } _\text { electron } = ( 2.0\times10^ { -17 } \text { j } ) - ( 7.53\times10^ { -19 } \text { j } ) =1.9\times10^ { -17 } \text { j } $ therefore , each photoelectron has a kinetic energy of $ 1.9\times10^ { -17 } \text { j } $ . summary based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a specific metal surface . the energy of the incident photon must be equal to the sum of the work function and the kinetic energy of a photoelectron : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ try it ! when we shine light with a frequency of $ 6.20 \times 10^ { 14 } \ , \text { hz } $ on a mystery metal , we observe the ejected electrons have a kinetic energy of $ 3.28\times 10^ { -20 } \ , \text j $ . some possible candidates for the mystery metal are shown in the table below : metal | work function $ \phi $ ( joules , $ \text j $ ) : - : | : - : calcium , $ \text { ca } $ | $ 4.60\times 10^ { -19 } $ tin , $ \text { sn } $ | $ 7.08\times 10^ { -19 } $ sodium , $ \text { na } $ | $ 3.78\times 10^ { -19 } $ hafnium , $ \text { hf } $ | $ 6.25\times 10^ { -19 } $ samarium , $ \text { sm } $ | $ 4.33\times 10^ { -19 } $ based on this information , what is the most likely identity of our mystery metal ?
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the dock represents a metal surface , the beach balls represent electrons , and the ocean waves represent light waves . if a single large wave were to shake the dock , we would expect the energy from the big wave would send the beach balls flying off the dock with much more kinetic energy compared to a single , small wave . this is also what physicists believed would happen if the light intensity was increased .
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why we connect extra small potential difference with x ray tube ?
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key points based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . contrary to the predictions , experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of particles called photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a metal surface , and the value of $ \phi $ depends on the metal . the energy of the incident photon must be equal to the sum of the metal 's work function and the photoelectron kinetic energy : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ introduction : what is the photoelectric effect ? when light shines on a metal , electrons can be ejected from the surface of the metal in a phenomenon known as the photoelectric effect . this process is also often referred to as photoemission , and the electrons that are ejected from the metal are called photoelectrons . in terms of their behavior and their properties , photoelectrons are no different from other electrons . the prefix , photo- , simply tells us that the electrons have been ejected from a metal surface by incident light . in this article , we will discuss how 19th century physicists attempted ( but failed ! ) to explain the photoelectric effect using classical physics . this ultimately led to the development of the modern description of electromagnetic radiation , which has both wave-like and particle-like properties . predictions based on light as a wave to explain the photoelectric effect , 19th-century physicists theorized that the oscillating electric field of the incoming light wave was heating the electrons and causing them to vibrate , eventually freeing them from the metal surface . this hypothesis was based on the assumption that light traveled purely as a wave through space . ( see this article for more information about the basic properties of light . ) scientists also believed that the energy of the light wave was proportional to its brightness , which is related to the wave 's amplitude . in order to test their hypotheses , they performed experiments to look at the effect of light amplitude and frequency on the rate of electron ejection , as well as the kinetic energy of the photoelectrons . based on the classical description of light as a wave , they made the following predictions : the kinetic energy of emitted photoelectrons should increase with the light amplitude . the rate of electron emission , which is proportional to the measured electric current , should increase as the light frequency is increased . to help us understand why they made these predictions , we can compare a light wave to a water wave . imagine some beach balls sitting on a dock that extends out into the ocean . the dock represents a metal surface , the beach balls represent electrons , and the ocean waves represent light waves . if a single large wave were to shake the dock , we would expect the energy from the big wave would send the beach balls flying off the dock with much more kinetic energy compared to a single , small wave . this is also what physicists believed would happen if the light intensity was increased . light amplitude was expected to be proportional to the light energy , so higher amplitude light was predicted to result in photoelectrons with more kinetic energy . classical physicists also predicted that increasing the frequency of light waves ( at a constant amplitude ) would increase the rate of electrons being ejected , and thus increase the measured electric current . using our beach ball analogy , we would expect waves hitting the dock more frequently would result in more beach balls being knocked off the dock compared to the same sized waves hitting the dock less often . now that we know what physicists thought would happen , let 's look at what they actually observed experimentally ! when intuition fails : photons to the rescue ! when experiments were performed to look at the effect of light amplitude and frequency , the following results were observed : the kinetic energy of photoelectrons increases with light frequency . electric current remains constant as light frequency increases . electric current increases with light amplitude . the kinetic energy of photoelectrons remains constant as light amplitude increases . these results were completely at odds with the predictions based on the classical description of light as a wave ! in order to explain what was happening , it turned out that an entirely new model of light was needed . that model was developed by albert einstein , who proposed that light sometimes behaved as particles of electromagnetic energy which we now call photons . the energy of a photon could be calculated using planck 's equation : $ \text { e } _ { \text { photon } } =h\nu $ where $ \text { e } _ { \text { photon } } $ is the energy of a photon in joules ( $ \text { j } $ ) , $ h $ is planck 's constant $ ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) $ , and $ \nu $ is the frequency of the light in $ \text { hz } $ . according to planck 's equation , the energy of a photon is proportional to the frequency of the light , $ \nu $ . the amplitude of the light is then proportional to the number of photons with a given frequency . concept check : as the wavelength of a photon increases , what happens to the photon 's energy ? light frequency and the threshold frequency $ \nu_0 $ we can think of the incident light as a stream of photons with an energy determined by the light frequency . when a photon hits the metal surface , the photon 's energy is absorbed by an electron in the metal . the graphic below illustrates the relationship between light frequency and the kinetic energy of ejected electrons . the scientists observed that if the incident light had a frequency less than a minimum frequency $ \nu_0 $ , then no electrons were ejected regardless of the light amplitude . this minimum frequency is also called the threshold frequency , and the value of $ \nu_0 $ depends on the metal . for frequencies greater than $ \nu_0 $ , electrons would be ejected from the metal . furthermore , the kinetic energy of the photoelectrons was proportional to the light frequency . the relationship between photoelectron kinetic energy and light frequency is shown in graph ( a ) below . because the light amplitude was kept constant as the light frequency increased , the number of photons being absorbed by the metal remained constant . thus , the rate at which electrons were ejected from the metal ( or the electric current ) remained constant as well . the relationship between electron current and light frequency is illustrated in graph ( b ) above . is n't there more math somewhere ? we can analyze the frequency relationship using the law of conservation of energy . the total energy of the incoming photon , $ \text { e } \text { photon } $ , must be equal to the kinetic energy of the ejected electron , $ \text { ke } { \text { electron } } $ , plus the energy required to eject the electron from the metal . the energy required to free the electron from a particular metal is also called the metal 's work function , which is represented by the symbol $ \phi $ ( in units of $ \text j $ ) : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ like the threshold frequency $ \nu_0 $ , the value of $ \phi $ also changes depending on the metal . we can now write the energy of the photon in terms of the light frequency using planck 's equation : $ \text { e } \text { photon } =h\nu=\text { ke } \text { electron } +\phi $ rearranging this equation in terms of the electron 's kinetic energy , we get : $ \text { ke } _\text { electron } =h\nu-\phi $ we can see that kinetic energy of the photoelectron increases linearly with $ \nu $ as long as the photon energy is greater than the work function $ \phi $ , which is exactly the relationship shown in graph ( a ) above . we can also use this equation to find the photoelectron velocity $ \text v $ , which is related to $ \text { ke } _\text { electron } $ as follows : $ \text { ke } _\text { electron } =h\nu-\phi=\dfrac { 1 } { 2 } m_e\text v^2 $ where $ m_e $ is the rest mass of an electron , $ 9.1094 \times 10^ { -31 } \ , \text { kg } $ . exploring the wave amplitude trends in terms of photons , higher amplitude light means more photons hitting the metal surface . this results in more electrons ejected over a given time period . as long as the light frequency is greater than $ \nu_0 $ , increasing the light amplitude will cause the electron current to increase proportionally as shown in graph ( a ) below . since increasing the light amplitude has no effect on the energy of the incoming photon , the photoelectron kinetic energy remains constant as the light amplitude is increased ( see graph ( b ) above ) . if we try to explain this result using our dock-and-beach-balls analogy , the relationship in graph ( b ) indicates that no matter the height of the wave hitting the dock $ - $ whether it 's a tiny swell , or a huge tsunami $ - $ the individual beach balls would be launched off the dock with the exact same speed ! thus , our intuition and analogy do n't do a very good job of explaining these particular experiments . example $ 1 $ : the photoelectric effect for copper the work function of copper metal is $ \phi=7.53\times10^ { -19 } \text { j } $ . if we shine light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ on copper metal , will the photoelectric effect be observed ? in order to eject electrons , we need the energy of the photons to be greater than the work function of copper . we can use planck 's equation to calculate the energy of the photon , $ \text { e } _ { \text { photon } } $ : $ \begin { align } \text { e } _\text { photon } & amp ; = h\nu \ & amp ; = ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) ( 3.0\times10^ { 16 } \text { hz } ) ~~~~\text { plug in values for $ h $ and $ \nu $ } \ & amp ; = 2.0\times10^ { -17 } \text { j } \end { align } $ if we compare our calculated photon energy , $ \text { e } _\text { photon } $ , to copper 's work function , we see that the photon energy is greater than $ \phi $ : $ ~2.0\times10^ { -17 } \text { j } ~ & gt ; ~7.53\times10^ { -19 } \text { j } $ $ ~~~~~~~~\text { e } _\text { photon } ~~~~~~~~~~~~~~~~~~~\phi $ thus , we would expect to see photoelectrons ejected from the copper . next , we will calculate the kinetic energy of the photoelectrons . example $ 2 $ : calculating the kinetic energy of a photoelectron what is the kinetic energy of the photoelectrons ejected from the copper by the light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ ? we can calculate the kinetic energy of the photoelectron using the equation that relates $ \text { ke } \text { electron } $ to the energy of the photon , $ \text { e } \text { photon } $ , and the work function , $ \phi $ : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ since we want to know $ \text { ke } _\text { electron } $ , we can start by rearranging the equation so that we will be solving for the kinetic energy of the electron : $ \text { ke } \text { electron } =\text { e } \text { photon } -\phi $ now we can insert our known values for $ \text { e } _\text { photon } $ and $ \phi $ from example 1 : $ \text { ke } _\text { electron } = ( 2.0\times10^ { -17 } \text { j } ) - ( 7.53\times10^ { -19 } \text { j } ) =1.9\times10^ { -17 } \text { j } $ therefore , each photoelectron has a kinetic energy of $ 1.9\times10^ { -17 } \text { j } $ . summary based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a specific metal surface . the energy of the incident photon must be equal to the sum of the work function and the kinetic energy of a photoelectron : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ try it ! when we shine light with a frequency of $ 6.20 \times 10^ { 14 } \ , \text { hz } $ on a mystery metal , we observe the ejected electrons have a kinetic energy of $ 3.28\times 10^ { -20 } \ , \text j $ . some possible candidates for the mystery metal are shown in the table below : metal | work function $ \phi $ ( joules , $ \text j $ ) : - : | : - : calcium , $ \text { ca } $ | $ 4.60\times 10^ { -19 } $ tin , $ \text { sn } $ | $ 7.08\times 10^ { -19 } $ sodium , $ \text { na } $ | $ 3.78\times 10^ { -19 } $ hafnium , $ \text { hf } $ | $ 6.25\times 10^ { -19 } $ samarium , $ \text { sm } $ | $ 4.33\times 10^ { -19 } $ based on this information , what is the most likely identity of our mystery metal ?
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the energy of the incident photon must be equal to the sum of the work function and the kinetic energy of a photoelectron : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ try it ! when we shine light with a frequency of $ 6.20 \times 10^ { 14 } \ , \text { hz } $ on a mystery metal , we observe the ejected electrons have a kinetic energy of $ 3.28\times 10^ { -20 } \ , \text j $ . some possible candidates for the mystery metal are shown in the table below : metal | work function $ \phi $ ( joules , $ \text j $ ) : - : | : - : calcium , $ \text { ca } $ | $ 4.60\times 10^ { -19 } $ tin , $ \text { sn } $ | $ 7.08\times 10^ { -19 } $ sodium , $ \text { na } $ | $ 3.78\times 10^ { -19 } $ hafnium , $ \text { hf } $ | $ 6.25\times 10^ { -19 } $ samarium , $ \text { sm } $ | $ 4.33\times 10^ { -19 } $ based on this information , what is the most likely identity of our mystery metal ?
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( please do n't look if you have n't completed it ) ephoton=hv=6.626x10tpo the-34 j x 6.20x10 to the 14 =4.10812x10 to the power -19 j keelectron=hv - work function =4.10812x10 to the power -19 j - 3.28x10 to the power of -20 = 3.78012x10 to the power -19 do i have to do the 1/2 me v2 ?
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key points based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . contrary to the predictions , experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of particles called photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a metal surface , and the value of $ \phi $ depends on the metal . the energy of the incident photon must be equal to the sum of the metal 's work function and the photoelectron kinetic energy : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ introduction : what is the photoelectric effect ? when light shines on a metal , electrons can be ejected from the surface of the metal in a phenomenon known as the photoelectric effect . this process is also often referred to as photoemission , and the electrons that are ejected from the metal are called photoelectrons . in terms of their behavior and their properties , photoelectrons are no different from other electrons . the prefix , photo- , simply tells us that the electrons have been ejected from a metal surface by incident light . in this article , we will discuss how 19th century physicists attempted ( but failed ! ) to explain the photoelectric effect using classical physics . this ultimately led to the development of the modern description of electromagnetic radiation , which has both wave-like and particle-like properties . predictions based on light as a wave to explain the photoelectric effect , 19th-century physicists theorized that the oscillating electric field of the incoming light wave was heating the electrons and causing them to vibrate , eventually freeing them from the metal surface . this hypothesis was based on the assumption that light traveled purely as a wave through space . ( see this article for more information about the basic properties of light . ) scientists also believed that the energy of the light wave was proportional to its brightness , which is related to the wave 's amplitude . in order to test their hypotheses , they performed experiments to look at the effect of light amplitude and frequency on the rate of electron ejection , as well as the kinetic energy of the photoelectrons . based on the classical description of light as a wave , they made the following predictions : the kinetic energy of emitted photoelectrons should increase with the light amplitude . the rate of electron emission , which is proportional to the measured electric current , should increase as the light frequency is increased . to help us understand why they made these predictions , we can compare a light wave to a water wave . imagine some beach balls sitting on a dock that extends out into the ocean . the dock represents a metal surface , the beach balls represent electrons , and the ocean waves represent light waves . if a single large wave were to shake the dock , we would expect the energy from the big wave would send the beach balls flying off the dock with much more kinetic energy compared to a single , small wave . this is also what physicists believed would happen if the light intensity was increased . light amplitude was expected to be proportional to the light energy , so higher amplitude light was predicted to result in photoelectrons with more kinetic energy . classical physicists also predicted that increasing the frequency of light waves ( at a constant amplitude ) would increase the rate of electrons being ejected , and thus increase the measured electric current . using our beach ball analogy , we would expect waves hitting the dock more frequently would result in more beach balls being knocked off the dock compared to the same sized waves hitting the dock less often . now that we know what physicists thought would happen , let 's look at what they actually observed experimentally ! when intuition fails : photons to the rescue ! when experiments were performed to look at the effect of light amplitude and frequency , the following results were observed : the kinetic energy of photoelectrons increases with light frequency . electric current remains constant as light frequency increases . electric current increases with light amplitude . the kinetic energy of photoelectrons remains constant as light amplitude increases . these results were completely at odds with the predictions based on the classical description of light as a wave ! in order to explain what was happening , it turned out that an entirely new model of light was needed . that model was developed by albert einstein , who proposed that light sometimes behaved as particles of electromagnetic energy which we now call photons . the energy of a photon could be calculated using planck 's equation : $ \text { e } _ { \text { photon } } =h\nu $ where $ \text { e } _ { \text { photon } } $ is the energy of a photon in joules ( $ \text { j } $ ) , $ h $ is planck 's constant $ ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) $ , and $ \nu $ is the frequency of the light in $ \text { hz } $ . according to planck 's equation , the energy of a photon is proportional to the frequency of the light , $ \nu $ . the amplitude of the light is then proportional to the number of photons with a given frequency . concept check : as the wavelength of a photon increases , what happens to the photon 's energy ? light frequency and the threshold frequency $ \nu_0 $ we can think of the incident light as a stream of photons with an energy determined by the light frequency . when a photon hits the metal surface , the photon 's energy is absorbed by an electron in the metal . the graphic below illustrates the relationship between light frequency and the kinetic energy of ejected electrons . the scientists observed that if the incident light had a frequency less than a minimum frequency $ \nu_0 $ , then no electrons were ejected regardless of the light amplitude . this minimum frequency is also called the threshold frequency , and the value of $ \nu_0 $ depends on the metal . for frequencies greater than $ \nu_0 $ , electrons would be ejected from the metal . furthermore , the kinetic energy of the photoelectrons was proportional to the light frequency . the relationship between photoelectron kinetic energy and light frequency is shown in graph ( a ) below . because the light amplitude was kept constant as the light frequency increased , the number of photons being absorbed by the metal remained constant . thus , the rate at which electrons were ejected from the metal ( or the electric current ) remained constant as well . the relationship between electron current and light frequency is illustrated in graph ( b ) above . is n't there more math somewhere ? we can analyze the frequency relationship using the law of conservation of energy . the total energy of the incoming photon , $ \text { e } \text { photon } $ , must be equal to the kinetic energy of the ejected electron , $ \text { ke } { \text { electron } } $ , plus the energy required to eject the electron from the metal . the energy required to free the electron from a particular metal is also called the metal 's work function , which is represented by the symbol $ \phi $ ( in units of $ \text j $ ) : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ like the threshold frequency $ \nu_0 $ , the value of $ \phi $ also changes depending on the metal . we can now write the energy of the photon in terms of the light frequency using planck 's equation : $ \text { e } \text { photon } =h\nu=\text { ke } \text { electron } +\phi $ rearranging this equation in terms of the electron 's kinetic energy , we get : $ \text { ke } _\text { electron } =h\nu-\phi $ we can see that kinetic energy of the photoelectron increases linearly with $ \nu $ as long as the photon energy is greater than the work function $ \phi $ , which is exactly the relationship shown in graph ( a ) above . we can also use this equation to find the photoelectron velocity $ \text v $ , which is related to $ \text { ke } _\text { electron } $ as follows : $ \text { ke } _\text { electron } =h\nu-\phi=\dfrac { 1 } { 2 } m_e\text v^2 $ where $ m_e $ is the rest mass of an electron , $ 9.1094 \times 10^ { -31 } \ , \text { kg } $ . exploring the wave amplitude trends in terms of photons , higher amplitude light means more photons hitting the metal surface . this results in more electrons ejected over a given time period . as long as the light frequency is greater than $ \nu_0 $ , increasing the light amplitude will cause the electron current to increase proportionally as shown in graph ( a ) below . since increasing the light amplitude has no effect on the energy of the incoming photon , the photoelectron kinetic energy remains constant as the light amplitude is increased ( see graph ( b ) above ) . if we try to explain this result using our dock-and-beach-balls analogy , the relationship in graph ( b ) indicates that no matter the height of the wave hitting the dock $ - $ whether it 's a tiny swell , or a huge tsunami $ - $ the individual beach balls would be launched off the dock with the exact same speed ! thus , our intuition and analogy do n't do a very good job of explaining these particular experiments . example $ 1 $ : the photoelectric effect for copper the work function of copper metal is $ \phi=7.53\times10^ { -19 } \text { j } $ . if we shine light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ on copper metal , will the photoelectric effect be observed ? in order to eject electrons , we need the energy of the photons to be greater than the work function of copper . we can use planck 's equation to calculate the energy of the photon , $ \text { e } _ { \text { photon } } $ : $ \begin { align } \text { e } _\text { photon } & amp ; = h\nu \ & amp ; = ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) ( 3.0\times10^ { 16 } \text { hz } ) ~~~~\text { plug in values for $ h $ and $ \nu $ } \ & amp ; = 2.0\times10^ { -17 } \text { j } \end { align } $ if we compare our calculated photon energy , $ \text { e } _\text { photon } $ , to copper 's work function , we see that the photon energy is greater than $ \phi $ : $ ~2.0\times10^ { -17 } \text { j } ~ & gt ; ~7.53\times10^ { -19 } \text { j } $ $ ~~~~~~~~\text { e } _\text { photon } ~~~~~~~~~~~~~~~~~~~\phi $ thus , we would expect to see photoelectrons ejected from the copper . next , we will calculate the kinetic energy of the photoelectrons . example $ 2 $ : calculating the kinetic energy of a photoelectron what is the kinetic energy of the photoelectrons ejected from the copper by the light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ ? we can calculate the kinetic energy of the photoelectron using the equation that relates $ \text { ke } \text { electron } $ to the energy of the photon , $ \text { e } \text { photon } $ , and the work function , $ \phi $ : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ since we want to know $ \text { ke } _\text { electron } $ , we can start by rearranging the equation so that we will be solving for the kinetic energy of the electron : $ \text { ke } \text { electron } =\text { e } \text { photon } -\phi $ now we can insert our known values for $ \text { e } _\text { photon } $ and $ \phi $ from example 1 : $ \text { ke } _\text { electron } = ( 2.0\times10^ { -17 } \text { j } ) - ( 7.53\times10^ { -19 } \text { j } ) =1.9\times10^ { -17 } \text { j } $ therefore , each photoelectron has a kinetic energy of $ 1.9\times10^ { -17 } \text { j } $ . summary based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a specific metal surface . the energy of the incident photon must be equal to the sum of the work function and the kinetic energy of a photoelectron : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ try it ! when we shine light with a frequency of $ 6.20 \times 10^ { 14 } \ , \text { hz } $ on a mystery metal , we observe the ejected electrons have a kinetic energy of $ 3.28\times 10^ { -20 } \ , \text j $ . some possible candidates for the mystery metal are shown in the table below : metal | work function $ \phi $ ( joules , $ \text j $ ) : - : | : - : calcium , $ \text { ca } $ | $ 4.60\times 10^ { -19 } $ tin , $ \text { sn } $ | $ 7.08\times 10^ { -19 } $ sodium , $ \text { na } $ | $ 3.78\times 10^ { -19 } $ hafnium , $ \text { hf } $ | $ 6.25\times 10^ { -19 } $ samarium , $ \text { sm } $ | $ 4.33\times 10^ { -19 } $ based on this information , what is the most likely identity of our mystery metal ?
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the amplitude of the light is then proportional to the number of photons with a given frequency . concept check : as the wavelength of a photon increases , what happens to the photon 's energy ? light frequency and the threshold frequency $ \nu_0 $ we can think of the incident light as a stream of photons with an energy determined by the light frequency .
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when a photon/em radiation comes into contact with an electron , what exactly happens at that moment ?
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key points based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . contrary to the predictions , experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of particles called photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a metal surface , and the value of $ \phi $ depends on the metal . the energy of the incident photon must be equal to the sum of the metal 's work function and the photoelectron kinetic energy : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ introduction : what is the photoelectric effect ? when light shines on a metal , electrons can be ejected from the surface of the metal in a phenomenon known as the photoelectric effect . this process is also often referred to as photoemission , and the electrons that are ejected from the metal are called photoelectrons . in terms of their behavior and their properties , photoelectrons are no different from other electrons . the prefix , photo- , simply tells us that the electrons have been ejected from a metal surface by incident light . in this article , we will discuss how 19th century physicists attempted ( but failed ! ) to explain the photoelectric effect using classical physics . this ultimately led to the development of the modern description of electromagnetic radiation , which has both wave-like and particle-like properties . predictions based on light as a wave to explain the photoelectric effect , 19th-century physicists theorized that the oscillating electric field of the incoming light wave was heating the electrons and causing them to vibrate , eventually freeing them from the metal surface . this hypothesis was based on the assumption that light traveled purely as a wave through space . ( see this article for more information about the basic properties of light . ) scientists also believed that the energy of the light wave was proportional to its brightness , which is related to the wave 's amplitude . in order to test their hypotheses , they performed experiments to look at the effect of light amplitude and frequency on the rate of electron ejection , as well as the kinetic energy of the photoelectrons . based on the classical description of light as a wave , they made the following predictions : the kinetic energy of emitted photoelectrons should increase with the light amplitude . the rate of electron emission , which is proportional to the measured electric current , should increase as the light frequency is increased . to help us understand why they made these predictions , we can compare a light wave to a water wave . imagine some beach balls sitting on a dock that extends out into the ocean . the dock represents a metal surface , the beach balls represent electrons , and the ocean waves represent light waves . if a single large wave were to shake the dock , we would expect the energy from the big wave would send the beach balls flying off the dock with much more kinetic energy compared to a single , small wave . this is also what physicists believed would happen if the light intensity was increased . light amplitude was expected to be proportional to the light energy , so higher amplitude light was predicted to result in photoelectrons with more kinetic energy . classical physicists also predicted that increasing the frequency of light waves ( at a constant amplitude ) would increase the rate of electrons being ejected , and thus increase the measured electric current . using our beach ball analogy , we would expect waves hitting the dock more frequently would result in more beach balls being knocked off the dock compared to the same sized waves hitting the dock less often . now that we know what physicists thought would happen , let 's look at what they actually observed experimentally ! when intuition fails : photons to the rescue ! when experiments were performed to look at the effect of light amplitude and frequency , the following results were observed : the kinetic energy of photoelectrons increases with light frequency . electric current remains constant as light frequency increases . electric current increases with light amplitude . the kinetic energy of photoelectrons remains constant as light amplitude increases . these results were completely at odds with the predictions based on the classical description of light as a wave ! in order to explain what was happening , it turned out that an entirely new model of light was needed . that model was developed by albert einstein , who proposed that light sometimes behaved as particles of electromagnetic energy which we now call photons . the energy of a photon could be calculated using planck 's equation : $ \text { e } _ { \text { photon } } =h\nu $ where $ \text { e } _ { \text { photon } } $ is the energy of a photon in joules ( $ \text { j } $ ) , $ h $ is planck 's constant $ ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) $ , and $ \nu $ is the frequency of the light in $ \text { hz } $ . according to planck 's equation , the energy of a photon is proportional to the frequency of the light , $ \nu $ . the amplitude of the light is then proportional to the number of photons with a given frequency . concept check : as the wavelength of a photon increases , what happens to the photon 's energy ? light frequency and the threshold frequency $ \nu_0 $ we can think of the incident light as a stream of photons with an energy determined by the light frequency . when a photon hits the metal surface , the photon 's energy is absorbed by an electron in the metal . the graphic below illustrates the relationship between light frequency and the kinetic energy of ejected electrons . the scientists observed that if the incident light had a frequency less than a minimum frequency $ \nu_0 $ , then no electrons were ejected regardless of the light amplitude . this minimum frequency is also called the threshold frequency , and the value of $ \nu_0 $ depends on the metal . for frequencies greater than $ \nu_0 $ , electrons would be ejected from the metal . furthermore , the kinetic energy of the photoelectrons was proportional to the light frequency . the relationship between photoelectron kinetic energy and light frequency is shown in graph ( a ) below . because the light amplitude was kept constant as the light frequency increased , the number of photons being absorbed by the metal remained constant . thus , the rate at which electrons were ejected from the metal ( or the electric current ) remained constant as well . the relationship between electron current and light frequency is illustrated in graph ( b ) above . is n't there more math somewhere ? we can analyze the frequency relationship using the law of conservation of energy . the total energy of the incoming photon , $ \text { e } \text { photon } $ , must be equal to the kinetic energy of the ejected electron , $ \text { ke } { \text { electron } } $ , plus the energy required to eject the electron from the metal . the energy required to free the electron from a particular metal is also called the metal 's work function , which is represented by the symbol $ \phi $ ( in units of $ \text j $ ) : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ like the threshold frequency $ \nu_0 $ , the value of $ \phi $ also changes depending on the metal . we can now write the energy of the photon in terms of the light frequency using planck 's equation : $ \text { e } \text { photon } =h\nu=\text { ke } \text { electron } +\phi $ rearranging this equation in terms of the electron 's kinetic energy , we get : $ \text { ke } _\text { electron } =h\nu-\phi $ we can see that kinetic energy of the photoelectron increases linearly with $ \nu $ as long as the photon energy is greater than the work function $ \phi $ , which is exactly the relationship shown in graph ( a ) above . we can also use this equation to find the photoelectron velocity $ \text v $ , which is related to $ \text { ke } _\text { electron } $ as follows : $ \text { ke } _\text { electron } =h\nu-\phi=\dfrac { 1 } { 2 } m_e\text v^2 $ where $ m_e $ is the rest mass of an electron , $ 9.1094 \times 10^ { -31 } \ , \text { kg } $ . exploring the wave amplitude trends in terms of photons , higher amplitude light means more photons hitting the metal surface . this results in more electrons ejected over a given time period . as long as the light frequency is greater than $ \nu_0 $ , increasing the light amplitude will cause the electron current to increase proportionally as shown in graph ( a ) below . since increasing the light amplitude has no effect on the energy of the incoming photon , the photoelectron kinetic energy remains constant as the light amplitude is increased ( see graph ( b ) above ) . if we try to explain this result using our dock-and-beach-balls analogy , the relationship in graph ( b ) indicates that no matter the height of the wave hitting the dock $ - $ whether it 's a tiny swell , or a huge tsunami $ - $ the individual beach balls would be launched off the dock with the exact same speed ! thus , our intuition and analogy do n't do a very good job of explaining these particular experiments . example $ 1 $ : the photoelectric effect for copper the work function of copper metal is $ \phi=7.53\times10^ { -19 } \text { j } $ . if we shine light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ on copper metal , will the photoelectric effect be observed ? in order to eject electrons , we need the energy of the photons to be greater than the work function of copper . we can use planck 's equation to calculate the energy of the photon , $ \text { e } _ { \text { photon } } $ : $ \begin { align } \text { e } _\text { photon } & amp ; = h\nu \ & amp ; = ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) ( 3.0\times10^ { 16 } \text { hz } ) ~~~~\text { plug in values for $ h $ and $ \nu $ } \ & amp ; = 2.0\times10^ { -17 } \text { j } \end { align } $ if we compare our calculated photon energy , $ \text { e } _\text { photon } $ , to copper 's work function , we see that the photon energy is greater than $ \phi $ : $ ~2.0\times10^ { -17 } \text { j } ~ & gt ; ~7.53\times10^ { -19 } \text { j } $ $ ~~~~~~~~\text { e } _\text { photon } ~~~~~~~~~~~~~~~~~~~\phi $ thus , we would expect to see photoelectrons ejected from the copper . next , we will calculate the kinetic energy of the photoelectrons . example $ 2 $ : calculating the kinetic energy of a photoelectron what is the kinetic energy of the photoelectrons ejected from the copper by the light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ ? we can calculate the kinetic energy of the photoelectron using the equation that relates $ \text { ke } \text { electron } $ to the energy of the photon , $ \text { e } \text { photon } $ , and the work function , $ \phi $ : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ since we want to know $ \text { ke } _\text { electron } $ , we can start by rearranging the equation so that we will be solving for the kinetic energy of the electron : $ \text { ke } \text { electron } =\text { e } \text { photon } -\phi $ now we can insert our known values for $ \text { e } _\text { photon } $ and $ \phi $ from example 1 : $ \text { ke } _\text { electron } = ( 2.0\times10^ { -17 } \text { j } ) - ( 7.53\times10^ { -19 } \text { j } ) =1.9\times10^ { -17 } \text { j } $ therefore , each photoelectron has a kinetic energy of $ 1.9\times10^ { -17 } \text { j } $ . summary based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a specific metal surface . the energy of the incident photon must be equal to the sum of the work function and the kinetic energy of a photoelectron : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ try it ! when we shine light with a frequency of $ 6.20 \times 10^ { 14 } \ , \text { hz } $ on a mystery metal , we observe the ejected electrons have a kinetic energy of $ 3.28\times 10^ { -20 } \ , \text j $ . some possible candidates for the mystery metal are shown in the table below : metal | work function $ \phi $ ( joules , $ \text j $ ) : - : | : - : calcium , $ \text { ca } $ | $ 4.60\times 10^ { -19 } $ tin , $ \text { sn } $ | $ 7.08\times 10^ { -19 } $ sodium , $ \text { na } $ | $ 3.78\times 10^ { -19 } $ hafnium , $ \text { hf } $ | $ 6.25\times 10^ { -19 } $ samarium , $ \text { sm } $ | $ 4.33\times 10^ { -19 } $ based on this information , what is the most likely identity of our mystery metal ?
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the energy required to free the electron from a particular metal is also called the metal 's work function , which is represented by the symbol $ \phi $ ( in units of $ \text j $ ) : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ like the threshold frequency $ \nu_0 $ , the value of $ \phi $ also changes depending on the metal . we can now write the energy of the photon in terms of the light frequency using planck 's equation : $ \text { e } \text { photon } =h\nu=\text { ke } \text { electron } +\phi $ rearranging this equation in terms of the electron 's kinetic energy , we get : $ \text { ke } _\text { electron } =h\nu-\phi $ we can see that kinetic energy of the photoelectron increases linearly with $ \nu $ as long as the photon energy is greater than the work function $ \phi $ , which is exactly the relationship shown in graph ( a ) above . we can also use this equation to find the photoelectron velocity $ \text v $ , which is related to $ \text { ke } _\text { electron } $ as follows : $ \text { ke } _\text { electron } =h\nu-\phi=\dfrac { 1 } { 2 } m_e\text v^2 $ where $ m_e $ is the rest mass of an electron , $ 9.1094 \times 10^ { -31 } \ , \text { kg } $ .
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how exactly is it transduced ?
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key points based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . contrary to the predictions , experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of particles called photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a metal surface , and the value of $ \phi $ depends on the metal . the energy of the incident photon must be equal to the sum of the metal 's work function and the photoelectron kinetic energy : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ introduction : what is the photoelectric effect ? when light shines on a metal , electrons can be ejected from the surface of the metal in a phenomenon known as the photoelectric effect . this process is also often referred to as photoemission , and the electrons that are ejected from the metal are called photoelectrons . in terms of their behavior and their properties , photoelectrons are no different from other electrons . the prefix , photo- , simply tells us that the electrons have been ejected from a metal surface by incident light . in this article , we will discuss how 19th century physicists attempted ( but failed ! ) to explain the photoelectric effect using classical physics . this ultimately led to the development of the modern description of electromagnetic radiation , which has both wave-like and particle-like properties . predictions based on light as a wave to explain the photoelectric effect , 19th-century physicists theorized that the oscillating electric field of the incoming light wave was heating the electrons and causing them to vibrate , eventually freeing them from the metal surface . this hypothesis was based on the assumption that light traveled purely as a wave through space . ( see this article for more information about the basic properties of light . ) scientists also believed that the energy of the light wave was proportional to its brightness , which is related to the wave 's amplitude . in order to test their hypotheses , they performed experiments to look at the effect of light amplitude and frequency on the rate of electron ejection , as well as the kinetic energy of the photoelectrons . based on the classical description of light as a wave , they made the following predictions : the kinetic energy of emitted photoelectrons should increase with the light amplitude . the rate of electron emission , which is proportional to the measured electric current , should increase as the light frequency is increased . to help us understand why they made these predictions , we can compare a light wave to a water wave . imagine some beach balls sitting on a dock that extends out into the ocean . the dock represents a metal surface , the beach balls represent electrons , and the ocean waves represent light waves . if a single large wave were to shake the dock , we would expect the energy from the big wave would send the beach balls flying off the dock with much more kinetic energy compared to a single , small wave . this is also what physicists believed would happen if the light intensity was increased . light amplitude was expected to be proportional to the light energy , so higher amplitude light was predicted to result in photoelectrons with more kinetic energy . classical physicists also predicted that increasing the frequency of light waves ( at a constant amplitude ) would increase the rate of electrons being ejected , and thus increase the measured electric current . using our beach ball analogy , we would expect waves hitting the dock more frequently would result in more beach balls being knocked off the dock compared to the same sized waves hitting the dock less often . now that we know what physicists thought would happen , let 's look at what they actually observed experimentally ! when intuition fails : photons to the rescue ! when experiments were performed to look at the effect of light amplitude and frequency , the following results were observed : the kinetic energy of photoelectrons increases with light frequency . electric current remains constant as light frequency increases . electric current increases with light amplitude . the kinetic energy of photoelectrons remains constant as light amplitude increases . these results were completely at odds with the predictions based on the classical description of light as a wave ! in order to explain what was happening , it turned out that an entirely new model of light was needed . that model was developed by albert einstein , who proposed that light sometimes behaved as particles of electromagnetic energy which we now call photons . the energy of a photon could be calculated using planck 's equation : $ \text { e } _ { \text { photon } } =h\nu $ where $ \text { e } _ { \text { photon } } $ is the energy of a photon in joules ( $ \text { j } $ ) , $ h $ is planck 's constant $ ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) $ , and $ \nu $ is the frequency of the light in $ \text { hz } $ . according to planck 's equation , the energy of a photon is proportional to the frequency of the light , $ \nu $ . the amplitude of the light is then proportional to the number of photons with a given frequency . concept check : as the wavelength of a photon increases , what happens to the photon 's energy ? light frequency and the threshold frequency $ \nu_0 $ we can think of the incident light as a stream of photons with an energy determined by the light frequency . when a photon hits the metal surface , the photon 's energy is absorbed by an electron in the metal . the graphic below illustrates the relationship between light frequency and the kinetic energy of ejected electrons . the scientists observed that if the incident light had a frequency less than a minimum frequency $ \nu_0 $ , then no electrons were ejected regardless of the light amplitude . this minimum frequency is also called the threshold frequency , and the value of $ \nu_0 $ depends on the metal . for frequencies greater than $ \nu_0 $ , electrons would be ejected from the metal . furthermore , the kinetic energy of the photoelectrons was proportional to the light frequency . the relationship between photoelectron kinetic energy and light frequency is shown in graph ( a ) below . because the light amplitude was kept constant as the light frequency increased , the number of photons being absorbed by the metal remained constant . thus , the rate at which electrons were ejected from the metal ( or the electric current ) remained constant as well . the relationship between electron current and light frequency is illustrated in graph ( b ) above . is n't there more math somewhere ? we can analyze the frequency relationship using the law of conservation of energy . the total energy of the incoming photon , $ \text { e } \text { photon } $ , must be equal to the kinetic energy of the ejected electron , $ \text { ke } { \text { electron } } $ , plus the energy required to eject the electron from the metal . the energy required to free the electron from a particular metal is also called the metal 's work function , which is represented by the symbol $ \phi $ ( in units of $ \text j $ ) : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ like the threshold frequency $ \nu_0 $ , the value of $ \phi $ also changes depending on the metal . we can now write the energy of the photon in terms of the light frequency using planck 's equation : $ \text { e } \text { photon } =h\nu=\text { ke } \text { electron } +\phi $ rearranging this equation in terms of the electron 's kinetic energy , we get : $ \text { ke } _\text { electron } =h\nu-\phi $ we can see that kinetic energy of the photoelectron increases linearly with $ \nu $ as long as the photon energy is greater than the work function $ \phi $ , which is exactly the relationship shown in graph ( a ) above . we can also use this equation to find the photoelectron velocity $ \text v $ , which is related to $ \text { ke } _\text { electron } $ as follows : $ \text { ke } _\text { electron } =h\nu-\phi=\dfrac { 1 } { 2 } m_e\text v^2 $ where $ m_e $ is the rest mass of an electron , $ 9.1094 \times 10^ { -31 } \ , \text { kg } $ . exploring the wave amplitude trends in terms of photons , higher amplitude light means more photons hitting the metal surface . this results in more electrons ejected over a given time period . as long as the light frequency is greater than $ \nu_0 $ , increasing the light amplitude will cause the electron current to increase proportionally as shown in graph ( a ) below . since increasing the light amplitude has no effect on the energy of the incoming photon , the photoelectron kinetic energy remains constant as the light amplitude is increased ( see graph ( b ) above ) . if we try to explain this result using our dock-and-beach-balls analogy , the relationship in graph ( b ) indicates that no matter the height of the wave hitting the dock $ - $ whether it 's a tiny swell , or a huge tsunami $ - $ the individual beach balls would be launched off the dock with the exact same speed ! thus , our intuition and analogy do n't do a very good job of explaining these particular experiments . example $ 1 $ : the photoelectric effect for copper the work function of copper metal is $ \phi=7.53\times10^ { -19 } \text { j } $ . if we shine light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ on copper metal , will the photoelectric effect be observed ? in order to eject electrons , we need the energy of the photons to be greater than the work function of copper . we can use planck 's equation to calculate the energy of the photon , $ \text { e } _ { \text { photon } } $ : $ \begin { align } \text { e } _\text { photon } & amp ; = h\nu \ & amp ; = ( 6.626\times10^ { -34 } \text { j } \cdot\text { s } ) ( 3.0\times10^ { 16 } \text { hz } ) ~~~~\text { plug in values for $ h $ and $ \nu $ } \ & amp ; = 2.0\times10^ { -17 } \text { j } \end { align } $ if we compare our calculated photon energy , $ \text { e } _\text { photon } $ , to copper 's work function , we see that the photon energy is greater than $ \phi $ : $ ~2.0\times10^ { -17 } \text { j } ~ & gt ; ~7.53\times10^ { -19 } \text { j } $ $ ~~~~~~~~\text { e } _\text { photon } ~~~~~~~~~~~~~~~~~~~\phi $ thus , we would expect to see photoelectrons ejected from the copper . next , we will calculate the kinetic energy of the photoelectrons . example $ 2 $ : calculating the kinetic energy of a photoelectron what is the kinetic energy of the photoelectrons ejected from the copper by the light with a frequency of $ 3.0\times 10^ { 16 } \text { hz } $ ? we can calculate the kinetic energy of the photoelectron using the equation that relates $ \text { ke } \text { electron } $ to the energy of the photon , $ \text { e } \text { photon } $ , and the work function , $ \phi $ : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ since we want to know $ \text { ke } _\text { electron } $ , we can start by rearranging the equation so that we will be solving for the kinetic energy of the electron : $ \text { ke } \text { electron } =\text { e } \text { photon } -\phi $ now we can insert our known values for $ \text { e } _\text { photon } $ and $ \phi $ from example 1 : $ \text { ke } _\text { electron } = ( 2.0\times10^ { -17 } \text { j } ) - ( 7.53\times10^ { -19 } \text { j } ) =1.9\times10^ { -17 } \text { j } $ therefore , each photoelectron has a kinetic energy of $ 1.9\times10^ { -17 } \text { j } $ . summary based on the wave model of light , physicists predicted that increasing light amplitude would increase the kinetic energy of emitted photoelectrons , while increasing the frequency would increase measured current . experiments showed that increasing the light frequency increased the kinetic energy of the photoelectrons , and increasing the light amplitude increased the current . based on these findings , einstein proposed that light behaved like a stream of photons with an energy of $ \text { e } =h\nu $ . the work function , $ \phi $ , is the minimum amount of energy required to induce photoemission of electrons from a specific metal surface . the energy of the incident photon must be equal to the sum of the work function and the kinetic energy of a photoelectron : $ \text { e } \text { photon } =\text { ke } \text { electron } +\phi $ try it ! when we shine light with a frequency of $ 6.20 \times 10^ { 14 } \ , \text { hz } $ on a mystery metal , we observe the ejected electrons have a kinetic energy of $ 3.28\times 10^ { -20 } \ , \text j $ . some possible candidates for the mystery metal are shown in the table below : metal | work function $ \phi $ ( joules , $ \text j $ ) : - : | : - : calcium , $ \text { ca } $ | $ 4.60\times 10^ { -19 } $ tin , $ \text { sn } $ | $ 7.08\times 10^ { -19 } $ sodium , $ \text { na } $ | $ 3.78\times 10^ { -19 } $ hafnium , $ \text { hf } $ | $ 6.25\times 10^ { -19 } $ samarium , $ \text { sm } $ | $ 4.33\times 10^ { -19 } $ based on this information , what is the most likely identity of our mystery metal ?
