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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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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408 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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256 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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875 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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4k 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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225 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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1k 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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188 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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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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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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2k 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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677 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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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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212 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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664 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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4k 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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2k 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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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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107 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
6k views

Do magnets work in outer space?

Is there any media where magnet lose its property?
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288 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
569 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 ...
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1answer
750 views

What kind of force is it when you push a door shut? [duplicate]

Possible Duplicate: How can I stand on the ground? EM or/and Pauli? It probably seems like a silly question to a physicist, but I'm from a pure maths background and don't know an awful lot ...
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Conservation of Energy in a magnet

When a permanent magnet attracts some object, lets say a steel ball, energy is converted into for instance kinetic energy and heat when attraction happens, and they eventually collide. Does this imply ...
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130 views

Electric generators?

When a magnet passes through a copper coil and electricity is induced into the coil, is there a magnetic resistance on the magnet as it passes through the coil?
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211 views

Why are electric charges allowed to be so light but magnetic monopoles have to be so heavy?

My question is in two parts. What is the origin of the electric field from an electric charge and why electron can have so small mass? While on the other hand for a magnetic monopole to create a ...
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Are the field lines the same as the trajectories of a particle with initial velocity zero

Is it true that the field lines of an electric field are identical to the trajectories of a charged particle with initial velocity zero? If so, how can one prove it? The claim is from a german ...
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130 views

Crystal magnetic response only skin deep?

The Hamiltonian for a single electron in a magnetic field reads $$H=\left(\frac{{\bf p}^{2}}{2m_{e}}+q_{e}\phi\right)+\mu_{B}\left({\bf \hat{L}}+g{\bf \hat{S}}\right)\cdot{\bf ...
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Can water be magnetized?

This may be a stupid question, so feel free to shoot it down. Assuming all atoms have a magnetic moment, I would assume the water molecule too would have a resultant magnetic moment; ergo, it may be ...
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3answers
595 views

How to get an integral formula for the flux time derivative

$$\frac{d}{dt}\int \limits_{A} \mathbf B d \mathbf A = \int \limits_{A} \left( \frac{\partial \mathbf B}{\partial t} + \mathbf v (\nabla \cdot \mathbf B ) + [\nabla \times [\mathbf v \times \mathbf B ...
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703 views

Why there is electromagnetic resistivity in vacuum?

I cant understand that. If there isn't a material that makes it hard to pass, why there is a resistivity in vacuum?
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3k views

Does a material exist that reduces a magnetic field without being affected by the magnetic field itself?

Consider a common bar magnet, magnet 1 resting on a surface with its North pole facing up. Suspended distance $y$ above it ...
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231 views

Wavefronts and phase velocity faster than $c$

Lets assume we have parallel wavefronts in a glass of water: and we put an inclined rod on the water surface: related to a very small inclining, Vy velocity is greater or much greater then Vx ...
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298 views

Why magnetic monopole found in spin ice don't modify the Maxwell's Equations?

Magnetic monopole predicted by Dirac nearly a century ago was found in spin ice as quasi-particle(2). My question is Why magnetic monopole found in spin ice don't modify the Maxwell's Equations? (I ...
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207 views

Is the magnetic field of a white-dwarf merely residual?

Follow-up to my other question How does Sol's magnetic field continue to exist at such high temperatures? Assuming Sol's magnetic field is generated by convective currents in it's plasma, how is ...
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388 views

Magnetic paradox in relativity?

Let 2 electrons A and B be moving parallel with constant velocity $c/10$ in (near) vacuum without a strong gravity field (where $c$ is speed-of-light). A and B create an electromagnetic field that is ...
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3k views

Finding the charge density

I can't figure out how to find the charge density for the following problem: A conductor is placed in an external electrostatic field. The external field is uniform before the conductor is ...
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Effects of EMP in superconductor-based devices/equipment?

What are possible effects of electromagnetic pulse / EMP on superconductor-based devices/equimpent/transportation? Are they resilient or more sensitive to EMP?
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Would ferromagnetic space debris have been magnetized by their orbit in the Earth's magnetosphere?

Given a nail, and a magnet it is possible to magnetize the nail by patiently rubbing the nail until it is magnetized; albeit the field strength may be less than that of the source. With several ...
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955 views

Maxwell equations invariant under Lorentz transformation but not Galilean transformations

Why Maxwell equations are not invariant under Galilean transformations, but invariant under Lorentz transformations? What is the deep physical meaning behind it?
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878 views

Ewings Molecular Theory of Magnetism & Induction Cookers

This question regards Ewings molecular theory of magnetism I.) Ewing's molecular theory of magnetism describes every magnetic substance as being a collection of dipoles that are initially in a state ...
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119 views

What are the Electric and Magnetic Properties of Aluminum Oxynitride?

Is Transparent Aluminum (Aluminum Oxynitride) a good conductor of electricity? Also, is it attracted by a magnet?
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208 views

Fields of Steady Currents Using Electrostatics

Suppose you have a uniform ring charge rotating at constant angular velocity so that you also have a uniform ring of steady current, and thus you can use the Biot-Savart Law to compute the magnetic ...
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416 views

How does Doppler effect differ between EM -waves in Electrodynamics and Sound -waves?

I have an electrodynamics -course that contains doupler -effect but unfortunately with little explanations. Is it the same thing as the classical doppler effect for example with sound, more here, or ...
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442 views

Inductance of loop to a square wire? What is the induced current and the induced $\bar E$?

I am practising for the elementary-physics -course Tfy-0.1064, this puzzle is a simplified version of the problem 3A here (sorry not in English). My basic idea here is to understand a scenario with ...
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3answers
601 views

Extract energy from magnets

Is it possible to "extract" energy from a magnet, making it lose its magnetism? Or, to put in another way, is magnetism a form of energy? (I am not talking about potential energy in a magnetic field). ...
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635 views

Is there a strong force analog to magnetic fields?

In special relativity, magnetism can be re-interpreted as an aspect of how electric charges interact when viewed from different inertial frames. Color charge is more complex than electric charge, but ...
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1answer
153 views

Do Maxwell equeations change somehow after Higg's boson finding?

When I was in some physics -lesson, probably something to do with Quantum Physics -- the teacher said that certain Maxwell equations would change if the Higg's boson is found. It is also possible that ...
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How is wireless communication possible?

Like all my questions, I fear this will be very naive, because my physics background is very limited. Please bear with me. I think of the electromagnetic field as a section of a vector bundle over ...