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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Bend or concentrate magnetic field?

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, ...
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1answer
140 views

Could we really charge metal plates using microwaves?

While skimming through Dielectric heating, I read that they use microwaves to charge the plates. How do they do that?
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1answer
6k views

Distribution of charge on a hollow metal sphere

A hollow metal sphere is electrically neutral (no excess charge). A small amount of negative charge is suddenly placed at one point P on this metal sphere. If we check on this excess negative charge a ...
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1answer
297 views

EM force, blocking force carrier photons in a static electric field

I am doing some personal research in this specific area and wanted to ask something related to photons and EM force. are involved. Here is a thought experiment that doesn't add up to observed results, ...
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2answers
2k views

Derivation of Ohm's Law

Is it possible to derive Ohm's law (perhaps in some appropriate limit) from Maxwell's Equations?
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1answer
376 views

The equation of a ferrofluid under a magnetic field?

What is the parametric equation guiding the geometry of a ferrofluid under a magnetic field? See also this Wikipedia page. From previous research, Maxwell's Equations and Navier-Stokes Equations were ...
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2answers
695 views

Charge, velocity-dependent potentials and Lagrangian

Given an electric charge $q$ of mass $m$ moving at a velocity ${\bf v}$ in a region containing both electric field ${\bf E}(t,x,y,z)$ and magnetic field ${\bf B}(t,x,y,z)$ (${\bf B}$ and ${\bf E}$ are ...
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1answer
374 views

Electromagnetic 4-potential and basic index contraction

I'm trying to learn about relativistic electrodynamics on my own, and I am struggling with derivatives of the 4-potential and index (Einstein) notation. I think I understand expressions such as ...
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1answer
301 views

Gaussian surface question

There is an infinite slab of charge, and a (Gaussian surface) cylinder whose ends are both outside of the slab. $\phi_A$ is the flux through this cylinder, by symmetry the component of the flux ...
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1answer
650 views

How will water affect the electric field?

How will 2 charged bodies act when the separation medium between them is water ?
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158 views

A crazy problem

Easy Consider the following figure Each red point is a particle of a known mass that carries charge Q/2 and connected to a the box by a thread of known length. This problem can be solved easily to ...
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1answer
339 views

What would it take for a physical phenomenon to be telekinetic?

I've just watched an episode by MinutePhysics called "Real World Telekinesis". In it, Neil Turok (I wonder if that is his actual name; I remember playing a game called "Turok: Dinosaur Hunter" on ...
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2answers
145 views

A particle of charge $-e$ orbits a particle of charge $Ze$, what is its orbital frequency?

A point particle $P$ of charge $Ze$ is fixed at the origin in 3-dimensions, while a point particle $E$ of mass $m$ and charge $-e$ moves in the electric field of $P$. I have the Newtonian equation of ...
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1answer
734 views

Proof of equality of the integral and differential form of Maxwell's equation

Just curious, can anyone show how the integral and differential form of Maxwell's equation is equivalent? (While it is conceptually obvious, I am thinking rigorous mathematical proof may be useful in ...
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804 views

If you are carrying a magnet, can you tell when you cross the event horizon of a black hole?

By the no hair theorem, a black hole is completely characterized by it's mass, charge and angular momentum. Therefore dipole and higher pole magnetic fields are completely expelled when a black hole ...
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1answer
5k views

Shouldn't the electric field in a solid insulating sphere be linear with radius?

I am a senior in High School who is taking the course AP Physics Electricity and Magnetism. I was studying Gauss's laws and I found this problem: A solid insulating sphere of radius R contains a ...
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1answer
69 views

Can a SQUID perform real time measurements of a slow varying magnetic flux?

It is well known that a SQUID can detect an extremely small magnetic flux. What if the flux is time-dependent? E.g. a slow varying sinusoidal magnetic flux $$\Phi=\Phi_0\sin(\omega t).$$ Can I ...
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1answer
4k views

Why are some materials diamagnetic, others paramagnetic, and others ferromagnetic?

Why are some materials diamagnetic, others paramagnetic, and others ferromagnetic? Or, put another way, which of their atomic properties determines which of the three forms of magnetism (if at all) ...
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484 views

Do intergalactic magnetic fields imply an Open Universe?

According to a recent paper on the arXiv, they do. How credible is this result? The abstract says: The detection of magnetic fields at high redshifts, and in empty intergalactic space, support ...
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1answer
415 views

If a magnetic monopole falls into a schwarzchild black hole, what happens to the magnetic field?

By the no-hair theorem, black holes can only have mass, charge and angular momentum. Does "charge" include "magnetic charge" (such as from a magnetic monopole)? Can black holes have magnetic charge ...
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1answer
623 views

When a neutral star with a magnetic field collapses to form a black hole, what happens to the magnetic field?

By the no-hair theorem, black holes are only characterized by mass, charge and angular momentum. If the star is neutral, the black hole will have only mass and angular momentum - and therefore it ...
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0answers
78 views

Good Magnetic Simulation Software? [duplicate]

Possible Duplicate: Where can I find simulation software for electricity and magnets? I am looking for a good, FREE software that allows me to play with magnets, coils, generators, the ...
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1answer
585 views

What happens to an embedded magnetic field when a black hole is formed from rotating charged dust?

Black holes have no-hair so there are uniquely specified by a mass, charge and angular momentum. Imagine a cloud of charged rotating dust. There will be a magnetic field associated with the current ...
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1answer
142 views

Is it possible to see domains in a metal/magnet under microscope

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 ...
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4answers
5k views

How does inductor store energy in the magnetic field?

