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Question: <p>Can someone please help me understand and answer the question of "why are the forces on a magnetic dipole different in a uniform magnetic field and non-uniform magnetic field?" I know in a uniform magnetic field the magnetic dipole material will tend to align with the field lines of the magnetic field it i... | https://physics.stackexchange.com/questions/66203/magnetic-force-on-a-magnetic-dipole |
Question: <p>We know from Flaming's Right Hand Rule how to calculate the direction of the magnetic force given the magnetic field and the velocity are in the same plane. Now suppose they are not in the same plane. As an example, consider a uniform magnetic field directed perpendicularly onto the screen and a charged pa... | https://physics.stackexchange.com/questions/69413/direction-of-magnetic-force-when-magnetic-field-and-velocity-are-not-in-same-pla |
Question: <p>As we know a solenoid is considered as a electromagnet(magnet) if there's a current flowing through it. if a soft iron core is placed inside the solenoid, the former get magnetised. Consider the solenoid as a hollow bar magnet, and the magnetised soft iron core inside as a bar magnet. The poles of the magn... | https://physics.stackexchange.com/questions/73953/is-it-correct-to-say-like-poles-attract-unlike-poles-repel-while-two-magnets |
Question: <p>Imagine that I have a particle of charge $q$ at the center of a spherical insulating shell of charge $Q$ and radius $R$.</p>
<p>Both the particle and shell are initially at rest.</p>
<p>Now I apply a force $\mathbf{F}$ to the particle which causes it to have an acceleration $d\mathbf{v}/dt$.</p>
<p>The ... | https://physics.stackexchange.com/questions/76598/particle-inside-a-charged-shell |
Question: <p>I was told long time ago that DC relay had a coil. There was a switch (2 wires, one is stable, the other one is flexible) inside the coil. The switch was parallel to the axial direction of the coil. </p>
<p>Today, I am thinking how AC relay works. I go back to think about DC relay. If what I was told is r... | https://physics.stackexchange.com/questions/79438/how-dc-and-ac-relays-works |
Question: <p>I tried to integrate E due to a line of charge sweeping across the plate, but got bogged down. Any suggestions?</p>
Answer: <p>The trick to this one is knowing how to do the integral. I am going to assume you got an integral that looks like $$\int_{-L/2}^{L/2} \frac{a \lambda dx}{(x^2+d^2)^{3/2}}.$$
The f... | https://physics.stackexchange.com/questions/79858/how-do-i-find-the-electric-field-above-the-center-of-a-square-plate-rather-than |
Question: <p>In Maxwell's equations, the curl of the electric field for a steady state processes (ie. No changing electric or magnetic field) zero. However, if we take a curl along the wire for some distance and perpendicularly out from the wire and back to its original position (perpendicularly entering the wire), it... | https://physics.stackexchange.com/questions/81063/the-curl-is-not-zero |
Question: <p>For my introductory course to electromagnetism (I'm an undergraduate student, so ELI5), I'm trying to get the right conceptual model of electron movement in a thin wire (with constant but non-zero cross section, like a cylinder) due to a constant current. It seems to me, that there are several contributing... | https://physics.stackexchange.com/questions/81638/electron-motion-in-a-wire |
Question: <p>Consider two electrons moving parallel to each other in the same direction with same constant velocity. Will they experience any force due to either of them?</p>
Answer: <p>Yes, they will feel both electric and magnetic force. If you apply a Lorentz boost and get into the frame where they are at rest, the... | https://physics.stackexchange.com/questions/83089/what-is-the-magnetic-effect-on-either-of-the-charges-moving-parallel |
Question: <p>If a particle of mass $M$ is given an electric charge $Q$, will its mass change?</p>
Answer: <p>What do you mean with "particle"? How would you add a charge?</p>
<p>If you add an electron to an atom you will increase the mass by the electron mass (of course) minus a tiny contribution coming from $m=E/c^2... | https://physics.stackexchange.com/questions/83382/is-mass-of-a-particle-changed-when-it-is-charged |
Question: <p>I'm trying to evaluate the magnetic field by calculating the Coloumb integral $\overrightarrow{A}$, and later I will take:
$$\overrightarrow{B}=\nabla \times \overrightarrow{A}$$</p>
<p>However, in the middle of everything, I get to (cylindrical coordinates):</p>
<p>$$\overrightarrow{A}=\frac{\mu_oI}{4\... | https://physics.stackexchange.com/questions/86084/why-is-th-hatr-component-zero-in-this-integral |
Question: <p>Why don't stationary electric charges posses magnetic field, while moving charges do?</p>
Answer: | https://physics.stackexchange.com/questions/87818/why-dont-stationary-electric-charges-possess-a-magnetic-field |
Question: <p>I have recently carried out an experiment to verify Faradays law for a falling magnet. My starting point was to keep both the area of the coil and the number of turns constant whilst changing the velocity (the different velocities were obtained by dropping from different heights).What would be good is if a... | https://physics.stackexchange.com/questions/88989/calculating-db-dt-from-velocity |
Question: <p>I am reading <a href="http://books.google.co.uk/books?id=Quv8awSN-RYC&printsec=frontcover&dq=magnetic%20techniques%20for%20the%20treatment%20of%20materials%20pdf&hl=en&sa=X&ei=ePKuUu2lH8yThQfs64D4CA&ved=0CDIQ6AEwAA#v=onepage&q&f=false" rel="nofollow">this</a> book, the part ... | https://physics.stackexchange.com/questions/90371/help-understanding-equation-for-characteristic-time-of-induced-magnetic-field |
Question: <p>If I had a very strong magnet on Earth and a very sensitive compass on Mars (just using planets to illustrate large distance), how long would the compass take to notice if I turned the magnet 180deg? I assume it can't beat the speed of light. Do the outer reaches of the magnetic field move as a rigid bod... | https://physics.stackexchange.com/questions/89701/speed-of-magnetic-signal-over-large-distance |
Question: <p>You can determine the direction of eddy currents according to Lenz's law.