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we can also use this equation to find the photoelectron velocity $ \text v $ , which is related to $ \text { ke } _\text { electron } $ as follows : $ \text { ke } _\text { electron } =h\nu-\phi=\dfrac { 1 } { 2 } m_e\text v^2 $ where $ m_e $ is the rest mass of an electron , $ 9.1094 \times 10^ { -31 } \ , \text { kg } $ . exploring the wave amplitude trends in terms of photons , higher amplitude light means more photons hitting the metal surface . this results in more electrons ejected over a given time period .
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why does the higher amplitude generate more photons ?
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known locally as mezquita-catedral , the great mosque of cordoba is one of the oldest structures still standing from the time muslims ruled al-andalus ( muslim iberia including most of spain , portugal , and a small section of southern france ) in the late 8th century . cordoba is a two hour train ride south of madrid , and draws visitors from all over the world . temple/church/mosque/church the buildings on this site are as complex as the extraordinarily rich history they illustrate . historians believe that there had first been a temple to the roman god , janus , on this site . the temple was converted into a church by invading visigoths who seized cordoba in 572 . next , the church was converted into a mosque and then completely rebuilt by the descendants of the exiled umayyads—the first islamic dynasty who had originally ruled from their capital damascus ( in present-day syria ) from 661 until 750 . a new capital following the overthrow of his family ( the umayyads ) in damascus by the incoming abbasids , prince abd al-rahman i escaped to southern spain . once there , he established control over almost all of the iberian peninsula and attempted to recreate the grandeur of damascus in his new capital , cordoba . he sponsored elaborate building programs , promoted agriculture , and even imported fruit trees and other plants from his former home . orange trees still stand in the courtyard of the mosque of cordoba , a beautiful , if bittersweet reminder of the umayyad exile . the hypostyle hall the building itself was expanded over two hundred years . it is comprised of a large hypostyle prayer hall ( hypostyle means , filled with columns ) , a courtyard with a fountain in the middle , an orange grove , a covered walkway circling the courtyard , and a minaret ( a tower used to call the faithful to prayer ) that is now encased in a squared , tapered bell tower . the expansive prayer hall seems magnified by its repeated geometry . it is built with recycled ancient roman columns from which sprout a striking combination of two-tiered , symmetrical arches , formed of stone and red brick . the mihrab the focal point in the prayer hall is the famous horseshoe arched mihrab or prayer niche . a mihrab is used in a mosque to identify the wall that faces mecca—the birth place of islam in what is now saudi arabia . this is practical as muslims face toward mecca during their daily prayers . the mihrab in the great mosque of cordoba is framed by an exquisitely decorated arch behind which is an unusually large space , the size of a small room . gold tesserae ( small pieces of glass with gold and color backing ) create a dazzling combination of dark blues , reddish browns , yellows and golds that form intricate calligraphic bands and vegetal motifs that adorn the arch . the horseshoe arch the horseshoe-style arch was common in the architecture of the visigoths , the people that ruled this area after the roman empire collapsed and before the umayyads arrived . the horseshoe arch eventually spread across north africa from morocco to egypt and is an easily identified characteristic of western islamic architecture ( though there are some early examples in the east as well ) . the dome above the mihrab , is an equally dazzling dome . it is built of crisscrossing ribs that create pointed arches all lavishly covered with gold mosaic in a radial pattern . this astonishing building technique anticipates later gothic rib vaulting , though on a more modest scale . the great mosque of cordoba is a prime example of the muslim world 's ability to brilliantly develop architectural styles based on pre-existing regional traditions . here is an extraordinary combination of the familiar and the innovative , a formal stylistic vocabulary that can be recognized as “ islamic ” even today . text by shadieh mirmobiny
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orange trees still stand in the courtyard of the mosque of cordoba , a beautiful , if bittersweet reminder of the umayyad exile . the hypostyle hall the building itself was expanded over two hundred years . it is comprised of a large hypostyle prayer hall ( hypostyle means , filled with columns ) , a courtyard with a fountain in the middle , an orange grove , a covered walkway circling the courtyard , and a minaret ( a tower used to call the faithful to prayer ) that is now encased in a squared , tapered bell tower .
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how could one draw a comparison between this and a religious building such as the chartres catherdral ?
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known locally as mezquita-catedral , the great mosque of cordoba is one of the oldest structures still standing from the time muslims ruled al-andalus ( muslim iberia including most of spain , portugal , and a small section of southern france ) in the late 8th century . cordoba is a two hour train ride south of madrid , and draws visitors from all over the world . temple/church/mosque/church the buildings on this site are as complex as the extraordinarily rich history they illustrate . historians believe that there had first been a temple to the roman god , janus , on this site . the temple was converted into a church by invading visigoths who seized cordoba in 572 . next , the church was converted into a mosque and then completely rebuilt by the descendants of the exiled umayyads—the first islamic dynasty who had originally ruled from their capital damascus ( in present-day syria ) from 661 until 750 . a new capital following the overthrow of his family ( the umayyads ) in damascus by the incoming abbasids , prince abd al-rahman i escaped to southern spain . once there , he established control over almost all of the iberian peninsula and attempted to recreate the grandeur of damascus in his new capital , cordoba . he sponsored elaborate building programs , promoted agriculture , and even imported fruit trees and other plants from his former home . orange trees still stand in the courtyard of the mosque of cordoba , a beautiful , if bittersweet reminder of the umayyad exile . the hypostyle hall the building itself was expanded over two hundred years . it is comprised of a large hypostyle prayer hall ( hypostyle means , filled with columns ) , a courtyard with a fountain in the middle , an orange grove , a covered walkway circling the courtyard , and a minaret ( a tower used to call the faithful to prayer ) that is now encased in a squared , tapered bell tower . the expansive prayer hall seems magnified by its repeated geometry . it is built with recycled ancient roman columns from which sprout a striking combination of two-tiered , symmetrical arches , formed of stone and red brick . the mihrab the focal point in the prayer hall is the famous horseshoe arched mihrab or prayer niche . a mihrab is used in a mosque to identify the wall that faces mecca—the birth place of islam in what is now saudi arabia . this is practical as muslims face toward mecca during their daily prayers . the mihrab in the great mosque of cordoba is framed by an exquisitely decorated arch behind which is an unusually large space , the size of a small room . gold tesserae ( small pieces of glass with gold and color backing ) create a dazzling combination of dark blues , reddish browns , yellows and golds that form intricate calligraphic bands and vegetal motifs that adorn the arch . the horseshoe arch the horseshoe-style arch was common in the architecture of the visigoths , the people that ruled this area after the roman empire collapsed and before the umayyads arrived . the horseshoe arch eventually spread across north africa from morocco to egypt and is an easily identified characteristic of western islamic architecture ( though there are some early examples in the east as well ) . the dome above the mihrab , is an equally dazzling dome . it is built of crisscrossing ribs that create pointed arches all lavishly covered with gold mosaic in a radial pattern . this astonishing building technique anticipates later gothic rib vaulting , though on a more modest scale . the great mosque of cordoba is a prime example of the muslim world 's ability to brilliantly develop architectural styles based on pre-existing regional traditions . here is an extraordinary combination of the familiar and the innovative , a formal stylistic vocabulary that can be recognized as “ islamic ” even today . text by shadieh mirmobiny
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the mihrab the focal point in the prayer hall is the famous horseshoe arched mihrab or prayer niche . a mihrab is used in a mosque to identify the wall that faces mecca—the birth place of islam in what is now saudi arabia . this is practical as muslims face toward mecca during their daily prayers .
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in time of abdul rahman iii .. was the mosque used by judges as a court ?
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known locally as mezquita-catedral , the great mosque of cordoba is one of the oldest structures still standing from the time muslims ruled al-andalus ( muslim iberia including most of spain , portugal , and a small section of southern france ) in the late 8th century . cordoba is a two hour train ride south of madrid , and draws visitors from all over the world . temple/church/mosque/church the buildings on this site are as complex as the extraordinarily rich history they illustrate . historians believe that there had first been a temple to the roman god , janus , on this site . the temple was converted into a church by invading visigoths who seized cordoba in 572 . next , the church was converted into a mosque and then completely rebuilt by the descendants of the exiled umayyads—the first islamic dynasty who had originally ruled from their capital damascus ( in present-day syria ) from 661 until 750 . a new capital following the overthrow of his family ( the umayyads ) in damascus by the incoming abbasids , prince abd al-rahman i escaped to southern spain . once there , he established control over almost all of the iberian peninsula and attempted to recreate the grandeur of damascus in his new capital , cordoba . he sponsored elaborate building programs , promoted agriculture , and even imported fruit trees and other plants from his former home . orange trees still stand in the courtyard of the mosque of cordoba , a beautiful , if bittersweet reminder of the umayyad exile . the hypostyle hall the building itself was expanded over two hundred years . it is comprised of a large hypostyle prayer hall ( hypostyle means , filled with columns ) , a courtyard with a fountain in the middle , an orange grove , a covered walkway circling the courtyard , and a minaret ( a tower used to call the faithful to prayer ) that is now encased in a squared , tapered bell tower . the expansive prayer hall seems magnified by its repeated geometry . it is built with recycled ancient roman columns from which sprout a striking combination of two-tiered , symmetrical arches , formed of stone and red brick . the mihrab the focal point in the prayer hall is the famous horseshoe arched mihrab or prayer niche . a mihrab is used in a mosque to identify the wall that faces mecca—the birth place of islam in what is now saudi arabia . this is practical as muslims face toward mecca during their daily prayers . the mihrab in the great mosque of cordoba is framed by an exquisitely decorated arch behind which is an unusually large space , the size of a small room . gold tesserae ( small pieces of glass with gold and color backing ) create a dazzling combination of dark blues , reddish browns , yellows and golds that form intricate calligraphic bands and vegetal motifs that adorn the arch . the horseshoe arch the horseshoe-style arch was common in the architecture of the visigoths , the people that ruled this area after the roman empire collapsed and before the umayyads arrived . the horseshoe arch eventually spread across north africa from morocco to egypt and is an easily identified characteristic of western islamic architecture ( though there are some early examples in the east as well ) . the dome above the mihrab , is an equally dazzling dome . it is built of crisscrossing ribs that create pointed arches all lavishly covered with gold mosaic in a radial pattern . this astonishing building technique anticipates later gothic rib vaulting , though on a more modest scale . the great mosque of cordoba is a prime example of the muslim world 's ability to brilliantly develop architectural styles based on pre-existing regional traditions . here is an extraordinary combination of the familiar and the innovative , a formal stylistic vocabulary that can be recognized as “ islamic ” even today . text by shadieh mirmobiny
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this is practical as muslims face toward mecca during their daily prayers . the mihrab in the great mosque of cordoba is framed by an exquisitely decorated arch behind which is an unusually large space , the size of a small room . gold tesserae ( small pieces of glass with gold and color backing ) create a dazzling combination of dark blues , reddish browns , yellows and golds that form intricate calligraphic bands and vegetal motifs that adorn the arch .
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were the accused ones put behind bars there in front of the judges and the public waiting for the judge to say whether they r guilty or not ?
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known locally as mezquita-catedral , the great mosque of cordoba is one of the oldest structures still standing from the time muslims ruled al-andalus ( muslim iberia including most of spain , portugal , and a small section of southern france ) in the late 8th century . cordoba is a two hour train ride south of madrid , and draws visitors from all over the world . temple/church/mosque/church the buildings on this site are as complex as the extraordinarily rich history they illustrate . historians believe that there had first been a temple to the roman god , janus , on this site . the temple was converted into a church by invading visigoths who seized cordoba in 572 . next , the church was converted into a mosque and then completely rebuilt by the descendants of the exiled umayyads—the first islamic dynasty who had originally ruled from their capital damascus ( in present-day syria ) from 661 until 750 . a new capital following the overthrow of his family ( the umayyads ) in damascus by the incoming abbasids , prince abd al-rahman i escaped to southern spain . once there , he established control over almost all of the iberian peninsula and attempted to recreate the grandeur of damascus in his new capital , cordoba . he sponsored elaborate building programs , promoted agriculture , and even imported fruit trees and other plants from his former home . orange trees still stand in the courtyard of the mosque of cordoba , a beautiful , if bittersweet reminder of the umayyad exile . the hypostyle hall the building itself was expanded over two hundred years . it is comprised of a large hypostyle prayer hall ( hypostyle means , filled with columns ) , a courtyard with a fountain in the middle , an orange grove , a covered walkway circling the courtyard , and a minaret ( a tower used to call the faithful to prayer ) that is now encased in a squared , tapered bell tower . the expansive prayer hall seems magnified by its repeated geometry . it is built with recycled ancient roman columns from which sprout a striking combination of two-tiered , symmetrical arches , formed of stone and red brick . the mihrab the focal point in the prayer hall is the famous horseshoe arched mihrab or prayer niche . a mihrab is used in a mosque to identify the wall that faces mecca—the birth place of islam in what is now saudi arabia . this is practical as muslims face toward mecca during their daily prayers . the mihrab in the great mosque of cordoba is framed by an exquisitely decorated arch behind which is an unusually large space , the size of a small room . gold tesserae ( small pieces of glass with gold and color backing ) create a dazzling combination of dark blues , reddish browns , yellows and golds that form intricate calligraphic bands and vegetal motifs that adorn the arch . the horseshoe arch the horseshoe-style arch was common in the architecture of the visigoths , the people that ruled this area after the roman empire collapsed and before the umayyads arrived . the horseshoe arch eventually spread across north africa from morocco to egypt and is an easily identified characteristic of western islamic architecture ( though there are some early examples in the east as well ) . the dome above the mihrab , is an equally dazzling dome . it is built of crisscrossing ribs that create pointed arches all lavishly covered with gold mosaic in a radial pattern . this astonishing building technique anticipates later gothic rib vaulting , though on a more modest scale . the great mosque of cordoba is a prime example of the muslim world 's ability to brilliantly develop architectural styles based on pre-existing regional traditions . here is an extraordinary combination of the familiar and the innovative , a formal stylistic vocabulary that can be recognized as “ islamic ” even today . text by shadieh mirmobiny
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known locally as mezquita-catedral , the great mosque of cordoba is one of the oldest structures still standing from the time muslims ruled al-andalus ( muslim iberia including most of spain , portugal , and a small section of southern france ) in the late 8th century . cordoba is a two hour train ride south of madrid , and draws visitors from all over the world .
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what was life like during this time period ?
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known locally as mezquita-catedral , the great mosque of cordoba is one of the oldest structures still standing from the time muslims ruled al-andalus ( muslim iberia including most of spain , portugal , and a small section of southern france ) in the late 8th century . cordoba is a two hour train ride south of madrid , and draws visitors from all over the world . temple/church/mosque/church the buildings on this site are as complex as the extraordinarily rich history they illustrate . historians believe that there had first been a temple to the roman god , janus , on this site . the temple was converted into a church by invading visigoths who seized cordoba in 572 . next , the church was converted into a mosque and then completely rebuilt by the descendants of the exiled umayyads—the first islamic dynasty who had originally ruled from their capital damascus ( in present-day syria ) from 661 until 750 . a new capital following the overthrow of his family ( the umayyads ) in damascus by the incoming abbasids , prince abd al-rahman i escaped to southern spain . once there , he established control over almost all of the iberian peninsula and attempted to recreate the grandeur of damascus in his new capital , cordoba . he sponsored elaborate building programs , promoted agriculture , and even imported fruit trees and other plants from his former home . orange trees still stand in the courtyard of the mosque of cordoba , a beautiful , if bittersweet reminder of the umayyad exile . the hypostyle hall the building itself was expanded over two hundred years . it is comprised of a large hypostyle prayer hall ( hypostyle means , filled with columns ) , a courtyard with a fountain in the middle , an orange grove , a covered walkway circling the courtyard , and a minaret ( a tower used to call the faithful to prayer ) that is now encased in a squared , tapered bell tower . the expansive prayer hall seems magnified by its repeated geometry . it is built with recycled ancient roman columns from which sprout a striking combination of two-tiered , symmetrical arches , formed of stone and red brick . the mihrab the focal point in the prayer hall is the famous horseshoe arched mihrab or prayer niche . a mihrab is used in a mosque to identify the wall that faces mecca—the birth place of islam in what is now saudi arabia . this is practical as muslims face toward mecca during their daily prayers . the mihrab in the great mosque of cordoba is framed by an exquisitely decorated arch behind which is an unusually large space , the size of a small room . gold tesserae ( small pieces of glass with gold and color backing ) create a dazzling combination of dark blues , reddish browns , yellows and golds that form intricate calligraphic bands and vegetal motifs that adorn the arch . the horseshoe arch the horseshoe-style arch was common in the architecture of the visigoths , the people that ruled this area after the roman empire collapsed and before the umayyads arrived . the horseshoe arch eventually spread across north africa from morocco to egypt and is an easily identified characteristic of western islamic architecture ( though there are some early examples in the east as well ) . the dome above the mihrab , is an equally dazzling dome . it is built of crisscrossing ribs that create pointed arches all lavishly covered with gold mosaic in a radial pattern . this astonishing building technique anticipates later gothic rib vaulting , though on a more modest scale . the great mosque of cordoba is a prime example of the muslim world 's ability to brilliantly develop architectural styles based on pre-existing regional traditions . here is an extraordinary combination of the familiar and the innovative , a formal stylistic vocabulary that can be recognized as “ islamic ” even today . text by shadieh mirmobiny
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this astonishing building technique anticipates later gothic rib vaulting , though on a more modest scale . the great mosque of cordoba is a prime example of the muslim world 's ability to brilliantly develop architectural styles based on pre-existing regional traditions . here is an extraordinary combination of the familiar and the innovative , a formal stylistic vocabulary that can be recognized as “ islamic ” even today .
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what is the great mosque of cordoba currently used for ?
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known locally as mezquita-catedral , the great mosque of cordoba is one of the oldest structures still standing from the time muslims ruled al-andalus ( muslim iberia including most of spain , portugal , and a small section of southern france ) in the late 8th century . cordoba is a two hour train ride south of madrid , and draws visitors from all over the world . temple/church/mosque/church the buildings on this site are as complex as the extraordinarily rich history they illustrate . historians believe that there had first been a temple to the roman god , janus , on this site . the temple was converted into a church by invading visigoths who seized cordoba in 572 . next , the church was converted into a mosque and then completely rebuilt by the descendants of the exiled umayyads—the first islamic dynasty who had originally ruled from their capital damascus ( in present-day syria ) from 661 until 750 . a new capital following the overthrow of his family ( the umayyads ) in damascus by the incoming abbasids , prince abd al-rahman i escaped to southern spain . once there , he established control over almost all of the iberian peninsula and attempted to recreate the grandeur of damascus in his new capital , cordoba . he sponsored elaborate building programs , promoted agriculture , and even imported fruit trees and other plants from his former home . orange trees still stand in the courtyard of the mosque of cordoba , a beautiful , if bittersweet reminder of the umayyad exile . the hypostyle hall the building itself was expanded over two hundred years . it is comprised of a large hypostyle prayer hall ( hypostyle means , filled with columns ) , a courtyard with a fountain in the middle , an orange grove , a covered walkway circling the courtyard , and a minaret ( a tower used to call the faithful to prayer ) that is now encased in a squared , tapered bell tower . the expansive prayer hall seems magnified by its repeated geometry . it is built with recycled ancient roman columns from which sprout a striking combination of two-tiered , symmetrical arches , formed of stone and red brick . the mihrab the focal point in the prayer hall is the famous horseshoe arched mihrab or prayer niche . a mihrab is used in a mosque to identify the wall that faces mecca—the birth place of islam in what is now saudi arabia . this is practical as muslims face toward mecca during their daily prayers . the mihrab in the great mosque of cordoba is framed by an exquisitely decorated arch behind which is an unusually large space , the size of a small room . gold tesserae ( small pieces of glass with gold and color backing ) create a dazzling combination of dark blues , reddish browns , yellows and golds that form intricate calligraphic bands and vegetal motifs that adorn the arch . the horseshoe arch the horseshoe-style arch was common in the architecture of the visigoths , the people that ruled this area after the roman empire collapsed and before the umayyads arrived . the horseshoe arch eventually spread across north africa from morocco to egypt and is an easily identified characteristic of western islamic architecture ( though there are some early examples in the east as well ) . the dome above the mihrab , is an equally dazzling dome . it is built of crisscrossing ribs that create pointed arches all lavishly covered with gold mosaic in a radial pattern . this astonishing building technique anticipates later gothic rib vaulting , though on a more modest scale . the great mosque of cordoba is a prime example of the muslim world 's ability to brilliantly develop architectural styles based on pre-existing regional traditions . here is an extraordinary combination of the familiar and the innovative , a formal stylistic vocabulary that can be recognized as “ islamic ” even today . text by shadieh mirmobiny
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this astonishing building technique anticipates later gothic rib vaulting , though on a more modest scale . the great mosque of cordoba is a prime example of the muslim world 's ability to brilliantly develop architectural styles based on pre-existing regional traditions . here is an extraordinary combination of the familiar and the innovative , a formal stylistic vocabulary that can be recognized as “ islamic ” even today .
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what religion does the mosque of cordoba currently promote ?
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known locally as mezquita-catedral , the great mosque of cordoba is one of the oldest structures still standing from the time muslims ruled al-andalus ( muslim iberia including most of spain , portugal , and a small section of southern france ) in the late 8th century . cordoba is a two hour train ride south of madrid , and draws visitors from all over the world . temple/church/mosque/church the buildings on this site are as complex as the extraordinarily rich history they illustrate . historians believe that there had first been a temple to the roman god , janus , on this site . the temple was converted into a church by invading visigoths who seized cordoba in 572 . next , the church was converted into a mosque and then completely rebuilt by the descendants of the exiled umayyads—the first islamic dynasty who had originally ruled from their capital damascus ( in present-day syria ) from 661 until 750 . a new capital following the overthrow of his family ( the umayyads ) in damascus by the incoming abbasids , prince abd al-rahman i escaped to southern spain . once there , he established control over almost all of the iberian peninsula and attempted to recreate the grandeur of damascus in his new capital , cordoba . he sponsored elaborate building programs , promoted agriculture , and even imported fruit trees and other plants from his former home . orange trees still stand in the courtyard of the mosque of cordoba , a beautiful , if bittersweet reminder of the umayyad exile . the hypostyle hall the building itself was expanded over two hundred years . it is comprised of a large hypostyle prayer hall ( hypostyle means , filled with columns ) , a courtyard with a fountain in the middle , an orange grove , a covered walkway circling the courtyard , and a minaret ( a tower used to call the faithful to prayer ) that is now encased in a squared , tapered bell tower . the expansive prayer hall seems magnified by its repeated geometry . it is built with recycled ancient roman columns from which sprout a striking combination of two-tiered , symmetrical arches , formed of stone and red brick . the mihrab the focal point in the prayer hall is the famous horseshoe arched mihrab or prayer niche . a mihrab is used in a mosque to identify the wall that faces mecca—the birth place of islam in what is now saudi arabia . this is practical as muslims face toward mecca during their daily prayers . the mihrab in the great mosque of cordoba is framed by an exquisitely decorated arch behind which is an unusually large space , the size of a small room . gold tesserae ( small pieces of glass with gold and color backing ) create a dazzling combination of dark blues , reddish browns , yellows and golds that form intricate calligraphic bands and vegetal motifs that adorn the arch . the horseshoe arch the horseshoe-style arch was common in the architecture of the visigoths , the people that ruled this area after the roman empire collapsed and before the umayyads arrived . the horseshoe arch eventually spread across north africa from morocco to egypt and is an easily identified characteristic of western islamic architecture ( though there are some early examples in the east as well ) . the dome above the mihrab , is an equally dazzling dome . it is built of crisscrossing ribs that create pointed arches all lavishly covered with gold mosaic in a radial pattern . this astonishing building technique anticipates later gothic rib vaulting , though on a more modest scale . the great mosque of cordoba is a prime example of the muslim world 's ability to brilliantly develop architectural styles based on pre-existing regional traditions . here is an extraordinary combination of the familiar and the innovative , a formal stylistic vocabulary that can be recognized as “ islamic ” even today . text by shadieh mirmobiny
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the dome above the mihrab , is an equally dazzling dome . it is built of crisscrossing ribs that create pointed arches all lavishly covered with gold mosaic in a radial pattern . this astonishing building technique anticipates later gothic rib vaulting , though on a more modest scale .
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how many arches in total are in the mosque ?
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known locally as mezquita-catedral , the great mosque of cordoba is one of the oldest structures still standing from the time muslims ruled al-andalus ( muslim iberia including most of spain , portugal , and a small section of southern france ) in the late 8th century . cordoba is a two hour train ride south of madrid , and draws visitors from all over the world . temple/church/mosque/church the buildings on this site are as complex as the extraordinarily rich history they illustrate . historians believe that there had first been a temple to the roman god , janus , on this site . the temple was converted into a church by invading visigoths who seized cordoba in 572 . next , the church was converted into a mosque and then completely rebuilt by the descendants of the exiled umayyads—the first islamic dynasty who had originally ruled from their capital damascus ( in present-day syria ) from 661 until 750 . a new capital following the overthrow of his family ( the umayyads ) in damascus by the incoming abbasids , prince abd al-rahman i escaped to southern spain . once there , he established control over almost all of the iberian peninsula and attempted to recreate the grandeur of damascus in his new capital , cordoba . he sponsored elaborate building programs , promoted agriculture , and even imported fruit trees and other plants from his former home . orange trees still stand in the courtyard of the mosque of cordoba , a beautiful , if bittersweet reminder of the umayyad exile . the hypostyle hall the building itself was expanded over two hundred years . it is comprised of a large hypostyle prayer hall ( hypostyle means , filled with columns ) , a courtyard with a fountain in the middle , an orange grove , a covered walkway circling the courtyard , and a minaret ( a tower used to call the faithful to prayer ) that is now encased in a squared , tapered bell tower . the expansive prayer hall seems magnified by its repeated geometry . it is built with recycled ancient roman columns from which sprout a striking combination of two-tiered , symmetrical arches , formed of stone and red brick . the mihrab the focal point in the prayer hall is the famous horseshoe arched mihrab or prayer niche . a mihrab is used in a mosque to identify the wall that faces mecca—the birth place of islam in what is now saudi arabia . this is practical as muslims face toward mecca during their daily prayers . the mihrab in the great mosque of cordoba is framed by an exquisitely decorated arch behind which is an unusually large space , the size of a small room . gold tesserae ( small pieces of glass with gold and color backing ) create a dazzling combination of dark blues , reddish browns , yellows and golds that form intricate calligraphic bands and vegetal motifs that adorn the arch . the horseshoe arch the horseshoe-style arch was common in the architecture of the visigoths , the people that ruled this area after the roman empire collapsed and before the umayyads arrived . the horseshoe arch eventually spread across north africa from morocco to egypt and is an easily identified characteristic of western islamic architecture ( though there are some early examples in the east as well ) . the dome above the mihrab , is an equally dazzling dome . it is built of crisscrossing ribs that create pointed arches all lavishly covered with gold mosaic in a radial pattern . this astonishing building technique anticipates later gothic rib vaulting , though on a more modest scale . the great mosque of cordoba is a prime example of the muslim world 's ability to brilliantly develop architectural styles based on pre-existing regional traditions . here is an extraordinary combination of the familiar and the innovative , a formal stylistic vocabulary that can be recognized as “ islamic ” even today . text by shadieh mirmobiny
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it is comprised of a large hypostyle prayer hall ( hypostyle means , filled with columns ) , a courtyard with a fountain in the middle , an orange grove , a covered walkway circling the courtyard , and a minaret ( a tower used to call the faithful to prayer ) that is now encased in a squared , tapered bell tower . the expansive prayer hall seems magnified by its repeated geometry . it is built with recycled ancient roman columns from which sprout a striking combination of two-tiered , symmetrical arches , formed of stone and red brick .
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how does the prayer hall inside the great mosque of cordoba , spain visually symbolize infinity ?
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known locally as mezquita-catedral , the great mosque of cordoba is one of the oldest structures still standing from the time muslims ruled al-andalus ( muslim iberia including most of spain , portugal , and a small section of southern france ) in the late 8th century . cordoba is a two hour train ride south of madrid , and draws visitors from all over the world . temple/church/mosque/church the buildings on this site are as complex as the extraordinarily rich history they illustrate . historians believe that there had first been a temple to the roman god , janus , on this site . the temple was converted into a church by invading visigoths who seized cordoba in 572 . next , the church was converted into a mosque and then completely rebuilt by the descendants of the exiled umayyads—the first islamic dynasty who had originally ruled from their capital damascus ( in present-day syria ) from 661 until 750 . a new capital following the overthrow of his family ( the umayyads ) in damascus by the incoming abbasids , prince abd al-rahman i escaped to southern spain . once there , he established control over almost all of the iberian peninsula and attempted to recreate the grandeur of damascus in his new capital , cordoba . he sponsored elaborate building programs , promoted agriculture , and even imported fruit trees and other plants from his former home . orange trees still stand in the courtyard of the mosque of cordoba , a beautiful , if bittersweet reminder of the umayyad exile . the hypostyle hall the building itself was expanded over two hundred years . it is comprised of a large hypostyle prayer hall ( hypostyle means , filled with columns ) , a courtyard with a fountain in the middle , an orange grove , a covered walkway circling the courtyard , and a minaret ( a tower used to call the faithful to prayer ) that is now encased in a squared , tapered bell tower . the expansive prayer hall seems magnified by its repeated geometry . it is built with recycled ancient roman columns from which sprout a striking combination of two-tiered , symmetrical arches , formed of stone and red brick . the mihrab the focal point in the prayer hall is the famous horseshoe arched mihrab or prayer niche . a mihrab is used in a mosque to identify the wall that faces mecca—the birth place of islam in what is now saudi arabia . this is practical as muslims face toward mecca during their daily prayers . the mihrab in the great mosque of cordoba is framed by an exquisitely decorated arch behind which is an unusually large space , the size of a small room . gold tesserae ( small pieces of glass with gold and color backing ) create a dazzling combination of dark blues , reddish browns , yellows and golds that form intricate calligraphic bands and vegetal motifs that adorn the arch . the horseshoe arch the horseshoe-style arch was common in the architecture of the visigoths , the people that ruled this area after the roman empire collapsed and before the umayyads arrived . the horseshoe arch eventually spread across north africa from morocco to egypt and is an easily identified characteristic of western islamic architecture ( though there are some early examples in the east as well ) . the dome above the mihrab , is an equally dazzling dome . it is built of crisscrossing ribs that create pointed arches all lavishly covered with gold mosaic in a radial pattern . this astonishing building technique anticipates later gothic rib vaulting , though on a more modest scale . the great mosque of cordoba is a prime example of the muslim world 's ability to brilliantly develop architectural styles based on pre-existing regional traditions . here is an extraordinary combination of the familiar and the innovative , a formal stylistic vocabulary that can be recognized as “ islamic ” even today . text by shadieh mirmobiny
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historians believe that there had first been a temple to the roman god , janus , on this site . the temple was converted into a church by invading visigoths who seized cordoba in 572 . next , the church was converted into a mosque and then completely rebuilt by the descendants of the exiled umayyads—the first islamic dynasty who had originally ruled from their capital damascus ( in present-day syria ) from 661 until 750 .
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why was only mezquita de cordoba preserved ?
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the chronology of mesopotamia is complicated . scholars refer to places ( sumer , for example ) and peoples ( the babylonians ) , but also empires ( babylonia ) and unfortunately for students of the ancient near east these organizing principles do not always agree . the result is that we might , for example , speak of the very ancient babylonians starting in the 1800s b.c.e . and then also the neo-babylonians more than a thousand years later . what came in between you ask ? well , quite a lot , but mostly the kassites and the assyrians . the assyrian empire which had dominated the near east came to an end at around 600 b.c.e . due to a number of factors including military pressure by the medes ( a pastoral mountain people , again from the zagros mountain range ) , the babylonians , and possibly also civil war . a neo-babylonian dynasty the babylonians rose to power in the late 7th century and were heirs of the urban traditions which had long existed in southern mesopotamia . they eventually ruled an empire as dominant in the near east as that held by the assyrians before them . this period is called neo-babylonian ( or new babylonia ) because babylon had also risen to power earlier and became an independent city-state , most famously during the reign of king hammurabi ( 1792-1750 b.c.e . ) . in the art of the neo-babylonian empire we see an effort to invoke the styles and iconography of the 3rd millennium rulers of babylonia . in fact , one neo-babylonian king , nabonidus , found a statue of sargon of akkad , set it in a temple and provided it with regular offerings . architecture the neo-babylonians are most famous for their architecture , notably at their capital city , babylon . nebuchadnezzar ( 604-561 b.c.e . ) largely rebuilt this ancient city including its walls and seven gates . it is also during this era that nebuchadnezzar purportedly built the `` hanging gardens of babylon '' for his wife because she missed the gardens of her homeland in media ( modern day iran ) . though mentioned by ancient greek and roman writers , the `` hanging gardens '' may , in fact , be legendary . the ishtar gate ( today in the pergamon museum in berlin ) was the most elaborate of the inner city gates constructed in babylon in antiquity . the whole gate was covered in lapis lazuli glazed bricks which would have rendered the façade with a jewel-like shine . alternating rows of lion and cattle march in a relief procession across the gleaming blue surface of the gate . text by dr. senta german
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largely rebuilt this ancient city including its walls and seven gates . it is also during this era that nebuchadnezzar purportedly built the `` hanging gardens of babylon '' for his wife because she missed the gardens of her homeland in media ( modern day iran ) . though mentioned by ancient greek and roman writers , the `` hanging gardens '' may , in fact , be legendary . the ishtar gate ( today in the pergamon museum in berlin ) was the most elaborate of the inner city gates constructed in babylon in antiquity .
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what are the legends surrounding the 'hanging gardens of babylon ' ?
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the chronology of mesopotamia is complicated . scholars refer to places ( sumer , for example ) and peoples ( the babylonians ) , but also empires ( babylonia ) and unfortunately for students of the ancient near east these organizing principles do not always agree . the result is that we might , for example , speak of the very ancient babylonians starting in the 1800s b.c.e . and then also the neo-babylonians more than a thousand years later . what came in between you ask ? well , quite a lot , but mostly the kassites and the assyrians . the assyrian empire which had dominated the near east came to an end at around 600 b.c.e . due to a number of factors including military pressure by the medes ( a pastoral mountain people , again from the zagros mountain range ) , the babylonians , and possibly also civil war . a neo-babylonian dynasty the babylonians rose to power in the late 7th century and were heirs of the urban traditions which had long existed in southern mesopotamia . they eventually ruled an empire as dominant in the near east as that held by the assyrians before them . this period is called neo-babylonian ( or new babylonia ) because babylon had also risen to power earlier and became an independent city-state , most famously during the reign of king hammurabi ( 1792-1750 b.c.e . ) . in the art of the neo-babylonian empire we see an effort to invoke the styles and iconography of the 3rd millennium rulers of babylonia . in fact , one neo-babylonian king , nabonidus , found a statue of sargon of akkad , set it in a temple and provided it with regular offerings . architecture the neo-babylonians are most famous for their architecture , notably at their capital city , babylon . nebuchadnezzar ( 604-561 b.c.e . ) largely rebuilt this ancient city including its walls and seven gates . it is also during this era that nebuchadnezzar purportedly built the `` hanging gardens of babylon '' for his wife because she missed the gardens of her homeland in media ( modern day iran ) . though mentioned by ancient greek and roman writers , the `` hanging gardens '' may , in fact , be legendary . the ishtar gate ( today in the pergamon museum in berlin ) was the most elaborate of the inner city gates constructed in babylon in antiquity . the whole gate was covered in lapis lazuli glazed bricks which would have rendered the façade with a jewel-like shine . alternating rows of lion and cattle march in a relief procession across the gleaming blue surface of the gate . text by dr. senta german
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it is also during this era that nebuchadnezzar purportedly built the `` hanging gardens of babylon '' for his wife because she missed the gardens of her homeland in media ( modern day iran ) . though mentioned by ancient greek and roman writers , the `` hanging gardens '' may , in fact , be legendary . the ishtar gate ( today in the pergamon museum in berlin ) was the most elaborate of the inner city gates constructed in babylon in antiquity .
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why are the hanging gardens believed to be legendary ?
