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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18 views

Reflection of light on a moving mirror - Lorentz transformations

Setting: Let's consider a moving mirror at constant speed in z-direction. A light ray of frequency $\omega$ falls onto the mirror. Its wave vector $k$ forms an angle $\theta$ with the vector normal to ...
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0answers
29 views

Deriving the classical electromagnetic point charge Lagrangian from the Abelian Yang-Mills Lagrangian density

Can I derive the point charge Lagrangian $$ L = -\frac{mc^2}{\gamma} - \frac{1}{c} J_{\mu} A'^{\mu}\tag{1} $$ from the Abelian Yang-Mills Lagrangian $$L = \int d^3x [ - \frac{1}{16 \pi} F_{\mu ...
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0answers
21 views

Why the changing magnetic flux horizontal component does not induce electricity?

Textbooks just seem to utter that change in the magnetic flux that is 'piercing' the plane contributes to electricity induction. They don't explain why. Is there any intuitive explanation?
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1answer
47 views

Does the medium a magnetic field is propagating through affect its speed?

I'm wondering if a material's magnetic susceptibility or magnetic permeability would have an effect on the speed a magnetic field would propagate through it. I know it won't speed it up but I'm ...
2
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1answer
50 views

How is the amplitude of light related to number of photons?

If you increase the number of photons leaving a light source you increase the brightness/intensity, so it could be said that intensity is directly proportional to number of photons. However intensity ...
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0answers
30 views

Is there a verified physical balance in the Maxwell source terms derived from the QM wavefunctions? [on hold]

In QM one construct the charge and current source distributions for Maxwell equations, seen in standard textbooks on quantum mechanics, so that the external EM field can be calculated. A nice feature ...
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2answers
44 views

Does charge of capacitor at constant voltage change after dielectric material is inserted?

I have a planar geometry capacitor, connected to a battery that supplies V volts. Initially there is vacuum/air in between both plates. Afterwards, some dielectric material is inserted in between both ...
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0answers
59 views

Switching on a light bulb. Initial EM/electron pulse propagation

TLDR When switching on an electrical device (e.g. a light bulb or a heater), there is an initial wave (pulse) travelling with very high speed (close to the speed of light) and “carrying the ...
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1answer
39 views

Field of Solenoid

I was reading this, where in the very beginning I stumbled on the "particle in a solenoid field theme". What's written in there is: The potentianl $\textbf{A}$ is chosen to be that of a solenoid ...
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2answers
50 views

Is the magnetic field zero inside an ideal conductor carrying a current? [duplicate]

By an ideal conductor, I mean one with zero resistance. The question is not about a superconductor. As I know superconductor and conductor with zero resistance are not the same thing. The question ...
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0answers
21 views

Electrical field in coaxial cavity

I already asked this question at electrical engineering SE, but I got the recommendation that in the Physics SE there will be a better chance to get answers. I have a geometry as follows: This is ...
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1answer
61 views

How can we detect electric field in electromagnetic wave?

Electromagnetic wave have magnetic and electric component but what is the proof for that? How "non electrostatic" electric field can be detected around coil?
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1answer
27 views

Applying Ampere's Law for Two Parallel Wires

This seems a simple question but I'm not able to understand it properly. Say we have two parallel wires carrying same current I in different directions. We need to calculate the magnetic field at any ...
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0answers
36 views

Experimental tests of electric and magnetic fields in a gravity field

Has anyone experimentally verified that the measured values of the electric and magnetic fields do not change due to gravity, that there is no post-Newtonian effect on the strength of either $E$ or $B$...
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0answers
16 views

Lightning, Electrical breakdown, and Current

Recently a discussion came up about this gif: http://i.imgur.com/r9Q8M4G.gifv This lead to a few questions about electrical breakdown of insulators. The disagreement we're having is whether or not a ...
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0answers
27 views

Can signal transmission from mobile phones affect battery life of other devices? [on hold]

Sometimes I hear that you shouldn't keep devices that contain certain batteries close to your mobile phone continuously since signal transmission can affect the lifetime of those batteries. Is this ...
2
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1answer
44 views

What conditions are necessary for Birkeland currents to form?