E.g. If a metal sheet is losing flux into the page, it will experience induced eddy currents in a clockwise direction to replace it. </p>
<p>However, this doesn't make sense to me logically. :S Consider a straight current-carrying w... | https://physics.stackexchange.com/questions/90739/lenzs-law-and-eddy-currents |
Question: <p>Here is what I know:</p>
<p>$F = E q = m a$ </p>
<p>so $a = \frac{E q}{ m}$</p>
<p>and we can increase the acceleration ($a$) of a particle in an electric field ($E$) by either decreasing its mass ($m$) or increasing its charge ($q$).</p>
<p>Here is where I am confused:</p>
<p>$a = \frac{v}{ t}$, t... | https://physics.stackexchange.com/questions/92170/why-doesnt-a-particles-velocity-effect-the-strength-exerted-on-it-by-an-electr |
Question: <p>Could someone help explain the uses of AC <a href="http://en.wikipedia.org/wiki/Electromagnet" rel="nofollow">electromagnets</a>. Wherever I look it says that DC electromagnets create stronger magnetic fields. I understand why AC electromagnets could be used in transformers but why use them in motors for e... | https://physics.stackexchange.com/questions/93356/ac-electromagnets |
Question: <p>I am a software engineer. This I understand very well. I am attempting to build a prototype with arduino circuits. This I know a little less about. Part of my project requires a electro-magnetic generator. This I know nothing about. </p>
<p>I looked up Gauss's law and embarrassingly the math is a bit abov... | https://physics.stackexchange.com/questions/93557/a-simple-way-to-calculate-the-potential-electrical-output-of-a-magnet |
Question: <p>How can one prove that:</p>
<p>The force exerted on a magnetic dipole $m$ in magnetic field $B$, in addition to $F=\nabla(m\cdot B)$, can be expressed by </p>
<p>$$F=(m\times \nabla)\times B.$$</p>
Answer: <p>In view of a known identity concerning the cross product:
$$(m\times \nabla)\times B = \nabla ... | https://physics.stackexchange.com/questions/94605/the-force-exerted-on-a-magnetic-dipole-m-in-magnetic-field-b |
Question: <p>If you place a conductor beside an insulator, the insulator will become negatively charged and the conductor will become positively charged. Air is an insulator. So why don't all conductors placed in air automatically become positively charged and the air around it become negatively charged?</p>
<p>See, f... | https://physics.stackexchange.com/questions/96169/why-arent-all-conductors-always-charged |
Question: <p>If I place a magnet on the underside of a metal object so that it is held there by its attraction to the metal, how can I determine the minimum pull force the magnet needs to have in order to keep it attracted to the metal and not fall off? Would the required pull force be equivalent to the magnet's weight... | https://physics.stackexchange.com/questions/96579/determining-the-minimum-pull-force-of-a-magnet-required-to-hold-it-in-place |
Question: <p>I've recently learned that If you move a conductor through a magnetic field, an emf is induced across the ends of the conductor: </p>
<p>$E = BLv $ </p>
<p>I've also been told that the same is true for a coil but that the equation is: </p>
<p>$E = BLvN$</p>
<p>And that for a coil, there is only an emf ... | https://physics.stackexchange.com/questions/98463/induced-emf-when-a-wire-or-coil-travel-through-a-magnetic-field |
Question: <p>One way of deriving laws of energy, impulse and angular momentum of electromagnetic field conservation is following:</p>
<ol>
<li><p>Introduce two values below:
$$
\mathbf P = \frac{c}{4 \pi}[\mathbf E \times \mathbf B], \quad W = \frac{1}{8 \pi}(\mathbf E^{2} + \mathbf B^{2}).