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the chronology of mesopotamia is complicated . scholars refer to places ( sumer , for example ) and peoples ( the babylonians ) , but also empires ( babylonia ) and unfortunately for students of the ancient near east these organizing principles do not always agree . the result is that we might , for example , speak of the very ancient babylonians starting in the 1800s b.c.e . and then also the neo-babylonians more than a thousand years later . what came in between you ask ? well , quite a lot , but mostly the kassites and the assyrians . the assyrian empire which had dominated the near east came to an end at around 600 b.c.e . due to a number of factors including military pressure by the medes ( a pastoral mountain people , again from the zagros mountain range ) , the babylonians , and possibly also civil war . a neo-babylonian dynasty the babylonians rose to power in the late 7th century and were heirs of the urban traditions which had long existed in southern mesopotamia . they eventually ruled an empire as dominant in the near east as that held by the assyrians before them . this period is called neo-babylonian ( or new babylonia ) because babylon had also risen to power earlier and became an independent city-state , most famously during the reign of king hammurabi ( 1792-1750 b.c.e . ) . in the art of the neo-babylonian empire we see an effort to invoke the styles and iconography of the 3rd millennium rulers of babylonia . in fact , one neo-babylonian king , nabonidus , found a statue of sargon of akkad , set it in a temple and provided it with regular offerings . architecture the neo-babylonians are most famous for their architecture , notably at their capital city , babylon . nebuchadnezzar ( 604-561 b.c.e . ) largely rebuilt this ancient city including its walls and seven gates . it is also during this era that nebuchadnezzar purportedly built the `` hanging gardens of babylon '' for his wife because she missed the gardens of her homeland in media ( modern day iran ) . though mentioned by ancient greek and roman writers , the `` hanging gardens '' may , in fact , be legendary . the ishtar gate ( today in the pergamon museum in berlin ) was the most elaborate of the inner city gates constructed in babylon in antiquity . the whole gate was covered in lapis lazuli glazed bricks which would have rendered the façade with a jewel-like shine . alternating rows of lion and cattle march in a relief procession across the gleaming blue surface of the gate . text by dr. senta german
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the assyrian empire which had dominated the near east came to an end at around 600 b.c.e . due to a number of factors including military pressure by the medes ( a pastoral mountain people , again from the zagros mountain range ) , the babylonians , and possibly also civil war . a neo-babylonian dynasty the babylonians rose to power in the late 7th century and were heirs of the urban traditions which had long existed in southern mesopotamia .
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what did people wear in these days ?
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the chronology of mesopotamia is complicated . scholars refer to places ( sumer , for example ) and peoples ( the babylonians ) , but also empires ( babylonia ) and unfortunately for students of the ancient near east these organizing principles do not always agree . the result is that we might , for example , speak of the very ancient babylonians starting in the 1800s b.c.e . and then also the neo-babylonians more than a thousand years later . what came in between you ask ? well , quite a lot , but mostly the kassites and the assyrians . the assyrian empire which had dominated the near east came to an end at around 600 b.c.e . due to a number of factors including military pressure by the medes ( a pastoral mountain people , again from the zagros mountain range ) , the babylonians , and possibly also civil war . a neo-babylonian dynasty the babylonians rose to power in the late 7th century and were heirs of the urban traditions which had long existed in southern mesopotamia . they eventually ruled an empire as dominant in the near east as that held by the assyrians before them . this period is called neo-babylonian ( or new babylonia ) because babylon had also risen to power earlier and became an independent city-state , most famously during the reign of king hammurabi ( 1792-1750 b.c.e . ) . in the art of the neo-babylonian empire we see an effort to invoke the styles and iconography of the 3rd millennium rulers of babylonia . in fact , one neo-babylonian king , nabonidus , found a statue of sargon of akkad , set it in a temple and provided it with regular offerings . architecture the neo-babylonians are most famous for their architecture , notably at their capital city , babylon . nebuchadnezzar ( 604-561 b.c.e . ) largely rebuilt this ancient city including its walls and seven gates . it is also during this era that nebuchadnezzar purportedly built the `` hanging gardens of babylon '' for his wife because she missed the gardens of her homeland in media ( modern day iran ) . though mentioned by ancient greek and roman writers , the `` hanging gardens '' may , in fact , be legendary . the ishtar gate ( today in the pergamon museum in berlin ) was the most elaborate of the inner city gates constructed in babylon in antiquity . the whole gate was covered in lapis lazuli glazed bricks which would have rendered the façade with a jewel-like shine . alternating rows of lion and cattle march in a relief procession across the gleaming blue surface of the gate . text by dr. senta german
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they eventually ruled an empire as dominant in the near east as that held by the assyrians before them . this period is called neo-babylonian ( or new babylonia ) because babylon had also risen to power earlier and became an independent city-state , most famously during the reign of king hammurabi ( 1792-1750 b.c.e . ) . in the art of the neo-babylonian empire we see an effort to invoke the styles and iconography of the 3rd millennium rulers of babylonia . in fact , one neo-babylonian king , nabonidus , found a statue of sargon of akkad , set it in a temple and provided it with regular offerings . architecture the neo-babylonians are most famous for their architecture , notably at their capital city , babylon .
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who was the best neo-babylonian ruler ?
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the chronology of mesopotamia is complicated . scholars refer to places ( sumer , for example ) and peoples ( the babylonians ) , but also empires ( babylonia ) and unfortunately for students of the ancient near east these organizing principles do not always agree . the result is that we might , for example , speak of the very ancient babylonians starting in the 1800s b.c.e . and then also the neo-babylonians more than a thousand years later . what came in between you ask ? well , quite a lot , but mostly the kassites and the assyrians . the assyrian empire which had dominated the near east came to an end at around 600 b.c.e . due to a number of factors including military pressure by the medes ( a pastoral mountain people , again from the zagros mountain range ) , the babylonians , and possibly also civil war . a neo-babylonian dynasty the babylonians rose to power in the late 7th century and were heirs of the urban traditions which had long existed in southern mesopotamia . they eventually ruled an empire as dominant in the near east as that held by the assyrians before them . this period is called neo-babylonian ( or new babylonia ) because babylon had also risen to power earlier and became an independent city-state , most famously during the reign of king hammurabi ( 1792-1750 b.c.e . ) . in the art of the neo-babylonian empire we see an effort to invoke the styles and iconography of the 3rd millennium rulers of babylonia . in fact , one neo-babylonian king , nabonidus , found a statue of sargon of akkad , set it in a temple and provided it with regular offerings . architecture the neo-babylonians are most famous for their architecture , notably at their capital city , babylon . nebuchadnezzar ( 604-561 b.c.e . ) largely rebuilt this ancient city including its walls and seven gates . it is also during this era that nebuchadnezzar purportedly built the `` hanging gardens of babylon '' for his wife because she missed the gardens of her homeland in media ( modern day iran ) . though mentioned by ancient greek and roman writers , the `` hanging gardens '' may , in fact , be legendary . the ishtar gate ( today in the pergamon museum in berlin ) was the most elaborate of the inner city gates constructed in babylon in antiquity . the whole gate was covered in lapis lazuli glazed bricks which would have rendered the façade with a jewel-like shine . alternating rows of lion and cattle march in a relief procession across the gleaming blue surface of the gate . text by dr. senta german
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the result is that we might , for example , speak of the very ancient babylonians starting in the 1800s b.c.e . and then also the neo-babylonians more than a thousand years later . what came in between you ask ?
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are neo-babylonians the same as the chaldeans ?
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the chronology of mesopotamia is complicated . scholars refer to places ( sumer , for example ) and peoples ( the babylonians ) , but also empires ( babylonia ) and unfortunately for students of the ancient near east these organizing principles do not always agree . the result is that we might , for example , speak of the very ancient babylonians starting in the 1800s b.c.e . and then also the neo-babylonians more than a thousand years later . what came in between you ask ? well , quite a lot , but mostly the kassites and the assyrians . the assyrian empire which had dominated the near east came to an end at around 600 b.c.e . due to a number of factors including military pressure by the medes ( a pastoral mountain people , again from the zagros mountain range ) , the babylonians , and possibly also civil war . a neo-babylonian dynasty the babylonians rose to power in the late 7th century and were heirs of the urban traditions which had long existed in southern mesopotamia . they eventually ruled an empire as dominant in the near east as that held by the assyrians before them . this period is called neo-babylonian ( or new babylonia ) because babylon had also risen to power earlier and became an independent city-state , most famously during the reign of king hammurabi ( 1792-1750 b.c.e . ) . in the art of the neo-babylonian empire we see an effort to invoke the styles and iconography of the 3rd millennium rulers of babylonia . in fact , one neo-babylonian king , nabonidus , found a statue of sargon of akkad , set it in a temple and provided it with regular offerings . architecture the neo-babylonians are most famous for their architecture , notably at their capital city , babylon . nebuchadnezzar ( 604-561 b.c.e . ) largely rebuilt this ancient city including its walls and seven gates . it is also during this era that nebuchadnezzar purportedly built the `` hanging gardens of babylon '' for his wife because she missed the gardens of her homeland in media ( modern day iran ) . though mentioned by ancient greek and roman writers , the `` hanging gardens '' may , in fact , be legendary . the ishtar gate ( today in the pergamon museum in berlin ) was the most elaborate of the inner city gates constructed in babylon in antiquity . the whole gate was covered in lapis lazuli glazed bricks which would have rendered the façade with a jewel-like shine . alternating rows of lion and cattle march in a relief procession across the gleaming blue surface of the gate . text by dr. senta german
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the result is that we might , for example , speak of the very ancient babylonians starting in the 1800s b.c.e . and then also the neo-babylonians more than a thousand years later . what came in between you ask ?
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why were they called neo babylonians were they a new generation of the babylonians ?
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the chronology of mesopotamia is complicated . scholars refer to places ( sumer , for example ) and peoples ( the babylonians ) , but also empires ( babylonia ) and unfortunately for students of the ancient near east these organizing principles do not always agree . the result is that we might , for example , speak of the very ancient babylonians starting in the 1800s b.c.e . and then also the neo-babylonians more than a thousand years later . what came in between you ask ? well , quite a lot , but mostly the kassites and the assyrians . the assyrian empire which had dominated the near east came to an end at around 600 b.c.e . due to a number of factors including military pressure by the medes ( a pastoral mountain people , again from the zagros mountain range ) , the babylonians , and possibly also civil war . a neo-babylonian dynasty the babylonians rose to power in the late 7th century and were heirs of the urban traditions which had long existed in southern mesopotamia . they eventually ruled an empire as dominant in the near east as that held by the assyrians before them . this period is called neo-babylonian ( or new babylonia ) because babylon had also risen to power earlier and became an independent city-state , most famously during the reign of king hammurabi ( 1792-1750 b.c.e . ) . in the art of the neo-babylonian empire we see an effort to invoke the styles and iconography of the 3rd millennium rulers of babylonia . in fact , one neo-babylonian king , nabonidus , found a statue of sargon of akkad , set it in a temple and provided it with regular offerings . architecture the neo-babylonians are most famous for their architecture , notably at their capital city , babylon . nebuchadnezzar ( 604-561 b.c.e . ) largely rebuilt this ancient city including its walls and seven gates . it is also during this era that nebuchadnezzar purportedly built the `` hanging gardens of babylon '' for his wife because she missed the gardens of her homeland in media ( modern day iran ) . though mentioned by ancient greek and roman writers , the `` hanging gardens '' may , in fact , be legendary . the ishtar gate ( today in the pergamon museum in berlin ) was the most elaborate of the inner city gates constructed in babylon in antiquity . the whole gate was covered in lapis lazuli glazed bricks which would have rendered the façade with a jewel-like shine . alternating rows of lion and cattle march in a relief procession across the gleaming blue surface of the gate . text by dr. senta german
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largely rebuilt this ancient city including its walls and seven gates . it is also during this era that nebuchadnezzar purportedly built the `` hanging gardens of babylon '' for his wife because she missed the gardens of her homeland in media ( modern day iran ) . though mentioned by ancient greek and roman writers , the `` hanging gardens '' may , in fact , be legendary .
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are the pastoral medes from media , where nebuchadnezzar 's wife was from ?
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the chronology of mesopotamia is complicated . scholars refer to places ( sumer , for example ) and peoples ( the babylonians ) , but also empires ( babylonia ) and unfortunately for students of the ancient near east these organizing principles do not always agree . the result is that we might , for example , speak of the very ancient babylonians starting in the 1800s b.c.e . and then also the neo-babylonians more than a thousand years later . what came in between you ask ? well , quite a lot , but mostly the kassites and the assyrians . the assyrian empire which had dominated the near east came to an end at around 600 b.c.e . due to a number of factors including military pressure by the medes ( a pastoral mountain people , again from the zagros mountain range ) , the babylonians , and possibly also civil war . a neo-babylonian dynasty the babylonians rose to power in the late 7th century and were heirs of the urban traditions which had long existed in southern mesopotamia . they eventually ruled an empire as dominant in the near east as that held by the assyrians before them . this period is called neo-babylonian ( or new babylonia ) because babylon had also risen to power earlier and became an independent city-state , most famously during the reign of king hammurabi ( 1792-1750 b.c.e . ) . in the art of the neo-babylonian empire we see an effort to invoke the styles and iconography of the 3rd millennium rulers of babylonia . in fact , one neo-babylonian king , nabonidus , found a statue of sargon of akkad , set it in a temple and provided it with regular offerings . architecture the neo-babylonians are most famous for their architecture , notably at their capital city , babylon . nebuchadnezzar ( 604-561 b.c.e . ) largely rebuilt this ancient city including its walls and seven gates . it is also during this era that nebuchadnezzar purportedly built the `` hanging gardens of babylon '' for his wife because she missed the gardens of her homeland in media ( modern day iran ) . though mentioned by ancient greek and roman writers , the `` hanging gardens '' may , in fact , be legendary . the ishtar gate ( today in the pergamon museum in berlin ) was the most elaborate of the inner city gates constructed in babylon in antiquity . the whole gate was covered in lapis lazuli glazed bricks which would have rendered the façade with a jewel-like shine . alternating rows of lion and cattle march in a relief procession across the gleaming blue surface of the gate . text by dr. senta german
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they eventually ruled an empire as dominant in the near east as that held by the assyrians before them . this period is called neo-babylonian ( or new babylonia ) because babylon had also risen to power earlier and became an independent city-state , most famously during the reign of king hammurabi ( 1792-1750 b.c.e . ) . in the art of the neo-babylonian empire we see an effort to invoke the styles and iconography of the 3rd millennium rulers of babylonia . in fact , one neo-babylonian king , nabonidus , found a statue of sargon of akkad , set it in a temple and provided it with regular offerings . architecture the neo-babylonians are most famous for their architecture , notably at their capital city , babylon . nebuchadnezzar ( 604-561 b.c.e . )
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where is the neo-babylonian empire located ?
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our brains are so complex , and the way they work is still such a mystery . it is not surprising that most of us go about our day without giving them much of a second thought . that all changes if you have a stroke . a stroke is an interruption of the blood flow within your brain that causes the death of brain cells . there are two ways this can happen : a blood clot can block a blood vessel in the brain causing an ischemic stroke . if the clot dissolves quickly and the blockage is only temporary , it is called a transient ischemic attack ( tia ) or mini stroke . a blood vessel can leak or burst inside your brain causing a brain bleed . if this happens , you have had a hemorrhagic stroke . what keeps your brain working ? most of your brain consists of neurons , or specialized nerve cells that connect together into networks that send and receive messages . they coordinate everything that our bodies do . however , in order to function properly , your brain needs a constant supply of oxygen and nutrients—and a lot of them . oxygen and nutrients travel in your blood and are delivered to your brain cells via two pairs of major arteries called the carotid and vertebral arteries . these major arteries branch into a dense network of small blood vessels that covers the surface and thread their way throughout your brain tissue ensuring that every cell is well supplied . how your brain is organized and what can go wrong your brain is arranged into three parts , the brain stem , cerebellum and cerebrum . different areas of the brain are generally responsible for different functions and actions : brain stem : this connects your brain to the top of your spine and controls lots of basic functions including your heart rate and blood pressure , breathing , consciousness , sleeping and eating . cerebellum : this is attached to the back of the brain stem . it helps control your coordination and balance , and fine tunes your muscle movements ( motor function ) . cerebrum : this is the largest part of the brain and is divided into two halves or hemispheres , which are further divided into four lobes , the frontal , parietal , temporal , and occipital lobe . the right side of the cerebrum controls the left side of your body and vice versa . the frontal lobe controls movement , and executive function , which is our ability to make good or bad decisions , make plans , and manage time . it is also involved in forming memories . the parietal lobe processes what we are seeing , hearing , smelling and touching , which lets us locate exactly where we are physically , and gives us hand-eye coordination . the temporal lobe controls hearing and memory , recognition of faces and languages , and is important for storing long-term memories . the occipital lobe processes the signals from our eyes and is primarily responsible for most things to do with sight . a stroke can happen in any part of the brain . around eight out of ten strokes are caused by a blockage due to a clot ( ischemic ) , while two out of ten are caused by a bleed ( hemorrhagic ) . $ ^1 $ ischemic strokes are more common . there are two types , thrombotic and embolic strokes . a thrombotic stroke occurs when the blood clot has formed in one of the major arteries leading to the brain , while an embolic stroke is when a blood clot forms somewhere else in the body , travels around your body in your bloodstream and then lodges in your brain . loose blood clots are usually linked to atherosclerosis , a buildup of plaque ( a combination of fatty materials , calcium and scar tissue ) , on the inside walls of your arteries , which narrows them , and interferes with or blocks the flow of blood . blood clots form when a plaque ruptures . hemorrhagic strokes are less common , but are more deadly . uncontrolled bleeding can flood an area of the brain , causing localized pressure and swelling that damages or kills the brain cells . hemorrhagic strokes can also cause a shortage of oxygen and nutrient delivery beyond the leak . bleeding may occur at the surface of your brain , just under your skull , or from a burst artery deep within your brain . high blood pressure and/or defects in your arteries are usually to blame for a brain bleed . the common defects include aneurysms , which are weak areas in the blood vessel wall that fill with blood , bulge out like a little balloon , and can burst , particularly if you have high blood pressure , and malformations of blood vessels that are usually present at birth . loss of blood flow due to a blockage , even for very short periods of time , can be enough to cause the neurons in that area to die due to a lack of oxygen and nutrients . that said , every stroke is different and sometimes your brain can compensate to some extent , by shifting the brain function of the damaged part of your brain to the corresponding area on the undamaged side of your brain . this means the damage caused by either type of stroke may be permanent but could only be temporary . signs and symptoms caused by a mini-stroke will usually last less than an hour , and generally do not do permanent damage . signs and symptoms that you are having a stroke usually the signs and symptoms of a stroke come on suddenly and include one or more of the following : your face may droop unnaturally on one side . you may not be able to raise your arm on one side . you may feel confused and have trouble understanding what people are saying . your speech may sound slurred and jumbled when you talk you may have difficulty seeing with one or both eyes . because different parts of your brain control different activities , a wide range of signs and symptoms can develop depending on where the damage is done : area of damage | possible effects | - | - | brain stem | a stroke in the brain stem is uncommon , but often fatal . brain stem strokes may cause problems with breathing , heart function , balance and coordination , chewing , swallowing , speaking , and seeing , as well as weakness and paralysis on both sides of your body . | cerebellum | strokes in the cerebellum are less common than in the cerebrum ( the large part of the brain ) , but can cause severe effects including problems with balance and coordination , dizziness , headaches , nausea and vomiting . | cerebrum - left hemisphere | strokes in the left hemisphere typically cause weakness or paralysis on the right side of your body , and cognitive problems including difficulties with reading , talking and thinking , and learning and remembering new information . | cerebrum - right hemisphere | strokes in the right hemisphere typically cause problems with vision , depth perception , short-term memory loss , and judgement , as well as weakness or paralysis on the left side , and a tendency to ignore things on your left side including your own left arm and leg . | are you at increased risk of having a stroke ? there are things that you can ’ t control such as your gender , family history and age , that affect the likelihood of whether or not you will have a stroke . the risk is higher if you are male . strokes also seem to run in families , so your risk goes up if one of your immediate relatives has had a stroke . your risk for strokes also increases as you get older . then there are other risk factors that increase your chances of having a stroke . these are called “ modifiable ” risk factors , which means they can potentially be treated or controlled . these risk factors tend to be interconnected and linked to lifestyle . the most important one for any kind of stroke is high blood pressure , which can damage and weaken your arteries so that they clog or burst more easily . high blood pressure is responsible for over 50 % of strokes. $ ^2 $ other important risk factors include atrial fibrillation , which means you an irregular heartbeat , high cholesterol , diabetes , physical inactivity and smoking . the more risk factors you have , the more likely you are to have a stroke . how likely are you to have a stroke ? every year , almost 17 million people worldwide have a stroke and almost 6 million people die because of it. $ ^3 $ stroke is responsible for almost 10 % of all deaths worldwide and is the number two killer after heart disease. $ ^3 $ death from stroke is highest in eastern europe and russia , and south east asia , and is generally more common in lower income countries. $ ^3 $ stroke in young and middle-aged people is happening more often than ever before , with most strokes occurring in people younger than 75 years old. $ ^3 $ unfortunately , about 5 million people worldwide are living with permanent disabilities because of stroke. $ ^4 $ how can you avoid a stroke ? your doctor can help you to reduce your risk of stroke by helping you tackle the risk factors that you can do something about . as a first step this will likely involve changes to your diet and exercise , which can help in so many ways . in addition to simply making you feel better , eating more healthily and exercising more often can help lower your blood pressure and cholesterol levels , prevent diabetes , and help you to lose weight . if lifestyle changes are not enough , your doctor may prescribe medications to help control some of these factors . other ways to prevent a stroke include drinking in moderation , quitting smoking and reducing the stresses in your life . your doctor can also give you help with all of these if you need it . diagnosing and treating a stroke a stroke is a medical emergency ! the faster you get medical treatment the better . if you have signs or symptoms of a stroke , you need to get a proper diagnosis and treatment as soon as possible to minimize damage to your brain . you may need several tests to help diagnose what has gone wrong and which parts of your brain have been affected , as well as to guide your treatment . your doctor will likely start with a physical examination , followed by a computerized tomography ( ct ) scan , to decide whether or not you are having a stroke and what kind it is . other tests that can provide your doctor with useful information include magnetic resonance imaging ( mri ) , which helps visualize any brain tissue damage , an angiography that examines blood flow through the brain , blood and urine tests , an echocardiogram that shows how well the valves of you heart are working and the size of your heart chambers , an electrocardiogram ( ecg ) that checks the electrical activity of your heart , and a neurological exam to check how your brain function has been affected by the stroke . treating an ischemic stroke - if the ct scan confirms you are having an ischemic stroke , your doctor will most likely give you a clot busting drug called tissue plasminogen activator as soon as possible . this drug works by dissolving the clot , which restores the blood flow in your brain , and which may reduce the damage . sometimes your doctors will try to physically break up and remove the clot , although this is much less common . treating a hemorrhagic stroke - your doctor will want to find the source of the bleed and try to control it , so as to reduce the pressure and any damage that it may cause . you may need surgery to do this and to repair any blood vessel damage . after you recover from the initial emergency , your doctors will want to treat your risk factors , with lifestyle modifications and medicines if necessary . consider the following : even though mini-strokes do not usually cause permanent brain damage , don ’ t just shrug it off . why do we say that ? a mini-stroke should really be considered a warning that something is going wrong . you can think of a mini-stroke as getting lucky because the blood clot quickly dissolved on its own . however , there ’ s no way to predict that is what will happen when another clot forms . while for many people there is no warning mini-stroke before a full stroke , if you do get one , there is a good chance that you will have a full stroke within the next 3 months . so , take it seriously ! go see your doctor to find out why it happened and to get treatment in order to prevent a full stroke from occurring .
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| cerebrum - right hemisphere | strokes in the right hemisphere typically cause problems with vision , depth perception , short-term memory loss , and judgement , as well as weakness or paralysis on the left side , and a tendency to ignore things on your left side including your own left arm and leg . | are you at increased risk of having a stroke ? there are things that you can ’ t control such as your gender , family history and age , that affect the likelihood of whether or not you will have a stroke .
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under the heading `` are you at increased risk of having a stroke ?
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our brains are so complex , and the way they work is still such a mystery . it is not surprising that most of us go about our day without giving them much of a second thought . that all changes if you have a stroke . a stroke is an interruption of the blood flow within your brain that causes the death of brain cells . there are two ways this can happen : a blood clot can block a blood vessel in the brain causing an ischemic stroke . if the clot dissolves quickly and the blockage is only temporary , it is called a transient ischemic attack ( tia ) or mini stroke . a blood vessel can leak or burst inside your brain causing a brain bleed . if this happens , you have had a hemorrhagic stroke . what keeps your brain working ? most of your brain consists of neurons , or specialized nerve cells that connect together into networks that send and receive messages . they coordinate everything that our bodies do . however , in order to function properly , your brain needs a constant supply of oxygen and nutrients—and a lot of them . oxygen and nutrients travel in your blood and are delivered to your brain cells via two pairs of major arteries called the carotid and vertebral arteries . these major arteries branch into a dense network of small blood vessels that covers the surface and thread their way throughout your brain tissue ensuring that every cell is well supplied . how your brain is organized and what can go wrong your brain is arranged into three parts , the brain stem , cerebellum and cerebrum . different areas of the brain are generally responsible for different functions and actions : brain stem : this connects your brain to the top of your spine and controls lots of basic functions including your heart rate and blood pressure , breathing , consciousness , sleeping and eating . cerebellum : this is attached to the back of the brain stem . it helps control your coordination and balance , and fine tunes your muscle movements ( motor function ) . cerebrum : this is the largest part of the brain and is divided into two halves or hemispheres , which are further divided into four lobes , the frontal , parietal , temporal , and occipital lobe . the right side of the cerebrum controls the left side of your body and vice versa . the frontal lobe controls movement , and executive function , which is our ability to make good or bad decisions , make plans , and manage time . it is also involved in forming memories . the parietal lobe processes what we are seeing , hearing , smelling and touching , which lets us locate exactly where we are physically , and gives us hand-eye coordination . the temporal lobe controls hearing and memory , recognition of faces and languages , and is important for storing long-term memories . the occipital lobe processes the signals from our eyes and is primarily responsible for most things to do with sight . a stroke can happen in any part of the brain . around eight out of ten strokes are caused by a blockage due to a clot ( ischemic ) , while two out of ten are caused by a bleed ( hemorrhagic ) . $ ^1 $ ischemic strokes are more common . there are two types , thrombotic and embolic strokes . a thrombotic stroke occurs when the blood clot has formed in one of the major arteries leading to the brain , while an embolic stroke is when a blood clot forms somewhere else in the body , travels around your body in your bloodstream and then lodges in your brain . loose blood clots are usually linked to atherosclerosis , a buildup of plaque ( a combination of fatty materials , calcium and scar tissue ) , on the inside walls of your arteries , which narrows them , and interferes with or blocks the flow of blood . blood clots form when a plaque ruptures . hemorrhagic strokes are less common , but are more deadly . uncontrolled bleeding can flood an area of the brain , causing localized pressure and swelling that damages or kills the brain cells . hemorrhagic strokes can also cause a shortage of oxygen and nutrient delivery beyond the leak . bleeding may occur at the surface of your brain , just under your skull , or from a burst artery deep within your brain . high blood pressure and/or defects in your arteries are usually to blame for a brain bleed . the common defects include aneurysms , which are weak areas in the blood vessel wall that fill with blood , bulge out like a little balloon , and can burst , particularly if you have high blood pressure , and malformations of blood vessels that are usually present at birth . loss of blood flow due to a blockage , even for very short periods of time , can be enough to cause the neurons in that area to die due to a lack of oxygen and nutrients . that said , every stroke is different and sometimes your brain can compensate to some extent , by shifting the brain function of the damaged part of your brain to the corresponding area on the undamaged side of your brain . this means the damage caused by either type of stroke may be permanent but could only be temporary . signs and symptoms caused by a mini-stroke will usually last less than an hour , and generally do not do permanent damage . signs and symptoms that you are having a stroke usually the signs and symptoms of a stroke come on suddenly and include one or more of the following : your face may droop unnaturally on one side . you may not be able to raise your arm on one side . you may feel confused and have trouble understanding what people are saying . your speech may sound slurred and jumbled when you talk you may have difficulty seeing with one or both eyes . because different parts of your brain control different activities , a wide range of signs and symptoms can develop depending on where the damage is done : area of damage | possible effects | - | - | brain stem | a stroke in the brain stem is uncommon , but often fatal . brain stem strokes may cause problems with breathing , heart function , balance and coordination , chewing , swallowing , speaking , and seeing , as well as weakness and paralysis on both sides of your body . | cerebellum | strokes in the cerebellum are less common than in the cerebrum ( the large part of the brain ) , but can cause severe effects including problems with balance and coordination , dizziness , headaches , nausea and vomiting . | cerebrum - left hemisphere | strokes in the left hemisphere typically cause weakness or paralysis on the right side of your body , and cognitive problems including difficulties with reading , talking and thinking , and learning and remembering new information . | cerebrum - right hemisphere | strokes in the right hemisphere typically cause problems with vision , depth perception , short-term memory loss , and judgement , as well as weakness or paralysis on the left side , and a tendency to ignore things on your left side including your own left arm and leg . | are you at increased risk of having a stroke ? there are things that you can ’ t control such as your gender , family history and age , that affect the likelihood of whether or not you will have a stroke . the risk is higher if you are male . strokes also seem to run in families , so your risk goes up if one of your immediate relatives has had a stroke . your risk for strokes also increases as you get older . then there are other risk factors that increase your chances of having a stroke . these are called “ modifiable ” risk factors , which means they can potentially be treated or controlled . these risk factors tend to be interconnected and linked to lifestyle . the most important one for any kind of stroke is high blood pressure , which can damage and weaken your arteries so that they clog or burst more easily . high blood pressure is responsible for over 50 % of strokes. $ ^2 $ other important risk factors include atrial fibrillation , which means you an irregular heartbeat , high cholesterol , diabetes , physical inactivity and smoking . the more risk factors you have , the more likely you are to have a stroke . how likely are you to have a stroke ? every year , almost 17 million people worldwide have a stroke and almost 6 million people die because of it. $ ^3 $ stroke is responsible for almost 10 % of all deaths worldwide and is the number two killer after heart disease. $ ^3 $ death from stroke is highest in eastern europe and russia , and south east asia , and is generally more common in lower income countries. $ ^3 $ stroke in young and middle-aged people is happening more often than ever before , with most strokes occurring in people younger than 75 years old. $ ^3 $ unfortunately , about 5 million people worldwide are living with permanent disabilities because of stroke. $ ^4 $ how can you avoid a stroke ? your doctor can help you to reduce your risk of stroke by helping you tackle the risk factors that you can do something about . as a first step this will likely involve changes to your diet and exercise , which can help in so many ways . in addition to simply making you feel better , eating more healthily and exercising more often can help lower your blood pressure and cholesterol levels , prevent diabetes , and help you to lose weight . if lifestyle changes are not enough , your doctor may prescribe medications to help control some of these factors . other ways to prevent a stroke include drinking in moderation , quitting smoking and reducing the stresses in your life . your doctor can also give you help with all of these if you need it . diagnosing and treating a stroke a stroke is a medical emergency ! the faster you get medical treatment the better . if you have signs or symptoms of a stroke , you need to get a proper diagnosis and treatment as soon as possible to minimize damage to your brain . you may need several tests to help diagnose what has gone wrong and which parts of your brain have been affected , as well as to guide your treatment . your doctor will likely start with a physical examination , followed by a computerized tomography ( ct ) scan , to decide whether or not you are having a stroke and what kind it is . other tests that can provide your doctor with useful information include magnetic resonance imaging ( mri ) , which helps visualize any brain tissue damage , an angiography that examines blood flow through the brain , blood and urine tests , an echocardiogram that shows how well the valves of you heart are working and the size of your heart chambers , an electrocardiogram ( ecg ) that checks the electrical activity of your heart , and a neurological exam to check how your brain function has been affected by the stroke . treating an ischemic stroke - if the ct scan confirms you are having an ischemic stroke , your doctor will most likely give you a clot busting drug called tissue plasminogen activator as soon as possible . this drug works by dissolving the clot , which restores the blood flow in your brain , and which may reduce the damage . sometimes your doctors will try to physically break up and remove the clot , although this is much less common . treating a hemorrhagic stroke - your doctor will want to find the source of the bleed and try to control it , so as to reduce the pressure and any damage that it may cause . you may need surgery to do this and to repair any blood vessel damage . after you recover from the initial emergency , your doctors will want to treat your risk factors , with lifestyle modifications and medicines if necessary . consider the following : even though mini-strokes do not usually cause permanent brain damage , don ’ t just shrug it off . why do we say that ? a mini-stroke should really be considered a warning that something is going wrong . you can think of a mini-stroke as getting lucky because the blood clot quickly dissolved on its own . however , there ’ s no way to predict that is what will happen when another clot forms . while for many people there is no warning mini-stroke before a full stroke , if you do get one , there is a good chance that you will have a full stroke within the next 3 months . so , take it seriously ! go see your doctor to find out why it happened and to get treatment in order to prevent a full stroke from occurring .
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the most important one for any kind of stroke is high blood pressure , which can damage and weaken your arteries so that they clog or burst more easily . high blood pressure is responsible for over 50 % of strokes. $ ^2 $ other important risk factors include atrial fibrillation , which means you an irregular heartbeat , high cholesterol , diabetes , physical inactivity and smoking . the more risk factors you have , the more likely you are to have a stroke .
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apart from the missing `` have '' , could n't this wording be understood to mean that atrial fibrillation=irregular heartbeat , high cholesterol , diabetes , physical inactivity and smoking ?
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our brains are so complex , and the way they work is still such a mystery . it is not surprising that most of us go about our day without giving them much of a second thought . that all changes if you have a stroke . a stroke is an interruption of the blood flow within your brain that causes the death of brain cells . there are two ways this can happen : a blood clot can block a blood vessel in the brain causing an ischemic stroke . if the clot dissolves quickly and the blockage is only temporary , it is called a transient ischemic attack ( tia ) or mini stroke . a blood vessel can leak or burst inside your brain causing a brain bleed . if this happens , you have had a hemorrhagic stroke . what keeps your brain working ? most of your brain consists of neurons , or specialized nerve cells that connect together into networks that send and receive messages . they coordinate everything that our bodies do . however , in order to function properly , your brain needs a constant supply of oxygen and nutrients—and a lot of them . oxygen and nutrients travel in your blood and are delivered to your brain cells via two pairs of major arteries called the carotid and vertebral arteries . these major arteries branch into a dense network of small blood vessels that covers the surface and thread their way throughout your brain tissue ensuring that every cell is well supplied . how your brain is organized and what can go wrong your brain is arranged into three parts , the brain stem , cerebellum and cerebrum . different areas of the brain are generally responsible for different functions and actions : brain stem : this connects your brain to the top of your spine and controls lots of basic functions including your heart rate and blood pressure , breathing , consciousness , sleeping and eating . cerebellum : this is attached to the back of the brain stem . it helps control your coordination and balance , and fine tunes your muscle movements ( motor function ) . cerebrum : this is the largest part of the brain and is divided into two halves or hemispheres , which are further divided into four lobes , the frontal , parietal , temporal , and occipital lobe . the right side of the cerebrum controls the left side of your body and vice versa . the frontal lobe controls movement , and executive function , which is our ability to make good or bad decisions , make plans , and manage time . it is also involved in forming memories . the parietal lobe processes what we are seeing , hearing , smelling and touching , which lets us locate exactly where we are physically , and gives us hand-eye coordination . the temporal lobe controls hearing and memory , recognition of faces and languages , and is important for storing long-term memories . the occipital lobe processes the signals from our eyes and is primarily responsible for most things to do with sight . a stroke can happen in any part of the brain . around eight out of ten strokes are caused by a blockage due to a clot ( ischemic ) , while two out of ten are caused by a bleed ( hemorrhagic ) . $ ^1 $ ischemic strokes are more common . there are two types , thrombotic and embolic strokes . a thrombotic stroke occurs when the blood clot has formed in one of the major arteries leading to the brain , while an embolic stroke is when a blood clot forms somewhere else in the body , travels around your body in your bloodstream and then lodges in your brain . loose blood clots are usually linked to atherosclerosis , a buildup of plaque ( a combination of fatty materials , calcium and scar tissue ) , on the inside walls of your arteries , which narrows them , and interferes with or blocks the flow of blood . blood clots form when a plaque ruptures . hemorrhagic strokes are less common , but are more deadly . uncontrolled bleeding can flood an area of the brain , causing localized pressure and swelling that damages or kills the brain cells . hemorrhagic strokes can also cause a shortage of oxygen and nutrient delivery beyond the leak . bleeding may occur at the surface of your brain , just under your skull , or from a burst artery deep within your brain . high blood pressure and/or defects in your arteries are usually to blame for a brain bleed . the common defects include aneurysms , which are weak areas in the blood vessel wall that fill with blood , bulge out like a little balloon , and can burst , particularly if you have high blood pressure , and malformations of blood vessels that are usually present at birth . loss of blood flow due to a blockage , even for very short periods of time , can be enough to cause the neurons in that area to die due to a lack of oxygen and nutrients . that said , every stroke is different and sometimes your brain can compensate to some extent , by shifting the brain function of the damaged part of your brain to the corresponding area on the undamaged side of your brain . this means the damage caused by either type of stroke may be permanent but could only be temporary . signs and symptoms caused by a mini-stroke will usually last less than an hour , and generally do not do permanent damage . signs and symptoms that you are having a stroke usually the signs and symptoms of a stroke come on suddenly and include one or more of the following : your face may droop unnaturally on one side . you may not be able to raise your arm on one side . you may feel confused and have trouble understanding what people are saying . your speech may sound slurred and jumbled when you talk you may have difficulty seeing with one or both eyes . because different parts of your brain control different activities , a wide range of signs and symptoms can develop depending on where the damage is done : area of damage | possible effects | - | - | brain stem | a stroke in the brain stem is uncommon , but often fatal . brain stem strokes may cause problems with breathing , heart function , balance and coordination , chewing , swallowing , speaking , and seeing , as well as weakness and paralysis on both sides of your body . | cerebellum | strokes in the cerebellum are less common than in the cerebrum ( the large part of the brain ) , but can cause severe effects including problems with balance and coordination , dizziness , headaches , nausea and vomiting . | cerebrum - left hemisphere | strokes in the left hemisphere typically cause weakness or paralysis on the right side of your body , and cognitive problems including difficulties with reading , talking and thinking , and learning and remembering new information . | cerebrum - right hemisphere | strokes in the right hemisphere typically cause problems with vision , depth perception , short-term memory loss , and judgement , as well as weakness or paralysis on the left side , and a tendency to ignore things on your left side including your own left arm and leg . | are you at increased risk of having a stroke ? there are things that you can ’ t control such as your gender , family history and age , that affect the likelihood of whether or not you will have a stroke . the risk is higher if you are male . strokes also seem to run in families , so your risk goes up if one of your immediate relatives has had a stroke . your risk for strokes also increases as you get older . then there are other risk factors that increase your chances of having a stroke . these are called “ modifiable ” risk factors , which means they can potentially be treated or controlled . these risk factors tend to be interconnected and linked to lifestyle . the most important one for any kind of stroke is high blood pressure , which can damage and weaken your arteries so that they clog or burst more easily . high blood pressure is responsible for over 50 % of strokes. $ ^2 $ other important risk factors include atrial fibrillation , which means you an irregular heartbeat , high cholesterol , diabetes , physical inactivity and smoking . the more risk factors you have , the more likely you are to have a stroke . how likely are you to have a stroke ? every year , almost 17 million people worldwide have a stroke and almost 6 million people die because of it. $ ^3 $ stroke is responsible for almost 10 % of all deaths worldwide and is the number two killer after heart disease. $ ^3 $ death from stroke is highest in eastern europe and russia , and south east asia , and is generally more common in lower income countries. $ ^3 $ stroke in young and middle-aged people is happening more often than ever before , with most strokes occurring in people younger than 75 years old. $ ^3 $ unfortunately , about 5 million people worldwide are living with permanent disabilities because of stroke. $ ^4 $ how can you avoid a stroke ? your doctor can help you to reduce your risk of stroke by helping you tackle the risk factors that you can do something about . as a first step this will likely involve changes to your diet and exercise , which can help in so many ways . in addition to simply making you feel better , eating more healthily and exercising more often can help lower your blood pressure and cholesterol levels , prevent diabetes , and help you to lose weight . if lifestyle changes are not enough , your doctor may prescribe medications to help control some of these factors . other ways to prevent a stroke include drinking in moderation , quitting smoking and reducing the stresses in your life . your doctor can also give you help with all of these if you need it . diagnosing and treating a stroke a stroke is a medical emergency ! the faster you get medical treatment the better . if you have signs or symptoms of a stroke , you need to get a proper diagnosis and treatment as soon as possible to minimize damage to your brain . you may need several tests to help diagnose what has gone wrong and which parts of your brain have been affected , as well as to guide your treatment . your doctor will likely start with a physical examination , followed by a computerized tomography ( ct ) scan , to decide whether or not you are having a stroke and what kind it is . other tests that can provide your doctor with useful information include magnetic resonance imaging ( mri ) , which helps visualize any brain tissue damage , an angiography that examines blood flow through the brain , blood and urine tests , an echocardiogram that shows how well the valves of you heart are working and the size of your heart chambers , an electrocardiogram ( ecg ) that checks the electrical activity of your heart , and a neurological exam to check how your brain function has been affected by the stroke . treating an ischemic stroke - if the ct scan confirms you are having an ischemic stroke , your doctor will most likely give you a clot busting drug called tissue plasminogen activator as soon as possible . this drug works by dissolving the clot , which restores the blood flow in your brain , and which may reduce the damage . sometimes your doctors will try to physically break up and remove the clot , although this is much less common . treating a hemorrhagic stroke - your doctor will want to find the source of the bleed and try to control it , so as to reduce the pressure and any damage that it may cause . you may need surgery to do this and to repair any blood vessel damage . after you recover from the initial emergency , your doctors will want to treat your risk factors , with lifestyle modifications and medicines if necessary . consider the following : even though mini-strokes do not usually cause permanent brain damage , don ’ t just shrug it off . why do we say that ? a mini-stroke should really be considered a warning that something is going wrong . you can think of a mini-stroke as getting lucky because the blood clot quickly dissolved on its own . however , there ’ s no way to predict that is what will happen when another clot forms . while for many people there is no warning mini-stroke before a full stroke , if you do get one , there is a good chance that you will have a full stroke within the next 3 months . so , take it seriously ! go see your doctor to find out why it happened and to get treatment in order to prevent a full stroke from occurring .