If charged particles flow through non-magnetised space will they form Birkeland current? Or can such currents only form along existing magnetic field lines? Part of the reason I ask is this: http://...
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2answers
1k views

If the strong nuclear force is stronger than electrostatic repulsion, why don't nuclei collapse into a point?

Today in class we were discussing the strong nuclear force, and our teacher was explaining about how the strong nuclear force counteracts the repulsion force between protons in a nucleus. When asked ...
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0answers
44 views

Compensating Parallax problem of a washing machine's drum [on hold]

We would know how it is possible inside a washing machine, when the drum is full with garments, so it is very heavy, to compensate, when the drum is rotating at high speed for the parallax of rotation,...
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1answer
66 views

Reflectivity and transmissivity greater than 1

In plasmonics, it is often seen that reflection coefficient and transmission coefficient are greater than 1. How is energy conservation valid in such cases?
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0answers
50 views

High School Physics-Electromagnetism [on hold]

An insulated smooth square frame ABCD of side $a$ is able to rotate about one of its side taken as positive axis. The plane is initially located at x-z plane. A magnetic field present in the region ...
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2answers
42 views

Could a strongly enough charged black hole allow for a strongly charged particle to escape the event horizon?

If there is a strongly charged black hole, and a particle with a strong charge of the same sign goes inside of the black hole's event horizon while moving quickly, is there a reason why it would not ...
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3answers
85 views

Why do magnetic coils consist of many thin wires?

Magnetic coils are usually made of thin wire turned into spring shape: Magnetic field which is generated by this solenoid is proportional to the number of turns N...
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1answer
79 views

Can neutrinos interact by the EM interaction and gravity?

A definition of a lepton is: A particle that does not interact by the strong force but does by the 3 other forces.$^1$ Neutrinos are leptons, so from the above definition one would expect it to ...
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1answer
88 views

Why can't rotating magnets in space or zero gravity be used to create infinite energy? [on hold]

I would like to know if a system like the one below will possibly work. I understand that the laws of physics forbid the "creation" of energy but despite my efforts I haven't been able to figure out ...
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0answers
21 views

Spikes and valleys of ferrofluid

I can understand that the spikes are formed because of the elongation of the ferrofluid due to the difference in forces experienced by the two ends of the particle. But I can't understand why there is ...
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1answer
40 views

Any good electricity and magnetism books for highschool students? [duplicate]

I really want to learn about electricity and magnetism for a long time but never have gotten to it, are there are good books that are conceptual on the topic of electromagnetism? I do not know ...
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2answers
614 views

Does a Faraday cage block outgoing signals?

I see lots of discussions about how a Faraday cage can block EM signals, but almost no one addresses the possible difference between incoming signals versus outgoing signals. It seems to me that those ...
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1answer
47 views

Photons inside laser cavity

In a laser, the pumping mechanism excites an electron to a metastable state. This electron remains in the metastable state for a longer time and is de-excited to the ground state by emitting photons (...
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1answer
42 views

Split up electromagnet coil, put in parallel.Why doesn't anyone do that?

If the goal is to make a strong electromagnet, wouldn't it be wiser to cut the coil in different sections and then connect them to a power source in parallel? total of 2k turns: (+)--- <- 1k -----...
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1answer
32 views

Why is the electric field perpendicular to a circuit zero?

Griffith briefly addresses the uniformity of the electric field in a wire using Laplace's equation by assuming that the electric field is always parallel to the wire (i.e. $\mathbf{E}\cdot\hat{n}=0$). ...
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0answers
22 views

Efficient weak form for numerically generating a static magnetic field from arbitrary current distribution (FEM)

This may stray into computational physics, but I'm curious to know if there is some more efficient way for what I am trying to do. Perhaps a better gauge formulation is needed. Consider two ...
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0answers
36 views

How to understand method of images in electrostatics without much maths

How do you explain Method of images for school students without much maths i.e without boundary condition or uniqueness theorem. If it's not possible what are the rules to be followed to solve ...
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2answers
70 views

Why don't electrons moving around in a orbit produce electromagnetic waves in their natural state? [duplicate]

If moving electrons produce changing electric field, and if changing electric field produces magnetic field, every electron must produce an electromagnetic wave. This means an atom in its natural ...
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1answer
32 views

Can this physical quantity be simplified into a smaller form?