$$</p></li>
<li><p>Using Ma... | https://physics.stackexchange.com/questions/32335/question-about-laws-of-conservation-in-electrodynamics |
Question: <p>Work done by a magnetic force(even over an infinitesimally short displacement)=0</p>
<p><em>Net Force</em> on a current loop in an external magnetic field is given by: $$\vec{F}=\nabla(\vec{\mu_m } \cdot \vec{B})$$</p>
<p>How does one prove: $$dW=\nabla(\vec{\mu_m} \cdot \vec{B})\cdot\vec{dr}=0$$</p>
<p... | https://physics.stackexchange.com/questions/34056/how-does-one-prove-nabla-vec-mu-m-cdot-vecb-cdot-vecdr-0 |
Question: <p>I took my son to a science museum where they had a solenoid oriented vertically with a plastic cylinder passing through the solenoid. An employee dropped an aluminum ring over the top of the cylinder when there was no current going through the solenoid. Then they turned on the current going through the so... | https://physics.stackexchange.com/questions/34265/what-law-of-electro-magnetics-explains-this |
Question: <p>What are possible effects of electromagnetic pulse / EMP on superconductor-based devices/equimpent/transportation?</p>
<p>Are they resilient or more sensitive to EMP?</p>
Answer: | https://physics.stackexchange.com/questions/36145/effects-of-emp-in-superconductor-based-devices-equipment |
Question: <p>Is there any media where magnet lose its property?</p>
Answer: <p>Magnets work perfectly in the vacuum – and in the absence of a gravitational field. They don't depend on any "environment" or "medium". And the electromagnetic force is independent of gravity, too.</p>
<p>In analogy with sound, some 19th c... | https://physics.stackexchange.com/questions/37920/do-magnets-work-in-outer-space |
Question: <p>I was just curious to know that is it possible to see domains of a magent/metal in motion on being magnetized, under microscope. If there is someone who has access to microscopes, can help me out on this. I was thinking of buying one.
Question is lil stupid but I am putting it here because I know no better... | https://physics.stackexchange.com/questions/39024/is-it-possible-to-see-domains-in-a-metal-magnet-under-microscope |
Question: <p>I need a full explantation for this concept.</p>
<p>Magnetic field lines can be entirely confined within the core of a toroid, but not within a straight solenoid.</p>
Answer: <p>This is a solenoid and its magnetic field lines.</p>
<p><img src="https://i.sstatic.net/R11ij.png" alt="solenoid"></p>
<p>Thi... | https://physics.stackexchange.com/questions/38067/magnetic-field-lines-can-be-entirely-confined-within-the-core-of-a-toroid-but-n |
Question: <p>What are the ways to modify the form of magnetic field from the permanent magnet? For example I have a permanent neodymium magnet. Its magnetic field is distributed at large volume around the magnet, with decreasing strength at larger distances from the magnet. I'd like to make it concentrated in very smal... | https://physics.stackexchange.com/questions/41011/bend-or-concentrate-magnetic-field |
Question: <p>Suppose $\vec{B}$ is a differentiable vector field defined everywhere such that $\nabla\cdot \vec{B}=0$. Define $\vec{A}$ by the integral
$$A_1=\int_0^1 \lambda(xB_2(\lambda x,\lambda y,\lambda z)- yB_3(\lambda x,\lambda y,\lambda z)) d\lambda$$
Together with its two cyclic permutations for $A_2,A_3$</p>
... | https://physics.stackexchange.com/questions/41210/proving-the-existence-of-the-magnetic-potential |
Question: <p>And what happens with the magnetic field of a star that goes supernova? The magnetic radiation is scattered through the cosmos? Each particle will go away with its own magnetic radiation?</p>
Answer: <p>In a star the magnetic field isn't a "thing" in it's own right, it's the result of motion of charged pa... | https://physics.stackexchange.com/questions/43550/how-do-you-destroy-magnetic-field-demagnetize |
Question: <p>Just thinking aloud ... It is possible for a star to grow so large it collapses under it's own gravity. Along a parallel path (so to speak) when a conductor carries a current too large for it to sustain, it burns out.</p>
<p>Can a ferromagnetic object be imparted a field too strong for it? What happens t... | https://physics.stackexchange.com/questions/43584/what-happens-when-a-ferromagnetic-object-encounters-a-field-too-strong-for-it |
Question: <p>The Lorentz model, describing the electron of the atom as an harmonic oscillator forced by an oscillating electric field $\vec{E}$, shows that the dipole moment $\vec{D}$ obeys the following equation in the stationary regime:
$$\vec{D}=\frac{q^2}{2m\omega_0}\frac{\vec{E}}{\omega_0-\omega-i\gamma_d}$$
where... | https://physics.stackexchange.com/questions/43878/lorentz-model-and-energy-exchange |
Question: <p>Can a magnet be cut with a hacksaw, by hand, without losing its essential characteristic of being magnetic? I know i would have to be very careful with heat but I don't know how careful</p>
Answer: <p>This would likely mess up the polarity of the magnet near the area where you are cutting. It would depen... | https://physics.stackexchange.com/questions/47574/will-a-magnet-loose-too-much-strength-it-cut-with-a-hacksaw |
Question: <p>This is not how to determine a magnet after it's created, but rather before it is created. How is the polarity of a magnet created (why does one side go this way and the other go the opposite)? Is it randomly decided based on forces acting on the soon-to-be magnet, or is it aligned with the Earth’s magne... | https://physics.stackexchange.com/questions/48130/how-is-the-polarity-of-a-magnet-decided-before-its-creation |