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| cerebrum - right hemisphere | strokes in the right hemisphere typically cause problems with vision , depth perception , short-term memory loss , and judgement , as well as weakness or paralysis on the left side , and a tendency to ignore things on your left side including your own left arm and leg . | are you at increased risk of having a stroke ? there are things that you can ’ t control such as your gender , family history and age , that affect the likelihood of whether or not you will have a stroke .
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does it have anything to do with increased rate of smoking and salt intake ?
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our brains are so complex , and the way they work is still such a mystery . it is not surprising that most of us go about our day without giving them much of a second thought . that all changes if you have a stroke . a stroke is an interruption of the blood flow within your brain that causes the death of brain cells . there are two ways this can happen : a blood clot can block a blood vessel in the brain causing an ischemic stroke . if the clot dissolves quickly and the blockage is only temporary , it is called a transient ischemic attack ( tia ) or mini stroke . a blood vessel can leak or burst inside your brain causing a brain bleed . if this happens , you have had a hemorrhagic stroke . what keeps your brain working ? most of your brain consists of neurons , or specialized nerve cells that connect together into networks that send and receive messages . they coordinate everything that our bodies do . however , in order to function properly , your brain needs a constant supply of oxygen and nutrients—and a lot of them . oxygen and nutrients travel in your blood and are delivered to your brain cells via two pairs of major arteries called the carotid and vertebral arteries . these major arteries branch into a dense network of small blood vessels that covers the surface and thread their way throughout your brain tissue ensuring that every cell is well supplied . how your brain is organized and what can go wrong your brain is arranged into three parts , the brain stem , cerebellum and cerebrum . different areas of the brain are generally responsible for different functions and actions : brain stem : this connects your brain to the top of your spine and controls lots of basic functions including your heart rate and blood pressure , breathing , consciousness , sleeping and eating . cerebellum : this is attached to the back of the brain stem . it helps control your coordination and balance , and fine tunes your muscle movements ( motor function ) . cerebrum : this is the largest part of the brain and is divided into two halves or hemispheres , which are further divided into four lobes , the frontal , parietal , temporal , and occipital lobe . the right side of the cerebrum controls the left side of your body and vice versa . the frontal lobe controls movement , and executive function , which is our ability to make good or bad decisions , make plans , and manage time . it is also involved in forming memories . the parietal lobe processes what we are seeing , hearing , smelling and touching , which lets us locate exactly where we are physically , and gives us hand-eye coordination . the temporal lobe controls hearing and memory , recognition of faces and languages , and is important for storing long-term memories . the occipital lobe processes the signals from our eyes and is primarily responsible for most things to do with sight . a stroke can happen in any part of the brain . around eight out of ten strokes are caused by a blockage due to a clot ( ischemic ) , while two out of ten are caused by a bleed ( hemorrhagic ) . $ ^1 $ ischemic strokes are more common . there are two types , thrombotic and embolic strokes . a thrombotic stroke occurs when the blood clot has formed in one of the major arteries leading to the brain , while an embolic stroke is when a blood clot forms somewhere else in the body , travels around your body in your bloodstream and then lodges in your brain . loose blood clots are usually linked to atherosclerosis , a buildup of plaque ( a combination of fatty materials , calcium and scar tissue ) , on the inside walls of your arteries , which narrows them , and interferes with or blocks the flow of blood . blood clots form when a plaque ruptures . hemorrhagic strokes are less common , but are more deadly . uncontrolled bleeding can flood an area of the brain , causing localized pressure and swelling that damages or kills the brain cells . hemorrhagic strokes can also cause a shortage of oxygen and nutrient delivery beyond the leak . bleeding may occur at the surface of your brain , just under your skull , or from a burst artery deep within your brain . high blood pressure and/or defects in your arteries are usually to blame for a brain bleed . the common defects include aneurysms , which are weak areas in the blood vessel wall that fill with blood , bulge out like a little balloon , and can burst , particularly if you have high blood pressure , and malformations of blood vessels that are usually present at birth . loss of blood flow due to a blockage , even for very short periods of time , can be enough to cause the neurons in that area to die due to a lack of oxygen and nutrients . that said , every stroke is different and sometimes your brain can compensate to some extent , by shifting the brain function of the damaged part of your brain to the corresponding area on the undamaged side of your brain . this means the damage caused by either type of stroke may be permanent but could only be temporary . signs and symptoms caused by a mini-stroke will usually last less than an hour , and generally do not do permanent damage . signs and symptoms that you are having a stroke usually the signs and symptoms of a stroke come on suddenly and include one or more of the following : your face may droop unnaturally on one side . you may not be able to raise your arm on one side . you may feel confused and have trouble understanding what people are saying . your speech may sound slurred and jumbled when you talk you may have difficulty seeing with one or both eyes . because different parts of your brain control different activities , a wide range of signs and symptoms can develop depending on where the damage is done : area of damage | possible effects | - | - | brain stem | a stroke in the brain stem is uncommon , but often fatal . brain stem strokes may cause problems with breathing , heart function , balance and coordination , chewing , swallowing , speaking , and seeing , as well as weakness and paralysis on both sides of your body . | cerebellum | strokes in the cerebellum are less common than in the cerebrum ( the large part of the brain ) , but can cause severe effects including problems with balance and coordination , dizziness , headaches , nausea and vomiting . | cerebrum - left hemisphere | strokes in the left hemisphere typically cause weakness or paralysis on the right side of your body , and cognitive problems including difficulties with reading , talking and thinking , and learning and remembering new information . | cerebrum - right hemisphere | strokes in the right hemisphere typically cause problems with vision , depth perception , short-term memory loss , and judgement , as well as weakness or paralysis on the left side , and a tendency to ignore things on your left side including your own left arm and leg . | are you at increased risk of having a stroke ? there are things that you can ’ t control such as your gender , family history and age , that affect the likelihood of whether or not you will have a stroke . the risk is higher if you are male . strokes also seem to run in families , so your risk goes up if one of your immediate relatives has had a stroke . your risk for strokes also increases as you get older . then there are other risk factors that increase your chances of having a stroke . these are called “ modifiable ” risk factors , which means they can potentially be treated or controlled . these risk factors tend to be interconnected and linked to lifestyle . the most important one for any kind of stroke is high blood pressure , which can damage and weaken your arteries so that they clog or burst more easily . high blood pressure is responsible for over 50 % of strokes. $ ^2 $ other important risk factors include atrial fibrillation , which means you an irregular heartbeat , high cholesterol , diabetes , physical inactivity and smoking . the more risk factors you have , the more likely you are to have a stroke . how likely are you to have a stroke ? every year , almost 17 million people worldwide have a stroke and almost 6 million people die because of it. $ ^3 $ stroke is responsible for almost 10 % of all deaths worldwide and is the number two killer after heart disease. $ ^3 $ death from stroke is highest in eastern europe and russia , and south east asia , and is generally more common in lower income countries. $ ^3 $ stroke in young and middle-aged people is happening more often than ever before , with most strokes occurring in people younger than 75 years old. $ ^3 $ unfortunately , about 5 million people worldwide are living with permanent disabilities because of stroke. $ ^4 $ how can you avoid a stroke ? your doctor can help you to reduce your risk of stroke by helping you tackle the risk factors that you can do something about . as a first step this will likely involve changes to your diet and exercise , which can help in so many ways . in addition to simply making you feel better , eating more healthily and exercising more often can help lower your blood pressure and cholesterol levels , prevent diabetes , and help you to lose weight . if lifestyle changes are not enough , your doctor may prescribe medications to help control some of these factors . other ways to prevent a stroke include drinking in moderation , quitting smoking and reducing the stresses in your life . your doctor can also give you help with all of these if you need it . diagnosing and treating a stroke a stroke is a medical emergency ! the faster you get medical treatment the better . if you have signs or symptoms of a stroke , you need to get a proper diagnosis and treatment as soon as possible to minimize damage to your brain . you may need several tests to help diagnose what has gone wrong and which parts of your brain have been affected , as well as to guide your treatment . your doctor will likely start with a physical examination , followed by a computerized tomography ( ct ) scan , to decide whether or not you are having a stroke and what kind it is . other tests that can provide your doctor with useful information include magnetic resonance imaging ( mri ) , which helps visualize any brain tissue damage , an angiography that examines blood flow through the brain , blood and urine tests , an echocardiogram that shows how well the valves of you heart are working and the size of your heart chambers , an electrocardiogram ( ecg ) that checks the electrical activity of your heart , and a neurological exam to check how your brain function has been affected by the stroke . treating an ischemic stroke - if the ct scan confirms you are having an ischemic stroke , your doctor will most likely give you a clot busting drug called tissue plasminogen activator as soon as possible . this drug works by dissolving the clot , which restores the blood flow in your brain , and which may reduce the damage . sometimes your doctors will try to physically break up and remove the clot , although this is much less common . treating a hemorrhagic stroke - your doctor will want to find the source of the bleed and try to control it , so as to reduce the pressure and any damage that it may cause . you may need surgery to do this and to repair any blood vessel damage . after you recover from the initial emergency , your doctors will want to treat your risk factors , with lifestyle modifications and medicines if necessary . consider the following : even though mini-strokes do not usually cause permanent brain damage , don ’ t just shrug it off . why do we say that ? a mini-stroke should really be considered a warning that something is going wrong . you can think of a mini-stroke as getting lucky because the blood clot quickly dissolved on its own . however , there ’ s no way to predict that is what will happen when another clot forms . while for many people there is no warning mini-stroke before a full stroke , if you do get one , there is a good chance that you will have a full stroke within the next 3 months . so , take it seriously ! go see your doctor to find out why it happened and to get treatment in order to prevent a full stroke from occurring .
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the occipital lobe processes the signals from our eyes and is primarily responsible for most things to do with sight . a stroke can happen in any part of the brain . around eight out of ten strokes are caused by a blockage due to a clot ( ischemic ) , while two out of ten are caused by a bleed ( hemorrhagic ) . $ ^1 $ ischemic strokes are more common .
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why does a stroke happen and is there anyway to prevent it ?
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our brains are so complex , and the way they work is still such a mystery . it is not surprising that most of us go about our day without giving them much of a second thought . that all changes if you have a stroke . a stroke is an interruption of the blood flow within your brain that causes the death of brain cells . there are two ways this can happen : a blood clot can block a blood vessel in the brain causing an ischemic stroke . if the clot dissolves quickly and the blockage is only temporary , it is called a transient ischemic attack ( tia ) or mini stroke . a blood vessel can leak or burst inside your brain causing a brain bleed . if this happens , you have had a hemorrhagic stroke . what keeps your brain working ? most of your brain consists of neurons , or specialized nerve cells that connect together into networks that send and receive messages . they coordinate everything that our bodies do . however , in order to function properly , your brain needs a constant supply of oxygen and nutrients—and a lot of them . oxygen and nutrients travel in your blood and are delivered to your brain cells via two pairs of major arteries called the carotid and vertebral arteries . these major arteries branch into a dense network of small blood vessels that covers the surface and thread their way throughout your brain tissue ensuring that every cell is well supplied . how your brain is organized and what can go wrong your brain is arranged into three parts , the brain stem , cerebellum and cerebrum . different areas of the brain are generally responsible for different functions and actions : brain stem : this connects your brain to the top of your spine and controls lots of basic functions including your heart rate and blood pressure , breathing , consciousness , sleeping and eating . cerebellum : this is attached to the back of the brain stem . it helps control your coordination and balance , and fine tunes your muscle movements ( motor function ) . cerebrum : this is the largest part of the brain and is divided into two halves or hemispheres , which are further divided into four lobes , the frontal , parietal , temporal , and occipital lobe . the right side of the cerebrum controls the left side of your body and vice versa . the frontal lobe controls movement , and executive function , which is our ability to make good or bad decisions , make plans , and manage time . it is also involved in forming memories . the parietal lobe processes what we are seeing , hearing , smelling and touching , which lets us locate exactly where we are physically , and gives us hand-eye coordination . the temporal lobe controls hearing and memory , recognition of faces and languages , and is important for storing long-term memories . the occipital lobe processes the signals from our eyes and is primarily responsible for most things to do with sight . a stroke can happen in any part of the brain . around eight out of ten strokes are caused by a blockage due to a clot ( ischemic ) , while two out of ten are caused by a bleed ( hemorrhagic ) . $ ^1 $ ischemic strokes are more common . there are two types , thrombotic and embolic strokes . a thrombotic stroke occurs when the blood clot has formed in one of the major arteries leading to the brain , while an embolic stroke is when a blood clot forms somewhere else in the body , travels around your body in your bloodstream and then lodges in your brain . loose blood clots are usually linked to atherosclerosis , a buildup of plaque ( a combination of fatty materials , calcium and scar tissue ) , on the inside walls of your arteries , which narrows them , and interferes with or blocks the flow of blood . blood clots form when a plaque ruptures . hemorrhagic strokes are less common , but are more deadly . uncontrolled bleeding can flood an area of the brain , causing localized pressure and swelling that damages or kills the brain cells . hemorrhagic strokes can also cause a shortage of oxygen and nutrient delivery beyond the leak . bleeding may occur at the surface of your brain , just under your skull , or from a burst artery deep within your brain . high blood pressure and/or defects in your arteries are usually to blame for a brain bleed . the common defects include aneurysms , which are weak areas in the blood vessel wall that fill with blood , bulge out like a little balloon , and can burst , particularly if you have high blood pressure , and malformations of blood vessels that are usually present at birth . loss of blood flow due to a blockage , even for very short periods of time , can be enough to cause the neurons in that area to die due to a lack of oxygen and nutrients . that said , every stroke is different and sometimes your brain can compensate to some extent , by shifting the brain function of the damaged part of your brain to the corresponding area on the undamaged side of your brain . this means the damage caused by either type of stroke may be permanent but could only be temporary . signs and symptoms caused by a mini-stroke will usually last less than an hour , and generally do not do permanent damage . signs and symptoms that you are having a stroke usually the signs and symptoms of a stroke come on suddenly and include one or more of the following : your face may droop unnaturally on one side . you may not be able to raise your arm on one side . you may feel confused and have trouble understanding what people are saying . your speech may sound slurred and jumbled when you talk you may have difficulty seeing with one or both eyes . because different parts of your brain control different activities , a wide range of signs and symptoms can develop depending on where the damage is done : area of damage | possible effects | - | - | brain stem | a stroke in the brain stem is uncommon , but often fatal . brain stem strokes may cause problems with breathing , heart function , balance and coordination , chewing , swallowing , speaking , and seeing , as well as weakness and paralysis on both sides of your body . | cerebellum | strokes in the cerebellum are less common than in the cerebrum ( the large part of the brain ) , but can cause severe effects including problems with balance and coordination , dizziness , headaches , nausea and vomiting . | cerebrum - left hemisphere | strokes in the left hemisphere typically cause weakness or paralysis on the right side of your body , and cognitive problems including difficulties with reading , talking and thinking , and learning and remembering new information . | cerebrum - right hemisphere | strokes in the right hemisphere typically cause problems with vision , depth perception , short-term memory loss , and judgement , as well as weakness or paralysis on the left side , and a tendency to ignore things on your left side including your own left arm and leg . | are you at increased risk of having a stroke ? there are things that you can ’ t control such as your gender , family history and age , that affect the likelihood of whether or not you will have a stroke . the risk is higher if you are male . strokes also seem to run in families , so your risk goes up if one of your immediate relatives has had a stroke . your risk for strokes also increases as you get older . then there are other risk factors that increase your chances of having a stroke . these are called “ modifiable ” risk factors , which means they can potentially be treated or controlled . these risk factors tend to be interconnected and linked to lifestyle . the most important one for any kind of stroke is high blood pressure , which can damage and weaken your arteries so that they clog or burst more easily . high blood pressure is responsible for over 50 % of strokes. $ ^2 $ other important risk factors include atrial fibrillation , which means you an irregular heartbeat , high cholesterol , diabetes , physical inactivity and smoking . the more risk factors you have , the more likely you are to have a stroke . how likely are you to have a stroke ? every year , almost 17 million people worldwide have a stroke and almost 6 million people die because of it. $ ^3 $ stroke is responsible for almost 10 % of all deaths worldwide and is the number two killer after heart disease. $ ^3 $ death from stroke is highest in eastern europe and russia , and south east asia , and is generally more common in lower income countries. $ ^3 $ stroke in young and middle-aged people is happening more often than ever before , with most strokes occurring in people younger than 75 years old. $ ^3 $ unfortunately , about 5 million people worldwide are living with permanent disabilities because of stroke. $ ^4 $ how can you avoid a stroke ? your doctor can help you to reduce your risk of stroke by helping you tackle the risk factors that you can do something about . as a first step this will likely involve changes to your diet and exercise , which can help in so many ways . in addition to simply making you feel better , eating more healthily and exercising more often can help lower your blood pressure and cholesterol levels , prevent diabetes , and help you to lose weight . if lifestyle changes are not enough , your doctor may prescribe medications to help control some of these factors . other ways to prevent a stroke include drinking in moderation , quitting smoking and reducing the stresses in your life . your doctor can also give you help with all of these if you need it . diagnosing and treating a stroke a stroke is a medical emergency ! the faster you get medical treatment the better . if you have signs or symptoms of a stroke , you need to get a proper diagnosis and treatment as soon as possible to minimize damage to your brain . you may need several tests to help diagnose what has gone wrong and which parts of your brain have been affected , as well as to guide your treatment . your doctor will likely start with a physical examination , followed by a computerized tomography ( ct ) scan , to decide whether or not you are having a stroke and what kind it is . other tests that can provide your doctor with useful information include magnetic resonance imaging ( mri ) , which helps visualize any brain tissue damage , an angiography that examines blood flow through the brain , blood and urine tests , an echocardiogram that shows how well the valves of you heart are working and the size of your heart chambers , an electrocardiogram ( ecg ) that checks the electrical activity of your heart , and a neurological exam to check how your brain function has been affected by the stroke . treating an ischemic stroke - if the ct scan confirms you are having an ischemic stroke , your doctor will most likely give you a clot busting drug called tissue plasminogen activator as soon as possible . this drug works by dissolving the clot , which restores the blood flow in your brain , and which may reduce the damage . sometimes your doctors will try to physically break up and remove the clot , although this is much less common . treating a hemorrhagic stroke - your doctor will want to find the source of the bleed and try to control it , so as to reduce the pressure and any damage that it may cause . you may need surgery to do this and to repair any blood vessel damage . after you recover from the initial emergency , your doctors will want to treat your risk factors , with lifestyle modifications and medicines if necessary . consider the following : even though mini-strokes do not usually cause permanent brain damage , don ’ t just shrug it off . why do we say that ? a mini-stroke should really be considered a warning that something is going wrong . you can think of a mini-stroke as getting lucky because the blood clot quickly dissolved on its own . however , there ’ s no way to predict that is what will happen when another clot forms . while for many people there is no warning mini-stroke before a full stroke , if you do get one , there is a good chance that you will have a full stroke within the next 3 months . so , take it seriously ! go see your doctor to find out why it happened and to get treatment in order to prevent a full stroke from occurring .
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your doctor can also give you help with all of these if you need it . diagnosing and treating a stroke a stroke is a medical emergency ! the faster you get medical treatment the better .
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what is the different between a stroke a n seizure ?
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our brains are so complex , and the way they work is still such a mystery . it is not surprising that most of us go about our day without giving them much of a second thought . that all changes if you have a stroke . a stroke is an interruption of the blood flow within your brain that causes the death of brain cells . there are two ways this can happen : a blood clot can block a blood vessel in the brain causing an ischemic stroke . if the clot dissolves quickly and the blockage is only temporary , it is called a transient ischemic attack ( tia ) or mini stroke . a blood vessel can leak or burst inside your brain causing a brain bleed . if this happens , you have had a hemorrhagic stroke . what keeps your brain working ? most of your brain consists of neurons , or specialized nerve cells that connect together into networks that send and receive messages . they coordinate everything that our bodies do . however , in order to function properly , your brain needs a constant supply of oxygen and nutrients—and a lot of them . oxygen and nutrients travel in your blood and are delivered to your brain cells via two pairs of major arteries called the carotid and vertebral arteries . these major arteries branch into a dense network of small blood vessels that covers the surface and thread their way throughout your brain tissue ensuring that every cell is well supplied . how your brain is organized and what can go wrong your brain is arranged into three parts , the brain stem , cerebellum and cerebrum . different areas of the brain are generally responsible for different functions and actions : brain stem : this connects your brain to the top of your spine and controls lots of basic functions including your heart rate and blood pressure , breathing , consciousness , sleeping and eating . cerebellum : this is attached to the back of the brain stem . it helps control your coordination and balance , and fine tunes your muscle movements ( motor function ) . cerebrum : this is the largest part of the brain and is divided into two halves or hemispheres , which are further divided into four lobes , the frontal , parietal , temporal , and occipital lobe . the right side of the cerebrum controls the left side of your body and vice versa . the frontal lobe controls movement , and executive function , which is our ability to make good or bad decisions , make plans , and manage time . it is also involved in forming memories . the parietal lobe processes what we are seeing , hearing , smelling and touching , which lets us locate exactly where we are physically , and gives us hand-eye coordination . the temporal lobe controls hearing and memory , recognition of faces and languages , and is important for storing long-term memories . the occipital lobe processes the signals from our eyes and is primarily responsible for most things to do with sight . a stroke can happen in any part of the brain . around eight out of ten strokes are caused by a blockage due to a clot ( ischemic ) , while two out of ten are caused by a bleed ( hemorrhagic ) . $ ^1 $ ischemic strokes are more common . there are two types , thrombotic and embolic strokes . a thrombotic stroke occurs when the blood clot has formed in one of the major arteries leading to the brain , while an embolic stroke is when a blood clot forms somewhere else in the body , travels around your body in your bloodstream and then lodges in your brain . loose blood clots are usually linked to atherosclerosis , a buildup of plaque ( a combination of fatty materials , calcium and scar tissue ) , on the inside walls of your arteries , which narrows them , and interferes with or blocks the flow of blood . blood clots form when a plaque ruptures . hemorrhagic strokes are less common , but are more deadly . uncontrolled bleeding can flood an area of the brain , causing localized pressure and swelling that damages or kills the brain cells . hemorrhagic strokes can also cause a shortage of oxygen and nutrient delivery beyond the leak . bleeding may occur at the surface of your brain , just under your skull , or from a burst artery deep within your brain . high blood pressure and/or defects in your arteries are usually to blame for a brain bleed . the common defects include aneurysms , which are weak areas in the blood vessel wall that fill with blood , bulge out like a little balloon , and can burst , particularly if you have high blood pressure , and malformations of blood vessels that are usually present at birth . loss of blood flow due to a blockage , even for very short periods of time , can be enough to cause the neurons in that area to die due to a lack of oxygen and nutrients . that said , every stroke is different and sometimes your brain can compensate to some extent , by shifting the brain function of the damaged part of your brain to the corresponding area on the undamaged side of your brain . this means the damage caused by either type of stroke may be permanent but could only be temporary . signs and symptoms caused by a mini-stroke will usually last less than an hour , and generally do not do permanent damage . signs and symptoms that you are having a stroke usually the signs and symptoms of a stroke come on suddenly and include one or more of the following : your face may droop unnaturally on one side . you may not be able to raise your arm on one side . you may feel confused and have trouble understanding what people are saying . your speech may sound slurred and jumbled when you talk you may have difficulty seeing with one or both eyes . because different parts of your brain control different activities , a wide range of signs and symptoms can develop depending on where the damage is done : area of damage | possible effects | - | - | brain stem | a stroke in the brain stem is uncommon , but often fatal . brain stem strokes may cause problems with breathing , heart function , balance and coordination , chewing , swallowing , speaking , and seeing , as well as weakness and paralysis on both sides of your body . | cerebellum | strokes in the cerebellum are less common than in the cerebrum ( the large part of the brain ) , but can cause severe effects including problems with balance and coordination , dizziness , headaches , nausea and vomiting . | cerebrum - left hemisphere | strokes in the left hemisphere typically cause weakness or paralysis on the right side of your body , and cognitive problems including difficulties with reading , talking and thinking , and learning and remembering new information . | cerebrum - right hemisphere | strokes in the right hemisphere typically cause problems with vision , depth perception , short-term memory loss , and judgement , as well as weakness or paralysis on the left side , and a tendency to ignore things on your left side including your own left arm and leg . | are you at increased risk of having a stroke ? there are things that you can ’ t control such as your gender , family history and age , that affect the likelihood of whether or not you will have a stroke . the risk is higher if you are male . strokes also seem to run in families , so your risk goes up if one of your immediate relatives has had a stroke . your risk for strokes also increases as you get older . then there are other risk factors that increase your chances of having a stroke . these are called “ modifiable ” risk factors , which means they can potentially be treated or controlled . these risk factors tend to be interconnected and linked to lifestyle . the most important one for any kind of stroke is high blood pressure , which can damage and weaken your arteries so that they clog or burst more easily . high blood pressure is responsible for over 50 % of strokes. $ ^2 $ other important risk factors include atrial fibrillation , which means you an irregular heartbeat , high cholesterol , diabetes , physical inactivity and smoking . the more risk factors you have , the more likely you are to have a stroke . how likely are you to have a stroke ? every year , almost 17 million people worldwide have a stroke and almost 6 million people die because of it. $ ^3 $ stroke is responsible for almost 10 % of all deaths worldwide and is the number two killer after heart disease. $ ^3 $ death from stroke is highest in eastern europe and russia , and south east asia , and is generally more common in lower income countries. $ ^3 $ stroke in young and middle-aged people is happening more often than ever before , with most strokes occurring in people younger than 75 years old. $ ^3 $ unfortunately , about 5 million people worldwide are living with permanent disabilities because of stroke. $ ^4 $ how can you avoid a stroke ? your doctor can help you to reduce your risk of stroke by helping you tackle the risk factors that you can do something about . as a first step this will likely involve changes to your diet and exercise , which can help in so many ways . in addition to simply making you feel better , eating more healthily and exercising more often can help lower your blood pressure and cholesterol levels , prevent diabetes , and help you to lose weight . if lifestyle changes are not enough , your doctor may prescribe medications to help control some of these factors . other ways to prevent a stroke include drinking in moderation , quitting smoking and reducing the stresses in your life . your doctor can also give you help with all of these if you need it . diagnosing and treating a stroke a stroke is a medical emergency ! the faster you get medical treatment the better . if you have signs or symptoms of a stroke , you need to get a proper diagnosis and treatment as soon as possible to minimize damage to your brain . you may need several tests to help diagnose what has gone wrong and which parts of your brain have been affected , as well as to guide your treatment . your doctor will likely start with a physical examination , followed by a computerized tomography ( ct ) scan , to decide whether or not you are having a stroke and what kind it is . other tests that can provide your doctor with useful information include magnetic resonance imaging ( mri ) , which helps visualize any brain tissue damage , an angiography that examines blood flow through the brain , blood and urine tests , an echocardiogram that shows how well the valves of you heart are working and the size of your heart chambers , an electrocardiogram ( ecg ) that checks the electrical activity of your heart , and a neurological exam to check how your brain function has been affected by the stroke . treating an ischemic stroke - if the ct scan confirms you are having an ischemic stroke , your doctor will most likely give you a clot busting drug called tissue plasminogen activator as soon as possible . this drug works by dissolving the clot , which restores the blood flow in your brain , and which may reduce the damage . sometimes your doctors will try to physically break up and remove the clot , although this is much less common . treating a hemorrhagic stroke - your doctor will want to find the source of the bleed and try to control it , so as to reduce the pressure and any damage that it may cause . you may need surgery to do this and to repair any blood vessel damage . after you recover from the initial emergency , your doctors will want to treat your risk factors , with lifestyle modifications and medicines if necessary . consider the following : even though mini-strokes do not usually cause permanent brain damage , don ’ t just shrug it off . why do we say that ? a mini-stroke should really be considered a warning that something is going wrong . you can think of a mini-stroke as getting lucky because the blood clot quickly dissolved on its own . however , there ’ s no way to predict that is what will happen when another clot forms . while for many people there is no warning mini-stroke before a full stroke , if you do get one , there is a good chance that you will have a full stroke within the next 3 months . so , take it seriously ! go see your doctor to find out why it happened and to get treatment in order to prevent a full stroke from occurring .
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you can think of a mini-stroke as getting lucky because the blood clot quickly dissolved on its own . however , there ’ s no way to predict that is what will happen when another clot forms . while for many people there is no warning mini-stroke before a full stroke , if you do get one , there is a good chance that you will have a full stroke within the next 3 months .
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is there a way to prevent strokes to never happen in your body ?
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our brains are so complex , and the way they work is still such a mystery . it is not surprising that most of us go about our day without giving them much of a second thought . that all changes if you have a stroke . a stroke is an interruption of the blood flow within your brain that causes the death of brain cells . there are two ways this can happen : a blood clot can block a blood vessel in the brain causing an ischemic stroke . if the clot dissolves quickly and the blockage is only temporary , it is called a transient ischemic attack ( tia ) or mini stroke . a blood vessel can leak or burst inside your brain causing a brain bleed . if this happens , you have had a hemorrhagic stroke . what keeps your brain working ? most of your brain consists of neurons , or specialized nerve cells that connect together into networks that send and receive messages . they coordinate everything that our bodies do . however , in order to function properly , your brain needs a constant supply of oxygen and nutrients—and a lot of them . oxygen and nutrients travel in your blood and are delivered to your brain cells via two pairs of major arteries called the carotid and vertebral arteries . these major arteries branch into a dense network of small blood vessels that covers the surface and thread their way throughout your brain tissue ensuring that every cell is well supplied . how your brain is organized and what can go wrong your brain is arranged into three parts , the brain stem , cerebellum and cerebrum . different areas of the brain are generally responsible for different functions and actions : brain stem : this connects your brain to the top of your spine and controls lots of basic functions including your heart rate and blood pressure , breathing , consciousness , sleeping and eating . cerebellum : this is attached to the back of the brain stem . it helps control your coordination and balance , and fine tunes your muscle movements ( motor function ) . cerebrum : this is the largest part of the brain and is divided into two halves or hemispheres , which are further divided into four lobes , the frontal , parietal , temporal , and occipital lobe . the right side of the cerebrum controls the left side of your body and vice versa . the frontal lobe controls movement , and executive function , which is our ability to make good or bad decisions , make plans , and manage time . it is also involved in forming memories . the parietal lobe processes what we are seeing , hearing , smelling and touching , which lets us locate exactly where we are physically , and gives us hand-eye coordination . the temporal lobe controls hearing and memory , recognition of faces and languages , and is important for storing long-term memories . the occipital lobe processes the signals from our eyes and is primarily responsible for most things to do with sight . a stroke can happen in any part of the brain . around eight out of ten strokes are caused by a blockage due to a clot ( ischemic ) , while two out of ten are caused by a bleed ( hemorrhagic ) . $ ^1 $ ischemic strokes are more common . there are two types , thrombotic and embolic strokes . a thrombotic stroke occurs when the blood clot has formed in one of the major arteries leading to the brain , while an embolic stroke is when a blood clot forms somewhere else in the body , travels around your body in your bloodstream and then lodges in your brain . loose blood clots are usually linked to atherosclerosis , a buildup of plaque ( a combination of fatty materials , calcium and scar tissue ) , on the inside walls of your arteries , which narrows them , and interferes with or blocks the flow of blood . blood clots form when a plaque ruptures . hemorrhagic strokes are less common , but are more deadly . uncontrolled bleeding can flood an area of the brain , causing localized pressure and swelling that damages or kills the brain cells . hemorrhagic strokes can also cause a shortage of oxygen and nutrient delivery beyond the leak . bleeding may occur at the surface of your brain , just under your skull , or from a burst artery deep within your brain . high blood pressure and/or defects in your arteries are usually to blame for a brain bleed . the common defects include aneurysms , which are weak areas in the blood vessel wall that fill with blood , bulge out like a little balloon , and can burst , particularly if you have high blood pressure , and malformations of blood vessels that are usually present at birth . loss of blood flow due to a blockage , even for very short periods of time , can be enough to cause the neurons in that area to die due to a lack of oxygen and nutrients . that said , every stroke is different and sometimes your brain can compensate to some extent , by shifting the brain function of the damaged part of your brain to the corresponding area on the undamaged side of your brain . this means the damage caused by either type of stroke may be permanent but could only be temporary . signs and symptoms caused by a mini-stroke will usually last less than an hour , and generally do not do permanent damage . signs and symptoms that you are having a stroke usually the signs and symptoms of a stroke come on suddenly and include one or more of the following : your face may droop unnaturally on one side . you may not be able to raise your arm on one side . you may feel confused and have trouble understanding what people are saying . your speech may sound slurred and jumbled when you talk you may have difficulty seeing with one or both eyes . because different parts of your brain control different activities , a wide range of signs and symptoms can develop depending on where the damage is done : area of damage | possible effects | - | - | brain stem | a stroke in the brain stem is uncommon , but often fatal . brain stem strokes may cause problems with breathing , heart function , balance and coordination , chewing , swallowing , speaking , and seeing , as well as weakness and paralysis on both sides of your body . | cerebellum | strokes in the cerebellum are less common than in the cerebrum ( the large part of the brain ) , but can cause severe effects including problems with balance and coordination , dizziness , headaches , nausea and vomiting . | cerebrum - left hemisphere | strokes in the left hemisphere typically cause weakness or paralysis on the right side of your body , and cognitive problems including difficulties with reading , talking and thinking , and learning and remembering new information . | cerebrum - right hemisphere | strokes in the right hemisphere typically cause problems with vision , depth perception , short-term memory loss , and judgement , as well as weakness or paralysis on the left side , and a tendency to ignore things on your left side including your own left arm and leg . | are you at increased risk of having a stroke ? there are things that you can ’ t control such as your gender , family history and age , that affect the likelihood of whether or not you will have a stroke . the risk is higher if you are male . strokes also seem to run in families , so your risk goes up if one of your immediate relatives has had a stroke . your risk for strokes also increases as you get older . then there are other risk factors that increase your chances of having a stroke . these are called “ modifiable ” risk factors , which means they can potentially be treated or controlled . these risk factors tend to be interconnected and linked to lifestyle . the most important one for any kind of stroke is high blood pressure , which can damage and weaken your arteries so that they clog or burst more easily . high blood pressure is responsible for over 50 % of strokes. $ ^2 $ other important risk factors include atrial fibrillation , which means you an irregular heartbeat , high cholesterol , diabetes , physical inactivity and smoking . the more risk factors you have , the more likely you are to have a stroke . how likely are you to have a stroke ? every year , almost 17 million people worldwide have a stroke and almost 6 million people die because of it. $ ^3 $ stroke is responsible for almost 10 % of all deaths worldwide and is the number two killer after heart disease. $ ^3 $ death from stroke is highest in eastern europe and russia , and south east asia , and is generally more common in lower income countries. $ ^3 $ stroke in young and middle-aged people is happening more often than ever before , with most strokes occurring in people younger than 75 years old. $ ^3 $ unfortunately , about 5 million people worldwide are living with permanent disabilities because of stroke. $ ^4 $ how can you avoid a stroke ? your doctor can help you to reduce your risk of stroke by helping you tackle the risk factors that you can do something about . as a first step this will likely involve changes to your diet and exercise , which can help in so many ways . in addition to simply making you feel better , eating more healthily and exercising more often can help lower your blood pressure and cholesterol levels , prevent diabetes , and help you to lose weight . if lifestyle changes are not enough , your doctor may prescribe medications to help control some of these factors . other ways to prevent a stroke include drinking in moderation , quitting smoking and reducing the stresses in your life . your doctor can also give you help with all of these if you need it . diagnosing and treating a stroke a stroke is a medical emergency ! the faster you get medical treatment the better . if you have signs or symptoms of a stroke , you need to get a proper diagnosis and treatment as soon as possible to minimize damage to your brain . you may need several tests to help diagnose what has gone wrong and which parts of your brain have been affected , as well as to guide your treatment . your doctor will likely start with a physical examination , followed by a computerized tomography ( ct ) scan , to decide whether or not you are having a stroke and what kind it is . other tests that can provide your doctor with useful information include magnetic resonance imaging ( mri ) , which helps visualize any brain tissue damage , an angiography that examines blood flow through the brain , blood and urine tests , an echocardiogram that shows how well the valves of you heart are working and the size of your heart chambers , an electrocardiogram ( ecg ) that checks the electrical activity of your heart , and a neurological exam to check how your brain function has been affected by the stroke . treating an ischemic stroke - if the ct scan confirms you are having an ischemic stroke , your doctor will most likely give you a clot busting drug called tissue plasminogen activator as soon as possible . this drug works by dissolving the clot , which restores the blood flow in your brain , and which may reduce the damage . sometimes your doctors will try to physically break up and remove the clot , although this is much less common . treating a hemorrhagic stroke - your doctor will want to find the source of the bleed and try to control it , so as to reduce the pressure and any damage that it may cause . you may need surgery to do this and to repair any blood vessel damage . after you recover from the initial emergency , your doctors will want to treat your risk factors , with lifestyle modifications and medicines if necessary . consider the following : even though mini-strokes do not usually cause permanent brain damage , don ’ t just shrug it off . why do we say that ? a mini-stroke should really be considered a warning that something is going wrong . you can think of a mini-stroke as getting lucky because the blood clot quickly dissolved on its own . however , there ’ s no way to predict that is what will happen when another clot forms . while for many people there is no warning mini-stroke before a full stroke , if you do get one , there is a good chance that you will have a full stroke within the next 3 months . so , take it seriously ! go see your doctor to find out why it happened and to get treatment in order to prevent a full stroke from occurring .
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the occipital lobe processes the signals from our eyes and is primarily responsible for most things to do with sight . a stroke can happen in any part of the brain . around eight out of ten strokes are caused by a blockage due to a clot ( ischemic ) , while two out of ten are caused by a bleed ( hemorrhagic ) . $ ^1 $ ischemic strokes are more common .
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when you have a stroke can it cause part of your body to go into shock and you become palatalized ?