I have a quantity I call fake current. $$ I' = \frac{\mathrm{d} \oint \nabla \mathcal{E} \cdot \mathrm{d} \vec{A}}{\mathrm{d} t} $$ Current is: $$ I = \frac{\mathrm{d} q}{\mathrm{d} t} $$ Charge ...
2
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3answers
474 views

What is the relationship between the magnetic units oersted and tesla?

How are the units oersted and tesla related? For example, how would you express $20\:\mathrm{Oe}$ in tesla?
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0answers
40 views

Why do we assume electromagnetic fields to be doubly differentiable? [duplicate]

It seems like the identities of curl of gradient, divergence of curl, and the simple derivations of electromagnetic waves from Maxwell equations all rely on the symmetry (interchangeability of their ...
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1answer
17 views

What is conductive half space in the context of electromagnetics?

What is conductive half space in the context of electromagnetism? I was looking into skin effect, where the author has used half space of a cylindrical conductor. But I am lost on what it means.
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0answers
41 views

Question about electric flux [closed]

Question: Suppose a point charge is located at the center of a spherical surface. The electric field at the surface and the total flux through the sphere are determined. If the radius of the sphere ...
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0answers
21 views

Can Fluctuation-Dissipation Theorem Apply to Magnetic Forces in Multi-Spin Systems

Let's say I have multiple spin systems (atoms in a protein) in a solution of water and the spin systems are all producing a magnetic field $\mathrm{B_{loc}}$ that affects nearby spin systems. Will the ...
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1answer
68 views

Why a homogeneous magnetic field will not deflect neutrons? [closed]

According to the comments below the answer of the question about Experiments with Alpha particles in a homogeneous magnetic field an inhomogeneous magnetic field will deflect neutrons. Why a ...
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0answers
28 views

I live close to high tension wires and also the rail lines over stevens pass wa. i constantly hear a pulsing hum and feel a vibration [duplicate]

I live very near high tension wires and the railway over Stevens Pass WA. I constantly hear a pulsing hum and feel a vibration could one of theses thing be the cause?
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1answer
37 views

Motion of charged particle in uniform magnetic field

To create a uniform magnetic field I took a current carrying solenoid connected to a battery, then I took a long straight wire connected to another battery, the wire passes from inside the solenoid. ...
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0answers
20 views

Field due to bound charges in matter [closed]

What is the field due to a long cylinder that carries uniform polarization perpendicular to the axis? I am not able to get the answer using the expressions for the surface bound charge density and ...
0
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0answers
21 views

How do I find the force? Is there anything wrong with this question? [closed]

How should I approach this question ? I can not get anything clear from the picture.
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1answer
45 views

Relativity, and Lenz's law with respect to the Lorentz force acting on a wire?

For this system: It's simple for me to predict the induced EMF, and if the wire were connected to a complete circuit(for current $I$ to flow), the opposing Lorentz force($-F$): However, if the ...
-1
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1answer
68 views

Experiments with Alpha particles in a homogeneous magnetic field [closed]

According to this picture the Alpha particles in a cloud chamber are straight lines. https://en.wikipedia.org/wiki/Cloud_chamber#/media/File:Cloud_chamber_bionerd.jpg This is natural because this ...
1
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1answer
41 views

Why don't the nucleus break apart? [duplicate]

The nucleus of an atom is made up of protons and neutrons. So if there are many protons inside nucleus even though there are neutrons why don't this protons may repel away breaking nucleus apart? The ...
1
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1answer
45 views

Speed of electricity in a tangled wire

Most sources claim that the speed of electricity in a wire (or signal/information speed) is the EM wave propagation speed of the metal. What about tangled wires? Am I correct in assuming that for the ...
62
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6answers
7k views

If like charges repel, why doesn't a charge break itself apart?

How can it be that, if like charges repel, they don't repel themselves? In other words, why don't charges break apart? About the possible duplicate: I want to know about charges in general, not ...