Question: <p>I'm looking to minimize the weight of some solenoid actuators I want to build, so I'm trying to better understand the effects of the shielding / frame commonly found on solenoid actuators.</p>
<p>My understanding is the force exerted on the plunger is essentially only dependent on the cross sectional area... | https://physics.stackexchange.com/questions/48427/does-the-shielding-around-a-solenoid-actuator-affect-the-force-on-the-plunger |
Question: <p>Can anyone see a reason for $$\left(1+{U_\rho U^\rho\over c^2}\right)\left(U_\nu{d^2 U^\nu\over d\tau^2}\right)=0$$?</p>
<p>Here $U^\rho$ is the 4-velocity for a particle and $\tau$ the proper time. The context is for a particle moving in an electromagnetic field.</p>
<p>I believe it may be useful to int... | https://physics.stackexchange.com/questions/49736/4-velocity-and-electromagnetic-fields |
Question: <p>I have two equal flat round magnets. I know amount of force $F$ which attracts iron objects to one of them and geometric characteristics of magnets. I want to fix first of magnet and some additional mass in the air by second magnet. To do so, I am going to orient magnets so that second magnet repulse first... | https://physics.stackexchange.com/questions/47612/how-to-count-magnetic-repulsion |
Question: <p>When a motor, connected to a battery that has a constant voltage, spins without a load it's speed is higher than with load. I'm told that because of back emfs the current is very small when there's no load because of the higher speed. And so when there is a load the back emf is less as the motor spins slow... | https://physics.stackexchange.com/questions/51332/relationship-between-current-through-a-motor-and-its-load |
Question: <p>When graphing the induced current in a coil while a magnet is dropped through it why is the total area equal to 0?
The area represents the charge in the coil but why must the resultant flow of charge be 0?</p>
Answer: <p>The EMF induced in the coil is given <a href="http://en.wikipedia.org/wiki/Faraday%27... | https://physics.stackexchange.com/questions/51341/current-induced-when-dropping-a-magnet-through-a-coil |
Question: <p>A <a href="http://en.wikipedia.org/wiki/Transformer" rel="nofollow">transformer</a> is basically a primary inductor connected to a voltage $U_P$ which you want to transform. You also have an iron rod and a secondary inductor. So when there is a current $I_P$ the iron rods becomes magnetic. When you connect... | https://physics.stackexchange.com/questions/51936/how-do-transformers-work |
Question: <p>Faraday's law is given by:</p>
<p>$\nabla \times E = -\frac{\partial{B}}{\partial{t}}$</p>
<p>On the right hand side of the equation, we have a quantity representing how $B$ changes over time. On the left hand side of the equation we have a quantity representing the spatial variation of $E$ (the curl of... | https://physics.stackexchange.com/questions/52749/how-to-interpret-faradays-law |
Question: <p>I heard that when you take two magnets and get them closer together so they reject each other (north pole to north pole or south pole to south pole) they weakens. Does anybody knows how to calculate how much it weakens depending on their distance? </p>
<p>And does it work the other way around? If you take... | https://physics.stackexchange.com/questions/55087/how-to-calculate-how-weak-does-a-magnet-get-when-you-get-an-other-magnet-closer |
Question: <p>A photon has an oscillating magnetic and electric field.</p>
<p>Is the magnetic field a dipole?</p>
Answer: <p>A photon is not the source of an oscillating magnetic and electric field, and it does not have poles. Your confusion stems from the fact that photons can be seen as field quanta for electromagne... | https://physics.stackexchange.com/questions/55554/does-a-photon-have-a-north-and-south-pole |
Question: <p>When a dielectric is placed in an electric field,it gets polarized. The electric field in a polarized material is less than the applied field. Now my query is, when a paramagnetic substance is kept in a magnetic field, the field in the substance is more than the applied fiekd. What is the reason for this ... | https://physics.stackexchange.com/questions/55991/magnetic-properties-of-matter |
Question: <p>Can someone please explain to me how the conservation of the energy momentum tensor $$\nabla_\beta T^{\alpha \beta}=0$$</p>
<p>imply the conservation of the Maxwell tensor $$\nabla_\beta F^{\alpha \beta}=0$$?</p>
<p>Additional info: </p>
<p>Note that the $\nabla_\beta$ denotes the covariant derivative.<... | https://physics.stackexchange.com/questions/56332/conservation-maxwell-tensor |
Question: <p>I'm learning about torque on a conductive coil in a magnetic field. I have been taught that $\vec\tau = \vec\mu \times \vec{B}$, where $\vec\mu$ is the magnetic dipole moment. Also, $\mu = I\vec{A}$, where $\vec A$ is the area vector of the loop.</p>
<p>To find the direction of the area vector, I am tol... | https://physics.stackexchange.com/questions/59498/direction-of-the-area-vector-with-regards-to-magnetic-dipole |
Question: <p>More turns -> stronger field<br>
more turns -> longer copper wire<br>
longer copper wire -> more resistance(ohm)<br>
<br>
at what turn does the resistance make the electromagnet weaker? - I want to make an ideal electromagnet.