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our brains are so complex , and the way they work is still such a mystery . it is not surprising that most of us go about our day without giving them much of a second thought . that all changes if you have a stroke . a stroke is an interruption of the blood flow within your brain that causes the death of brain cells . there are two ways this can happen : a blood clot can block a blood vessel in the brain causing an ischemic stroke . if the clot dissolves quickly and the blockage is only temporary , it is called a transient ischemic attack ( tia ) or mini stroke . a blood vessel can leak or burst inside your brain causing a brain bleed . if this happens , you have had a hemorrhagic stroke . what keeps your brain working ? most of your brain consists of neurons , or specialized nerve cells that connect together into networks that send and receive messages . they coordinate everything that our bodies do . however , in order to function properly , your brain needs a constant supply of oxygen and nutrients—and a lot of them . oxygen and nutrients travel in your blood and are delivered to your brain cells via two pairs of major arteries called the carotid and vertebral arteries . these major arteries branch into a dense network of small blood vessels that covers the surface and thread their way throughout your brain tissue ensuring that every cell is well supplied . how your brain is organized and what can go wrong your brain is arranged into three parts , the brain stem , cerebellum and cerebrum . different areas of the brain are generally responsible for different functions and actions : brain stem : this connects your brain to the top of your spine and controls lots of basic functions including your heart rate and blood pressure , breathing , consciousness , sleeping and eating . cerebellum : this is attached to the back of the brain stem . it helps control your coordination and balance , and fine tunes your muscle movements ( motor function ) . cerebrum : this is the largest part of the brain and is divided into two halves or hemispheres , which are further divided into four lobes , the frontal , parietal , temporal , and occipital lobe . the right side of the cerebrum controls the left side of your body and vice versa . the frontal lobe controls movement , and executive function , which is our ability to make good or bad decisions , make plans , and manage time . it is also involved in forming memories . the parietal lobe processes what we are seeing , hearing , smelling and touching , which lets us locate exactly where we are physically , and gives us hand-eye coordination . the temporal lobe controls hearing and memory , recognition of faces and languages , and is important for storing long-term memories . the occipital lobe processes the signals from our eyes and is primarily responsible for most things to do with sight . a stroke can happen in any part of the brain . around eight out of ten strokes are caused by a blockage due to a clot ( ischemic ) , while two out of ten are caused by a bleed ( hemorrhagic ) . $ ^1 $ ischemic strokes are more common . there are two types , thrombotic and embolic strokes . a thrombotic stroke occurs when the blood clot has formed in one of the major arteries leading to the brain , while an embolic stroke is when a blood clot forms somewhere else in the body , travels around your body in your bloodstream and then lodges in your brain . loose blood clots are usually linked to atherosclerosis , a buildup of plaque ( a combination of fatty materials , calcium and scar tissue ) , on the inside walls of your arteries , which narrows them , and interferes with or blocks the flow of blood . blood clots form when a plaque ruptures . hemorrhagic strokes are less common , but are more deadly . uncontrolled bleeding can flood an area of the brain , causing localized pressure and swelling that damages or kills the brain cells . hemorrhagic strokes can also cause a shortage of oxygen and nutrient delivery beyond the leak . bleeding may occur at the surface of your brain , just under your skull , or from a burst artery deep within your brain . high blood pressure and/or defects in your arteries are usually to blame for a brain bleed . the common defects include aneurysms , which are weak areas in the blood vessel wall that fill with blood , bulge out like a little balloon , and can burst , particularly if you have high blood pressure , and malformations of blood vessels that are usually present at birth . loss of blood flow due to a blockage , even for very short periods of time , can be enough to cause the neurons in that area to die due to a lack of oxygen and nutrients . that said , every stroke is different and sometimes your brain can compensate to some extent , by shifting the brain function of the damaged part of your brain to the corresponding area on the undamaged side of your brain . this means the damage caused by either type of stroke may be permanent but could only be temporary . signs and symptoms caused by a mini-stroke will usually last less than an hour , and generally do not do permanent damage . signs and symptoms that you are having a stroke usually the signs and symptoms of a stroke come on suddenly and include one or more of the following : your face may droop unnaturally on one side . you may not be able to raise your arm on one side . you may feel confused and have trouble understanding what people are saying . your speech may sound slurred and jumbled when you talk you may have difficulty seeing with one or both eyes . because different parts of your brain control different activities , a wide range of signs and symptoms can develop depending on where the damage is done : area of damage | possible effects | - | - | brain stem | a stroke in the brain stem is uncommon , but often fatal . brain stem strokes may cause problems with breathing , heart function , balance and coordination , chewing , swallowing , speaking , and seeing , as well as weakness and paralysis on both sides of your body . | cerebellum | strokes in the cerebellum are less common than in the cerebrum ( the large part of the brain ) , but can cause severe effects including problems with balance and coordination , dizziness , headaches , nausea and vomiting . | cerebrum - left hemisphere | strokes in the left hemisphere typically cause weakness or paralysis on the right side of your body , and cognitive problems including difficulties with reading , talking and thinking , and learning and remembering new information . | cerebrum - right hemisphere | strokes in the right hemisphere typically cause problems with vision , depth perception , short-term memory loss , and judgement , as well as weakness or paralysis on the left side , and a tendency to ignore things on your left side including your own left arm and leg . | are you at increased risk of having a stroke ? there are things that you can ’ t control such as your gender , family history and age , that affect the likelihood of whether or not you will have a stroke . the risk is higher if you are male . strokes also seem to run in families , so your risk goes up if one of your immediate relatives has had a stroke . your risk for strokes also increases as you get older . then there are other risk factors that increase your chances of having a stroke . these are called “ modifiable ” risk factors , which means they can potentially be treated or controlled . these risk factors tend to be interconnected and linked to lifestyle . the most important one for any kind of stroke is high blood pressure , which can damage and weaken your arteries so that they clog or burst more easily . high blood pressure is responsible for over 50 % of strokes. $ ^2 $ other important risk factors include atrial fibrillation , which means you an irregular heartbeat , high cholesterol , diabetes , physical inactivity and smoking . the more risk factors you have , the more likely you are to have a stroke . how likely are you to have a stroke ? every year , almost 17 million people worldwide have a stroke and almost 6 million people die because of it. $ ^3 $ stroke is responsible for almost 10 % of all deaths worldwide and is the number two killer after heart disease. $ ^3 $ death from stroke is highest in eastern europe and russia , and south east asia , and is generally more common in lower income countries. $ ^3 $ stroke in young and middle-aged people is happening more often than ever before , with most strokes occurring in people younger than 75 years old. $ ^3 $ unfortunately , about 5 million people worldwide are living with permanent disabilities because of stroke. $ ^4 $ how can you avoid a stroke ? your doctor can help you to reduce your risk of stroke by helping you tackle the risk factors that you can do something about . as a first step this will likely involve changes to your diet and exercise , which can help in so many ways . in addition to simply making you feel better , eating more healthily and exercising more often can help lower your blood pressure and cholesterol levels , prevent diabetes , and help you to lose weight . if lifestyle changes are not enough , your doctor may prescribe medications to help control some of these factors . other ways to prevent a stroke include drinking in moderation , quitting smoking and reducing the stresses in your life . your doctor can also give you help with all of these if you need it . diagnosing and treating a stroke a stroke is a medical emergency ! the faster you get medical treatment the better . if you have signs or symptoms of a stroke , you need to get a proper diagnosis and treatment as soon as possible to minimize damage to your brain . you may need several tests to help diagnose what has gone wrong and which parts of your brain have been affected , as well as to guide your treatment . your doctor will likely start with a physical examination , followed by a computerized tomography ( ct ) scan , to decide whether or not you are having a stroke and what kind it is . other tests that can provide your doctor with useful information include magnetic resonance imaging ( mri ) , which helps visualize any brain tissue damage , an angiography that examines blood flow through the brain , blood and urine tests , an echocardiogram that shows how well the valves of you heart are working and the size of your heart chambers , an electrocardiogram ( ecg ) that checks the electrical activity of your heart , and a neurological exam to check how your brain function has been affected by the stroke . treating an ischemic stroke - if the ct scan confirms you are having an ischemic stroke , your doctor will most likely give you a clot busting drug called tissue plasminogen activator as soon as possible . this drug works by dissolving the clot , which restores the blood flow in your brain , and which may reduce the damage . sometimes your doctors will try to physically break up and remove the clot , although this is much less common . treating a hemorrhagic stroke - your doctor will want to find the source of the bleed and try to control it , so as to reduce the pressure and any damage that it may cause . you may need surgery to do this and to repair any blood vessel damage . after you recover from the initial emergency , your doctors will want to treat your risk factors , with lifestyle modifications and medicines if necessary . consider the following : even though mini-strokes do not usually cause permanent brain damage , don ’ t just shrug it off . why do we say that ? a mini-stroke should really be considered a warning that something is going wrong . you can think of a mini-stroke as getting lucky because the blood clot quickly dissolved on its own . however , there ’ s no way to predict that is what will happen when another clot forms . while for many people there is no warning mini-stroke before a full stroke , if you do get one , there is a good chance that you will have a full stroke within the next 3 months . so , take it seriously ! go see your doctor to find out why it happened and to get treatment in order to prevent a full stroke from occurring .
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loose blood clots are usually linked to atherosclerosis , a buildup of plaque ( a combination of fatty materials , calcium and scar tissue ) , on the inside walls of your arteries , which narrows them , and interferes with or blocks the flow of blood . blood clots form when a plaque ruptures . hemorrhagic strokes are less common , but are more deadly .
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what would you call it and why do blood clots never seem to make it too other main arteries , just the brain and heart ?
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our brains are so complex , and the way they work is still such a mystery . it is not surprising that most of us go about our day without giving them much of a second thought . that all changes if you have a stroke . a stroke is an interruption of the blood flow within your brain that causes the death of brain cells . there are two ways this can happen : a blood clot can block a blood vessel in the brain causing an ischemic stroke . if the clot dissolves quickly and the blockage is only temporary , it is called a transient ischemic attack ( tia ) or mini stroke . a blood vessel can leak or burst inside your brain causing a brain bleed . if this happens , you have had a hemorrhagic stroke . what keeps your brain working ? most of your brain consists of neurons , or specialized nerve cells that connect together into networks that send and receive messages . they coordinate everything that our bodies do . however , in order to function properly , your brain needs a constant supply of oxygen and nutrients—and a lot of them . oxygen and nutrients travel in your blood and are delivered to your brain cells via two pairs of major arteries called the carotid and vertebral arteries . these major arteries branch into a dense network of small blood vessels that covers the surface and thread their way throughout your brain tissue ensuring that every cell is well supplied . how your brain is organized and what can go wrong your brain is arranged into three parts , the brain stem , cerebellum and cerebrum . different areas of the brain are generally responsible for different functions and actions : brain stem : this connects your brain to the top of your spine and controls lots of basic functions including your heart rate and blood pressure , breathing , consciousness , sleeping and eating . cerebellum : this is attached to the back of the brain stem . it helps control your coordination and balance , and fine tunes your muscle movements ( motor function ) . cerebrum : this is the largest part of the brain and is divided into two halves or hemispheres , which are further divided into four lobes , the frontal , parietal , temporal , and occipital lobe . the right side of the cerebrum controls the left side of your body and vice versa . the frontal lobe controls movement , and executive function , which is our ability to make good or bad decisions , make plans , and manage time . it is also involved in forming memories . the parietal lobe processes what we are seeing , hearing , smelling and touching , which lets us locate exactly where we are physically , and gives us hand-eye coordination . the temporal lobe controls hearing and memory , recognition of faces and languages , and is important for storing long-term memories . the occipital lobe processes the signals from our eyes and is primarily responsible for most things to do with sight . a stroke can happen in any part of the brain . around eight out of ten strokes are caused by a blockage due to a clot ( ischemic ) , while two out of ten are caused by a bleed ( hemorrhagic ) . $ ^1 $ ischemic strokes are more common . there are two types , thrombotic and embolic strokes . a thrombotic stroke occurs when the blood clot has formed in one of the major arteries leading to the brain , while an embolic stroke is when a blood clot forms somewhere else in the body , travels around your body in your bloodstream and then lodges in your brain . loose blood clots are usually linked to atherosclerosis , a buildup of plaque ( a combination of fatty materials , calcium and scar tissue ) , on the inside walls of your arteries , which narrows them , and interferes with or blocks the flow of blood . blood clots form when a plaque ruptures . hemorrhagic strokes are less common , but are more deadly . uncontrolled bleeding can flood an area of the brain , causing localized pressure and swelling that damages or kills the brain cells . hemorrhagic strokes can also cause a shortage of oxygen and nutrient delivery beyond the leak . bleeding may occur at the surface of your brain , just under your skull , or from a burst artery deep within your brain . high blood pressure and/or defects in your arteries are usually to blame for a brain bleed . the common defects include aneurysms , which are weak areas in the blood vessel wall that fill with blood , bulge out like a little balloon , and can burst , particularly if you have high blood pressure , and malformations of blood vessels that are usually present at birth . loss of blood flow due to a blockage , even for very short periods of time , can be enough to cause the neurons in that area to die due to a lack of oxygen and nutrients . that said , every stroke is different and sometimes your brain can compensate to some extent , by shifting the brain function of the damaged part of your brain to the corresponding area on the undamaged side of your brain . this means the damage caused by either type of stroke may be permanent but could only be temporary . signs and symptoms caused by a mini-stroke will usually last less than an hour , and generally do not do permanent damage . signs and symptoms that you are having a stroke usually the signs and symptoms of a stroke come on suddenly and include one or more of the following : your face may droop unnaturally on one side . you may not be able to raise your arm on one side . you may feel confused and have trouble understanding what people are saying . your speech may sound slurred and jumbled when you talk you may have difficulty seeing with one or both eyes . because different parts of your brain control different activities , a wide range of signs and symptoms can develop depending on where the damage is done : area of damage | possible effects | - | - | brain stem | a stroke in the brain stem is uncommon , but often fatal . brain stem strokes may cause problems with breathing , heart function , balance and coordination , chewing , swallowing , speaking , and seeing , as well as weakness and paralysis on both sides of your body . | cerebellum | strokes in the cerebellum are less common than in the cerebrum ( the large part of the brain ) , but can cause severe effects including problems with balance and coordination , dizziness , headaches , nausea and vomiting . | cerebrum - left hemisphere | strokes in the left hemisphere typically cause weakness or paralysis on the right side of your body , and cognitive problems including difficulties with reading , talking and thinking , and learning and remembering new information . | cerebrum - right hemisphere | strokes in the right hemisphere typically cause problems with vision , depth perception , short-term memory loss , and judgement , as well as weakness or paralysis on the left side , and a tendency to ignore things on your left side including your own left arm and leg . | are you at increased risk of having a stroke ? there are things that you can ’ t control such as your gender , family history and age , that affect the likelihood of whether or not you will have a stroke . the risk is higher if you are male . strokes also seem to run in families , so your risk goes up if one of your immediate relatives has had a stroke . your risk for strokes also increases as you get older . then there are other risk factors that increase your chances of having a stroke . these are called “ modifiable ” risk factors , which means they can potentially be treated or controlled . these risk factors tend to be interconnected and linked to lifestyle . the most important one for any kind of stroke is high blood pressure , which can damage and weaken your arteries so that they clog or burst more easily . high blood pressure is responsible for over 50 % of strokes. $ ^2 $ other important risk factors include atrial fibrillation , which means you an irregular heartbeat , high cholesterol , diabetes , physical inactivity and smoking . the more risk factors you have , the more likely you are to have a stroke . how likely are you to have a stroke ? every year , almost 17 million people worldwide have a stroke and almost 6 million people die because of it. $ ^3 $ stroke is responsible for almost 10 % of all deaths worldwide and is the number two killer after heart disease. $ ^3 $ death from stroke is highest in eastern europe and russia , and south east asia , and is generally more common in lower income countries. $ ^3 $ stroke in young and middle-aged people is happening more often than ever before , with most strokes occurring in people younger than 75 years old. $ ^3 $ unfortunately , about 5 million people worldwide are living with permanent disabilities because of stroke. $ ^4 $ how can you avoid a stroke ? your doctor can help you to reduce your risk of stroke by helping you tackle the risk factors that you can do something about . as a first step this will likely involve changes to your diet and exercise , which can help in so many ways . in addition to simply making you feel better , eating more healthily and exercising more often can help lower your blood pressure and cholesterol levels , prevent diabetes , and help you to lose weight . if lifestyle changes are not enough , your doctor may prescribe medications to help control some of these factors . other ways to prevent a stroke include drinking in moderation , quitting smoking and reducing the stresses in your life . your doctor can also give you help with all of these if you need it . diagnosing and treating a stroke a stroke is a medical emergency ! the faster you get medical treatment the better . if you have signs or symptoms of a stroke , you need to get a proper diagnosis and treatment as soon as possible to minimize damage to your brain . you may need several tests to help diagnose what has gone wrong and which parts of your brain have been affected , as well as to guide your treatment . your doctor will likely start with a physical examination , followed by a computerized tomography ( ct ) scan , to decide whether or not you are having a stroke and what kind it is . other tests that can provide your doctor with useful information include magnetic resonance imaging ( mri ) , which helps visualize any brain tissue damage , an angiography that examines blood flow through the brain , blood and urine tests , an echocardiogram that shows how well the valves of you heart are working and the size of your heart chambers , an electrocardiogram ( ecg ) that checks the electrical activity of your heart , and a neurological exam to check how your brain function has been affected by the stroke . treating an ischemic stroke - if the ct scan confirms you are having an ischemic stroke , your doctor will most likely give you a clot busting drug called tissue plasminogen activator as soon as possible . this drug works by dissolving the clot , which restores the blood flow in your brain , and which may reduce the damage . sometimes your doctors will try to physically break up and remove the clot , although this is much less common . treating a hemorrhagic stroke - your doctor will want to find the source of the bleed and try to control it , so as to reduce the pressure and any damage that it may cause . you may need surgery to do this and to repair any blood vessel damage . after you recover from the initial emergency , your doctors will want to treat your risk factors , with lifestyle modifications and medicines if necessary . consider the following : even though mini-strokes do not usually cause permanent brain damage , don ’ t just shrug it off . why do we say that ? a mini-stroke should really be considered a warning that something is going wrong . you can think of a mini-stroke as getting lucky because the blood clot quickly dissolved on its own . however , there ’ s no way to predict that is what will happen when another clot forms . while for many people there is no warning mini-stroke before a full stroke , if you do get one , there is a good chance that you will have a full stroke within the next 3 months . so , take it seriously ! go see your doctor to find out why it happened and to get treatment in order to prevent a full stroke from occurring .
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there are two ways this can happen : a blood clot can block a blood vessel in the brain causing an ischemic stroke . if the clot dissolves quickly and the blockage is only temporary , it is called a transient ischemic attack ( tia ) or mini stroke . a blood vessel can leak or burst inside your brain causing a brain bleed .
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hi , why is cva an `` accident '' , and tia an `` attack '' ?
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our brains are so complex , and the way they work is still such a mystery . it is not surprising that most of us go about our day without giving them much of a second thought . that all changes if you have a stroke . a stroke is an interruption of the blood flow within your brain that causes the death of brain cells . there are two ways this can happen : a blood clot can block a blood vessel in the brain causing an ischemic stroke . if the clot dissolves quickly and the blockage is only temporary , it is called a transient ischemic attack ( tia ) or mini stroke . a blood vessel can leak or burst inside your brain causing a brain bleed . if this happens , you have had a hemorrhagic stroke . what keeps your brain working ? most of your brain consists of neurons , or specialized nerve cells that connect together into networks that send and receive messages . they coordinate everything that our bodies do . however , in order to function properly , your brain needs a constant supply of oxygen and nutrients—and a lot of them . oxygen and nutrients travel in your blood and are delivered to your brain cells via two pairs of major arteries called the carotid and vertebral arteries . these major arteries branch into a dense network of small blood vessels that covers the surface and thread their way throughout your brain tissue ensuring that every cell is well supplied . how your brain is organized and what can go wrong your brain is arranged into three parts , the brain stem , cerebellum and cerebrum . different areas of the brain are generally responsible for different functions and actions : brain stem : this connects your brain to the top of your spine and controls lots of basic functions including your heart rate and blood pressure , breathing , consciousness , sleeping and eating . cerebellum : this is attached to the back of the brain stem . it helps control your coordination and balance , and fine tunes your muscle movements ( motor function ) . cerebrum : this is the largest part of the brain and is divided into two halves or hemispheres , which are further divided into four lobes , the frontal , parietal , temporal , and occipital lobe . the right side of the cerebrum controls the left side of your body and vice versa . the frontal lobe controls movement , and executive function , which is our ability to make good or bad decisions , make plans , and manage time . it is also involved in forming memories . the parietal lobe processes what we are seeing , hearing , smelling and touching , which lets us locate exactly where we are physically , and gives us hand-eye coordination . the temporal lobe controls hearing and memory , recognition of faces and languages , and is important for storing long-term memories . the occipital lobe processes the signals from our eyes and is primarily responsible for most things to do with sight . a stroke can happen in any part of the brain . around eight out of ten strokes are caused by a blockage due to a clot ( ischemic ) , while two out of ten are caused by a bleed ( hemorrhagic ) . $ ^1 $ ischemic strokes are more common . there are two types , thrombotic and embolic strokes . a thrombotic stroke occurs when the blood clot has formed in one of the major arteries leading to the brain , while an embolic stroke is when a blood clot forms somewhere else in the body , travels around your body in your bloodstream and then lodges in your brain . loose blood clots are usually linked to atherosclerosis , a buildup of plaque ( a combination of fatty materials , calcium and scar tissue ) , on the inside walls of your arteries , which narrows them , and interferes with or blocks the flow of blood . blood clots form when a plaque ruptures . hemorrhagic strokes are less common , but are more deadly . uncontrolled bleeding can flood an area of the brain , causing localized pressure and swelling that damages or kills the brain cells . hemorrhagic strokes can also cause a shortage of oxygen and nutrient delivery beyond the leak . bleeding may occur at the surface of your brain , just under your skull , or from a burst artery deep within your brain . high blood pressure and/or defects in your arteries are usually to blame for a brain bleed . the common defects include aneurysms , which are weak areas in the blood vessel wall that fill with blood , bulge out like a little balloon , and can burst , particularly if you have high blood pressure , and malformations of blood vessels that are usually present at birth . loss of blood flow due to a blockage , even for very short periods of time , can be enough to cause the neurons in that area to die due to a lack of oxygen and nutrients . that said , every stroke is different and sometimes your brain can compensate to some extent , by shifting the brain function of the damaged part of your brain to the corresponding area on the undamaged side of your brain . this means the damage caused by either type of stroke may be permanent but could only be temporary . signs and symptoms caused by a mini-stroke will usually last less than an hour , and generally do not do permanent damage . signs and symptoms that you are having a stroke usually the signs and symptoms of a stroke come on suddenly and include one or more of the following : your face may droop unnaturally on one side . you may not be able to raise your arm on one side . you may feel confused and have trouble understanding what people are saying . your speech may sound slurred and jumbled when you talk you may have difficulty seeing with one or both eyes . because different parts of your brain control different activities , a wide range of signs and symptoms can develop depending on where the damage is done : area of damage | possible effects | - | - | brain stem | a stroke in the brain stem is uncommon , but often fatal . brain stem strokes may cause problems with breathing , heart function , balance and coordination , chewing , swallowing , speaking , and seeing , as well as weakness and paralysis on both sides of your body . | cerebellum | strokes in the cerebellum are less common than in the cerebrum ( the large part of the brain ) , but can cause severe effects including problems with balance and coordination , dizziness , headaches , nausea and vomiting . | cerebrum - left hemisphere | strokes in the left hemisphere typically cause weakness or paralysis on the right side of your body , and cognitive problems including difficulties with reading , talking and thinking , and learning and remembering new information . | cerebrum - right hemisphere | strokes in the right hemisphere typically cause problems with vision , depth perception , short-term memory loss , and judgement , as well as weakness or paralysis on the left side , and a tendency to ignore things on your left side including your own left arm and leg . | are you at increased risk of having a stroke ? there are things that you can ’ t control such as your gender , family history and age , that affect the likelihood of whether or not you will have a stroke . the risk is higher if you are male . strokes also seem to run in families , so your risk goes up if one of your immediate relatives has had a stroke . your risk for strokes also increases as you get older . then there are other risk factors that increase your chances of having a stroke . these are called “ modifiable ” risk factors , which means they can potentially be treated or controlled . these risk factors tend to be interconnected and linked to lifestyle . the most important one for any kind of stroke is high blood pressure , which can damage and weaken your arteries so that they clog or burst more easily . high blood pressure is responsible for over 50 % of strokes. $ ^2 $ other important risk factors include atrial fibrillation , which means you an irregular heartbeat , high cholesterol , diabetes , physical inactivity and smoking . the more risk factors you have , the more likely you are to have a stroke . how likely are you to have a stroke ? every year , almost 17 million people worldwide have a stroke and almost 6 million people die because of it. $ ^3 $ stroke is responsible for almost 10 % of all deaths worldwide and is the number two killer after heart disease. $ ^3 $ death from stroke is highest in eastern europe and russia , and south east asia , and is generally more common in lower income countries. $ ^3 $ stroke in young and middle-aged people is happening more often than ever before , with most strokes occurring in people younger than 75 years old. $ ^3 $ unfortunately , about 5 million people worldwide are living with permanent disabilities because of stroke. $ ^4 $ how can you avoid a stroke ? your doctor can help you to reduce your risk of stroke by helping you tackle the risk factors that you can do something about . as a first step this will likely involve changes to your diet and exercise , which can help in so many ways . in addition to simply making you feel better , eating more healthily and exercising more often can help lower your blood pressure and cholesterol levels , prevent diabetes , and help you to lose weight . if lifestyle changes are not enough , your doctor may prescribe medications to help control some of these factors . other ways to prevent a stroke include drinking in moderation , quitting smoking and reducing the stresses in your life . your doctor can also give you help with all of these if you need it . diagnosing and treating a stroke a stroke is a medical emergency ! the faster you get medical treatment the better . if you have signs or symptoms of a stroke , you need to get a proper diagnosis and treatment as soon as possible to minimize damage to your brain . you may need several tests to help diagnose what has gone wrong and which parts of your brain have been affected , as well as to guide your treatment . your doctor will likely start with a physical examination , followed by a computerized tomography ( ct ) scan , to decide whether or not you are having a stroke and what kind it is . other tests that can provide your doctor with useful information include magnetic resonance imaging ( mri ) , which helps visualize any brain tissue damage , an angiography that examines blood flow through the brain , blood and urine tests , an echocardiogram that shows how well the valves of you heart are working and the size of your heart chambers , an electrocardiogram ( ecg ) that checks the electrical activity of your heart , and a neurological exam to check how your brain function has been affected by the stroke . treating an ischemic stroke - if the ct scan confirms you are having an ischemic stroke , your doctor will most likely give you a clot busting drug called tissue plasminogen activator as soon as possible . this drug works by dissolving the clot , which restores the blood flow in your brain , and which may reduce the damage . sometimes your doctors will try to physically break up and remove the clot , although this is much less common . treating a hemorrhagic stroke - your doctor will want to find the source of the bleed and try to control it , so as to reduce the pressure and any damage that it may cause . you may need surgery to do this and to repair any blood vessel damage . after you recover from the initial emergency , your doctors will want to treat your risk factors , with lifestyle modifications and medicines if necessary . consider the following : even though mini-strokes do not usually cause permanent brain damage , don ’ t just shrug it off . why do we say that ? a mini-stroke should really be considered a warning that something is going wrong . you can think of a mini-stroke as getting lucky because the blood clot quickly dissolved on its own . however , there ’ s no way to predict that is what will happen when another clot forms . while for many people there is no warning mini-stroke before a full stroke , if you do get one , there is a good chance that you will have a full stroke within the next 3 months . so , take it seriously ! go see your doctor to find out why it happened and to get treatment in order to prevent a full stroke from occurring .
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it is also involved in forming memories . the parietal lobe processes what we are seeing , hearing , smelling and touching , which lets us locate exactly where we are physically , and gives us hand-eye coordination . the temporal lobe controls hearing and memory , recognition of faces and languages , and is important for storing long-term memories .
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where did the parietal lobe definition go ?
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our brains are so complex , and the way they work is still such a mystery . it is not surprising that most of us go about our day without giving them much of a second thought . that all changes if you have a stroke . a stroke is an interruption of the blood flow within your brain that causes the death of brain cells . there are two ways this can happen : a blood clot can block a blood vessel in the brain causing an ischemic stroke . if the clot dissolves quickly and the blockage is only temporary , it is called a transient ischemic attack ( tia ) or mini stroke . a blood vessel can leak or burst inside your brain causing a brain bleed . if this happens , you have had a hemorrhagic stroke . what keeps your brain working ? most of your brain consists of neurons , or specialized nerve cells that connect together into networks that send and receive messages . they coordinate everything that our bodies do . however , in order to function properly , your brain needs a constant supply of oxygen and nutrients—and a lot of them . oxygen and nutrients travel in your blood and are delivered to your brain cells via two pairs of major arteries called the carotid and vertebral arteries . these major arteries branch into a dense network of small blood vessels that covers the surface and thread their way throughout your brain tissue ensuring that every cell is well supplied . how your brain is organized and what can go wrong your brain is arranged into three parts , the brain stem , cerebellum and cerebrum . different areas of the brain are generally responsible for different functions and actions : brain stem : this connects your brain to the top of your spine and controls lots of basic functions including your heart rate and blood pressure , breathing , consciousness , sleeping and eating . cerebellum : this is attached to the back of the brain stem . it helps control your coordination and balance , and fine tunes your muscle movements ( motor function ) . cerebrum : this is the largest part of the brain and is divided into two halves or hemispheres , which are further divided into four lobes , the frontal , parietal , temporal , and occipital lobe . the right side of the cerebrum controls the left side of your body and vice versa . the frontal lobe controls movement , and executive function , which is our ability to make good or bad decisions , make plans , and manage time . it is also involved in forming memories . the parietal lobe processes what we are seeing , hearing , smelling and touching , which lets us locate exactly where we are physically , and gives us hand-eye coordination . the temporal lobe controls hearing and memory , recognition of faces and languages , and is important for storing long-term memories . the occipital lobe processes the signals from our eyes and is primarily responsible for most things to do with sight . a stroke can happen in any part of the brain . around eight out of ten strokes are caused by a blockage due to a clot ( ischemic ) , while two out of ten are caused by a bleed ( hemorrhagic ) . $ ^1 $ ischemic strokes are more common . there are two types , thrombotic and embolic strokes . a thrombotic stroke occurs when the blood clot has formed in one of the major arteries leading to the brain , while an embolic stroke is when a blood clot forms somewhere else in the body , travels around your body in your bloodstream and then lodges in your brain . loose blood clots are usually linked to atherosclerosis , a buildup of plaque ( a combination of fatty materials , calcium and scar tissue ) , on the inside walls of your arteries , which narrows them , and interferes with or blocks the flow of blood . blood clots form when a plaque ruptures . hemorrhagic strokes are less common , but are more deadly . uncontrolled bleeding can flood an area of the brain , causing localized pressure and swelling that damages or kills the brain cells . hemorrhagic strokes can also cause a shortage of oxygen and nutrient delivery beyond the leak . bleeding may occur at the surface of your brain , just under your skull , or from a burst artery deep within your brain . high blood pressure and/or defects in your arteries are usually to blame for a brain bleed . the common defects include aneurysms , which are weak areas in the blood vessel wall that fill with blood , bulge out like a little balloon , and can burst , particularly if you have high blood pressure , and malformations of blood vessels that are usually present at birth . loss of blood flow due to a blockage , even for very short periods of time , can be enough to cause the neurons in that area to die due to a lack of oxygen and nutrients . that said , every stroke is different and sometimes your brain can compensate to some extent , by shifting the brain function of the damaged part of your brain to the corresponding area on the undamaged side of your brain . this means the damage caused by either type of stroke may be permanent but could only be temporary . signs and symptoms caused by a mini-stroke will usually last less than an hour , and generally do not do permanent damage . signs and symptoms that you are having a stroke usually the signs and symptoms of a stroke come on suddenly and include one or more of the following : your face may droop unnaturally on one side . you may not be able to raise your arm on one side . you may feel confused and have trouble understanding what people are saying . your speech may sound slurred and jumbled when you talk you may have difficulty seeing with one or both eyes . because different parts of your brain control different activities , a wide range of signs and symptoms can develop depending on where the damage is done : area of damage | possible effects | - | - | brain stem | a stroke in the brain stem is uncommon , but often fatal . brain stem strokes may cause problems with breathing , heart function , balance and coordination , chewing , swallowing , speaking , and seeing , as well as weakness and paralysis on both sides of your body . | cerebellum | strokes in the cerebellum are less common than in the cerebrum ( the large part of the brain ) , but can cause severe effects including problems with balance and coordination , dizziness , headaches , nausea and vomiting . | cerebrum - left hemisphere | strokes in the left hemisphere typically cause weakness or paralysis on the right side of your body , and cognitive problems including difficulties with reading , talking and thinking , and learning and remembering new information . | cerebrum - right hemisphere | strokes in the right hemisphere typically cause problems with vision , depth perception , short-term memory loss , and judgement , as well as weakness or paralysis on the left side , and a tendency to ignore things on your left side including your own left arm and leg . | are you at increased risk of having a stroke ? there are things that you can ’ t control such as your gender , family history and age , that affect the likelihood of whether or not you will have a stroke . the risk is higher if you are male . strokes also seem to run in families , so your risk goes up if one of your immediate relatives has had a stroke . your risk for strokes also increases as you get older . then there are other risk factors that increase your chances of having a stroke . these are called “ modifiable ” risk factors , which means they can potentially be treated or controlled . these risk factors tend to be interconnected and linked to lifestyle . the most important one for any kind of stroke is high blood pressure , which can damage and weaken your arteries so that they clog or burst more easily . high blood pressure is responsible for over 50 % of strokes. $ ^2 $ other important risk factors include atrial fibrillation , which means you an irregular heartbeat , high cholesterol , diabetes , physical inactivity and smoking . the more risk factors you have , the more likely you are to have a stroke . how likely are you to have a stroke ? every year , almost 17 million people worldwide have a stroke and almost 6 million people die because of it. $ ^3 $ stroke is responsible for almost 10 % of all deaths worldwide and is the number two killer after heart disease. $ ^3 $ death from stroke is highest in eastern europe and russia , and south east asia , and is generally more common in lower income countries. $ ^3 $ stroke in young and middle-aged people is happening more often than ever before , with most strokes occurring in people younger than 75 years old. $ ^3 $ unfortunately , about 5 million people worldwide are living with permanent disabilities because of stroke. $ ^4 $ how can you avoid a stroke ? your doctor can help you to reduce your risk of stroke by helping you tackle the risk factors that you can do something about . as a first step this will likely involve changes to your diet and exercise , which can help in so many ways . in addition to simply making you feel better , eating more healthily and exercising more often can help lower your blood pressure and cholesterol levels , prevent diabetes , and help you to lose weight . if lifestyle changes are not enough , your doctor may prescribe medications to help control some of these factors . other ways to prevent a stroke include drinking in moderation , quitting smoking and reducing the stresses in your life . your doctor can also give you help with all of these if you need it . diagnosing and treating a stroke a stroke is a medical emergency ! the faster you get medical treatment the better . if you have signs or symptoms of a stroke , you need to get a proper diagnosis and treatment as soon as possible to minimize damage to your brain . you may need several tests to help diagnose what has gone wrong and which parts of your brain have been affected , as well as to guide your treatment . your doctor will likely start with a physical examination , followed by a computerized tomography ( ct ) scan , to decide whether or not you are having a stroke and what kind it is . other tests that can provide your doctor with useful information include magnetic resonance imaging ( mri ) , which helps visualize any brain tissue damage , an angiography that examines blood flow through the brain , blood and urine tests , an echocardiogram that shows how well the valves of you heart are working and the size of your heart chambers , an electrocardiogram ( ecg ) that checks the electrical activity of your heart , and a neurological exam to check how your brain function has been affected by the stroke . treating an ischemic stroke - if the ct scan confirms you are having an ischemic stroke , your doctor will most likely give you a clot busting drug called tissue plasminogen activator as soon as possible . this drug works by dissolving the clot , which restores the blood flow in your brain , and which may reduce the damage . sometimes your doctors will try to physically break up and remove the clot , although this is much less common . treating a hemorrhagic stroke - your doctor will want to find the source of the bleed and try to control it , so as to reduce the pressure and any damage that it may cause . you may need surgery to do this and to repair any blood vessel damage . after you recover from the initial emergency , your doctors will want to treat your risk factors , with lifestyle modifications and medicines if necessary . consider the following : even though mini-strokes do not usually cause permanent brain damage , don ’ t just shrug it off . why do we say that ? a mini-stroke should really be considered a warning that something is going wrong . you can think of a mini-stroke as getting lucky because the blood clot quickly dissolved on its own . however , there ’ s no way to predict that is what will happen when another clot forms . while for many people there is no warning mini-stroke before a full stroke , if you do get one , there is a good chance that you will have a full stroke within the next 3 months . so , take it seriously ! go see your doctor to find out why it happened and to get treatment in order to prevent a full stroke from occurring .
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the occipital lobe processes the signals from our eyes and is primarily responsible for most things to do with sight . a stroke can happen in any part of the brain . around eight out of ten strokes are caused by a blockage due to a clot ( ischemic ) , while two out of ten are caused by a bleed ( hemorrhagic ) . $ ^1 $ ischemic strokes are more common .
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is there a way that we can make stroke never happen in our body ?
