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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what is the specific cause of permanent magnetism [duplicate]

Why can't we answer this simple question? Where does the magnetic field of a permanent magnet come from? What is different about a magnetizable atom that allows it? Why is it perpetual? Or is it ...
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Do We Need Maxwell's Equations Since They Fail to Account for An Experimental Fact at Least in One Occasion?

This question is an outgrowth of What is the difference between electric potential, potential difference (PD), voltage and electromotive force (EMF)? where @sb1 mentioned Faraday's law. However, ...
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4answers
676 views

Coulomb's Law in the presence of a strong gravitational field

I was under the impression that the $1/r^2$ falloff of various forces were because of the way the area of a expanding sphere scales. But that strict $1/r^2$ falloff would only be globally true in a ...
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1answer
4k views

Can you magnetize iron with a hammer?

We know that a piece of ferromagnet, such as iron, can be magnetized by putting in a strong magnetic field to get domains parallel to the field grow. I also remember from pop. culture and MacGyver ...
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283 views

Time dilation only on electromagnetic force?

We've seen by experiment that the speed of light c appears to be constant for each observer (leading to all well-known consequences of relativity). I'm wondering if this appearance of constancy of c ...
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What are the characteristics of the magnetic field surrounding a human brain?

The human brain is said to produce a magnetic field resulting from the action potentials released inside the brain. What's the nature of such a field in terms of size and strength, and what is the ...
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756 views

Lorentz force in Dirac theory and its classical limit

It is well known that in Dirac theory the time derivative of $P_i=p_i+A_i$ operator (where $p_i=∂/∂_i$, $A_i$ - EM field vector potential) is an analogue of the Lorentz force: $\frac{dP_i}{dt} = ...
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475 views

What's a good reference for the electrodynamics of moving media?

The answer to a previous question suggests that a moving, permanently magnetized material has an effective electric polarization $\vec{v}\times\vec{M}$. This is easy to check in the case of ...
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Is the force carrier of the magnetism in a common household magnet a photon?

As I have understood it, the Standard Model includes particles that carry the different forces, e.g. the electromagnetic (EM) force, the gravitational (G) force. When talking about EM fields such as ...
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Magnetic field insulators

I was wondering if there is any way to stop the magnetic field, without having the insulator turned into magnet. Let me present this as a simple case, there is a magnet to the left and a piece of iron ...
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361 views

Coulomb interaction as virtual particles exchange?

I've been reading about virtual particle exchanges in physics books and in Physics SA posts, where a particle interpretation of gravity and Coulomb interaction is established. The Feynman Diagram ...
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2k views

What are the limits of applicability of Coulomb's Law?

Coulomb's law is formally parallel to Newton's Law of Universal Gravitation, which is known to give way to General Relativity for very large masses. Does Coulomb's Law have any similar limits of ...
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252 views

Naive Question About Batteries

I do apologize for the ignorance that I'm sure is imbedded in this question, but I'd like to understand the exact point at which the following argument goes wrong: 1) A battery (let's say an ...
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1answer
6k views

How to debunk 'The Electric Universe'? [closed]

My father is a generally intelligent person, however he has latched onto a theory which I believe to be completely incorrect. He doesn't believe in gravity, but rather subscribes to an 'Electrical ...
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3answers
209 views

Ampere's law and external currents

In Ampere's law the current outside the curve taken is not included in the expression. Does this mean that only the currents crossing the area bounded by the curve taken contribute to the magnetic ...
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2answers
919 views

Why doesn't the magnetic field polarize when polarizing light?

If the magnetic field doesn't polarize does it follow the electric field path of propagation? or does it vanish?
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132 views

Can the two electromagnetic field tensors be combined into a more general tensor?

Given the electromagnetic field tensor $$\begin{align} F_{\mu\nu} = \begin{pmatrix} 0 & -E_{x} & -E_{y} & -E_{z} \\ E_{x} & 0 & B_{z} & -B_{y} \\ E_{y} & -B_{z} & 0 ...
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201 views

Geodesic for Electromagnetic forces

Considering the fact that electrons tend to take the maximum conductance path to flow from A to B. This is justified by saying that $\vec{E}$ is larger in conductors. But once similarly it was thought ...
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2answers
314 views

Coincidence, purposeful definition, or something else in formulas for energy

In the small amount of physics that I have learned thus far, there seems to be a (possibly superficial pattern) that I have been wondering about. The formula for the kinetic energy of a moving ...
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The relation between permittivity and conductivity

I am able to measure relative permittivity $\varepsilon_r$ of a fluid, and I want to calculate conductivity of same fluid. Can anyone suggest me how to do this? I found one formula to calculate ...
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3answers
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formula for transparency of very thin film of metal

Is there formula that gives transparency of very thin film of given metal (tens of nanometers) to the visible light/light of given wavelength ? Which properties of metals are needed for the formula ? ...
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3answers
670 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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3answers
171 views

Are magnetism and electricity the same thing? [closed]

I have read at certain place electricity and magnetism are the same thing, bit in reality we see both have different properties.
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4answers
276 views

Why does a magnetic field go anticlockwise of the direction of current?

Why never clockwise? How does it 'know' to go anticlockwise?
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1answer
101 views

What is the sum of the electrons' magnetic moments in a wire?

Electrons have magnetic dipole moment. This magnetic moment will be influenced in an electric field in case the electron get moved non-parallel to the current. The magnetic moments will be more or ...
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2answers
175 views

Why is this not a violation of parity invarance for EM

I read that Wu's experiment illustrates that parity violation is possible for weak processes. In that experiment, when Co-60 undergoes beta decay, the emitted electrons come out opposite to the ...
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3answers
1k views

Why does charge accumulate at points?