<br><br>
(Sorry for being vague but I'm looking for some kind of formula or an ... | https://physics.stackexchange.com/questions/60945/electromagnet-ideal-turns-depending-on-ohm |
Question: <p>Why are diamagnetic materials repelled when placed in magnetic field and why are paramagnetic materials attracted when placed in magnetic field?</p>
Answer: <blockquote>
<p>Okay... I write this as an inspiration by Feynman..!</p>
</blockquote>
<p>These "WHY?" and "How's such a thing possible?" are quit... | https://physics.stackexchange.com/questions/62653/attraction-and-repulsion-of-magnetic-materials |
Question: <p>I've had a wild idea which I can not discuss at length in this forum, but it comes down to the following problem:</p>
<p>A sphere of radius R=~10μm and mass m=~10-16Kgr is travelling towards the earth at v = ~10^8m/sec. The sphere carries a charge Q and intersects the earth's magnetic field perpendicularl... | https://physics.stackexchange.com/questions/62723/is-it-possible-for-a-charged-fast-moving-object-to-slow-down-and-enter-geo-stat |
Question: <p>Suppose that a spherical metal sphere with mass $m=10^{-16}kgr$ radius $R=10μm$ charge $Q=10^{-9}C$ travels with $v=c/3$ and is trapped in the earth's magnetosphere at a distance around $r = 1000km$. <em>The exact numbers are not that important, I am providing them for order of magnitude considerations</em... | https://physics.stackexchange.com/questions/63520/small-charged-spheres-motion-in-earths-magnetosphere |
Question: <p>I have a doubt regarding the significance of a force on a wire. Well, first of all, I know that if I have a particle and if there are several forces acting over it, then we can compute one total force $F$ that gives the same effect as the combination of the several forces, and this force is just the vector... | https://physics.stackexchange.com/questions/65368/what-really-is-the-magnetic-force-on-a-wire |
Question: <p>If I calculate the energy contained in the electric field for an electric dipole p in an electric field E, I get (ignoring the terms independent of orientation):</p>
<p>$U = - \vec{p} \cdot \vec{E}$</p>
<p>which is as expected. However, if I do the same for a magnetic dipole m in a magnetic field B, I g... | https://physics.stackexchange.com/questions/7238/energy-in-magnetic-fields |
Question: <p>Earth's N and S magnetic poles "wander independently of each other and are not at exactly opposite positions on the globe" [from WIKI's "Earth's magnetic field"]. Can these independent motions be consistent with the supposed "dynamo effect" from electric currents of a liquid outer core? Can Earth's spheroi... | https://physics.stackexchange.com/questions/7264/why-is-there-independent-motion-of-earths-magnetic-poles |
Question: <p>It has been more than a decade since I did all vector related math and physics so pardon me if my question does not make sense. I am reading some article that says it was inspired from Coulomb's law and gives the following expression to calculate the partial force that one particle is exerting on another a... | https://physics.stackexchange.com/questions/8856/need-some-help-interpreting-a-formula-inspired-from-coulombs-law |
Question: <p>I have two air coils (assume they are simple, circular wire loops). They both have diameter <strong>d</strong>. There is a distance <strong>D</strong> between their centres.</p>
<p><strong>D</strong> is much greater than <strong>d</strong> (more than 10x greater)</p>
<p>Both coils are at different angles... | https://physics.stackexchange.com/questions/8968/how-to-estimate-inductive-coupling-between-distant-air-coils |
Question: <p>In an electron gun, the heating filament heats the cathode, releasing electrons by thermionic emission. I've read that <em>"electrons are negatively charged particles and the positively charged cylindrical anode develops a strong electric field that exerts a force on the electrons, accelerating them along ... | https://physics.stackexchange.com/questions/11175/electron-gun-electron-in-cylindrical-anode |
Question: <p>Can there be a charge configuration in space such that at any instant of time I can change the electric field at one and only one point?</p>
Answer: <p>The electric field obeys Maxwell's equations and in particula the Gauss's law. This means that $\rm div E \sim \rho$. If you change the field at only one... | https://physics.stackexchange.com/questions/13662/one-point-to-change-electric-field |
Question: <p>By biot-savart:</p>
<p>$$\bar{H} = \frac{I}{4\pi} \oint \frac{d\bar{l} \times \bar{r}}{r^{3}}$$</p>
<p>so</p>
<p>$$\bar{H} = \frac{I}{2a} \hat{n}$$</p>
<p>Please, explain the last implication. I cannot find such integral to match the results. The radius of the loop is $a$. The current is $I$. $d\bar{l}... | https://physics.stackexchange.com/questions/14067/magnetic-field-in-the-centre-of-circular-loop-wire-with-current |
Question: <p>You have a coil over an iron hearth. There is a current in coil which creates the flux $\phi_{1}$. The flux then distributes over the wider area in the iron (using wrong word?): $\phi_{2}$ the flux over the middle and the $\phi_{3}$ over the left.</p>
<pre><code> |-----------------|
... | https://physics.stackexchange.com/questions/14071/mangnetic-flux-summing-up-like-kirhoff |