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our brains are so complex , and the way they work is still such a mystery . it is not surprising that most of us go about our day without giving them much of a second thought . that all changes if you have a stroke . a stroke is an interruption of the blood flow within your brain that causes the death of brain cells . there are two ways this can happen : a blood clot can block a blood vessel in the brain causing an ischemic stroke . if the clot dissolves quickly and the blockage is only temporary , it is called a transient ischemic attack ( tia ) or mini stroke . a blood vessel can leak or burst inside your brain causing a brain bleed . if this happens , you have had a hemorrhagic stroke . what keeps your brain working ? most of your brain consists of neurons , or specialized nerve cells that connect together into networks that send and receive messages . they coordinate everything that our bodies do . however , in order to function properly , your brain needs a constant supply of oxygen and nutrients—and a lot of them . oxygen and nutrients travel in your blood and are delivered to your brain cells via two pairs of major arteries called the carotid and vertebral arteries . these major arteries branch into a dense network of small blood vessels that covers the surface and thread their way throughout your brain tissue ensuring that every cell is well supplied . how your brain is organized and what can go wrong your brain is arranged into three parts , the brain stem , cerebellum and cerebrum . different areas of the brain are generally responsible for different functions and actions : brain stem : this connects your brain to the top of your spine and controls lots of basic functions including your heart rate and blood pressure , breathing , consciousness , sleeping and eating . cerebellum : this is attached to the back of the brain stem . it helps control your coordination and balance , and fine tunes your muscle movements ( motor function ) . cerebrum : this is the largest part of the brain and is divided into two halves or hemispheres , which are further divided into four lobes , the frontal , parietal , temporal , and occipital lobe . the right side of the cerebrum controls the left side of your body and vice versa . the frontal lobe controls movement , and executive function , which is our ability to make good or bad decisions , make plans , and manage time . it is also involved in forming memories . the parietal lobe processes what we are seeing , hearing , smelling and touching , which lets us locate exactly where we are physically , and gives us hand-eye coordination . the temporal lobe controls hearing and memory , recognition of faces and languages , and is important for storing long-term memories . the occipital lobe processes the signals from our eyes and is primarily responsible for most things to do with sight . a stroke can happen in any part of the brain . around eight out of ten strokes are caused by a blockage due to a clot ( ischemic ) , while two out of ten are caused by a bleed ( hemorrhagic ) . $ ^1 $ ischemic strokes are more common . there are two types , thrombotic and embolic strokes . a thrombotic stroke occurs when the blood clot has formed in one of the major arteries leading to the brain , while an embolic stroke is when a blood clot forms somewhere else in the body , travels around your body in your bloodstream and then lodges in your brain . loose blood clots are usually linked to atherosclerosis , a buildup of plaque ( a combination of fatty materials , calcium and scar tissue ) , on the inside walls of your arteries , which narrows them , and interferes with or blocks the flow of blood . blood clots form when a plaque ruptures . hemorrhagic strokes are less common , but are more deadly . uncontrolled bleeding can flood an area of the brain , causing localized pressure and swelling that damages or kills the brain cells . hemorrhagic strokes can also cause a shortage of oxygen and nutrient delivery beyond the leak . bleeding may occur at the surface of your brain , just under your skull , or from a burst artery deep within your brain . high blood pressure and/or defects in your arteries are usually to blame for a brain bleed . the common defects include aneurysms , which are weak areas in the blood vessel wall that fill with blood , bulge out like a little balloon , and can burst , particularly if you have high blood pressure , and malformations of blood vessels that are usually present at birth . loss of blood flow due to a blockage , even for very short periods of time , can be enough to cause the neurons in that area to die due to a lack of oxygen and nutrients . that said , every stroke is different and sometimes your brain can compensate to some extent , by shifting the brain function of the damaged part of your brain to the corresponding area on the undamaged side of your brain . this means the damage caused by either type of stroke may be permanent but could only be temporary . signs and symptoms caused by a mini-stroke will usually last less than an hour , and generally do not do permanent damage . signs and symptoms that you are having a stroke usually the signs and symptoms of a stroke come on suddenly and include one or more of the following : your face may droop unnaturally on one side . you may not be able to raise your arm on one side . you may feel confused and have trouble understanding what people are saying . your speech may sound slurred and jumbled when you talk you may have difficulty seeing with one or both eyes . because different parts of your brain control different activities , a wide range of signs and symptoms can develop depending on where the damage is done : area of damage | possible effects | - | - | brain stem | a stroke in the brain stem is uncommon , but often fatal . brain stem strokes may cause problems with breathing , heart function , balance and coordination , chewing , swallowing , speaking , and seeing , as well as weakness and paralysis on both sides of your body . | cerebellum | strokes in the cerebellum are less common than in the cerebrum ( the large part of the brain ) , but can cause severe effects including problems with balance and coordination , dizziness , headaches , nausea and vomiting . | cerebrum - left hemisphere | strokes in the left hemisphere typically cause weakness or paralysis on the right side of your body , and cognitive problems including difficulties with reading , talking and thinking , and learning and remembering new information . | cerebrum - right hemisphere | strokes in the right hemisphere typically cause problems with vision , depth perception , short-term memory loss , and judgement , as well as weakness or paralysis on the left side , and a tendency to ignore things on your left side including your own left arm and leg . | are you at increased risk of having a stroke ? there are things that you can ’ t control such as your gender , family history and age , that affect the likelihood of whether or not you will have a stroke . the risk is higher if you are male . strokes also seem to run in families , so your risk goes up if one of your immediate relatives has had a stroke . your risk for strokes also increases as you get older . then there are other risk factors that increase your chances of having a stroke . these are called “ modifiable ” risk factors , which means they can potentially be treated or controlled . these risk factors tend to be interconnected and linked to lifestyle . the most important one for any kind of stroke is high blood pressure , which can damage and weaken your arteries so that they clog or burst more easily . high blood pressure is responsible for over 50 % of strokes. $ ^2 $ other important risk factors include atrial fibrillation , which means you an irregular heartbeat , high cholesterol , diabetes , physical inactivity and smoking . the more risk factors you have , the more likely you are to have a stroke . how likely are you to have a stroke ? every year , almost 17 million people worldwide have a stroke and almost 6 million people die because of it. $ ^3 $ stroke is responsible for almost 10 % of all deaths worldwide and is the number two killer after heart disease. $ ^3 $ death from stroke is highest in eastern europe and russia , and south east asia , and is generally more common in lower income countries. $ ^3 $ stroke in young and middle-aged people is happening more often than ever before , with most strokes occurring in people younger than 75 years old. $ ^3 $ unfortunately , about 5 million people worldwide are living with permanent disabilities because of stroke. $ ^4 $ how can you avoid a stroke ? your doctor can help you to reduce your risk of stroke by helping you tackle the risk factors that you can do something about . as a first step this will likely involve changes to your diet and exercise , which can help in so many ways . in addition to simply making you feel better , eating more healthily and exercising more often can help lower your blood pressure and cholesterol levels , prevent diabetes , and help you to lose weight . if lifestyle changes are not enough , your doctor may prescribe medications to help control some of these factors . other ways to prevent a stroke include drinking in moderation , quitting smoking and reducing the stresses in your life . your doctor can also give you help with all of these if you need it . diagnosing and treating a stroke a stroke is a medical emergency ! the faster you get medical treatment the better . if you have signs or symptoms of a stroke , you need to get a proper diagnosis and treatment as soon as possible to minimize damage to your brain . you may need several tests to help diagnose what has gone wrong and which parts of your brain have been affected , as well as to guide your treatment . your doctor will likely start with a physical examination , followed by a computerized tomography ( ct ) scan , to decide whether or not you are having a stroke and what kind it is . other tests that can provide your doctor with useful information include magnetic resonance imaging ( mri ) , which helps visualize any brain tissue damage , an angiography that examines blood flow through the brain , blood and urine tests , an echocardiogram that shows how well the valves of you heart are working and the size of your heart chambers , an electrocardiogram ( ecg ) that checks the electrical activity of your heart , and a neurological exam to check how your brain function has been affected by the stroke . treating an ischemic stroke - if the ct scan confirms you are having an ischemic stroke , your doctor will most likely give you a clot busting drug called tissue plasminogen activator as soon as possible . this drug works by dissolving the clot , which restores the blood flow in your brain , and which may reduce the damage . sometimes your doctors will try to physically break up and remove the clot , although this is much less common . treating a hemorrhagic stroke - your doctor will want to find the source of the bleed and try to control it , so as to reduce the pressure and any damage that it may cause . you may need surgery to do this and to repair any blood vessel damage . after you recover from the initial emergency , your doctors will want to treat your risk factors , with lifestyle modifications and medicines if necessary . consider the following : even though mini-strokes do not usually cause permanent brain damage , don ’ t just shrug it off . why do we say that ? a mini-stroke should really be considered a warning that something is going wrong . you can think of a mini-stroke as getting lucky because the blood clot quickly dissolved on its own . however , there ’ s no way to predict that is what will happen when another clot forms . while for many people there is no warning mini-stroke before a full stroke , if you do get one , there is a good chance that you will have a full stroke within the next 3 months . so , take it seriously ! go see your doctor to find out why it happened and to get treatment in order to prevent a full stroke from occurring .
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these major arteries branch into a dense network of small blood vessels that covers the surface and thread their way throughout your brain tissue ensuring that every cell is well supplied . how your brain is organized and what can go wrong your brain is arranged into three parts , the brain stem , cerebellum and cerebrum . different areas of the brain are generally responsible for different functions and actions : brain stem : this connects your brain to the top of your spine and controls lots of basic functions including your heart rate and blood pressure , breathing , consciousness , sleeping and eating .
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is it possible to live without certain areas of the brain , like the frontal lobe ?
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art history might seem like a relatively straightforward concept : “ art ” and “ history ” are subjects most of us first studied in elementary school . in practice , however , the idea of “ the history of art ” raises complex questions . what exactly do we mean by art , and what kind of history ( or histories ) should we explore ? let ’ s consider each term further . art versus artifact the word “ art ” is derived from the latin ars , which originally meant “ skill ” or “ craft. ” these meanings are still primary in other english words derived from ars , such as “ artifact ” ( a thing made by human skill ) and “ artisan ” ( a person skilled at making things ) . the meanings of “ art ” and “ artist , ” however , are not so straightforward . we understand art as involving more than just skilled craftsmanship . what exactly distinguishes a work of art from an artifact , or an artist from an artisan ? when asked this question , students typically come up with several ideas . one is beauty . much art is visually striking , and in the 18th , 19th and early 20th centuries , the analysis of aesthetic qualities was indeed central in art history . during this time , art that imitated ancient greek and roman art ( the art of classical antiquity ) , was considered to embody a timeless perfection . art historians focused on the so-called fine arts—painting , sculpture , and architecture—analyzing the virtues of their forms . over the past century and a half , however , both art and art history have evolved radically . artists turned away from the classical tradition , embracing new media and aesthetic ideals , and art historians shifted their focus from the analysis of art ’ s formal beauty to interpretation of its cultural meaning . today we understand beauty as subjective—a cultural construct that varies across time and space . while most art continues to be primarily visual , and visual analysis is still a fundamental tool used by art historians , beauty itself is no longer considered an essential attribute of art . a second common answer to the question of what distinguishes art emphasizes originality , creativity , and imagination . this reflects a modern understanding of art as a manifestation of the ingenuity of the artist . this idea , however , originated five hundred years ago in renaissance europe , and is not directly applicable to many of the works studied by art historians . for example , in the case of ancient egyptian art or byzantine icons , the preservation of tradition was more valued than innovation . while the idea of ingenuity is certainly important in the history of art , it is not a universal attribute of the works studied by art historians . all this might lead one to conclude that definitions of art , like those of beauty , are subjective and unstable . one solution to this dilemma is to propose that art is distinguished primarily by its visual agency , that is , by its ability to captivate viewers . artifacts may be interesting , but art , i suggest , has the potential to move us—emotionally , intellectually , or otherwise . it may do this through its visual characteristics ( scale , composition , color , etc . ) , expression of ideas , craftsmanship , ingenuity , rarity , or some combination of these or other qualities . how art engages varies , but in some manner , art takes us beyond the everyday and ordinary experience . the greatest examples attest to the extremes of human ambition , skill , imagination , perception , and feeling . as such , art prompts us to reflect on fundamental aspects of what it is to be human . any artifact , as a product of human skill , might provide insight into the human condition . but art , in moving beyond the commonplace , has the potential to do so in more profound ways . art , then , is perhaps best understood as a special class of artifact , exceptional in its ability to make us think and feel through visual experience . history : making sense of the past like definitions of art and beauty , ideas about history have changed over time . it might seem that writing history should be straightforward—it ’ s all based on facts , isn ’ t it ? in theory , yes , but the evidence surviving from the past is vast , fragmentary , and messy . historians must make decisions about what to include and exclude , how to organize the material , and what to say about it . in doing so , they create narratives that explain the past in ways that make sense in the present . inevitably , as the present changes , these narratives are updated , rewritten , or discarded altogether and replaced with new ones . all history , then , is subjective—as much a product of the time and place it was written as of the evidence from the past that it interprets . the discipline of art history developed in europe during the colonial period ( roughly the 15th to the mid-20th century ) . early art historians emphasized the european tradition , celebrating its greek and roman origins and the ideals of academic art . by the mid-20th century , a standard narrative for “ western art ” was established that traced its development from the prehistoric , ancient , and medieval mediterranean to modern europe and the united states . art from the rest of the world , labeled “ non-western art , ” was typically treated only marginally and from a colonialist perspective . the immense sociocultural changes that took place in the 20th century led art historians to amend these narratives . accounts of western art that once featured only white males were revised to include artists of color and women . the traditional focus on painting , sculpture , and architecture was expanded to include so-called minor arts such as ceramics and textiles and contemporary media such as video and performance art . interest in non-western art increased , accelerating dramatically in recent years . today , the biggest social development facing art history is globalism . as our world becomes increasingly interconnected , familiarity with different cultures and facility with diversity are essential . art history , as the story of exceptional artifacts from a broad range of cultures , has a role to play in developing these skills . now art historians ponder and debate how to reconcile the discipline ’ s european intellectual origins and its problematic colonialist legacy with contemporary multiculturalism and how to write art history in a global era . smarthistory ’ s videos and articles reflect this history of art history . since the site was originally created to support a course in western art and history , the content initially focused on the most celebrated works of the western canon . with the key periods and civilizations of this tradition now well-represented and a growing number of scholars contributing , the range of objects and topics has increased in recent years . most importantly , substantial coverage of world traditions outside the west has been added . as the site continues to expand , the works and perspectives presented will evolve instep with contemporary trends in art history . in fact , as innovators in the use of digital media and the internet to create , disseminate , and interrogate art historical knowledge , smarthistory and its users have the potential to help shape the future of the discipline .
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art versus artifact the word “ art ” is derived from the latin ars , which originally meant “ skill ” or “ craft. ” these meanings are still primary in other english words derived from ars , such as “ artifact ” ( a thing made by human skill ) and “ artisan ” ( a person skilled at making things ) . the meanings of “ art ” and “ artist , ” however , are not so straightforward . we understand art as involving more than just skilled craftsmanship .
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so , if art does n't have a straightforward definition , anything that is n't directly composed of a linear definition can become a piece ?
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overview the populists were an agrarian-based political movement aimed at improving conditions for the country ’ s farmers and agrarian workers . the populist movement was preceded by the farmer ’ s alliance and the grange . the people ’ s party was a political party founded in 1891 by leaders of the populist movement . it fielded a candidate in the us presidential election of 1892 and garnered 8.5 % of the popular vote , which was a substantial amount of support for a third party . the populists allied with the labor movement and were folded into the democratic party in 1896 , though a small remnant of the people ’ s party continued to exist until it was formally disbanded in 1908 . agrarian activism in the united states beginning in the late nineteenth century , the nation ’ s farmers began to organize to defend their interests against what they perceived to be the interests of the eastern establishment and banking elite . as the number of landless tenant farmers rose , and as the debts of independent farmers skyrocketed due to burdensome loan terms and interest rates from banks , discontent among the nation ’ s agrarian workers burgeoned . in 1876 , the farmer ’ s alliance was established in texas with the goal of ending the crop-lien system that had thrown so many farmers into poverty . the crop-lien system operated in the cotton-growing south , among sharecroppers and tenant farmers , both white and black , who did not own the land that they worked . these workers took out loans to obtain the seed , tools , and other supplies they needed to grow the cotton . after the harvest , they were required to pay back the loans in the form of cotton crops . when cotton prices tanked , these workers were sometimes left with nothing after their crops were collected by creditors. $ ^1 $ the farmer ’ s alliance was not the only organization that sprung up to defend the nation ’ s agrarian workers . the national grange of the order of patrons of husbandry , known as the grange , was founded in 1868 in new york to advocate on behalf of rural communities . from 1873 to 1875 , local chapters of the grange were established across the country , and membership skyrocketed. $ ^2 $ this was partly due to the panic of 1873 , a financial crisis that resulted in a number of bank failures and the bankruptcy of several of the nation ’ s railroads . the panic of 1873 depressed wages for workers , and the prices of agricultural products plummeted , saddling farmers with massive amounts of debt that they had little hope of paying off. $ ^3 $ the people ’ s party in 1891 , the people ’ s party , also known as the populist party , or populists , was formed as a political party representing the interests of the nation ’ s agricultural sector . the farmer ’ s alliance was a major part of the populist coalition . the people ’ s party nominated james b. weaver , a former us representative from the state of iowa , as its candidate in the 1892 presidential election . campaigning on a platform designed to strengthen farmers and weaken the monopolistic power of big business , banks , and railroad corporations , the people ’ s party garnered 8.5 % of the popular vote , carrying the states of colorado , idaho , kansas , and nevada . because of the mass appeal of the populist movement , the democratic party began to champion many of its policy goals . in the 1896 presidential election , the democrats nominated william jennings bryan as its candidate , and the populists agreed to support him . the people ’ s party was thus folded into the democratic party and began to fade from the national scene . the effect of the fusion of the populist party and the democratic party was a disaster in the south . though there had always been conflict within the populist movement about whether african americans should be included , the democratic party in the south was unabashedly racist . though bryan performed strongly in the areas of greatest populist influence , he lost the election to republican william mckinley. $ ^4 $ the people ’ s party continued to function and fielded candidates in both the 1904 and 1908 presidential elections , but the heyday of the party ’ s influence was over . although the people ’ s party was formally disbanded in 1908 , the progressive movement would take up many of the goals and causes of populism , including anti-trust legislation , greater federal regulation of private industry , and stronger support for the nation ’ s agricultural and working classes. $ ^5 $ what do you think ? what were the nation ’ s farmers so upset about ? what sorts of policies did agrarian activists champion ? how would you measure the achievements of the populist movement ?
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the populist movement was preceded by the farmer ’ s alliance and the grange . the people ’ s party was a political party founded in 1891 by leaders of the populist movement . it fielded a candidate in the us presidential election of 1892 and garnered 8.5 % of the popular vote , which was a substantial amount of support for a third party .
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why did the the populist party oppose the use of foreign labour ?
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overview the populists were an agrarian-based political movement aimed at improving conditions for the country ’ s farmers and agrarian workers . the populist movement was preceded by the farmer ’ s alliance and the grange . the people ’ s party was a political party founded in 1891 by leaders of the populist movement . it fielded a candidate in the us presidential election of 1892 and garnered 8.5 % of the popular vote , which was a substantial amount of support for a third party . the populists allied with the labor movement and were folded into the democratic party in 1896 , though a small remnant of the people ’ s party continued to exist until it was formally disbanded in 1908 . agrarian activism in the united states beginning in the late nineteenth century , the nation ’ s farmers began to organize to defend their interests against what they perceived to be the interests of the eastern establishment and banking elite . as the number of landless tenant farmers rose , and as the debts of independent farmers skyrocketed due to burdensome loan terms and interest rates from banks , discontent among the nation ’ s agrarian workers burgeoned . in 1876 , the farmer ’ s alliance was established in texas with the goal of ending the crop-lien system that had thrown so many farmers into poverty . the crop-lien system operated in the cotton-growing south , among sharecroppers and tenant farmers , both white and black , who did not own the land that they worked . these workers took out loans to obtain the seed , tools , and other supplies they needed to grow the cotton . after the harvest , they were required to pay back the loans in the form of cotton crops . when cotton prices tanked , these workers were sometimes left with nothing after their crops were collected by creditors. $ ^1 $ the farmer ’ s alliance was not the only organization that sprung up to defend the nation ’ s agrarian workers . the national grange of the order of patrons of husbandry , known as the grange , was founded in 1868 in new york to advocate on behalf of rural communities . from 1873 to 1875 , local chapters of the grange were established across the country , and membership skyrocketed. $ ^2 $ this was partly due to the panic of 1873 , a financial crisis that resulted in a number of bank failures and the bankruptcy of several of the nation ’ s railroads . the panic of 1873 depressed wages for workers , and the prices of agricultural products plummeted , saddling farmers with massive amounts of debt that they had little hope of paying off. $ ^3 $ the people ’ s party in 1891 , the people ’ s party , also known as the populist party , or populists , was formed as a political party representing the interests of the nation ’ s agricultural sector . the farmer ’ s alliance was a major part of the populist coalition . the people ’ s party nominated james b. weaver , a former us representative from the state of iowa , as its candidate in the 1892 presidential election . campaigning on a platform designed to strengthen farmers and weaken the monopolistic power of big business , banks , and railroad corporations , the people ’ s party garnered 8.5 % of the popular vote , carrying the states of colorado , idaho , kansas , and nevada . because of the mass appeal of the populist movement , the democratic party began to champion many of its policy goals . in the 1896 presidential election , the democrats nominated william jennings bryan as its candidate , and the populists agreed to support him . the people ’ s party was thus folded into the democratic party and began to fade from the national scene . the effect of the fusion of the populist party and the democratic party was a disaster in the south . though there had always been conflict within the populist movement about whether african americans should be included , the democratic party in the south was unabashedly racist . though bryan performed strongly in the areas of greatest populist influence , he lost the election to republican william mckinley. $ ^4 $ the people ’ s party continued to function and fielded candidates in both the 1904 and 1908 presidential elections , but the heyday of the party ’ s influence was over . although the people ’ s party was formally disbanded in 1908 , the progressive movement would take up many of the goals and causes of populism , including anti-trust legislation , greater federal regulation of private industry , and stronger support for the nation ’ s agricultural and working classes. $ ^5 $ what do you think ? what were the nation ’ s farmers so upset about ? what sorts of policies did agrarian activists champion ? how would you measure the achievements of the populist movement ?
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the people ’ s party nominated james b. weaver , a former us representative from the state of iowa , as its candidate in the 1892 presidential election . campaigning on a platform designed to strengthen farmers and weaken the monopolistic power of big business , banks , and railroad corporations , the people ’ s party garnered 8.5 % of the popular vote , carrying the states of colorado , idaho , kansas , and nevada . because of the mass appeal of the populist movement , the democratic party began to champion many of its policy goals .
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what are corporations and conservationists and what was the conflict between corporations and conservationists with regard to natural resources ?
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overview the populists were an agrarian-based political movement aimed at improving conditions for the country ’ s farmers and agrarian workers . the populist movement was preceded by the farmer ’ s alliance and the grange . the people ’ s party was a political party founded in 1891 by leaders of the populist movement . it fielded a candidate in the us presidential election of 1892 and garnered 8.5 % of the popular vote , which was a substantial amount of support for a third party . the populists allied with the labor movement and were folded into the democratic party in 1896 , though a small remnant of the people ’ s party continued to exist until it was formally disbanded in 1908 . agrarian activism in the united states beginning in the late nineteenth century , the nation ’ s farmers began to organize to defend their interests against what they perceived to be the interests of the eastern establishment and banking elite . as the number of landless tenant farmers rose , and as the debts of independent farmers skyrocketed due to burdensome loan terms and interest rates from banks , discontent among the nation ’ s agrarian workers burgeoned . in 1876 , the farmer ’ s alliance was established in texas with the goal of ending the crop-lien system that had thrown so many farmers into poverty . the crop-lien system operated in the cotton-growing south , among sharecroppers and tenant farmers , both white and black , who did not own the land that they worked . these workers took out loans to obtain the seed , tools , and other supplies they needed to grow the cotton . after the harvest , they were required to pay back the loans in the form of cotton crops . when cotton prices tanked , these workers were sometimes left with nothing after their crops were collected by creditors. $ ^1 $ the farmer ’ s alliance was not the only organization that sprung up to defend the nation ’ s agrarian workers . the national grange of the order of patrons of husbandry , known as the grange , was founded in 1868 in new york to advocate on behalf of rural communities . from 1873 to 1875 , local chapters of the grange were established across the country , and membership skyrocketed. $ ^2 $ this was partly due to the panic of 1873 , a financial crisis that resulted in a number of bank failures and the bankruptcy of several of the nation ’ s railroads . the panic of 1873 depressed wages for workers , and the prices of agricultural products plummeted , saddling farmers with massive amounts of debt that they had little hope of paying off. $ ^3 $ the people ’ s party in 1891 , the people ’ s party , also known as the populist party , or populists , was formed as a political party representing the interests of the nation ’ s agricultural sector . the farmer ’ s alliance was a major part of the populist coalition . the people ’ s party nominated james b. weaver , a former us representative from the state of iowa , as its candidate in the 1892 presidential election . campaigning on a platform designed to strengthen farmers and weaken the monopolistic power of big business , banks , and railroad corporations , the people ’ s party garnered 8.5 % of the popular vote , carrying the states of colorado , idaho , kansas , and nevada . because of the mass appeal of the populist movement , the democratic party began to champion many of its policy goals . in the 1896 presidential election , the democrats nominated william jennings bryan as its candidate , and the populists agreed to support him . the people ’ s party was thus folded into the democratic party and began to fade from the national scene . the effect of the fusion of the populist party and the democratic party was a disaster in the south . though there had always been conflict within the populist movement about whether african americans should be included , the democratic party in the south was unabashedly racist . though bryan performed strongly in the areas of greatest populist influence , he lost the election to republican william mckinley. $ ^4 $ the people ’ s party continued to function and fielded candidates in both the 1904 and 1908 presidential elections , but the heyday of the party ’ s influence was over . although the people ’ s party was formally disbanded in 1908 , the progressive movement would take up many of the goals and causes of populism , including anti-trust legislation , greater federal regulation of private industry , and stronger support for the nation ’ s agricultural and working classes. $ ^5 $ what do you think ? what were the nation ’ s farmers so upset about ? what sorts of policies did agrarian activists champion ? how would you measure the achievements of the populist movement ?
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it fielded a candidate in the us presidential election of 1892 and garnered 8.5 % of the popular vote , which was a substantial amount of support for a third party . the populists allied with the labor movement and were folded into the democratic party in 1896 , though a small remnant of the people ’ s party continued to exist until it was formally disbanded in 1908 . agrarian activism in the united states beginning in the late nineteenth century , the nation ’ s farmers began to organize to defend their interests against what they perceived to be the interests of the eastern establishment and banking elite .
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who did the populists run in 1904 and 1908 ?
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overview the populists were an agrarian-based political movement aimed at improving conditions for the country ’ s farmers and agrarian workers . the populist movement was preceded by the farmer ’ s alliance and the grange . the people ’ s party was a political party founded in 1891 by leaders of the populist movement . it fielded a candidate in the us presidential election of 1892 and garnered 8.5 % of the popular vote , which was a substantial amount of support for a third party . the populists allied with the labor movement and were folded into the democratic party in 1896 , though a small remnant of the people ’ s party continued to exist until it was formally disbanded in 1908 . agrarian activism in the united states beginning in the late nineteenth century , the nation ’ s farmers began to organize to defend their interests against what they perceived to be the interests of the eastern establishment and banking elite . as the number of landless tenant farmers rose , and as the debts of independent farmers skyrocketed due to burdensome loan terms and interest rates from banks , discontent among the nation ’ s agrarian workers burgeoned . in 1876 , the farmer ’ s alliance was established in texas with the goal of ending the crop-lien system that had thrown so many farmers into poverty . the crop-lien system operated in the cotton-growing south , among sharecroppers and tenant farmers , both white and black , who did not own the land that they worked . these workers took out loans to obtain the seed , tools , and other supplies they needed to grow the cotton . after the harvest , they were required to pay back the loans in the form of cotton crops . when cotton prices tanked , these workers were sometimes left with nothing after their crops were collected by creditors. $ ^1 $ the farmer ’ s alliance was not the only organization that sprung up to defend the nation ’ s agrarian workers . the national grange of the order of patrons of husbandry , known as the grange , was founded in 1868 in new york to advocate on behalf of rural communities . from 1873 to 1875 , local chapters of the grange were established across the country , and membership skyrocketed. $ ^2 $ this was partly due to the panic of 1873 , a financial crisis that resulted in a number of bank failures and the bankruptcy of several of the nation ’ s railroads . the panic of 1873 depressed wages for workers , and the prices of agricultural products plummeted , saddling farmers with massive amounts of debt that they had little hope of paying off. $ ^3 $ the people ’ s party in 1891 , the people ’ s party , also known as the populist party , or populists , was formed as a political party representing the interests of the nation ’ s agricultural sector . the farmer ’ s alliance was a major part of the populist coalition . the people ’ s party nominated james b. weaver , a former us representative from the state of iowa , as its candidate in the 1892 presidential election . campaigning on a platform designed to strengthen farmers and weaken the monopolistic power of big business , banks , and railroad corporations , the people ’ s party garnered 8.5 % of the popular vote , carrying the states of colorado , idaho , kansas , and nevada . because of the mass appeal of the populist movement , the democratic party began to champion many of its policy goals . in the 1896 presidential election , the democrats nominated william jennings bryan as its candidate , and the populists agreed to support him . the people ’ s party was thus folded into the democratic party and began to fade from the national scene . the effect of the fusion of the populist party and the democratic party was a disaster in the south . though there had always been conflict within the populist movement about whether african americans should be included , the democratic party in the south was unabashedly racist . though bryan performed strongly in the areas of greatest populist influence , he lost the election to republican william mckinley. $ ^4 $ the people ’ s party continued to function and fielded candidates in both the 1904 and 1908 presidential elections , but the heyday of the party ’ s influence was over . although the people ’ s party was formally disbanded in 1908 , the progressive movement would take up many of the goals and causes of populism , including anti-trust legislation , greater federal regulation of private industry , and stronger support for the nation ’ s agricultural and working classes. $ ^5 $ what do you think ? what were the nation ’ s farmers so upset about ? what sorts of policies did agrarian activists champion ? how would you measure the achievements of the populist movement ?
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the panic of 1873 depressed wages for workers , and the prices of agricultural products plummeted , saddling farmers with massive amounts of debt that they had little hope of paying off. $ ^3 $ the people ’ s party in 1891 , the people ’ s party , also known as the populist party , or populists , was formed as a political party representing the interests of the nation ’ s agricultural sector . the farmer ’ s alliance was a major part of the populist coalition . the people ’ s party nominated james b. weaver , a former us representative from the state of iowa , as its candidate in the 1892 presidential election .
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how long did the farmer 's alliance last ?
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overview the populists were an agrarian-based political movement aimed at improving conditions for the country ’ s farmers and agrarian workers . the populist movement was preceded by the farmer ’ s alliance and the grange . the people ’ s party was a political party founded in 1891 by leaders of the populist movement . it fielded a candidate in the us presidential election of 1892 and garnered 8.5 % of the popular vote , which was a substantial amount of support for a third party . the populists allied with the labor movement and were folded into the democratic party in 1896 , though a small remnant of the people ’ s party continued to exist until it was formally disbanded in 1908 . agrarian activism in the united states beginning in the late nineteenth century , the nation ’ s farmers began to organize to defend their interests against what they perceived to be the interests of the eastern establishment and banking elite . as the number of landless tenant farmers rose , and as the debts of independent farmers skyrocketed due to burdensome loan terms and interest rates from banks , discontent among the nation ’ s agrarian workers burgeoned . in 1876 , the farmer ’ s alliance was established in texas with the goal of ending the crop-lien system that had thrown so many farmers into poverty . the crop-lien system operated in the cotton-growing south , among sharecroppers and tenant farmers , both white and black , who did not own the land that they worked . these workers took out loans to obtain the seed , tools , and other supplies they needed to grow the cotton . after the harvest , they were required to pay back the loans in the form of cotton crops . when cotton prices tanked , these workers were sometimes left with nothing after their crops were collected by creditors. $ ^1 $ the farmer ’ s alliance was not the only organization that sprung up to defend the nation ’ s agrarian workers . the national grange of the order of patrons of husbandry , known as the grange , was founded in 1868 in new york to advocate on behalf of rural communities . from 1873 to 1875 , local chapters of the grange were established across the country , and membership skyrocketed. $ ^2 $ this was partly due to the panic of 1873 , a financial crisis that resulted in a number of bank failures and the bankruptcy of several of the nation ’ s railroads . the panic of 1873 depressed wages for workers , and the prices of agricultural products plummeted , saddling farmers with massive amounts of debt that they had little hope of paying off. $ ^3 $ the people ’ s party in 1891 , the people ’ s party , also known as the populist party , or populists , was formed as a political party representing the interests of the nation ’ s agricultural sector . the farmer ’ s alliance was a major part of the populist coalition . the people ’ s party nominated james b. weaver , a former us representative from the state of iowa , as its candidate in the 1892 presidential election . campaigning on a platform designed to strengthen farmers and weaken the monopolistic power of big business , banks , and railroad corporations , the people ’ s party garnered 8.5 % of the popular vote , carrying the states of colorado , idaho , kansas , and nevada . because of the mass appeal of the populist movement , the democratic party began to champion many of its policy goals . in the 1896 presidential election , the democrats nominated william jennings bryan as its candidate , and the populists agreed to support him . the people ’ s party was thus folded into the democratic party and began to fade from the national scene . the effect of the fusion of the populist party and the democratic party was a disaster in the south . though there had always been conflict within the populist movement about whether african americans should be included , the democratic party in the south was unabashedly racist . though bryan performed strongly in the areas of greatest populist influence , he lost the election to republican william mckinley. $ ^4 $ the people ’ s party continued to function and fielded candidates in both the 1904 and 1908 presidential elections , but the heyday of the party ’ s influence was over . although the people ’ s party was formally disbanded in 1908 , the progressive movement would take up many of the goals and causes of populism , including anti-trust legislation , greater federal regulation of private industry , and stronger support for the nation ’ s agricultural and working classes. $ ^5 $ what do you think ? what were the nation ’ s farmers so upset about ? what sorts of policies did agrarian activists champion ? how would you measure the achievements of the populist movement ?
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although the people ’ s party was formally disbanded in 1908 , the progressive movement would take up many of the goals and causes of populism , including anti-trust legislation , greater federal regulation of private industry , and stronger support for the nation ’ s agricultural and working classes. $ ^5 $ what do you think ? what were the nation ’ s farmers so upset about ? what sorts of policies did agrarian activists champion ?
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what , in the omaha platform , would appeal to groups other than farmers ?
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overview the populists were an agrarian-based political movement aimed at improving conditions for the country ’ s farmers and agrarian workers . the populist movement was preceded by the farmer ’ s alliance and the grange . the people ’ s party was a political party founded in 1891 by leaders of the populist movement . it fielded a candidate in the us presidential election of 1892 and garnered 8.5 % of the popular vote , which was a substantial amount of support for a third party . the populists allied with the labor movement and were folded into the democratic party in 1896 , though a small remnant of the people ’ s party continued to exist until it was formally disbanded in 1908 . agrarian activism in the united states beginning in the late nineteenth century , the nation ’ s farmers began to organize to defend their interests against what they perceived to be the interests of the eastern establishment and banking elite . as the number of landless tenant farmers rose , and as the debts of independent farmers skyrocketed due to burdensome loan terms and interest rates from banks , discontent among the nation ’ s agrarian workers burgeoned . in 1876 , the farmer ’ s alliance was established in texas with the goal of ending the crop-lien system that had thrown so many farmers into poverty . the crop-lien system operated in the cotton-growing south , among sharecroppers and tenant farmers , both white and black , who did not own the land that they worked . these workers took out loans to obtain the seed , tools , and other supplies they needed to grow the cotton . after the harvest , they were required to pay back the loans in the form of cotton crops . when cotton prices tanked , these workers were sometimes left with nothing after their crops were collected by creditors. $ ^1 $ the farmer ’ s alliance was not the only organization that sprung up to defend the nation ’ s agrarian workers . the national grange of the order of patrons of husbandry , known as the grange , was founded in 1868 in new york to advocate on behalf of rural communities . from 1873 to 1875 , local chapters of the grange were established across the country , and membership skyrocketed. $ ^2 $ this was partly due to the panic of 1873 , a financial crisis that resulted in a number of bank failures and the bankruptcy of several of the nation ’ s railroads . the panic of 1873 depressed wages for workers , and the prices of agricultural products plummeted , saddling farmers with massive amounts of debt that they had little hope of paying off. $ ^3 $ the people ’ s party in 1891 , the people ’ s party , also known as the populist party , or populists , was formed as a political party representing the interests of the nation ’ s agricultural sector . the farmer ’ s alliance was a major part of the populist coalition . the people ’ s party nominated james b. weaver , a former us representative from the state of iowa , as its candidate in the 1892 presidential election . campaigning on a platform designed to strengthen farmers and weaken the monopolistic power of big business , banks , and railroad corporations , the people ’ s party garnered 8.5 % of the popular vote , carrying the states of colorado , idaho , kansas , and nevada . because of the mass appeal of the populist movement , the democratic party began to champion many of its policy goals . in the 1896 presidential election , the democrats nominated william jennings bryan as its candidate , and the populists agreed to support him . the people ’ s party was thus folded into the democratic party and began to fade from the national scene . the effect of the fusion of the populist party and the democratic party was a disaster in the south . though there had always been conflict within the populist movement about whether african americans should be included , the democratic party in the south was unabashedly racist . though bryan performed strongly in the areas of greatest populist influence , he lost the election to republican william mckinley. $ ^4 $ the people ’ s party continued to function and fielded candidates in both the 1904 and 1908 presidential elections , but the heyday of the party ’ s influence was over . although the people ’ s party was formally disbanded in 1908 , the progressive movement would take up many of the goals and causes of populism , including anti-trust legislation , greater federal regulation of private industry , and stronger support for the nation ’ s agricultural and working classes. $ ^5 $ what do you think ? what were the nation ’ s farmers so upset about ? what sorts of policies did agrarian activists champion ? how would you measure the achievements of the populist movement ?
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the populist movement was preceded by the farmer ’ s alliance and the grange . the people ’ s party was a political party founded in 1891 by leaders of the populist movement . it fielded a candidate in the us presidential election of 1892 and garnered 8.5 % of the popular vote , which was a substantial amount of support for a third party .
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why people should support the populist movement instead of the 2 major political party ?
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excerpts from charles lyell , principles of geology charles lyell ( 1797 — 1875 ) was a british lawyer and the foremost geologist of his day . he is best known as the author of principles of geology . it popularized geologist james hutton ’ s concept of “ uniformitarianism ” — the idea that the earth was shaped by slow-moving forces still in operation today . uniformitarian ideas opposed the common belief among many geologists that unique catastrophes or supernatural events , like the biblical flood in the story of noah , shaped earth ’ s surface . the motto of uniformitarianism was “ the present is the key to the past. ” lyell ’ s friend , charles darwin , took that idea and extended it to biology . in fact , lyell ’ s principles of geology was one of the few books that darwin carried on his famous voyage on the hms beagle — a voyage that led him to write the origin of the species . what follows is a summarized version of the original text . geology defined — compared to history — its relation to other physical sciences geology is the science which investigates the successive changes that have taken place in the organic and inorganic kingdoms of nature . it inquires into the causes of these changes . and it describes the influence which they have exerted in modifying the surface and external structure of our planet . by this research into the state of the earth and its inhabitants at former periods , we acquire a more perfect knowledge of its present condition . our views concerning the laws governing its animate and inanimate productions become more comprehensive . when we study history , we obtain a more profound insight into human nature . we can draw comparisons between the present and former states of society . we trace the long series of events which have gradually led to the current state of affairs . by connecting effects with their causes , we are enabled to classify and retain in the memory a multitude of complicated relations — the various peculiarities of national character . more deeply can we understand the different degrees of moral and intellectual refinement , and numerous other circumstances . without historical associations , these would be uninteresting or imperfectly understood . the present condition of nations is the result of many previous changes . some are extremely remote , and others recent , some gradual , others sudden and violent . in a similar way , the state of the natural world is the result of a long succession of events . if we seek to enlarge our experience of the present inner workings of nature , we must investigate the effects of her operations in past eras . on looking back into the history of nations , we often discover with surprise how the outcome of some battle has influenced the fate of millions today . this remote event may be connected to the current geo- graphical boundaries of a great state , the language now spoken by the inhabitants , their peculiar manners , laws , and religious opinions . but far more astonishing and unexpected are the connections brought to light when we dig deeper into the history of nature . the form of a coast , the layout of the interior of a country , the existence and extent of lakes , valleys , and mountains , can often be traced to earthquakes and volcanoes in regions which are now tranquil . these ancient upheavals are the reason why some lands are fertile , and others are sterile . they determine the elevation of land above the sea , the climate , and various peculiarities . on the other hand , much of the earth ’ s surface was formed by slow operations such as the gradual depositing of sediment in a lake or in the ocean , or to a great increase of testacea and corals . to select another example , we find in certain areas underground deposits of coal , consisting of vegetable matter which drifted into what were formerly seas and lakes . these seas and lakes have since been filled up . the lands the forests once grew upon have disappeared or changed their form , the rivers and currents which floated the vegetable masses can no longer be traced . and the plants belonged to species which have passed away from the surface of our planet ages ago . yet the wealth and numerical strength of a nation may now be mainly dependent on the distribution of fuel determined by that ancient state of things . geology is closely related to almost all the physical sciences , as history is to the moral . a historian should , if possible , be at once profoundly acquainted with ethics , politics , jurisprudence , the military art , theology ; in a word , with all branches of knowledge by which any insight into human affairs , or into the moral and intellectual nature of man , can be obtained . likewise , a geologist should be well versed in chemistry , natural philosophy , mineralogy , zoology , comparative anatomy , botany ; in short , in every science relating to organic and inorganic nature . with these accomplishments , the historian and geologist would rarely fail to draw correct and philosophical conclusions from the various monuments brought to them by former events . they would know what combination of causes similar effects were relatable to . and they would often be abled to infer information concerning many events unrecorded in the archives of former ages . but since no one individual can be expert in so many subjects , it is necessary that men who have devoted their lives to different departments should unite their efforts . the historian receives assistance from experts on ancient times and from scholars of moral and political science . in the same way , the geologist should avail himself of the aid of many naturalists . he should particularly gain the help of those who have studied the fossil remains of lost species of animals and plants . to be fair , we can only compare one class of historical monuments to the records studied in geology — those which unintentionally mark past events . the canoes , for example , and stone hatchets found in our peat bogs , inform us about the arts and manners of the earliest inhabitants . for further discussion do you think that it ’ s possible today to study any important question from the perspective of just one academic discipline ? or do most interesting questions require you to consider the perspectives of many disciplines ? share your response to these questions in the questions area below .
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but since no one individual can be expert in so many subjects , it is necessary that men who have devoted their lives to different departments should unite their efforts . the historian receives assistance from experts on ancient times and from scholars of moral and political science . in the same way , the geologist should avail himself of the aid of many naturalists .
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why a historian has to be acquainted with political science , jurisprudnece , military art ?
