The classical theory of electric and magnetic fields, both in the static and dynamic case. Also covers general questions about magnets, electric attraction/repulsion etc. Distinct from electrical-engineering.

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A rod filled with water and charged particles is rotated in magnetic field

Assume we have a rod of diameter $d$ and length $l$. It is filled with a mixture of water and, say, sodium chloride. Thus there are positively charged sodium ions and negatively charged chloride ions ...
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2answers
500 views

What is a photon's speed inside a dieletric?

We know that EM waves are slowed down in a dielectric. But at what speed does the photons that make up the wave travel? Do they always travel at the speed $c$, but colliding/being absorbed and re-...
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660 views

Does the electromagnetic field “spin”?

Due to electron "spin", a small magnetic field is produced. Maxwell's equations imply that magnetic fields are due to changes in electric fields. Is the magnetic field produced then because the ...
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669 views

Revealing Electric field lines through Grass seeds in mineral oil

In one of Walter Lewin's famous lectures, he takes a small container almost completely filled with mineral oil and grass seeds (I'll keep looking for the video to link to it). He connects two ...
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2answers
68 views

heavy nuclei surface exposed to positron gas

Suppose there is a material with heavy nuclei attached on its surface, presumably binded by the outer shell electrons. Now, the surface is exposed to a cold positron gas, which annihilates against ...
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700 views

Is there a simple model explaining Faraday effect?

I find magneto-optical effects fascinating, and especially the Faraday effect. But most sources only give a phenomenological description, while I want a deeper explanation of its mechanism. Is there a ...
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438 views

On Aharonov–Bohm effect

Aharonov–Bohm effect in brief is due to some singularities in space. In books it's infinite solenoid most of the time, which makes some regions of space not simply connected. What intrigues me is the ...
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364 views

Loop of wire in a varying magnetic field

Let us suppose we have a loop of wire with some definite resistance in a magnetic field. Let the magnetic field be varying. This varying magnetic field will st up an EMF in the wire. My questions are ...
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90 views

A charged particle moves in a plane subject to the oscillatory potential

A charged particle moves in a plane subject to the oscillatory potential: $U(r)=\frac{m\omega^2 r^2}{2}$ There is also a constant EM-field described by: $\vec{A}=\frac{1}{2}[\vec{B}\times\vec{r}]$ ...
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33k views

Using A.C or D.C to create an electromagnet

Does it matter if I use A.C or D.C as a source to create an electromagnet? Or Does it depend on the voltage of current? For example: I have a coil which has about 50 turns. If I use same amount of ...
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6answers
8k views

How to find the poles on a spherical magnet?

To any nonmagnet, the whole sphere is a magnet. To another spherical magnet though, there is a rough area on the surface where it is strongly repelled. Given a spherical magnet, how should the poles ...
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888 views

Does the wavelength always decrease in a medium?

I was studying a GRE Physics Test problem where optical light with a wavelength of 500 nm travels through a gas with refractive index $n$. If we look at the equations for wave motion and index ...
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371 views

existence of other forces obeying inv square law

Is there any restriction in what we know of physics to the existence of other type of forces that obey the inverse square law in 3 dimensions. I mean other than electromagnetic and gravitational. ...
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90 views

Why doesn't a uniformly moving particle radiate?

When considering a uniformly moving charged particle, we have the following fields: $$\vec E = \frac{q(1-\beta^2)}{4\pi\epsilon R_a}\vec R$$ $$\vec B = \frac{1}{c^2}\vec u \times \vec E$$ With $\vec ...
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2answers
34 views

Why does current follow a conductor above a ground plane

Suppose there is a conductor above a ground plane. Current flows from a source through the conductor to a load on the other side. Depending on the frequency of the current the return path through the ...
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42 views

Does magnetic fields exert forces only on moving charges?

I am confused here a bit,i read that magnetic fields exert force only on charges moving but when we take magnet and keep it near a stationary metal (assume light in weight), the magnet attracts it? ...
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47 views

Introducing a phase, what changes?