Question: <p>With present day materials and technology what is the physical size of a one milli Tesla magnet? How much "power" it has to attract pieces of iron? Please compare it with the objects we have around. What difference in size and "power" it gets each order of magnitude that I go up? What is a weak magnet what... | https://physics.stackexchange.com/questions/15343/what-is-the-physical-size-of-a-magnet |
Question: <p>If running a current through a magnet can reverse the magnetic field, then how strong does the current have to be and how would it best be run through the magnet.</p>
Answer: <p>If you had solenoid or another type of electromagnet that produced its magnetic field from a current carrying like a Helmholtz c... | https://physics.stackexchange.com/questions/15856/magnetic-fields |
Question: <p>First up, I needed to compute the potential at some external point due to charge stuffed inside the region between two concentric cylinders, the volume charge density being given.<br/> Two methods came to mind but they are apparently yielding different answers(maybe I goofed up somewhere)
<br/> The first i... | https://physics.stackexchange.com/questions/16472/poissons-equation |
Question: <p>We consider a flat rectangular plate moving horizontally in a vertical magnetic field,motion being in a direction perpendicular to the length of the plate. We have an emf=BLV between the tips,in the lenhgth wise direction[the axial emf]. During the formation of the axial emf a current flows along the lengt... | https://physics.stackexchange.com/questions/18915/power-generation-from-axial-and-transverse-emf |
Question: <p>The rumor was you could make a magnet by leaving a piece of iron on a train track. The train going over it would magnetize it. </p>
<p>Is it true?</p>
Answer: <p>This is almost a duplicate to <a href="https://physics.stackexchange.com/questions/18340/can-you-magnetize-iron-with-a-hammer/18341#comment4349... | https://physics.stackexchange.com/questions/19374/magnetization-of-coin-on-a-railway-track |
Question: <p>My son asked me this question and I was stumped - my intuition says that is the south pole was strong enough the attraction between the north and south poles would outweigh the repulsion between the two north poles - but how strong would the south pole need to be in this case?</p>
Answer: <p>Assuming long... | https://physics.stackexchange.com/questions/19383/would-the-north-poles-of-two-magnets-repel-each-other-if-a-weaker-south-pole-was |
Question: <p>A common analogy for gravity is the ball-on-a-rubber-sheet model. In this model, mass distorts spacetime and creates a 'valley' into which other mass can fall. Is this same principal valid for magnetic fields as well (proton-electron)? If so, then how is the repulsion effect modelled?</p>
<p>I ask because... | https://physics.stackexchange.com/questions/20455/how-are-magnetic-fields-transmitted |
Question: <p>I was watching a program about disaster preparedness, and it was suggested that the metal enclosure of a common shipping container (of the <a href="http://en.wikipedia.org/wiki/Intermodal_container" rel="nofollow">intermodal variety</a>) would be sufficient to protect its contents from a large electromagne... | https://physics.stackexchange.com/questions/21180/would-a-metal-enclosure-such-as-a-shipping-container-protect-its-contents-from |
Question: <p>Does inducing a current in a wire result in any changes in the strength of a permanent magnet? Specifically, what would the results of the following controlled experiment be? </p>
<p>You set up two alternators that each simply consist of a permanent magnet located inside a stationary loop of wire as depic... | https://physics.stackexchange.com/questions/21062/does-inducing-a-current-in-a-wire-have-any-effect-on-the-strength-of-a-permanent |
Question: <p>Are there any non magnetic materials that attract to each other as if they were magnetic?</p>
<p>This is an argument I am having with a friend. </p>
<p>Thanks,</p>
Answer: | https://physics.stackexchange.com/questions/24446/are-there-any-non-magnetic-materials-that-attract-to-each-other-as-if-they-were |
Question: <p>I have two nails (made of Fe). A and B.</p>
<p>A can not lift B.
If I rub A on the magnets north pole, then it can lift B.
Then if I rub it again but on the south pole, it can not lift B. </p>
<p>why is that? Why cant it lift B anymore?</p>
<p>the title I have chosen for this question is really bad. I... | https://physics.stackexchange.com/questions/24616/magnetized-nail-lifting-another-nail |
Question: <p>Given a stream of moving charged particles that encounter a uniform magnetic field such that they are trapped in a circular orbit, what effect do these particles have on the net magnetic field over time? Would the magnetic field get stronger or weaker as the number of trapped particles increase?</p>
Answe... | https://physics.stackexchange.com/questions/29744/effect-of-charged-particles-trapped-in-magnetic-field-on-that-field |
Question: <p>and thank you in advance for taking the time to read my question. To give an idea of my working level, I'm a 21 year old computer science student entering my senior year at college. It's been a few years since my Electricity/Magnetism course, and i'm a bit rusty on the Lorentz Force.