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excerpts from charles lyell , principles of geology charles lyell ( 1797 — 1875 ) was a british lawyer and the foremost geologist of his day . he is best known as the author of principles of geology . it popularized geologist james hutton ’ s concept of “ uniformitarianism ” — the idea that the earth was shaped by slow-moving forces still in operation today . uniformitarian ideas opposed the common belief among many geologists that unique catastrophes or supernatural events , like the biblical flood in the story of noah , shaped earth ’ s surface . the motto of uniformitarianism was “ the present is the key to the past. ” lyell ’ s friend , charles darwin , took that idea and extended it to biology . in fact , lyell ’ s principles of geology was one of the few books that darwin carried on his famous voyage on the hms beagle — a voyage that led him to write the origin of the species . what follows is a summarized version of the original text . geology defined — compared to history — its relation to other physical sciences geology is the science which investigates the successive changes that have taken place in the organic and inorganic kingdoms of nature . it inquires into the causes of these changes . and it describes the influence which they have exerted in modifying the surface and external structure of our planet . by this research into the state of the earth and its inhabitants at former periods , we acquire a more perfect knowledge of its present condition . our views concerning the laws governing its animate and inanimate productions become more comprehensive . when we study history , we obtain a more profound insight into human nature . we can draw comparisons between the present and former states of society . we trace the long series of events which have gradually led to the current state of affairs . by connecting effects with their causes , we are enabled to classify and retain in the memory a multitude of complicated relations — the various peculiarities of national character . more deeply can we understand the different degrees of moral and intellectual refinement , and numerous other circumstances . without historical associations , these would be uninteresting or imperfectly understood . the present condition of nations is the result of many previous changes . some are extremely remote , and others recent , some gradual , others sudden and violent . in a similar way , the state of the natural world is the result of a long succession of events . if we seek to enlarge our experience of the present inner workings of nature , we must investigate the effects of her operations in past eras . on looking back into the history of nations , we often discover with surprise how the outcome of some battle has influenced the fate of millions today . this remote event may be connected to the current geo- graphical boundaries of a great state , the language now spoken by the inhabitants , their peculiar manners , laws , and religious opinions . but far more astonishing and unexpected are the connections brought to light when we dig deeper into the history of nature . the form of a coast , the layout of the interior of a country , the existence and extent of lakes , valleys , and mountains , can often be traced to earthquakes and volcanoes in regions which are now tranquil . these ancient upheavals are the reason why some lands are fertile , and others are sterile . they determine the elevation of land above the sea , the climate , and various peculiarities . on the other hand , much of the earth ’ s surface was formed by slow operations such as the gradual depositing of sediment in a lake or in the ocean , or to a great increase of testacea and corals . to select another example , we find in certain areas underground deposits of coal , consisting of vegetable matter which drifted into what were formerly seas and lakes . these seas and lakes have since been filled up . the lands the forests once grew upon have disappeared or changed their form , the rivers and currents which floated the vegetable masses can no longer be traced . and the plants belonged to species which have passed away from the surface of our planet ages ago . yet the wealth and numerical strength of a nation may now be mainly dependent on the distribution of fuel determined by that ancient state of things . geology is closely related to almost all the physical sciences , as history is to the moral . a historian should , if possible , be at once profoundly acquainted with ethics , politics , jurisprudence , the military art , theology ; in a word , with all branches of knowledge by which any insight into human affairs , or into the moral and intellectual nature of man , can be obtained . likewise , a geologist should be well versed in chemistry , natural philosophy , mineralogy , zoology , comparative anatomy , botany ; in short , in every science relating to organic and inorganic nature . with these accomplishments , the historian and geologist would rarely fail to draw correct and philosophical conclusions from the various monuments brought to them by former events . they would know what combination of causes similar effects were relatable to . and they would often be abled to infer information concerning many events unrecorded in the archives of former ages . but since no one individual can be expert in so many subjects , it is necessary that men who have devoted their lives to different departments should unite their efforts . the historian receives assistance from experts on ancient times and from scholars of moral and political science . in the same way , the geologist should avail himself of the aid of many naturalists . he should particularly gain the help of those who have studied the fossil remains of lost species of animals and plants . to be fair , we can only compare one class of historical monuments to the records studied in geology — those which unintentionally mark past events . the canoes , for example , and stone hatchets found in our peat bogs , inform us about the arts and manners of the earliest inhabitants . for further discussion do you think that it ’ s possible today to study any important question from the perspective of just one academic discipline ? or do most interesting questions require you to consider the perspectives of many disciplines ? share your response to these questions in the questions area below .
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excerpts from charles lyell , principles of geology charles lyell ( 1797 — 1875 ) was a british lawyer and the foremost geologist of his day . he is best known as the author of principles of geology .
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what is a time chart ?
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key points invasive species are species that have been introduced into areas outside their native range and can cause—or have caused—harm in their new area. $ ^1 $ invasive species may outcompete native species for resources or habitat , altering community structure and potentially leading to extinctions . asian carp illustrate the potential impact of invasive species . introduced into the united states by humans , these fish species have colonized waterways and may threaten native fish populations , and fisheries , in the great lakes . introduction take a look at the photo below . just another pretty morning drive in the hills of tennessee ! but wait a minute ... those trees ... they 're covered with something . look closer , and you 'll see that almost the entire landscape is covered with a thick , green blanket . this blanket is made up of an invasive plant called kudzu . kudzu is one dramatic example of what can happen when a species gets introduced into a new ecosystem where it has abundant resources and few predators . the kudzu plant was introduced to the united states from asia in the late 1800s as an ornamental plant , and it and was planted widely in the south in the early 1900s to reduce soil erosion . what the people who planted this vine did not know was that it would rapidly take over the landscape , growing as much as a foot a day and enshrouding ground , shrubs , trees , and even houses and old cars in a suffocating girdle of vines. $ ^2 $ invasive species like kudzu are a vivid—and scary ! —example of how ecological changes , including those caused by humans , can alter communities and ecosystems . in this article , we 'll look in more detail at what an invasive species is and how invasive species can disrupt ecosystems—often reducing the numbers of native species and altering the overall structure of the community . what is an invasive species ? an invasive species is a species that has been introduced to an area outside of its native range and has the potential to cause harm—or has already caused harm—in its new location. $ ^1 $ many invasive species are found in the united states , and a few examples are shown in the pictures below . whether you 're enjoying a forest hike , taking a summer boat trip , or just walking down a city street , chances are that you 've encountered an invasive species . case study : asian carp let 's take a look at what 's arguably the kudzu of the aquatic world : the asian carp . since they were introduced to the united states in the 1970s , asian carp have rocketed in numbers thanks to their vast appetite and speedy reproduction , now forming up to 95 % of the biomass in some mississippi and illinois rivers . not only that , these fish have led to an international lawsuit about waterway access between the united states and canada ! this is a dramatic example of what can happen when an invasive species gets a foothold in a new place . where did this story begin ? asian carp—which are not a single species , but a group of related species—were introduced to the united states in the 1970s. $ ^2 $ they were imported largely by fisheries and sewage treatment plants , which used the carp 's filter feeding abilities to rid ponds of excess plankton . however , some fish escaped . by the 1980s , these fish had colonized waterways of the mississippi river basin , including the illinois and missouri rivers . because they are big eaters and fast reproducers , asian carp can often outcompete native fish species with whom they share habitats and food sources . black carp eat mussels and snails , limiting their availability for native fish and damaging shellfish populations . another asian carp species , the silver carp , eats plankton , a key food for many native fish species in their larval and juvenile stages. $ ^2 $ although asian carp can be eaten , the fish are bony and are generally not a desired food in most parts of the united states . also , if you go out for a fishing trip , be careful : you could get smacked by an asian carp ! the fish , frightened by the sound of approaching motorboats , often thrust themselves into the air and may land in the boat or directly hit the boaters , see jumping carp below . the great lakes and their prized salmon and lake trout fisheries are also threatened by the asian carp . these invasive fish have already colonized rivers and canals that lead into lake michigan , including the major supply waterway linking the great lakes to the mississippi river . to keep the carp from leaving this canal , electric barriers have been used to discourage migration . however , the threat is serious enough that several states and canada have sued to have the chicago channel permanently cut off from lake michigan . we do n't yet know whether the asian carp will prove to be mostly a nuisance—like invasive species such as the zebra mussel—or whether it will ultimately destroy the largest freshwater fishery in the world . the story of the asian carp shows how population and community ecology , fisheries management , and politics can intersect and how ecology can have very real importance for the human food supply and the us economy . on a more personal note , it also shows how ecology can matter for folks enjoying a day on the river ... who might happen to get smacked with a flying carp !
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key points invasive species are species that have been introduced into areas outside their native range and can cause—or have caused—harm in their new area. $ ^1 $ invasive species may outcompete native species for resources or habitat , altering community structure and potentially leading to extinctions . asian carp illustrate the potential impact of invasive species .
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what damage can the european starling do ?
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key points invasive species are species that have been introduced into areas outside their native range and can cause—or have caused—harm in their new area. $ ^1 $ invasive species may outcompete native species for resources or habitat , altering community structure and potentially leading to extinctions . asian carp illustrate the potential impact of invasive species . introduced into the united states by humans , these fish species have colonized waterways and may threaten native fish populations , and fisheries , in the great lakes . introduction take a look at the photo below . just another pretty morning drive in the hills of tennessee ! but wait a minute ... those trees ... they 're covered with something . look closer , and you 'll see that almost the entire landscape is covered with a thick , green blanket . this blanket is made up of an invasive plant called kudzu . kudzu is one dramatic example of what can happen when a species gets introduced into a new ecosystem where it has abundant resources and few predators . the kudzu plant was introduced to the united states from asia in the late 1800s as an ornamental plant , and it and was planted widely in the south in the early 1900s to reduce soil erosion . what the people who planted this vine did not know was that it would rapidly take over the landscape , growing as much as a foot a day and enshrouding ground , shrubs , trees , and even houses and old cars in a suffocating girdle of vines. $ ^2 $ invasive species like kudzu are a vivid—and scary ! —example of how ecological changes , including those caused by humans , can alter communities and ecosystems . in this article , we 'll look in more detail at what an invasive species is and how invasive species can disrupt ecosystems—often reducing the numbers of native species and altering the overall structure of the community . what is an invasive species ? an invasive species is a species that has been introduced to an area outside of its native range and has the potential to cause harm—or has already caused harm—in its new location. $ ^1 $ many invasive species are found in the united states , and a few examples are shown in the pictures below . whether you 're enjoying a forest hike , taking a summer boat trip , or just walking down a city street , chances are that you 've encountered an invasive species . case study : asian carp let 's take a look at what 's arguably the kudzu of the aquatic world : the asian carp . since they were introduced to the united states in the 1970s , asian carp have rocketed in numbers thanks to their vast appetite and speedy reproduction , now forming up to 95 % of the biomass in some mississippi and illinois rivers . not only that , these fish have led to an international lawsuit about waterway access between the united states and canada ! this is a dramatic example of what can happen when an invasive species gets a foothold in a new place . where did this story begin ? asian carp—which are not a single species , but a group of related species—were introduced to the united states in the 1970s. $ ^2 $ they were imported largely by fisheries and sewage treatment plants , which used the carp 's filter feeding abilities to rid ponds of excess plankton . however , some fish escaped . by the 1980s , these fish had colonized waterways of the mississippi river basin , including the illinois and missouri rivers . because they are big eaters and fast reproducers , asian carp can often outcompete native fish species with whom they share habitats and food sources . black carp eat mussels and snails , limiting their availability for native fish and damaging shellfish populations . another asian carp species , the silver carp , eats plankton , a key food for many native fish species in their larval and juvenile stages. $ ^2 $ although asian carp can be eaten , the fish are bony and are generally not a desired food in most parts of the united states . also , if you go out for a fishing trip , be careful : you could get smacked by an asian carp ! the fish , frightened by the sound of approaching motorboats , often thrust themselves into the air and may land in the boat or directly hit the boaters , see jumping carp below . the great lakes and their prized salmon and lake trout fisheries are also threatened by the asian carp . these invasive fish have already colonized rivers and canals that lead into lake michigan , including the major supply waterway linking the great lakes to the mississippi river . to keep the carp from leaving this canal , electric barriers have been used to discourage migration . however , the threat is serious enough that several states and canada have sued to have the chicago channel permanently cut off from lake michigan . we do n't yet know whether the asian carp will prove to be mostly a nuisance—like invasive species such as the zebra mussel—or whether it will ultimately destroy the largest freshwater fishery in the world . the story of the asian carp shows how population and community ecology , fisheries management , and politics can intersect and how ecology can have very real importance for the human food supply and the us economy . on a more personal note , it also shows how ecology can matter for folks enjoying a day on the river ... who might happen to get smacked with a flying carp !
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in this article , we 'll look in more detail at what an invasive species is and how invasive species can disrupt ecosystems—often reducing the numbers of native species and altering the overall structure of the community . what is an invasive species ? an invasive species is a species that has been introduced to an area outside of its native range and has the potential to cause harm—or has already caused harm—in its new location. $ ^1 $ many invasive species are found in the united states , and a few examples are shown in the pictures below .
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why do n't canada and america just make a dam just like other countries do for most invasive species ?
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for centuries , the roman forum ( forum romanum ) was the civic , juridical , and social heart of the ancient city of rome , a place where civic buildings , sacred buildings , and monuments were to be both found and admired . beginning in the first century b.c.e. , a new series of public spaces , also dubbed as fora ( fora being the plural form of the latin noun forum ) began to be created . these fora ( called imperial fora since they were built by roman emperors during the roman imperial period ) would eventually number five in all and were important public spaces that relied upon the visual potential of monumental art and architecture to reinforce ideological messages . topography and chronology the imperial fora are located in an area bounded on the southwest by the capitoline hill , on the northeast by the quirinal hill , and extending toward the esquiline hill to the east . the fora were initially built between c. 54 b.c.e . and 113 c.e. , with continuing additions , restorations , and modifications through late antiquity . in the middle ages the fora were spaces re-used for building materials , housing , industry , and burials . gradually these spaces faded from view , buried beneath the medieval and modern city of rome . a massive campaign of excavation in the twentieth century on the orders of the fascist dictator benito mussolini returned large areas of the fora to view . ongoing archaeological investigation continues to reveal additional elements of the fora and to provide additional data that allow for their contextualization . forum of julius caesar the forum of julius caesar ( also known as the forum iulium or forum caesaris ) was the first of the imperial fora complexes to be built . pompey the great , a political rival of caesar , had dedicated a monumental theater and portico complex in the campus martius in 55 b.c.e . and this perhaps spurred caesar ’ s ambition to construct a new forum complex . caesar ’ s project required the acquisition of land at the flank of the capitoline hill and he was aided in this early on by political allies , including cicero , with the initial land purchased at a cost of sixty million sesterces ( cic . ad att . 4.16.9 ) . additional land acquisition may have ballooned the total cost to one hundred million sesterces ( suetonius divus iulius 26 ; pliny the elder natural history 36.103 ) . the construction of caesar ’ s forum resulted in significant reorganization of the northwest corner of the forum romanum . the forum of caesar takes the form of a rectangle measuring 160 by 75 m. the centerpiece of the complex was the temple of venus genetrix , dedicated to the goddess that caesar celebrated as his distant ancestor . the octastyle ( eight columns across the façade ) temple was made of solid marble and sat atop a high podium . the long sides of the forum square , flanking the temple , housed two storeys of rooms that may have served political and/or mercantile functions . the complex was dedicated during the festivities surrounding caesar ’ s triumph in september of 46 b.c.e . forum of augustus the forum of augustus ( known as the forum augustum or forum augusti ) followed the forum of caesar as the second of the imperial fora . at the battle of philippi in 42 b.c.e. , augustus vowed a temple to mars in exchange for help in avenging the slain caesar ( suet . aug. 29.2 ) , but the temple and forum complex would not be dedicated until 2 b.c.e . ( res gestae 21 ) . the forum of augustus provided additional room for the meeting of law courts and was built on land acquired by augustus . the temple at the center of the forum augusti was sacred to mars ultor ( “ mars the avenger ” ) , and was surrounded by a portico that defined the forum space and played a key role in the visual narrative of the public art program installed in the forum . as augustus had emerged as the sole leader of the roman state , it was important for him to create and display messages of continuity and stability . the visual program in the forum of augustus is complex . the architectural sculpture adorning the temple of mars ultor inserts augustus into the julian family ( gens iulia ) by portraying augustus in the context of divinities ( mars , venus , and cupid ) and the deified mortal—julius caesar ( divus iulius ) . flanking the temple in the exedrae ( the semicircular , recessed areas behind the colonnades to the left and right of the temple ) of the porticoes were sculptural groups depicting both romulus and aeneas , thus connecting augustus to rome ’ s two legendary founders ( ovid fasti 5.549-570 ) . to complete the narrative cycle , statues of famous romans of the republican period adorned the attic of the porticoes . these famous men ( summi viri ) were portrayed alongside small , inscribed plaques ( tituli ) bearing their political and military accomplishments . in this way , augustus portrayed himself as the ideal man to lead the roman state ; he was connected to rome ’ s divine origins and he represented continuity with its republican tradition . this powerful visual narrative represents an important early use of public art to transmit ideological messages in the western world . subsequent emperors continued to elaborate upon the forum of augustus . the emperor tiberius added two arches in 19 c.e . meant to honor the german victories of drusus and germanicus ( tacitus annales 2.64 ; cil 6.911 ) and the emperor hadrian restored the forum complex in the second century . pliny the elder deemed the forum of augustus one of three most beautiful monuments in the city of rome ( pliny the elder natural history 36.102.5 ) . templum pacis / forum of vespasian the next imperial forum to be built was commissioned by the emperor vespasian following the suppression of the great jewish revolt that lasted from 66 to 73 c.e . vespasian came to power following civil chaos in 69 c.e . and , together with his eldest son , titus , suppressed the revolt and sacked the city of jerusalem . during the summer of 71 c.e . vespasian and titus jointly celebrated a lavish triumph at rome—an ancient ritual celebrating significant military victories . one of the key tenets of vespasian ’ s new administration was the restoration of the city , including the construction of new buildings and monuments . he dedicated a forum complex that housed a temple dedicated to peace ( pax ) in 71 c.e. , completing it by 75 c.e . ( flavius josephus jewish war 7.5.7 ) . this innovative complex was deemed one of rome ’ s most beautiful monuments by pliny the elder and housed not only significant spoils from jerusalem but also masterworks of greek art that had previously been hoarded by the emperor nero . the temple of peace ( templum pacis ) stands out among the imperial fora for its innovative architectural design . rather than featuring a central temple seated atop a prominent podium , the templum pacis complex consists of a square portico ( dimensions 110 x 135 m ) with the temple itself set within the eastern side of the portico , flanked by ancillary rooms . this left the square itself open for the installation of decorative water features and plantings which are seen both archaeologically and on fragments of the severan marble plan of the city of rome ( forma urbis romae ) that was mounted in the forum complex in the third century c.e . the fragments of the severan plan provide valuable information about the design of this architectural complex and has led scholars to speculate that the inspiration for its design may have been the great market ( macellum magnum ) of the city that had likely been destroyed in the great fire of rome in 64 c.e . it is especially significant to note that this is a public space and that vespasian ’ s generosity granted the populace of rome access not only to a beautiful , monumental square , but also to art and the spoils of military victory ( including spoils from the temple in jerusalem ) . forum transitorium the forum transitorium , also referred to as the forum of nerva , was begun by domitian , the younger son of vespasian . incomplete at the time of domitian ’ s assassination in 96 c.e. , the complex was completed by nerva in 97 c.e . this is a narrow forum complex that abuts both the forum of augustus and the templum pacis and is constrained by these pre-existing structures ( dimensions : 131 x 45 meters ) ; as well as the argiletum , a street that ran the length of the forum . the forum transitorium ’ s temple was sacred to minerva , who had been a patron divinity of domitian , and the architectural sculpture that decorated the porticoes featured imagery connected to minerva and scenes from the private lives of women . forum of trajan the forum of trajan ( forum traiani ) , the final imperial forum , was both the largest and the most lavish . inaugurated in 112 c.e. , the architectural complex relied upon imposing architectural and sculptural features to glorify the accomplishments and principate of the emperor trajan . the elaborate forum complex has a vast footprint , measuring 200 x 120 meters . the open square of the forum is flanked by porticoes that contain exedrae and point viewer attention toward the main structure , the massive basilica ulpia . the architect apollodorus of damascus was responsible for the innovative design . on the western side of the basilica was another courtyard , flanked by two libraries ( one greek and one latin ) , that contained a monumental honorific column , known today as the column of trajan . the column of trajan , inaugurated in 113 c.e. , is a main feature of the forum of trajan and is , in its own right , a masterwork of roman art . the column carries an helical frieze of historical relief that provides a pictorial narrative of the events of trajan ’ s wars in dacia ( 101–102 and 105–106 c.e . ) , culminating with the death of the enemy commander , decebalus . the column stands 38 meters tall and its frieze wraps around the column shaft 23 times , with a total length of roughly 190 meters . carved in bas relief , the exquisite frieze carefully narrates trajan ’ s campaigns and its level of detail is simply astounding . the column ’ s frieze may draw inspiration from earlier roman triumphal art , the tradition of which was inclined to depict scenes from the foreign campaigns and , in so doing , glorify the accomplishments of the commander and his soldiers . throughout the forum of trajan the theme of military victory , and its celebration , permeate the monumental decorative programs . when trajan died in 117 c.e. , sources tell us that the roman senate allowed a special dispensation whereby trajan ’ s cremated remains could be deposited in the base of the column and that a temple to his cult ( templum divi traiani et plotinae ) was added to the forum complex between 125 and 138 c.e . ( historia augusta - hadrian 19.9 ) . an ongoing point of scholarly contention is the position and appearance of this plan . traditional reconstructions favor a free-standing temple at the western end of the forum , while more recent reconstructions instead favor a shrine positioned against the western exedra of the forum of augustus . ongoing archaeological fieldwork may yet shed light on this contentious topographical debate . interpretation the imperial fora represent important architectural landscapes in the city of rome . they demonstrate the efficacy of public art and architecture with respect to creating collective identity and communicating clear messages that both disseminate and reinforce ideology . the strength and accomplishments of the roman state , not to mention its stability , are key themes in any such program of message making . we should also not underestimate the psychological effect of these grandiose , soaring , bedecked complexes , based around massive open plazas , on the minds and experiences of city dwellers ( many of whom lived in crowded squalor ) . the imperial fora demonstrate that within the mechanisms of roman urbanism , civic architecture occupies a crucial role . we are reminded of this efficacy by an ancient example that is perhaps no different from the reaction of a modern visitor to the city of rome . the emperor constantius ii , visiting rome in the mid-fourth century c.e. , was amazed by the forum of trajan , something he considered “ a construction unique under the heavens ” ( ammianus marcellinus 16.10.15 ) . essay by dr. jeffrey a. becker additional resources : j. anderson , the historical topography of the imperial fora ( collection latomus ; 182 ) ( brussels : latomus , 1984 ) . s. baiani et al. , crypta balbi-fori imperiali : archeologia urbana a roma e interventi di restauro nell'anno del grande giubileo ( rome : kappa , 2000 ) . a. carandini and p. carafa , eds. , atlante di roma antica : biografia e ritratti della città 2 v. ( milan : electa , 2012 ) . a. claridge , rome : an archaeological guide 2nd ed . ( oxford : oxford university press , 2010 ) . f. coarelli et al. , the column of trajan ( rome : colombo , 2000 ) . r. darwall-smith , emperors and architecture : a study of flavian rome ( collection latomus ; 231 ) ( brussels : latomus , 1996 ) . j. geiger , the first hall of fame : a study of the statues in the forum augustum ( leiden : e. j. brill , 2008 ) . e. la rocca , i fori imperiali ( rome : enel , 1995 ) . t. j. luce , `` livy , augustus , and the forum augustum . '' in between republic and empire , ed . by k. raaflaub , k. and m. toher , pp . 123-38 ( berkeley : university of california press , 1990 ) . r. meneghini , “ templum divi traiani , ” bullettino della commissione archeologica comunale di roma 97 ( 1996 ) pp . 47-55 . r. meneghini and r. s. valenzani , scavi dei fori imperiali : il foro di augusto : l'area centrale ( rome : “ l ’ erma ” di bretschneider , 2010 ) . j. e. packer , the forum of trajan in rome : a study of the monuments 2 v. ( berkeley : university of california press , 1997 ) . j. e. packer , “ trajan ’ s forum again : the column and the temple in the master plan attributed to apollodorus ( ? ) , ” journal of roman archaeology 7:274-6 . s. b. platner and t. ashby , a topographical dictionary of ancient rome ( oxford : clarendon press , 1929 ) . l. richardson , jr. , a new topographical dictionary of ancient rome ( baltimore : johns hopkins university press , 1992 ) . r. ulrich , “ julius caesar and the creation of the forum iulium , ” american journal of archaeology 97.1:49-80 . l. ungaro , il museo dei fori imperiali nei mercati di traiano ( milan : electa , 2007 ) . mercati di traiano museo dei fori imperiali ( markets of trajan and the imperial fora museum ) fori imperiali ( sovrintendenza capitolina )
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( oxford : oxford university press , 2010 ) . f. coarelli et al. , the column of trajan ( rome : colombo , 2000 ) . r. darwall-smith , emperors and architecture : a study of flavian rome ( collection latomus ; 231 ) ( brussels : latomus , 1996 ) .
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has there ever been talk of bringing the 'column of trajan ' indoors ?
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for centuries , the roman forum ( forum romanum ) was the civic , juridical , and social heart of the ancient city of rome , a place where civic buildings , sacred buildings , and monuments were to be both found and admired . beginning in the first century b.c.e. , a new series of public spaces , also dubbed as fora ( fora being the plural form of the latin noun forum ) began to be created . these fora ( called imperial fora since they were built by roman emperors during the roman imperial period ) would eventually number five in all and were important public spaces that relied upon the visual potential of monumental art and architecture to reinforce ideological messages . topography and chronology the imperial fora are located in an area bounded on the southwest by the capitoline hill , on the northeast by the quirinal hill , and extending toward the esquiline hill to the east . the fora were initially built between c. 54 b.c.e . and 113 c.e. , with continuing additions , restorations , and modifications through late antiquity . in the middle ages the fora were spaces re-used for building materials , housing , industry , and burials . gradually these spaces faded from view , buried beneath the medieval and modern city of rome . a massive campaign of excavation in the twentieth century on the orders of the fascist dictator benito mussolini returned large areas of the fora to view . ongoing archaeological investigation continues to reveal additional elements of the fora and to provide additional data that allow for their contextualization . forum of julius caesar the forum of julius caesar ( also known as the forum iulium or forum caesaris ) was the first of the imperial fora complexes to be built . pompey the great , a political rival of caesar , had dedicated a monumental theater and portico complex in the campus martius in 55 b.c.e . and this perhaps spurred caesar ’ s ambition to construct a new forum complex . caesar ’ s project required the acquisition of land at the flank of the capitoline hill and he was aided in this early on by political allies , including cicero , with the initial land purchased at a cost of sixty million sesterces ( cic . ad att . 4.16.9 ) . additional land acquisition may have ballooned the total cost to one hundred million sesterces ( suetonius divus iulius 26 ; pliny the elder natural history 36.103 ) . the construction of caesar ’ s forum resulted in significant reorganization of the northwest corner of the forum romanum . the forum of caesar takes the form of a rectangle measuring 160 by 75 m. the centerpiece of the complex was the temple of venus genetrix , dedicated to the goddess that caesar celebrated as his distant ancestor . the octastyle ( eight columns across the façade ) temple was made of solid marble and sat atop a high podium . the long sides of the forum square , flanking the temple , housed two storeys of rooms that may have served political and/or mercantile functions . the complex was dedicated during the festivities surrounding caesar ’ s triumph in september of 46 b.c.e . forum of augustus the forum of augustus ( known as the forum augustum or forum augusti ) followed the forum of caesar as the second of the imperial fora . at the battle of philippi in 42 b.c.e. , augustus vowed a temple to mars in exchange for help in avenging the slain caesar ( suet . aug. 29.2 ) , but the temple and forum complex would not be dedicated until 2 b.c.e . ( res gestae 21 ) . the forum of augustus provided additional room for the meeting of law courts and was built on land acquired by augustus . the temple at the center of the forum augusti was sacred to mars ultor ( “ mars the avenger ” ) , and was surrounded by a portico that defined the forum space and played a key role in the visual narrative of the public art program installed in the forum . as augustus had emerged as the sole leader of the roman state , it was important for him to create and display messages of continuity and stability . the visual program in the forum of augustus is complex . the architectural sculpture adorning the temple of mars ultor inserts augustus into the julian family ( gens iulia ) by portraying augustus in the context of divinities ( mars , venus , and cupid ) and the deified mortal—julius caesar ( divus iulius ) . flanking the temple in the exedrae ( the semicircular , recessed areas behind the colonnades to the left and right of the temple ) of the porticoes were sculptural groups depicting both romulus and aeneas , thus connecting augustus to rome ’ s two legendary founders ( ovid fasti 5.549-570 ) . to complete the narrative cycle , statues of famous romans of the republican period adorned the attic of the porticoes . these famous men ( summi viri ) were portrayed alongside small , inscribed plaques ( tituli ) bearing their political and military accomplishments . in this way , augustus portrayed himself as the ideal man to lead the roman state ; he was connected to rome ’ s divine origins and he represented continuity with its republican tradition . this powerful visual narrative represents an important early use of public art to transmit ideological messages in the western world . subsequent emperors continued to elaborate upon the forum of augustus . the emperor tiberius added two arches in 19 c.e . meant to honor the german victories of drusus and germanicus ( tacitus annales 2.64 ; cil 6.911 ) and the emperor hadrian restored the forum complex in the second century . pliny the elder deemed the forum of augustus one of three most beautiful monuments in the city of rome ( pliny the elder natural history 36.102.5 ) . templum pacis / forum of vespasian the next imperial forum to be built was commissioned by the emperor vespasian following the suppression of the great jewish revolt that lasted from 66 to 73 c.e . vespasian came to power following civil chaos in 69 c.e . and , together with his eldest son , titus , suppressed the revolt and sacked the city of jerusalem . during the summer of 71 c.e . vespasian and titus jointly celebrated a lavish triumph at rome—an ancient ritual celebrating significant military victories . one of the key tenets of vespasian ’ s new administration was the restoration of the city , including the construction of new buildings and monuments . he dedicated a forum complex that housed a temple dedicated to peace ( pax ) in 71 c.e. , completing it by 75 c.e . ( flavius josephus jewish war 7.5.7 ) . this innovative complex was deemed one of rome ’ s most beautiful monuments by pliny the elder and housed not only significant spoils from jerusalem but also masterworks of greek art that had previously been hoarded by the emperor nero . the temple of peace ( templum pacis ) stands out among the imperial fora for its innovative architectural design . rather than featuring a central temple seated atop a prominent podium , the templum pacis complex consists of a square portico ( dimensions 110 x 135 m ) with the temple itself set within the eastern side of the portico , flanked by ancillary rooms . this left the square itself open for the installation of decorative water features and plantings which are seen both archaeologically and on fragments of the severan marble plan of the city of rome ( forma urbis romae ) that was mounted in the forum complex in the third century c.e . the fragments of the severan plan provide valuable information about the design of this architectural complex and has led scholars to speculate that the inspiration for its design may have been the great market ( macellum magnum ) of the city that had likely been destroyed in the great fire of rome in 64 c.e . it is especially significant to note that this is a public space and that vespasian ’ s generosity granted the populace of rome access not only to a beautiful , monumental square , but also to art and the spoils of military victory ( including spoils from the temple in jerusalem ) . forum transitorium the forum transitorium , also referred to as the forum of nerva , was begun by domitian , the younger son of vespasian . incomplete at the time of domitian ’ s assassination in 96 c.e. , the complex was completed by nerva in 97 c.e . this is a narrow forum complex that abuts both the forum of augustus and the templum pacis and is constrained by these pre-existing structures ( dimensions : 131 x 45 meters ) ; as well as the argiletum , a street that ran the length of the forum . the forum transitorium ’ s temple was sacred to minerva , who had been a patron divinity of domitian , and the architectural sculpture that decorated the porticoes featured imagery connected to minerva and scenes from the private lives of women . forum of trajan the forum of trajan ( forum traiani ) , the final imperial forum , was both the largest and the most lavish . inaugurated in 112 c.e. , the architectural complex relied upon imposing architectural and sculptural features to glorify the accomplishments and principate of the emperor trajan . the elaborate forum complex has a vast footprint , measuring 200 x 120 meters . the open square of the forum is flanked by porticoes that contain exedrae and point viewer attention toward the main structure , the massive basilica ulpia . the architect apollodorus of damascus was responsible for the innovative design . on the western side of the basilica was another courtyard , flanked by two libraries ( one greek and one latin ) , that contained a monumental honorific column , known today as the column of trajan . the column of trajan , inaugurated in 113 c.e. , is a main feature of the forum of trajan and is , in its own right , a masterwork of roman art . the column carries an helical frieze of historical relief that provides a pictorial narrative of the events of trajan ’ s wars in dacia ( 101–102 and 105–106 c.e . ) , culminating with the death of the enemy commander , decebalus . the column stands 38 meters tall and its frieze wraps around the column shaft 23 times , with a total length of roughly 190 meters . carved in bas relief , the exquisite frieze carefully narrates trajan ’ s campaigns and its level of detail is simply astounding . the column ’ s frieze may draw inspiration from earlier roman triumphal art , the tradition of which was inclined to depict scenes from the foreign campaigns and , in so doing , glorify the accomplishments of the commander and his soldiers . throughout the forum of trajan the theme of military victory , and its celebration , permeate the monumental decorative programs . when trajan died in 117 c.e. , sources tell us that the roman senate allowed a special dispensation whereby trajan ’ s cremated remains could be deposited in the base of the column and that a temple to his cult ( templum divi traiani et plotinae ) was added to the forum complex between 125 and 138 c.e . ( historia augusta - hadrian 19.9 ) . an ongoing point of scholarly contention is the position and appearance of this plan . traditional reconstructions favor a free-standing temple at the western end of the forum , while more recent reconstructions instead favor a shrine positioned against the western exedra of the forum of augustus . ongoing archaeological fieldwork may yet shed light on this contentious topographical debate . interpretation the imperial fora represent important architectural landscapes in the city of rome . they demonstrate the efficacy of public art and architecture with respect to creating collective identity and communicating clear messages that both disseminate and reinforce ideology . the strength and accomplishments of the roman state , not to mention its stability , are key themes in any such program of message making . we should also not underestimate the psychological effect of these grandiose , soaring , bedecked complexes , based around massive open plazas , on the minds and experiences of city dwellers ( many of whom lived in crowded squalor ) . the imperial fora demonstrate that within the mechanisms of roman urbanism , civic architecture occupies a crucial role . we are reminded of this efficacy by an ancient example that is perhaps no different from the reaction of a modern visitor to the city of rome . the emperor constantius ii , visiting rome in the mid-fourth century c.e. , was amazed by the forum of trajan , something he considered “ a construction unique under the heavens ” ( ammianus marcellinus 16.10.15 ) . essay by dr. jeffrey a. becker additional resources : j. anderson , the historical topography of the imperial fora ( collection latomus ; 182 ) ( brussels : latomus , 1984 ) . s. baiani et al. , crypta balbi-fori imperiali : archeologia urbana a roma e interventi di restauro nell'anno del grande giubileo ( rome : kappa , 2000 ) . a. carandini and p. carafa , eds. , atlante di roma antica : biografia e ritratti della città 2 v. ( milan : electa , 2012 ) . a. claridge , rome : an archaeological guide 2nd ed . ( oxford : oxford university press , 2010 ) . f. coarelli et al. , the column of trajan ( rome : colombo , 2000 ) . r. darwall-smith , emperors and architecture : a study of flavian rome ( collection latomus ; 231 ) ( brussels : latomus , 1996 ) . j. geiger , the first hall of fame : a study of the statues in the forum augustum ( leiden : e. j. brill , 2008 ) . e. la rocca , i fori imperiali ( rome : enel , 1995 ) . t. j. luce , `` livy , augustus , and the forum augustum . '' in between republic and empire , ed . by k. raaflaub , k. and m. toher , pp . 123-38 ( berkeley : university of california press , 1990 ) . r. meneghini , “ templum divi traiani , ” bullettino della commissione archeologica comunale di roma 97 ( 1996 ) pp . 47-55 . r. meneghini and r. s. valenzani , scavi dei fori imperiali : il foro di augusto : l'area centrale ( rome : “ l ’ erma ” di bretschneider , 2010 ) . j. e. packer , the forum of trajan in rome : a study of the monuments 2 v. ( berkeley : university of california press , 1997 ) . j. e. packer , “ trajan ’ s forum again : the column and the temple in the master plan attributed to apollodorus ( ? ) , ” journal of roman archaeology 7:274-6 . s. b. platner and t. ashby , a topographical dictionary of ancient rome ( oxford : clarendon press , 1929 ) . l. richardson , jr. , a new topographical dictionary of ancient rome ( baltimore : johns hopkins university press , 1992 ) . r. ulrich , “ julius caesar and the creation of the forum iulium , ” american journal of archaeology 97.1:49-80 . l. ungaro , il museo dei fori imperiali nei mercati di traiano ( milan : electa , 2007 ) . mercati di traiano museo dei fori imperiali ( markets of trajan and the imperial fora museum ) fori imperiali ( sovrintendenza capitolina )
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vespasian came to power following civil chaos in 69 c.e . and , together with his eldest son , titus , suppressed the revolt and sacked the city of jerusalem . during the summer of 71 c.e .
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also , was the `` sack '' of jerusalem the single most profitable sacking of a foreign city for the roman empire ?