This question is related to: Mach-Zehnder interferometer and the Fresnel-Arago laws Let us say we have unpolarised wave taking the form: $$\psi=\psi_0 e^{i(kx-\omega t)+i\phi(t)}$$ Where $\phi$ ...
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102 views

Can bending spacetime produce electromagnetic fields?

Let's say that we can somehow bent spacetime, can this produce electromagnetic fields? or EMF can only be emitted from charged particles of matter?
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93 views

Magnetic force between moving charges

Given two infinite parallel charged rods with equal charge density $\lambda$. They are moving with same constant velocity $\vec v$ parallel to the rods. Find the speed $v$ for which the magnetic ...
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93 views

Why are electric and magnetic fields perpendicular in an electromagnetic wave?

I want to know why electric and magnetic fields are perpendicular in an electromagnetic wave and what would happen if they weren't.
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71 views

What phenomena occur in a low voltage arc between copper and graphite electrodes, and why is the result dependent on electrode polarity?

I was playing around with a laboratory power supply, drawing arcs between electrodes of various materials. I noticed phenomena that I found interesting, and couldn't really explain myself: The ...
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1answer
50 views

Zero friction wheel with magnetism

Is it possible to create a zero friclion wheel using magnetism? I have been thinking on this a lot.
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115 views

Question about source terms in scalar quantum field theory

I'm having a bit of a mental block when trying to interpret the inhomogeneous Klein-Gordon equation $$(\Box +m^{2})\phi(x,t)=j(x,t)$$ In particular, how does one interpret the term on the right-hand ...
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81 views

How does the energy remain conserved in a transformer?

The induced voltage in the secondary coil of a transformer is given as $\frac { { N }_{ S } }{ { N }_{ P } } *{ V }_{ P }$ (where ${ N }_{ P}$ and ${ N }_{ S }$ are the number of turns in the primary ...
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62 views

Why is the magnetic moment of a proton weaker than the electron?

I know that the nucleus of an atom does not contribute to the magnetization of an atom or material, and that the magnetic moments of protons are much weaker than electrons. Why is the magnetic moment ...
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73 views

How does parallel plate lose energy when deflecting charged particles

Say you have a parallel plate setup, each plate is charged with ±Q of charge, and is then disconnected from the power source and is insulated from the environment. There is no way the plates can be ...
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130 views

Why does energy flow between a high voltage transmission line and linemen approaching it on a helicopter?

The video High power line workers shows linemen servicing a live high voltage transmission line. As the helicopter approaches the line, the lineman reaches out with a metallic wand that is ...
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52 views

Conservation of Angular Momentum in Einstein - de Haas effect

I am not really sure why the law of conservation of angular momentum should hold true in the Einstein - de Haas effect. Consider the following excerpt about the phenomenon (taken from Magnetism in ...
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162 views

Does waving a magnet around create light?

If I wave around a bar magnet, the magnetic field in the space around it changes. Is this enough to go through the whole speed of light derivation implying that the motion creates an electromagnetic ...
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2answers
73 views

Curl of a simple magnetic field and resulting current distribution

I've been doing some thinking lately and here is my question: If one imagines that there is an auxiliary magnetic field $H$ whose spatial dependence is given by equation: $$H(x,y,z)=y\hat{i}$$ ...
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66 views

Solved Gauss' Law for $\vec{E}$ without boundary conditions?

Why can I solve for the electric field of a point charge Q at the origin without boundary conditions? $\nabla\cdot\vec{E}=\rho/\varepsilon_0 = \delta(\vec{r})/\varepsilon_0$ is a 1st order ...
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37 views

Is polarization a stable state?

Do a polarized light beam stays polarized over large distance or does it kind of relax and eventually become unpolarized?
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1answer
130 views

Are the conducting electrons in a metal counted as free or bound charges?

Caused by another question on the propagation of EM waves in a metal, I got a bit confused on the notion of free and bound charges in a metal (sometimes called induced or external). Are the free ...
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1answer
57 views

Description of transparency of a Faraday cage to different frequencies?