I wanted to create a ... | https://physics.stackexchange.com/questions/29512/how-to-transfer-energy-from-a-generator-to-a-storeage-battery |
Question: <p>If i have a EM wave with frequency 1MHZ and εr=9 in a perfect dielectric ,is it possible to find the wavelength λ and wave propagation speed ? It seems impossible to me..</p>
Answer: <p>(1) $\lambda \nu = c$</p>
<p>(2) $c^2 = \frac{1}{\mu_0 \epsilon_r \epsilon_0}$</p>
| https://physics.stackexchange.com/questions/30710/find-wavelength-from-relative-permittivity-and-frequency |
Question: <p>A half-ring shaped conductor is being placed around a solenoid. This solenoid has a changing magnetic field.</p>
<p>a) There is a current and EMF (Electromagnetic force) in the half-ring shaped conductor
b) There is a current but no EMF in the half-ring shaped conductor
c) There is no current but there is... | https://physics.stackexchange.com/questions/30715/emf-in-a-half-ring-shaped-conductor-around-a-solenoid |
Question: <p>So, I know $\oint E\centerdot dA = 4\pi Q_{enc}$</p>
<p>I'm trying to solve for a TEM mode with two concentric (infinite) cylindrical wave guides of radius a and b, $a<b$. I know that for TEM modes, I can solve by assuming that the outside and inside are at two different potentials, $\pm V$. </p>
<p>I... | https://physics.stackexchange.com/questions/29950/how-to-apply-guass-law-to-voltages |
Question: <p>I'm reading a book on electromagnetism and I am a bit confused about some things in Maxwells equations. This is what I don't like about many physics books: they are very wordy, but at the end you don't know what is an experimental fact, what is a "theorem", what is an assumption and so on,...</p>
<p>Anywa... | https://physics.stackexchange.com/questions/30405/faradys-law-and-div-b-0 |
Question: <p>In 'Introduction to Electrodynamics' by D. Griffiths, shortly after introducing the Maxwell stress tensor there is a paragraph concerning the physical interpretation of the stress tensor $\boldsymbol{T}$</p>
<blockquote>
<p>Physically, $\boldsymbol{T}$ is the force per unit area (or stress) acting on th... | https://physics.stackexchange.com/questions/409568/physical-interpretation-of-the-maxwell-stress-tensor |
Question: <p>Can a magnet ever wear out or lose strength?</p>
<p>If you break a magnet it (seemingly) gets weaker, but what about from normal use?</p>
<p>Or even very heavy use, like placing 2 magnets facing each other, so that they detract from each other, does that strain cause it to wear quicker?</p>
<hr>
<p><su... | https://physics.stackexchange.com/questions/411253/do-magnets-wear-out |
Question: <p>Would the forces between two circular loops, carrying currents in the same direction, be attractive or repulsive?
Would the forces between two circular loops, carrying current in the opposite directions, be attractive or repulsive?
How to find a force acting on a circular loop?
Please explain with a pict... | https://physics.stackexchange.com/questions/413159/force-on-circular-loop |
Question: <p>$$\mathbf B=\mathbf V \times \mathbf E \mu _0 \epsilon _0$$</p>
<p>$\mathbf V$ is the velocity vector of moving electric field. Rest of the parameters follow usual notations for those.</p>
Answer: <p>First of all, <strong>fields don't move</strong> because fields are everywhere in space. For example temp... | https://physics.stackexchange.com/questions/419379/is-it-correct-way-of-saying-that-a-moving-electric-field-causes-magnetic-field |
Question: <p>Electromagnetism;Ampere's Law
Application for finding magnetic field strength(B) inside a current carrying solenoid</p>
<p>Question is that why we multiply the current in one loop to the number of turns(enclosed in amperian rectangular loop) ALTHOUGH the current flowing(charges flowing per unit time) is S... | https://physics.stackexchange.com/questions/423382/electromagnetism-amperes-law-application-to-solenoid |
Question: <p>We know that a resonator consists of an inductor and capacitor. And we also know that tuning them in a specific way will get an Electromagnetic radiation detected with similar characteristics. But when the frequency of the original EM changes how do we detect the change(Like In the FM Radios, the frequency... | https://physics.stackexchange.com/questions/424907/how-is-the-waveform-of-an-electromagnetic-radiation-detected-and-generated-by-a |
Question: <p>I’m pretty familiar with maxwells equations, light waves, fields and materials etc, but I’m not clear on how the the various fields are actually measured. How is this typically done? Can the fields inside a material be directly measured?</p>
Answer: | https://physics.stackexchange.com/questions/429980/how-do-you-measure-and-distinguish-between-e-and-d-fields-and-b-and-h-fields |
Question: <p>When a conductor is moving relative to a magnetic field (for example a magnet falling in copper pipe, or a Eddy current brake in a train) , it is considered that the conductor moves, the conductor contains electrons, therefore the electrons are moving relative to the magnetic field, therefore EMF is genera... | https://physics.stackexchange.com/questions/430088/forces-on-moving-charges-in-a-magnetic-field |
Question: <p>My chemistry teacher used to tell us that if you had a soup bowl with only electrons in it, the explosion could make you fly to Pluto. Was he right? Could this happen?</p>