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for centuries , the roman forum ( forum romanum ) was the civic , juridical , and social heart of the ancient city of rome , a place where civic buildings , sacred buildings , and monuments were to be both found and admired . beginning in the first century b.c.e. , a new series of public spaces , also dubbed as fora ( fora being the plural form of the latin noun forum ) began to be created . these fora ( called imperial fora since they were built by roman emperors during the roman imperial period ) would eventually number five in all and were important public spaces that relied upon the visual potential of monumental art and architecture to reinforce ideological messages . topography and chronology the imperial fora are located in an area bounded on the southwest by the capitoline hill , on the northeast by the quirinal hill , and extending toward the esquiline hill to the east . the fora were initially built between c. 54 b.c.e . and 113 c.e. , with continuing additions , restorations , and modifications through late antiquity . in the middle ages the fora were spaces re-used for building materials , housing , industry , and burials . gradually these spaces faded from view , buried beneath the medieval and modern city of rome . a massive campaign of excavation in the twentieth century on the orders of the fascist dictator benito mussolini returned large areas of the fora to view . ongoing archaeological investigation continues to reveal additional elements of the fora and to provide additional data that allow for their contextualization . forum of julius caesar the forum of julius caesar ( also known as the forum iulium or forum caesaris ) was the first of the imperial fora complexes to be built . pompey the great , a political rival of caesar , had dedicated a monumental theater and portico complex in the campus martius in 55 b.c.e . and this perhaps spurred caesar ’ s ambition to construct a new forum complex . caesar ’ s project required the acquisition of land at the flank of the capitoline hill and he was aided in this early on by political allies , including cicero , with the initial land purchased at a cost of sixty million sesterces ( cic . ad att . 4.16.9 ) . additional land acquisition may have ballooned the total cost to one hundred million sesterces ( suetonius divus iulius 26 ; pliny the elder natural history 36.103 ) . the construction of caesar ’ s forum resulted in significant reorganization of the northwest corner of the forum romanum . the forum of caesar takes the form of a rectangle measuring 160 by 75 m. the centerpiece of the complex was the temple of venus genetrix , dedicated to the goddess that caesar celebrated as his distant ancestor . the octastyle ( eight columns across the façade ) temple was made of solid marble and sat atop a high podium . the long sides of the forum square , flanking the temple , housed two storeys of rooms that may have served political and/or mercantile functions . the complex was dedicated during the festivities surrounding caesar ’ s triumph in september of 46 b.c.e . forum of augustus the forum of augustus ( known as the forum augustum or forum augusti ) followed the forum of caesar as the second of the imperial fora . at the battle of philippi in 42 b.c.e. , augustus vowed a temple to mars in exchange for help in avenging the slain caesar ( suet . aug. 29.2 ) , but the temple and forum complex would not be dedicated until 2 b.c.e . ( res gestae 21 ) . the forum of augustus provided additional room for the meeting of law courts and was built on land acquired by augustus . the temple at the center of the forum augusti was sacred to mars ultor ( “ mars the avenger ” ) , and was surrounded by a portico that defined the forum space and played a key role in the visual narrative of the public art program installed in the forum . as augustus had emerged as the sole leader of the roman state , it was important for him to create and display messages of continuity and stability . the visual program in the forum of augustus is complex . the architectural sculpture adorning the temple of mars ultor inserts augustus into the julian family ( gens iulia ) by portraying augustus in the context of divinities ( mars , venus , and cupid ) and the deified mortal—julius caesar ( divus iulius ) . flanking the temple in the exedrae ( the semicircular , recessed areas behind the colonnades to the left and right of the temple ) of the porticoes were sculptural groups depicting both romulus and aeneas , thus connecting augustus to rome ’ s two legendary founders ( ovid fasti 5.549-570 ) . to complete the narrative cycle , statues of famous romans of the republican period adorned the attic of the porticoes . these famous men ( summi viri ) were portrayed alongside small , inscribed plaques ( tituli ) bearing their political and military accomplishments . in this way , augustus portrayed himself as the ideal man to lead the roman state ; he was connected to rome ’ s divine origins and he represented continuity with its republican tradition . this powerful visual narrative represents an important early use of public art to transmit ideological messages in the western world . subsequent emperors continued to elaborate upon the forum of augustus . the emperor tiberius added two arches in 19 c.e . meant to honor the german victories of drusus and germanicus ( tacitus annales 2.64 ; cil 6.911 ) and the emperor hadrian restored the forum complex in the second century . pliny the elder deemed the forum of augustus one of three most beautiful monuments in the city of rome ( pliny the elder natural history 36.102.5 ) . templum pacis / forum of vespasian the next imperial forum to be built was commissioned by the emperor vespasian following the suppression of the great jewish revolt that lasted from 66 to 73 c.e . vespasian came to power following civil chaos in 69 c.e . and , together with his eldest son , titus , suppressed the revolt and sacked the city of jerusalem . during the summer of 71 c.e . vespasian and titus jointly celebrated a lavish triumph at rome—an ancient ritual celebrating significant military victories . one of the key tenets of vespasian ’ s new administration was the restoration of the city , including the construction of new buildings and monuments . he dedicated a forum complex that housed a temple dedicated to peace ( pax ) in 71 c.e. , completing it by 75 c.e . ( flavius josephus jewish war 7.5.7 ) . this innovative complex was deemed one of rome ’ s most beautiful monuments by pliny the elder and housed not only significant spoils from jerusalem but also masterworks of greek art that had previously been hoarded by the emperor nero . the temple of peace ( templum pacis ) stands out among the imperial fora for its innovative architectural design . rather than featuring a central temple seated atop a prominent podium , the templum pacis complex consists of a square portico ( dimensions 110 x 135 m ) with the temple itself set within the eastern side of the portico , flanked by ancillary rooms . this left the square itself open for the installation of decorative water features and plantings which are seen both archaeologically and on fragments of the severan marble plan of the city of rome ( forma urbis romae ) that was mounted in the forum complex in the third century c.e . the fragments of the severan plan provide valuable information about the design of this architectural complex and has led scholars to speculate that the inspiration for its design may have been the great market ( macellum magnum ) of the city that had likely been destroyed in the great fire of rome in 64 c.e . it is especially significant to note that this is a public space and that vespasian ’ s generosity granted the populace of rome access not only to a beautiful , monumental square , but also to art and the spoils of military victory ( including spoils from the temple in jerusalem ) . forum transitorium the forum transitorium , also referred to as the forum of nerva , was begun by domitian , the younger son of vespasian . incomplete at the time of domitian ’ s assassination in 96 c.e. , the complex was completed by nerva in 97 c.e . this is a narrow forum complex that abuts both the forum of augustus and the templum pacis and is constrained by these pre-existing structures ( dimensions : 131 x 45 meters ) ; as well as the argiletum , a street that ran the length of the forum . the forum transitorium ’ s temple was sacred to minerva , who had been a patron divinity of domitian , and the architectural sculpture that decorated the porticoes featured imagery connected to minerva and scenes from the private lives of women . forum of trajan the forum of trajan ( forum traiani ) , the final imperial forum , was both the largest and the most lavish . inaugurated in 112 c.e. , the architectural complex relied upon imposing architectural and sculptural features to glorify the accomplishments and principate of the emperor trajan . the elaborate forum complex has a vast footprint , measuring 200 x 120 meters . the open square of the forum is flanked by porticoes that contain exedrae and point viewer attention toward the main structure , the massive basilica ulpia . the architect apollodorus of damascus was responsible for the innovative design . on the western side of the basilica was another courtyard , flanked by two libraries ( one greek and one latin ) , that contained a monumental honorific column , known today as the column of trajan . the column of trajan , inaugurated in 113 c.e. , is a main feature of the forum of trajan and is , in its own right , a masterwork of roman art . the column carries an helical frieze of historical relief that provides a pictorial narrative of the events of trajan ’ s wars in dacia ( 101–102 and 105–106 c.e . ) , culminating with the death of the enemy commander , decebalus . the column stands 38 meters tall and its frieze wraps around the column shaft 23 times , with a total length of roughly 190 meters . carved in bas relief , the exquisite frieze carefully narrates trajan ’ s campaigns and its level of detail is simply astounding . the column ’ s frieze may draw inspiration from earlier roman triumphal art , the tradition of which was inclined to depict scenes from the foreign campaigns and , in so doing , glorify the accomplishments of the commander and his soldiers . throughout the forum of trajan the theme of military victory , and its celebration , permeate the monumental decorative programs . when trajan died in 117 c.e. , sources tell us that the roman senate allowed a special dispensation whereby trajan ’ s cremated remains could be deposited in the base of the column and that a temple to his cult ( templum divi traiani et plotinae ) was added to the forum complex between 125 and 138 c.e . ( historia augusta - hadrian 19.9 ) . an ongoing point of scholarly contention is the position and appearance of this plan . traditional reconstructions favor a free-standing temple at the western end of the forum , while more recent reconstructions instead favor a shrine positioned against the western exedra of the forum of augustus . ongoing archaeological fieldwork may yet shed light on this contentious topographical debate . interpretation the imperial fora represent important architectural landscapes in the city of rome . they demonstrate the efficacy of public art and architecture with respect to creating collective identity and communicating clear messages that both disseminate and reinforce ideology . the strength and accomplishments of the roman state , not to mention its stability , are key themes in any such program of message making . we should also not underestimate the psychological effect of these grandiose , soaring , bedecked complexes , based around massive open plazas , on the minds and experiences of city dwellers ( many of whom lived in crowded squalor ) . the imperial fora demonstrate that within the mechanisms of roman urbanism , civic architecture occupies a crucial role . we are reminded of this efficacy by an ancient example that is perhaps no different from the reaction of a modern visitor to the city of rome . the emperor constantius ii , visiting rome in the mid-fourth century c.e. , was amazed by the forum of trajan , something he considered “ a construction unique under the heavens ” ( ammianus marcellinus 16.10.15 ) . essay by dr. jeffrey a. becker additional resources : j. anderson , the historical topography of the imperial fora ( collection latomus ; 182 ) ( brussels : latomus , 1984 ) . s. baiani et al. , crypta balbi-fori imperiali : archeologia urbana a roma e interventi di restauro nell'anno del grande giubileo ( rome : kappa , 2000 ) . a. carandini and p. carafa , eds. , atlante di roma antica : biografia e ritratti della città 2 v. ( milan : electa , 2012 ) . a. claridge , rome : an archaeological guide 2nd ed . ( oxford : oxford university press , 2010 ) . f. coarelli et al. , the column of trajan ( rome : colombo , 2000 ) . r. darwall-smith , emperors and architecture : a study of flavian rome ( collection latomus ; 231 ) ( brussels : latomus , 1996 ) . j. geiger , the first hall of fame : a study of the statues in the forum augustum ( leiden : e. j. brill , 2008 ) . e. la rocca , i fori imperiali ( rome : enel , 1995 ) . t. j. luce , `` livy , augustus , and the forum augustum . '' in between republic and empire , ed . by k. raaflaub , k. and m. toher , pp . 123-38 ( berkeley : university of california press , 1990 ) . r. meneghini , “ templum divi traiani , ” bullettino della commissione archeologica comunale di roma 97 ( 1996 ) pp . 47-55 . r. meneghini and r. s. valenzani , scavi dei fori imperiali : il foro di augusto : l'area centrale ( rome : “ l ’ erma ” di bretschneider , 2010 ) . j. e. packer , the forum of trajan in rome : a study of the monuments 2 v. ( berkeley : university of california press , 1997 ) . j. e. packer , “ trajan ’ s forum again : the column and the temple in the master plan attributed to apollodorus ( ? ) , ” journal of roman archaeology 7:274-6 . s. b. platner and t. ashby , a topographical dictionary of ancient rome ( oxford : clarendon press , 1929 ) . l. richardson , jr. , a new topographical dictionary of ancient rome ( baltimore : johns hopkins university press , 1992 ) . r. ulrich , “ julius caesar and the creation of the forum iulium , ” american journal of archaeology 97.1:49-80 . l. ungaro , il museo dei fori imperiali nei mercati di traiano ( milan : electa , 2007 ) . mercati di traiano museo dei fori imperiali ( markets of trajan and the imperial fora museum ) fori imperiali ( sovrintendenza capitolina )
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for centuries , the roman forum ( forum romanum ) was the civic , juridical , and social heart of the ancient city of rome , a place where civic buildings , sacred buildings , and monuments were to be both found and admired . beginning in the first century b.c.e. , a new series of public spaces , also dubbed as fora ( fora being the plural form of the latin noun forum ) began to be created .
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i wonder if those sorts of details are purely an aesthetic choice ?
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for centuries , the roman forum ( forum romanum ) was the civic , juridical , and social heart of the ancient city of rome , a place where civic buildings , sacred buildings , and monuments were to be both found and admired . beginning in the first century b.c.e. , a new series of public spaces , also dubbed as fora ( fora being the plural form of the latin noun forum ) began to be created . these fora ( called imperial fora since they were built by roman emperors during the roman imperial period ) would eventually number five in all and were important public spaces that relied upon the visual potential of monumental art and architecture to reinforce ideological messages . topography and chronology the imperial fora are located in an area bounded on the southwest by the capitoline hill , on the northeast by the quirinal hill , and extending toward the esquiline hill to the east . the fora were initially built between c. 54 b.c.e . and 113 c.e. , with continuing additions , restorations , and modifications through late antiquity . in the middle ages the fora were spaces re-used for building materials , housing , industry , and burials . gradually these spaces faded from view , buried beneath the medieval and modern city of rome . a massive campaign of excavation in the twentieth century on the orders of the fascist dictator benito mussolini returned large areas of the fora to view . ongoing archaeological investigation continues to reveal additional elements of the fora and to provide additional data that allow for their contextualization . forum of julius caesar the forum of julius caesar ( also known as the forum iulium or forum caesaris ) was the first of the imperial fora complexes to be built . pompey the great , a political rival of caesar , had dedicated a monumental theater and portico complex in the campus martius in 55 b.c.e . and this perhaps spurred caesar ’ s ambition to construct a new forum complex . caesar ’ s project required the acquisition of land at the flank of the capitoline hill and he was aided in this early on by political allies , including cicero , with the initial land purchased at a cost of sixty million sesterces ( cic . ad att . 4.16.9 ) . additional land acquisition may have ballooned the total cost to one hundred million sesterces ( suetonius divus iulius 26 ; pliny the elder natural history 36.103 ) . the construction of caesar ’ s forum resulted in significant reorganization of the northwest corner of the forum romanum . the forum of caesar takes the form of a rectangle measuring 160 by 75 m. the centerpiece of the complex was the temple of venus genetrix , dedicated to the goddess that caesar celebrated as his distant ancestor . the octastyle ( eight columns across the façade ) temple was made of solid marble and sat atop a high podium . the long sides of the forum square , flanking the temple , housed two storeys of rooms that may have served political and/or mercantile functions . the complex was dedicated during the festivities surrounding caesar ’ s triumph in september of 46 b.c.e . forum of augustus the forum of augustus ( known as the forum augustum or forum augusti ) followed the forum of caesar as the second of the imperial fora . at the battle of philippi in 42 b.c.e. , augustus vowed a temple to mars in exchange for help in avenging the slain caesar ( suet . aug. 29.2 ) , but the temple and forum complex would not be dedicated until 2 b.c.e . ( res gestae 21 ) . the forum of augustus provided additional room for the meeting of law courts and was built on land acquired by augustus . the temple at the center of the forum augusti was sacred to mars ultor ( “ mars the avenger ” ) , and was surrounded by a portico that defined the forum space and played a key role in the visual narrative of the public art program installed in the forum . as augustus had emerged as the sole leader of the roman state , it was important for him to create and display messages of continuity and stability . the visual program in the forum of augustus is complex . the architectural sculpture adorning the temple of mars ultor inserts augustus into the julian family ( gens iulia ) by portraying augustus in the context of divinities ( mars , venus , and cupid ) and the deified mortal—julius caesar ( divus iulius ) . flanking the temple in the exedrae ( the semicircular , recessed areas behind the colonnades to the left and right of the temple ) of the porticoes were sculptural groups depicting both romulus and aeneas , thus connecting augustus to rome ’ s two legendary founders ( ovid fasti 5.549-570 ) . to complete the narrative cycle , statues of famous romans of the republican period adorned the attic of the porticoes . these famous men ( summi viri ) were portrayed alongside small , inscribed plaques ( tituli ) bearing their political and military accomplishments . in this way , augustus portrayed himself as the ideal man to lead the roman state ; he was connected to rome ’ s divine origins and he represented continuity with its republican tradition . this powerful visual narrative represents an important early use of public art to transmit ideological messages in the western world . subsequent emperors continued to elaborate upon the forum of augustus . the emperor tiberius added two arches in 19 c.e . meant to honor the german victories of drusus and germanicus ( tacitus annales 2.64 ; cil 6.911 ) and the emperor hadrian restored the forum complex in the second century . pliny the elder deemed the forum of augustus one of three most beautiful monuments in the city of rome ( pliny the elder natural history 36.102.5 ) . templum pacis / forum of vespasian the next imperial forum to be built was commissioned by the emperor vespasian following the suppression of the great jewish revolt that lasted from 66 to 73 c.e . vespasian came to power following civil chaos in 69 c.e . and , together with his eldest son , titus , suppressed the revolt and sacked the city of jerusalem . during the summer of 71 c.e . vespasian and titus jointly celebrated a lavish triumph at rome—an ancient ritual celebrating significant military victories . one of the key tenets of vespasian ’ s new administration was the restoration of the city , including the construction of new buildings and monuments . he dedicated a forum complex that housed a temple dedicated to peace ( pax ) in 71 c.e. , completing it by 75 c.e . ( flavius josephus jewish war 7.5.7 ) . this innovative complex was deemed one of rome ’ s most beautiful monuments by pliny the elder and housed not only significant spoils from jerusalem but also masterworks of greek art that had previously been hoarded by the emperor nero . the temple of peace ( templum pacis ) stands out among the imperial fora for its innovative architectural design . rather than featuring a central temple seated atop a prominent podium , the templum pacis complex consists of a square portico ( dimensions 110 x 135 m ) with the temple itself set within the eastern side of the portico , flanked by ancillary rooms . this left the square itself open for the installation of decorative water features and plantings which are seen both archaeologically and on fragments of the severan marble plan of the city of rome ( forma urbis romae ) that was mounted in the forum complex in the third century c.e . the fragments of the severan plan provide valuable information about the design of this architectural complex and has led scholars to speculate that the inspiration for its design may have been the great market ( macellum magnum ) of the city that had likely been destroyed in the great fire of rome in 64 c.e . it is especially significant to note that this is a public space and that vespasian ’ s generosity granted the populace of rome access not only to a beautiful , monumental square , but also to art and the spoils of military victory ( including spoils from the temple in jerusalem ) . forum transitorium the forum transitorium , also referred to as the forum of nerva , was begun by domitian , the younger son of vespasian . incomplete at the time of domitian ’ s assassination in 96 c.e. , the complex was completed by nerva in 97 c.e . this is a narrow forum complex that abuts both the forum of augustus and the templum pacis and is constrained by these pre-existing structures ( dimensions : 131 x 45 meters ) ; as well as the argiletum , a street that ran the length of the forum . the forum transitorium ’ s temple was sacred to minerva , who had been a patron divinity of domitian , and the architectural sculpture that decorated the porticoes featured imagery connected to minerva and scenes from the private lives of women . forum of trajan the forum of trajan ( forum traiani ) , the final imperial forum , was both the largest and the most lavish . inaugurated in 112 c.e. , the architectural complex relied upon imposing architectural and sculptural features to glorify the accomplishments and principate of the emperor trajan . the elaborate forum complex has a vast footprint , measuring 200 x 120 meters . the open square of the forum is flanked by porticoes that contain exedrae and point viewer attention toward the main structure , the massive basilica ulpia . the architect apollodorus of damascus was responsible for the innovative design . on the western side of the basilica was another courtyard , flanked by two libraries ( one greek and one latin ) , that contained a monumental honorific column , known today as the column of trajan . the column of trajan , inaugurated in 113 c.e. , is a main feature of the forum of trajan and is , in its own right , a masterwork of roman art . the column carries an helical frieze of historical relief that provides a pictorial narrative of the events of trajan ’ s wars in dacia ( 101–102 and 105–106 c.e . ) , culminating with the death of the enemy commander , decebalus . the column stands 38 meters tall and its frieze wraps around the column shaft 23 times , with a total length of roughly 190 meters . carved in bas relief , the exquisite frieze carefully narrates trajan ’ s campaigns and its level of detail is simply astounding . the column ’ s frieze may draw inspiration from earlier roman triumphal art , the tradition of which was inclined to depict scenes from the foreign campaigns and , in so doing , glorify the accomplishments of the commander and his soldiers . throughout the forum of trajan the theme of military victory , and its celebration , permeate the monumental decorative programs . when trajan died in 117 c.e. , sources tell us that the roman senate allowed a special dispensation whereby trajan ’ s cremated remains could be deposited in the base of the column and that a temple to his cult ( templum divi traiani et plotinae ) was added to the forum complex between 125 and 138 c.e . ( historia augusta - hadrian 19.9 ) . an ongoing point of scholarly contention is the position and appearance of this plan . traditional reconstructions favor a free-standing temple at the western end of the forum , while more recent reconstructions instead favor a shrine positioned against the western exedra of the forum of augustus . ongoing archaeological fieldwork may yet shed light on this contentious topographical debate . interpretation the imperial fora represent important architectural landscapes in the city of rome . they demonstrate the efficacy of public art and architecture with respect to creating collective identity and communicating clear messages that both disseminate and reinforce ideology . the strength and accomplishments of the roman state , not to mention its stability , are key themes in any such program of message making . we should also not underestimate the psychological effect of these grandiose , soaring , bedecked complexes , based around massive open plazas , on the minds and experiences of city dwellers ( many of whom lived in crowded squalor ) . the imperial fora demonstrate that within the mechanisms of roman urbanism , civic architecture occupies a crucial role . we are reminded of this efficacy by an ancient example that is perhaps no different from the reaction of a modern visitor to the city of rome . the emperor constantius ii , visiting rome in the mid-fourth century c.e. , was amazed by the forum of trajan , something he considered “ a construction unique under the heavens ” ( ammianus marcellinus 16.10.15 ) . essay by dr. jeffrey a. becker additional resources : j. anderson , the historical topography of the imperial fora ( collection latomus ; 182 ) ( brussels : latomus , 1984 ) . s. baiani et al. , crypta balbi-fori imperiali : archeologia urbana a roma e interventi di restauro nell'anno del grande giubileo ( rome : kappa , 2000 ) . a. carandini and p. carafa , eds. , atlante di roma antica : biografia e ritratti della città 2 v. ( milan : electa , 2012 ) . a. claridge , rome : an archaeological guide 2nd ed . ( oxford : oxford university press , 2010 ) . f. coarelli et al. , the column of trajan ( rome : colombo , 2000 ) . r. darwall-smith , emperors and architecture : a study of flavian rome ( collection latomus ; 231 ) ( brussels : latomus , 1996 ) . j. geiger , the first hall of fame : a study of the statues in the forum augustum ( leiden : e. j. brill , 2008 ) . e. la rocca , i fori imperiali ( rome : enel , 1995 ) . t. j. luce , `` livy , augustus , and the forum augustum . '' in between republic and empire , ed . by k. raaflaub , k. and m. toher , pp . 123-38 ( berkeley : university of california press , 1990 ) . r. meneghini , “ templum divi traiani , ” bullettino della commissione archeologica comunale di roma 97 ( 1996 ) pp . 47-55 . r. meneghini and r. s. valenzani , scavi dei fori imperiali : il foro di augusto : l'area centrale ( rome : “ l ’ erma ” di bretschneider , 2010 ) . j. e. packer , the forum of trajan in rome : a study of the monuments 2 v. ( berkeley : university of california press , 1997 ) . j. e. packer , “ trajan ’ s forum again : the column and the temple in the master plan attributed to apollodorus ( ? ) , ” journal of roman archaeology 7:274-6 . s. b. platner and t. ashby , a topographical dictionary of ancient rome ( oxford : clarendon press , 1929 ) . l. richardson , jr. , a new topographical dictionary of ancient rome ( baltimore : johns hopkins university press , 1992 ) . r. ulrich , “ julius caesar and the creation of the forum iulium , ” american journal of archaeology 97.1:49-80 . l. ungaro , il museo dei fori imperiali nei mercati di traiano ( milan : electa , 2007 ) . mercati di traiano museo dei fori imperiali ( markets of trajan and the imperial fora museum ) fori imperiali ( sovrintendenza capitolina )
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the visual program in the forum of augustus is complex . the architectural sculpture adorning the temple of mars ultor inserts augustus into the julian family ( gens iulia ) by portraying augustus in the context of divinities ( mars , venus , and cupid ) and the deified mortal—julius caesar ( divus iulius ) . flanking the temple in the exedrae ( the semicircular , recessed areas behind the colonnades to the left and right of the temple ) of the porticoes were sculptural groups depicting both romulus and aeneas , thus connecting augustus to rome ’ s two legendary founders ( ovid fasti 5.549-570 ) .
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i ask , was the mars utor temple a throwback to an earlier style ?
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overview social darwinism is a term scholars use to describe the practice of misapplying the biological evolutionary language of charles darwin to politics , the economy , and society . many social darwinists embraced laissez-faire capitalism and racism . they believed that government should not interfere in the “ survival of the fittest ” by helping the poor , and promoted the idea that some races are biologically superior to others . the ideas of social darwinism pervaded many aspects of american society in the gilded age , including policies that affected immigration , imperialism , and public health . charles darwin charles darwin ’ s on the origin of species ( 1859 ) is one of the most important books in the annals of both science and history . in origin and in his subsequent writing darwin offered a revolutionary scientific theory : the process of evolution through natural selection. $ ^1 $ in short , natural selection means that plants and animals evolve over time in nature as new species arise from spontaneous mutations at the point of reproduction and battle with other plants and animals to get food , avoid being killed , and have offspring . darwin pointed to fossil records , among other evidence , in support of his theory . social darwinism soon , some sociologists and others were taking up words and ideas which darwin had used to describe the biological world , and they were adopting them to their own ideas and theories about the human social world . in the late nineteenth and early twentieth centuries , these social darwinists took up the language of evolution to frame an understanding of the growing gulf between the rich and the poor as well as the many differences between cultures all over the world . the explanation they arrived at was that businessmen and others who were economically and socially successful were so because they were biologically and socially “ naturally ” the fittest . conversely , they reasoned that the poor were “ naturally ” weak and unfit and it would be an error to allow the weak of the species to continue to breed . the believed that the dictum “ survival of the fittest ” ( a term coined not by charles darwin but by sociologist herbert spencer ) meant that only the fittest should survive. $ ^2 $ unlike darwin , these sociologists and others were not biologists . they were adapting and corrupting darwin ’ s language for their own social , economic , and political explanations . while darwin ’ s theory remains a cornerstone of modern biology to this day , the views of the social darwinists are no longer accepted , as they were based on an erroneous interpretation of the theory of evolution . social darwinism , poverty , and eugenics social darwinian language like this extended into theories of race and racism , eugenics , the claimed national superiority of one people over another , and immigration law . many sociologists and political theorists turned to social darwinism to argue against government programs to aid the poor , as they believed that poverty was the result of natural inferiority , which should be bred out of the human population . herbert spencer gave as an example a young woman from upstate new york named margaret , whom he described as a “ gutter-child. ” because government aid had kept her alive , margaret had , as spencer wrote , “ proved to be the prolific mother ” of two hundred descendants who were “ idiots , imbeciles , drunkards , lunatics , paupers , and prostitutes. ” spencer concluded by asking , “ was it kindness or cruelty which , generation after generation , enabled these to multiply and become an increasing curse to the society around them ? ” $ ^3 $ these ideas inspired the eugenics movement of the nineteenth and twentieth centuries , which sought to improve the health and intelligence of the human race by sterilizing individuals it deemed `` feeble-minded '' or otherwise `` unfit . '' eugenic sterilizations , which disproportionately targeted women , minorities , and immigrants , continued in the united states until the 1970s. $ ^4 $ social darwinism , immigration , and imperialism the pernicious beliefs of social darwinism also shaped americans ' relationship with peoples of other nations . as a massive number of immigrants came to the united states during the second industrial revolution , white , anglo-saxon americans viewed these newcomers—who differed from earlier immigrants in that they were less likely to speak english and more likely to be catholic or jewish rather than protestant—with disdain . many whites believed that these new immigrants , who hailed from eastern or southern europe , were racially inferior and consequently `` less evolved '' than immigrants from england , ireland , or germany. $ ^5 $ similarly , social darwinism was used as a justification for american imperialism in cuba , puerto rico , and the philippines following the spanish-american war , as many adherents of imperialism argued that it was the duty of white americans to bring civilization to `` backwards '' peoples . during and after world war ii , the arguments of social darwinists and eugenicists lost popularity in the united states due to their association with nazi racial propaganda . modern biological science has completely discredited the theory of social darwinism . what do you think ? describe charles darwin ’ s theory of evolution in your own words . how does it differ from herbert spencer 's idea of social darwinism ? how did the ideas of social darwinism influence politics and society in the gilded age ?
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while darwin ’ s theory remains a cornerstone of modern biology to this day , the views of the social darwinists are no longer accepted , as they were based on an erroneous interpretation of the theory of evolution . social darwinism , poverty , and eugenics social darwinian language like this extended into theories of race and racism , eugenics , the claimed national superiority of one people over another , and immigration law . many sociologists and political theorists turned to social darwinism to argue against government programs to aid the poor , as they believed that poverty was the result of natural inferiority , which should be bred out of the human population .
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how do these ideas of a race being higher than another even come to be ?
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overview social darwinism is a term scholars use to describe the practice of misapplying the biological evolutionary language of charles darwin to politics , the economy , and society . many social darwinists embraced laissez-faire capitalism and racism . they believed that government should not interfere in the “ survival of the fittest ” by helping the poor , and promoted the idea that some races are biologically superior to others . the ideas of social darwinism pervaded many aspects of american society in the gilded age , including policies that affected immigration , imperialism , and public health . charles darwin charles darwin ’ s on the origin of species ( 1859 ) is one of the most important books in the annals of both science and history . in origin and in his subsequent writing darwin offered a revolutionary scientific theory : the process of evolution through natural selection. $ ^1 $ in short , natural selection means that plants and animals evolve over time in nature as new species arise from spontaneous mutations at the point of reproduction and battle with other plants and animals to get food , avoid being killed , and have offspring . darwin pointed to fossil records , among other evidence , in support of his theory . social darwinism soon , some sociologists and others were taking up words and ideas which darwin had used to describe the biological world , and they were adopting them to their own ideas and theories about the human social world . in the late nineteenth and early twentieth centuries , these social darwinists took up the language of evolution to frame an understanding of the growing gulf between the rich and the poor as well as the many differences between cultures all over the world . the explanation they arrived at was that businessmen and others who were economically and socially successful were so because they were biologically and socially “ naturally ” the fittest . conversely , they reasoned that the poor were “ naturally ” weak and unfit and it would be an error to allow the weak of the species to continue to breed . the believed that the dictum “ survival of the fittest ” ( a term coined not by charles darwin but by sociologist herbert spencer ) meant that only the fittest should survive. $ ^2 $ unlike darwin , these sociologists and others were not biologists . they were adapting and corrupting darwin ’ s language for their own social , economic , and political explanations . while darwin ’ s theory remains a cornerstone of modern biology to this day , the views of the social darwinists are no longer accepted , as they were based on an erroneous interpretation of the theory of evolution . social darwinism , poverty , and eugenics social darwinian language like this extended into theories of race and racism , eugenics , the claimed national superiority of one people over another , and immigration law . many sociologists and political theorists turned to social darwinism to argue against government programs to aid the poor , as they believed that poverty was the result of natural inferiority , which should be bred out of the human population . herbert spencer gave as an example a young woman from upstate new york named margaret , whom he described as a “ gutter-child. ” because government aid had kept her alive , margaret had , as spencer wrote , “ proved to be the prolific mother ” of two hundred descendants who were “ idiots , imbeciles , drunkards , lunatics , paupers , and prostitutes. ” spencer concluded by asking , “ was it kindness or cruelty which , generation after generation , enabled these to multiply and become an increasing curse to the society around them ? ” $ ^3 $ these ideas inspired the eugenics movement of the nineteenth and twentieth centuries , which sought to improve the health and intelligence of the human race by sterilizing individuals it deemed `` feeble-minded '' or otherwise `` unfit . '' eugenic sterilizations , which disproportionately targeted women , minorities , and immigrants , continued in the united states until the 1970s. $ ^4 $ social darwinism , immigration , and imperialism the pernicious beliefs of social darwinism also shaped americans ' relationship with peoples of other nations . as a massive number of immigrants came to the united states during the second industrial revolution , white , anglo-saxon americans viewed these newcomers—who differed from earlier immigrants in that they were less likely to speak english and more likely to be catholic or jewish rather than protestant—with disdain . many whites believed that these new immigrants , who hailed from eastern or southern europe , were racially inferior and consequently `` less evolved '' than immigrants from england , ireland , or germany. $ ^5 $ similarly , social darwinism was used as a justification for american imperialism in cuba , puerto rico , and the philippines following the spanish-american war , as many adherents of imperialism argued that it was the duty of white americans to bring civilization to `` backwards '' peoples . during and after world war ii , the arguments of social darwinists and eugenicists lost popularity in the united states due to their association with nazi racial propaganda . modern biological science has completely discredited the theory of social darwinism . what do you think ? describe charles darwin ’ s theory of evolution in your own words . how does it differ from herbert spencer 's idea of social darwinism ? how did the ideas of social darwinism influence politics and society in the gilded age ?
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many whites believed that these new immigrants , who hailed from eastern or southern europe , were racially inferior and consequently `` less evolved '' than immigrants from england , ireland , or germany. $ ^5 $ similarly , social darwinism was used as a justification for american imperialism in cuba , puerto rico , and the philippines following the spanish-american war , as many adherents of imperialism argued that it was the duty of white americans to bring civilization to `` backwards '' peoples . during and after world war ii , the arguments of social darwinists and eugenicists lost popularity in the united states due to their association with nazi racial propaganda . modern biological science has completely discredited the theory of social darwinism .
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how is racial equality important ?
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overview social darwinism is a term scholars use to describe the practice of misapplying the biological evolutionary language of charles darwin to politics , the economy , and society . many social darwinists embraced laissez-faire capitalism and racism . they believed that government should not interfere in the “ survival of the fittest ” by helping the poor , and promoted the idea that some races are biologically superior to others . the ideas of social darwinism pervaded many aspects of american society in the gilded age , including policies that affected immigration , imperialism , and public health . charles darwin charles darwin ’ s on the origin of species ( 1859 ) is one of the most important books in the annals of both science and history . in origin and in his subsequent writing darwin offered a revolutionary scientific theory : the process of evolution through natural selection. $ ^1 $ in short , natural selection means that plants and animals evolve over time in nature as new species arise from spontaneous mutations at the point of reproduction and battle with other plants and animals to get food , avoid being killed , and have offspring . darwin pointed to fossil records , among other evidence , in support of his theory . social darwinism soon , some sociologists and others were taking up words and ideas which darwin had used to describe the biological world , and they were adopting them to their own ideas and theories about the human social world . in the late nineteenth and early twentieth centuries , these social darwinists took up the language of evolution to frame an understanding of the growing gulf between the rich and the poor as well as the many differences between cultures all over the world . the explanation they arrived at was that businessmen and others who were economically and socially successful were so because they were biologically and socially “ naturally ” the fittest . conversely , they reasoned that the poor were “ naturally ” weak and unfit and it would be an error to allow the weak of the species to continue to breed . the believed that the dictum “ survival of the fittest ” ( a term coined not by charles darwin but by sociologist herbert spencer ) meant that only the fittest should survive. $ ^2 $ unlike darwin , these sociologists and others were not biologists . they were adapting and corrupting darwin ’ s language for their own social , economic , and political explanations . while darwin ’ s theory remains a cornerstone of modern biology to this day , the views of the social darwinists are no longer accepted , as they were based on an erroneous interpretation of the theory of evolution . social darwinism , poverty , and eugenics social darwinian language like this extended into theories of race and racism , eugenics , the claimed national superiority of one people over another , and immigration law . many sociologists and political theorists turned to social darwinism to argue against government programs to aid the poor , as they believed that poverty was the result of natural inferiority , which should be bred out of the human population . herbert spencer gave as an example a young woman from upstate new york named margaret , whom he described as a “ gutter-child. ” because government aid had kept her alive , margaret had , as spencer wrote , “ proved to be the prolific mother ” of two hundred descendants who were “ idiots , imbeciles , drunkards , lunatics , paupers , and prostitutes. ” spencer concluded by asking , “ was it kindness or cruelty which , generation after generation , enabled these to multiply and become an increasing curse to the society around them ? ” $ ^3 $ these ideas inspired the eugenics movement of the nineteenth and twentieth centuries , which sought to improve the health and intelligence of the human race by sterilizing individuals it deemed `` feeble-minded '' or otherwise `` unfit . '' eugenic sterilizations , which disproportionately targeted women , minorities , and immigrants , continued in the united states until the 1970s. $ ^4 $ social darwinism , immigration , and imperialism the pernicious beliefs of social darwinism also shaped americans ' relationship with peoples of other nations . as a massive number of immigrants came to the united states during the second industrial revolution , white , anglo-saxon americans viewed these newcomers—who differed from earlier immigrants in that they were less likely to speak english and more likely to be catholic or jewish rather than protestant—with disdain . many whites believed that these new immigrants , who hailed from eastern or southern europe , were racially inferior and consequently `` less evolved '' than immigrants from england , ireland , or germany. $ ^5 $ similarly , social darwinism was used as a justification for american imperialism in cuba , puerto rico , and the philippines following the spanish-american war , as many adherents of imperialism argued that it was the duty of white americans to bring civilization to `` backwards '' peoples . during and after world war ii , the arguments of social darwinists and eugenicists lost popularity in the united states due to their association with nazi racial propaganda . modern biological science has completely discredited the theory of social darwinism . what do you think ? describe charles darwin ’ s theory of evolution in your own words . how does it differ from herbert spencer 's idea of social darwinism ? how did the ideas of social darwinism influence politics and society in the gilded age ?
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herbert spencer gave as an example a young woman from upstate new york named margaret , whom he described as a “ gutter-child. ” because government aid had kept her alive , margaret had , as spencer wrote , “ proved to be the prolific mother ” of two hundred descendants who were “ idiots , imbeciles , drunkards , lunatics , paupers , and prostitutes. ” spencer concluded by asking , “ was it kindness or cruelty which , generation after generation , enabled these to multiply and become an increasing curse to the society around them ? ” $ ^3 $ these ideas inspired the eugenics movement of the nineteenth and twentieth centuries , which sought to improve the health and intelligence of the human race by sterilizing individuals it deemed `` feeble-minded '' or otherwise `` unfit . '' eugenic sterilizations , which disproportionately targeted women , minorities , and immigrants , continued in the united states until the 1970s. $ ^4 $ social darwinism , immigration , and imperialism the pernicious beliefs of social darwinism also shaped americans ' relationship with peoples of other nations . as a massive number of immigrants came to the united states during the second industrial revolution , white , anglo-saxon americans viewed these newcomers—who differed from earlier immigrants in that they were less likely to speak english and more likely to be catholic or jewish rather than protestant—with disdain .
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apart from mass immigration to america , what other events caused the spread of social darwinism ?
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overview social darwinism is a term scholars use to describe the practice of misapplying the biological evolutionary language of charles darwin to politics , the economy , and society . many social darwinists embraced laissez-faire capitalism and racism . they believed that government should not interfere in the “ survival of the fittest ” by helping the poor , and promoted the idea that some races are biologically superior to others . the ideas of social darwinism pervaded many aspects of american society in the gilded age , including policies that affected immigration , imperialism , and public health . charles darwin charles darwin ’ s on the origin of species ( 1859 ) is one of the most important books in the annals of both science and history . in origin and in his subsequent writing darwin offered a revolutionary scientific theory : the process of evolution through natural selection. $ ^1 $ in short , natural selection means that plants and animals evolve over time in nature as new species arise from spontaneous mutations at the point of reproduction and battle with other plants and animals to get food , avoid being killed , and have offspring . darwin pointed to fossil records , among other evidence , in support of his theory . social darwinism soon , some sociologists and others were taking up words and ideas which darwin had used to describe the biological world , and they were adopting them to their own ideas and theories about the human social world . in the late nineteenth and early twentieth centuries , these social darwinists took up the language of evolution to frame an understanding of the growing gulf between the rich and the poor as well as the many differences between cultures all over the world . the explanation they arrived at was that businessmen and others who were economically and socially successful were so because they were biologically and socially “ naturally ” the fittest . conversely , they reasoned that the poor were “ naturally ” weak and unfit and it would be an error to allow the weak of the species to continue to breed . the believed that the dictum “ survival of the fittest ” ( a term coined not by charles darwin but by sociologist herbert spencer ) meant that only the fittest should survive. $ ^2 $ unlike darwin , these sociologists and others were not biologists . they were adapting and corrupting darwin ’ s language for their own social , economic , and political explanations . while darwin ’ s theory remains a cornerstone of modern biology to this day , the views of the social darwinists are no longer accepted , as they were based on an erroneous interpretation of the theory of evolution . social darwinism , poverty , and eugenics social darwinian language like this extended into theories of race and racism , eugenics , the claimed national superiority of one people over another , and immigration law . many sociologists and political theorists turned to social darwinism to argue against government programs to aid the poor , as they believed that poverty was the result of natural inferiority , which should be bred out of the human population . herbert spencer gave as an example a young woman from upstate new york named margaret , whom he described as a “ gutter-child. ” because government aid had kept her alive , margaret had , as spencer wrote , “ proved to be the prolific mother ” of two hundred descendants who were “ idiots , imbeciles , drunkards , lunatics , paupers , and prostitutes. ” spencer concluded by asking , “ was it kindness or cruelty which , generation after generation , enabled these to multiply and become an increasing curse to the society around them ? ” $ ^3 $ these ideas inspired the eugenics movement of the nineteenth and twentieth centuries , which sought to improve the health and intelligence of the human race by sterilizing individuals it deemed `` feeble-minded '' or otherwise `` unfit . '' eugenic sterilizations , which disproportionately targeted women , minorities , and immigrants , continued in the united states until the 1970s. $ ^4 $ social darwinism , immigration , and imperialism the pernicious beliefs of social darwinism also shaped americans ' relationship with peoples of other nations . as a massive number of immigrants came to the united states during the second industrial revolution , white , anglo-saxon americans viewed these newcomers—who differed from earlier immigrants in that they were less likely to speak english and more likely to be catholic or jewish rather than protestant—with disdain . many whites believed that these new immigrants , who hailed from eastern or southern europe , were racially inferior and consequently `` less evolved '' than immigrants from england , ireland , or germany. $ ^5 $ similarly , social darwinism was used as a justification for american imperialism in cuba , puerto rico , and the philippines following the spanish-american war , as many adherents of imperialism argued that it was the duty of white americans to bring civilization to `` backwards '' peoples . during and after world war ii , the arguments of social darwinists and eugenicists lost popularity in the united states due to their association with nazi racial propaganda . modern biological science has completely discredited the theory of social darwinism . what do you think ? describe charles darwin ’ s theory of evolution in your own words . how does it differ from herbert spencer 's idea of social darwinism ? how did the ideas of social darwinism influence politics and society in the gilded age ?
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describe charles darwin ’ s theory of evolution in your own words . how does it differ from herbert spencer 's idea of social darwinism ? how did the ideas of social darwinism influence politics and society in the gilded age ?
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were there any significant people or parties that disagreed with the idea of social darwinism ?
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