A Faraday cage within a static electric field leaves an internal electric field equal to $\vec{0}$ (as long as there are enough mobile electrons in the conductor to counteract the external $\vec{E}$). ...
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56 views

Is a traveling magnetic field identical to the field of a moving magnet?

A traveling magnetic field is created by means of applying out-of-phase currents to a number of coils. Is it identical to that created by a moving magnet, including relativistic effects?
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64 views

What is 'momentum outflow'?

Feynman, in his lecture, on Field momentum, used this term while relating the momentum of matter the field is interacting with & the field's momentum itself. Here is the excerpt: Just as the ...
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2answers
120 views

What happens when a field turns on or off?

Short Setup I am curious about the the mechanics of fields, whether electromagnetic, gravitational, etc. So as a specific example in order to simplify (hopefully) how to ask this question, consider ...
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1answer
155 views

Which is more fundamental: $H$ or $B$? [closed]

According to Wikipedia, $B$ is called the Magnetic flux density / Magnetic induction / Magnetic field, while $H$ is called the Magnetic field intensity / Magnetic field strength / Magnetic field /...
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116 views

How strong a magnetic field would be needed to deflect cosmic rays?

How strong a magnetic field would be needed to deflect cosmic rays? For example, lets imagine we wanted to protect the occupants of the International Space Station from cosmic rays. I assume we would ...
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1answer
83 views

Effects of magnets on memory cards

I have always believed in keeping magnets and data storage devices far away from each other. Friends say I'm excessively cautious about it, but I seem to have a lot less data loss than they do! As ...
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197 views

$\vec{E}$-and $\vec{B}$-fields in RCL circuit

Consider a basic RCL-Circuit consisting of an ideal resistor, an ideal capacitor and an ideal inductor in series. Assume that at time $t = 0$ the current is zero and the capacitor is charged with ...
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75 views

Gradient in the Frenet-Serret coordinate

I was simply thinking that the gradient in the Frenet-Serret coordinate at a particular point is similar to the gradient in the Cartesian coordinate. I simply assumed that Frenet space is an ...
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4answers
314 views

How does an inductor store magnetic energy?

I am trying to figure out what the potential energy of an inductor with a current really means. In a capacitor, the energy stored works like this: if you let the plates attract each other, before ...
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1answer
123 views

Resource for mass-charge interaction

My GR professor mentioned that trajectories of charged particles in GR are not the same as those of non-charged particles (i.e. charged particles don't move on geodesics). As I understood it, the ...
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2answers
322 views

Force between two point charges moving parallel to each other

When we observe two point charges moving parallel to each other we can see two forces acting on each of the charges: the Coulomb force the magnetic force ($\mathbf{F}=q\mathbf{v}×\mathbf{B}$) (...
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4answers
359 views

What is the meaning of EM field having curl?

We know that the "sourceful" fields like gravity or electric static field due to charge are all curl=0. But both E/M fields have curl and they mutually "curling" into each other, making them kind of "...
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1answer
98 views

Do two bodies spinning about the same axis in the opposite direction repel each other?

I recently read about the GEM equations, which look very much like the Maxwell's equations. Does this mean the behavior of mass is like the the behavior of the electric charge? So for example if you ...
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2answers
147 views

Gravity vs. Electromagnetism Scenario

Imagine a two dimensional world where there are only two electrons. They are set right beside each other. Of course, immediately they will start to separate, being repelled. My question is, as they ...
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1answer
2k views

How much magnetic field will be required to levitate a human? [duplicate]

According to this video: http://www.youtube.com/watch?v=BqKeiiezqzc it should be possible to levitate humans because the water in our bodies is diamagnetic - but it is stated (at 1:14) "although ...
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205 views

Do electrons in the conduction band have a quantum number?

Sorry if this is a silly question, but I haven't seen the concept anywhere and was wondering why. If valence electrons can have a quantum number, why can't conduction electrons? Is there something ...