I learnt from book that magnetic field does no work because the force is proportional to $\vec{v}\times\vec{B}$ where $\vec{v}$ is the particle velocity. That vector cross product is always at right ...
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2answers
602 views

How do magnetically levitated trains (maglevs) stay on the tracks?

Just went on one yesterday, and had a bit of a thrill. And I was musing on the fact that electromagnetic forces are so strong, that they can keep a whole train up in the air. But then, wouldn't ...
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4answers
302 views

The necessity of the B field

It is fairly easy using basic special relativity to arrive at the conclusion that the magnetic force effect on nearby charges of wires carrying currents on nearby charges is only due to the length ...
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1answer
99 views

Conducting surface inside conducting surface

Let's say there's a closed conducting surface. Then by Gauss's Law the E field bound by the surface must equal the charge inside. There's no charge inside, so the E field cancels. This is a Faraday ...
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2answers
467 views

Invariance of Maxwell's Equations under inverting variables - Reference and use

Some months ago, an ArXiv paper mentioned in passing that Maxwell's Equations were invariant under reciprocating the variables, or at least this results in a dual set of Maxwell Equations. (Actually I ...
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2answers
292 views

Will the positive ions in an aqueous solution be attracted to a charged body ?

If I had a negatively charged body , say an electret , and i put it in a container of NaCl solution . Will the positive ions of sodium be attracted to it ? and why? If no, why do the positive ions ...
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1answer
1k views

Induced current in parallel wires

Consider two parallel wires of finite radius. When a current is applied to one of the wire for a short period of time, what is the current induced in the other wire? Applying Maxwell's equations, it ...
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1answer
5k views

Does Faraday cage block magnetic field?

I want to block magnetic field of the very strong magnet, can I put it inside faraday cage to block its magnetic field?
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1answer
248 views

Stability of a rotating ring of multiple electrons at relativistic speeds

There was a time when physicists where concerned about electron internal structure. The rotating ring model was one of the proposals to explain how a charge density could become stable against ...
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2answers
2k views

Inductance - Sign convention problem…

My problem is with a circuit containing a resistor of suitable resistance $R$ and a solenoid. At time $t<0$, there was a battery that created a current in the circuit and at $t=0$, the battery is ...
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199 views

Why energy saving light bulbs contain rare earth?

Reading a french article talking about a recycling unit of rare earth from energy saving light bulbs near Lyon - France (here is the official press release of the Salvay company), I was wondering : ...
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Magnetic field lines

When I searched the net about magnetic field lines, Wikipedia told something about contour lines and that magnetic materials placed along a magnetic field has some specific loci, which i did not ...
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3answers
1k views

Does an oscillating electrical monopole radiate?

For example, the displacement R(r,t) of the single charge q is given by $$R = R_0\cos(\omega t)$$ In the view of multipole expansion, what is the monopole moment and the dipole moment for this ...
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1answer
3k views

How is Gauss' Law (integral form) arrived at from Coulomb's Law, and how is the differential form arrived at from that?

On a similar note: when using Gauss' Law, do you even begin with Coulomb's law, or does one take it as given that flux is the surface integral of the Electric field in the direction of the normal to ...
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4answers
3k views

How to make something charged using electricity?

If I had a piece of metal and i wanted it to be negatively charged. How can I do that?
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826 views

Why is there a factor of 1/2 in the interaction energy of an induced dipole with the field that induces it?

In this paper, there's the following sentence: ...and the factor 1/2 takes into account that the dipole moment is an induced, not a permanent one. Without any further explanation. I looked ...
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2answers
2k views

Where does the equation $E_q = \frac{kq}{r^2}$ come from in this problem?

A point charge is placed at each corner of a square with side length $a$. The charges all have the same magnitude $q$. Two of the charges are positive and two are negative, as shown in the ...
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233 views

Does a rotating magnetic monopole have electric and magnetic moment in classical view?

Would a rotating sphere of magnetic monopole charge have electric moment ? In a duality transformation E->B.c etc. how is the magnetic moment translated m = I.S -> ? Mel = d/dt(-Qmag/c).S ? A more ...
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1answer
810 views

Does a microwave resonantly excite the rotational levels when cooking?

Wikipedia states there is no resonance absorption, but says at the same time that the molecules are oscillating like dipoles, which is kind of the same if you are exciting the rotational levels ? The ...
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3answers
5k views

Does special relativity make magnetic fields irrelevant?

I've heard that special relativity makes the concept of magnetic fields irrelevant, replacing them with relativistic effects between charges moving in different velocity frames. Is this true? If so, ...
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1answer
3k views

Magnetic field lines can be entirely confined within the core of a toroid, but not within a straight solenoid. Why?

I need a full explantation for this concept. Magnetic field lines can be entirely confined within the core of a toroid, but not within a straight solenoid.
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3answers
6k views

Will two magnets lose magnetism if they stick to each other for infinitely long time?

Here we have two magnets and they are sticking to each other. What I've learned that could possibly explain it is one magnet holds positive charge and the other one holds negative. But when the ...
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1answer
132 views

Is more energy required to magnetize based on its distance to other objects?

I have had this question since I was in college physics, but never could figure out how to express it. Well, now I think I have it. Let's imagine two scenarios A and B. Both scenarios start with two ...
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2answers
9k views

Do magnets work in outer space?

Is there any media where magnet lose its property?
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1answer
353 views

E and H fields created by fiber optics?

When an EM wave travels down a conductor, it creates and electric and magnetic field around (H) the wire and normal to (E) the wire. My question is, when light travels down an optical material such ...
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3answers
632 views

Maxwell equation boundary conditions on a conducting sheet

I'm having difficulties solving boundary conditions for an infinitely thin conducting layer in a presence of an alternating field. I use the Maxwell equations: $\nabla \cdot \mathbf B = 0$ $\nabla ...