This is a very trivial question, but I can't seem to reason it out, again, as to why charges gather at points and edges.
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296 views

Transmission Line, TEM wave, transverse Laplacian operator (electromagnetic)

Time-Harmonic Electromagnetic Fields (1961) by R. F. Harrington, ISBN 07-026745-6, p. 63, he discusses TEM mode in a transmission line. The wave travels in the z direction. He defines the transverse ...
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Can a light be bent by a magnetic field?

I'm struck with two competing ideas on the question in the title. Listing #1: http://van.physics.illinois.edu/qa/listing.php?id=2009 Q: "How far can a magnetic field bend light?" A: "Unfortunately, ...
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198 views

Where can I find a complete list of metamaterials up to today?

Where might I find a list of all the metamaterials up-to-date?
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489 views

Software for simulating 3D Newtonian dynamics of simple geometric objects (with force fields)

I'm looking for something short of a molecular dynamics package, where I can build up simple geometric shapes with flexible linkages/etc and simulate the consequences of electrostatic repulsion ...
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97 views

Conducting rod moving through magnetic field

If a conducting rod moves through a magnetic field which way do its electrons move? In my revision guide it shows the following picture (more or less, but the following is my drawing of it -- I ...
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1answer
39 views

Is the electron's magnetic dipole moment influenced by the measurement method?

The electric charge of an electron at rest is a constant value and is not influenced by the measurement instrument. The measurement instrument by itself can give more or less accurate result, but does ...
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3answers
261 views

The propagation of electric field

In case of a charged particle which is travelling at a uniform velocity, the electric field due to it at a given point doesn't change instantaneously . The reason for this delay in change of electric ...
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1answer
174 views

Maxwell's equation for non inertial observer

Applying Maxwell's equation we can prove that light will move at the speed of light for every inertial frame, is it true as well for non-inertial frames? How light moves slowly near a black hole??
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165 views

Are there new concepts for the explanation of the wave-particle duality?

Whenever we can observe photons immediate, they are particles. That includes that photons have a inner structure with periodically varying electric and magnetic fields. The EM field of a radio antenna ...
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767 views

How electromagnetic fields travel through vacuum?

How electromagnetic fields travel through vacuum is it right to say that they propagate or travel? do they alternately form each other by charged particles?
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2answers
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Is it possible to detect fake Tungsten aka Wolfram gold bars with a strong magnet?

Tungsten aka Wolfram is paramagnetic so it is weakly attracted to magnets. A guy devised the following to test for Tungsten in gold bars: http://www.youtube.com/watch?v=foELQ7T8_90 But he is using ...
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3answers
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Magnitude of magnetic field at the center of circular wire

I'm preparing for an exam by solving the sample questions , here is the one I'm having difficulty with : Following is the given circuit. Which contains two resistance $R_1$ and $R_2$ in form of ...
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2answers
458 views

Deriving the Lorentz force from velocity dependent potential

We can achieve a simplified version of the Lorentz force by $$F=q\bigg[-\nabla(\phi-\mathbf{A}\cdot\mathbf{v})-\frac{d\mathbf{A}}{dt}\bigg],$$ where $\mathbf{A}$ is the magnetic vector potential and ...
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5answers
776 views

Relativistic charge density in a closed loop

When charges of conductance are at rest, there is an average distance between them. The relativistic origin of magnetic field says that distances between electrons shrink when they are set into a ...
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0answers
128 views

Einstein +Maxwell 's tensor

Why is it true that we can deduce that Einstein's GR equations coupled with Maxwell's EM equations may be written in the form $$R_{ij}=C(F_{ik}F_j^{\,\,k}-{1\over 4}g_{ij}F_{mn}F^{mn})$$ without ...
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2answers
270 views

Non-linear dynamics of classical hydrogen atom

I'd like to know if there have been attempts in solving the full problem of the dynamics of a classical hydrogen atom. Taking into account Newton equations for the electron and the proton and Maxwell ...
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68 views

How to repeat the Biot-Savart experiment for the direct current in a straight wire and the corresponding magnetic field without side effects?

As I read Biot and Savart took a compass needle and this needle make some rotation when the current was switched on and off. As it was clear that a changing current induces a magnetic field the ...
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0answers
92 views

If we put diamagnetic material under strong electromagnet.Would the opposing magnetic fields strong enough to attract ferromagnetic materials?

Suppose we put a diamagnetic material (such as Bismuth or Pyrolytic Carbon) under a strong magnet (see image below). It would create opposing magnetic fields. Would the opposing magnetic field be ...
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1answer
155 views

Post Problem Analysis - Rod in a cylindrical time varying magnetic field?

A metal rod of length $l$ is placed (as shown in figure) in a cylindrical time varying magnetic field. Find the potential difference across it. My answer: As electric fields as forming circles ...
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2answers
377 views

Electric charge is lorentz invariant

I know that electric charge is lorentz invariant quantity and I can easily think of experiment to check that. Is a though experiment that can prove that also?
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2answers
767 views

Calculate force of electric charges “suspended” by strings [closed]

In a question: Two small plastic balls hang from threads of negligible mass. Each ball has a mass of 0.110g and a charge of magnitude q. The balls are attracted to each other, and the ...
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1answer
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Relationship between current through a motor and it's load

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 ...
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The limit of radio wave penetration

Why can I listen to my mobile phone's radio clearly inside the bus, inside the train, but not inside the elevator? Also, there is an interference of radio signal when the train is accelerating or ...