Answer: <p>The answer would depend how densely the electrons are packed. Let's say we have 1 kg of electrons, meaning we would have ab... | https://physics.stackexchange.com/questions/431751/what-if-you-had-a-bowl-of-electrons |
Question: <p>According to <a href="https://ws680.nist.gov/publication/get_pdf.cfm?pub_id=906602" rel="nofollow noreferrer">this</a> source, the divergence of the Poynting vector is related to the total energy density of an electromagnetic wave, which is (locally) expressed as</p>
<p><span class="math-container">$$-\nab... | https://physics.stackexchange.com/questions/432949/how-can-electromagnetic-waves-heat-non-conducting-media |
Question: <p>What causes a moving positive point charge moving right in a uniform into the page magnetic field to specifically move upwards? why not downwards?</p>
<p>Upwards and downwards (on the plane of the paper) are viable options. <strong>why does the charge only move upwards?</strong></p>
<p>Doesn't this viol... | https://physics.stackexchange.com/questions/434268/what-causes-a-moving-positive-point-charge-moving-right-in-a-uniform-into-the-pa |
Question: <p>It is intuitive to think of an electric field, which describes the variance in the force acting on a charged particle if it were located in a certain position. However it is not so easy to understand what magnetism is and what flux is.
Apparently magnetism is an effect of special relativity for moving char... | https://physics.stackexchange.com/questions/439108/what-exactly-is-magnetic-flux |
Question: <p>For instance, to get the TOTAL energy of an EM wave(s) or intensity you square the amplitude. But do you first add or combine the strengths of the e and m fields?</p>
Answer: <p>Suppose you have two sources of Electric field, <span class="math-container">$E_1$</span>, and <span class="math-container">$E_... | https://physics.stackexchange.com/questions/439761/is-the-amplitude-of-an-em-wave-the-combination-of-the-electric-and-magnetic-fiel |
Question: <p>(Correct where applicable)</p>
<p>Light is a wave on the electromagnetic field (or the electromagnetic field can be interpreted as a representation of the magnitude and direction of the force photons will have on another charge).</p>
<p>When we concentrate light, we are essentially changing the paths of ... | https://physics.stackexchange.com/questions/441765/can-concentrating-light-increase-the-intensity-of-the-electromagnetic-field |
Question: <p>If virtual particles cancel out after being created from spacetime flunctuations because they come in matter-antimatter pairs, how do virtual photons cancel out, due to a photon being its own antiparticle?</p>
Answer: | https://physics.stackexchange.com/questions/441939/how-do-virtual-photons-exist-without-violating-conservation-of-energy |
Question: <p>I'm currently working at an assignment, and I'm having some trouble understanding how the magnetic field deflects the silver atoms passing trough it. From what I understood, the atoms are deflected up or down of a specific amount according to their magnetic moment, but I can't understand what is causing th... | https://physics.stackexchange.com/questions/447457/reason-for-force-in-stern-gerlach-experiment |
Question: <p>Now i have been studying a chapter called current electricity and i found out that moving chages can create electricity why is this possible? Is it the holes and the electrons combining together and creeating heat and light and us pecieving it as electricity?
I haven't put much thought into it but i am als... | https://physics.stackexchange.com/questions/449075/why-does-a-moving-charge-create-electricity |
Question: <p>Assume an infinite wire carrying DC current. According to Ampere's force law， the moving electrons inside the wire are influenced by the Lorenz force pointing to the center. As a result, the current distribution is changed and finally all current flows in the center.</p>
<p>My question is, what is wrong w... | https://physics.stackexchange.com/questions/454909/magnetic-field-inside-a-current-carrying-wire |
Question: <p>In other words, if a coil is wound around a fixed magnet and the combination is rotated or otherwise moved, will the coil produce emf? Must the permanent magnet move relative the the coil to produce emf? I recall seeing a demonstration during a physics presentation back in the 70s where this was the case. ... | https://physics.stackexchange.com/questions/458916/can-a-coil-and-a-magnet-moving-together-produce-a-voltage |
Question: <p>Can a magnetic field be induced without an electric field?
Because, as far as I know, a time varying electric field induces a magnetic field an vice versa.
But in the case of conductors carrying currennt, it doesn't seem that electric field varies with time, then how is a magnetic field induced?</p>
Answ... | https://physics.stackexchange.com/questions/463014/can-a-magnetic-field-be-induced-without-an-electric-field |
Question: <p>We say the electric flux is the number of field "lines", thus electric flux density is the number of field "lines" per a given area. However, let's say we had a point charge <span class="math-container">$Q$</span> centered at the origin and we were to enclose this charge with a surface of radius <span clas... | https://physics.stackexchange.com/questions/464020/what-is-electric-flux-density |
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