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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4
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2answers
339 views

What is happening to the electrons, and E & H fields, in an antenna with a standing wave inside?

Diagrams like the one shown below are often shown to explain antenna theory, but I have always had problem with the concept of voltage being a wave, and because of this the diagrams never make any ...
3
votes
6answers
9k views

How does a spinning electron produce a magnetic field?

I learned in my undergraduate physics class that atoms have magnetic fields produced by the orbit of electrons and the spin of electrons. I understand how an orbit can induce a magnetic field because ...
7
votes
1answer
171 views

Electron in the proximity of a magnetic monopole

I am puzzling about an exercise in the book "Electromagnetic Theory" by Ferraro (p.543). An electron (mass $m$, charge $-e$) in a monopole magnetic field ...
9
votes
1answer
147 views

Optical chirality and its possible hierarchy of generalizations

Optical chirality refers to a constant of motion of the electromagnetic field, which measures in some sense how chiral a light field is. Specifically, the pseudoscalar quantity $$ ...
1
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2answers
494 views

Reducing Eddy Currents?

A conductor that passes a magnetic field, decreases its velocity due to the opposing magnetic forces created by the Eddy Currents. This "magnetic breaking" effect can be reduced if we change the ...
0
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2answers
129 views

Is light electromagnetic waves or quantumn particle waves? [duplicate]

Is light electromagnetic waves or quantum physical particle waves. Or are they the same? Note: My question is specifically how electromagnetism plays into the quantum physics and the double slit ...
1
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0answers
58 views

Electric field due to charge in one direction

I am supposed to calculate the electric field due to the charge density $\rho(x) = Ax e^{-\lambda |x|},$ where the density is supposed to be homogenous in $y,z$ direction. The problem is, that the ...
0
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0answers
148 views

Does the Fringe effect occur in capacitors in the interdigitated form?

I am currently doing my undergrad dissertation on graphene supercapacitors. I have read that the fringe effect is a well established phenomenon on parallel plate capacitors, but does it also occur in ...
1
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1answer
2k views

In which direction does the current flow in a wire moving north to south along the Earth?

I stumbled upon this question and I can't seem to figure it out. I think you have to use the right hand rule, but it doesn't get me the right answer. The question is something along the lines of: ...
13
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1answer
640 views

Physical Interpretation of EM Field Lagrangian

Using differential forms and their picture interpretations, I wonder if it's possible to give a nice geometric & physical motivation for the form of the Electromagnetic Lagrangian density? The ...
2
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1answer
197 views

Confusion with curl of Lorentz magnetic force

Since the magnetic force is a no work force, $dW=\vec F\cdot d\vec r=0$ for $\vec F(\vec r)=q(\vec v(\vec r) \times \vec B(\vec r))$, therefore $\oint \vec F \cdot d\vec r=0$ by Stoke's theorem. ...
1
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2answers
127 views

Eddy currents and EMF?

Im confused, can both phenomenons happen at the same time?! A conductor the passes a powerful magnetic field at extremely high speeds, will induced EMF AND Eddy currents simultaneously?!
2
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0answers
113 views

Deriving the relativistic Larmor equation

I have derived the Larmor equation as $$P = \frac{q^2}{6\pi \epsilon_0 c^3} |\ddot{r}|^2.$$ How do I make this relativistic? Apparently, I have to consider the acceleration parallel and ...
2
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0answers
65 views

Is a magnetic field just a moving charge? [duplicate]

I am trying to understand electromagnetism. I would like to pare myself down to the minimum number of necessary concepts. From my physics education (high school only), I understand that a moving ...
2
votes
0answers
35 views

How do the single photon energy and em-signal energy correlate? [duplicate]

If the photon (as a quantum of the electromagnetic field) has no defined(?) amplitude, how does (or where from?) the electromagnetic wave's amplitude appear? The formulation of the question is not ...
20
votes
6answers
2k views

Could a hard drive actually have been erased as described in Cryptonomicon?

In chapter 80, The Primary, Neal Stephenson has one of his character describe how the drives of a computer carried through a door (by the police, who where raiding the facility) will have been erased. ...
0
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0answers
47 views

Laminations and current capacity,

When a conductor that's purpose is to carry current ,is laminated to reduce eddy currents, does it affect the current capacity for that same conductor? Will it reduce the current capacity?
2
votes
3answers
98 views

Is dimensional analysis always sufficient to establish equivalence of quantities?

In dealing with the Biot-Savart law, it was argued that $$ q\frac{d\vec{s}}{dt}\equiv Id\vec{s} $$ using the fact that the units are equal. Does this kind of argument always work? It seems too ...
3
votes
2answers
164 views

When to use which representation for an electric field

In class we covered three types of possibilities to evaluate the electric field for static problems. Unfortunately, most physics textbooks cover these ways without addressing the question of ...
0
votes
2answers
233 views

Magnetic field resistance material: are there any? [duplicate]

I was wondering with a question for a quite long time, thought to ask here. I need to know is there any material or element which can block magnetic field? I mean I am searching for such material or ...
4
votes
2answers
243 views

Why can't an excess of electrons or holes by themselves cause current flow?

I am a beginner in electrical engineering. Often times (most cases actually), the underlying physics aren't really explained to us and we are just left to assume that it works "because it works." This ...
1
vote
0answers
29 views

How might inducted current/ voltage in multiple coil layers connected in parallel behave?

This is a branch from this question. In the event that two or more layers are connected in parallel - would the energy created across each layer likely be significantly less? In the event of (say) ...
1
vote
1answer
127 views

How might eddy currents and terminal velocity be broken down?

This is a branch from this question. With regards eddy currents and terminal velocity I have located a homework question but would appreciate more detail (and translation of the symbols described ...
0
votes
1answer
272 views

Magnetic Induction - How would different coil configurations affect the outcome?

This is a branch question (from this question) related to magnetic induction: These deal with how different configurations of coiled layers might affect the outcome: If one were to bundle multiple ...
3
votes
3answers
2k views

Is an electron attracted to one of the magnetic poles in this scenario?

Do magnets attract electrons? I don't think so, but maybe in certain cases they can be? I guess it would depend on what direction the velocity and magnetic field is in so that the force acting on the ...
3
votes
1answer
109 views

What does $\int_C V \,d\mathbf{l}$ mean?

What does $$\int_C V \,d\mathbf{l}$$ mean? I initially thought it was simply a line integral around $C$, that is, if $\mathbf{r}: [0,1] \longrightarrow \mathbb{R}^3$ is a paremetrization of $C$, then ...
6
votes
2answers
778 views

Analogy between fluid dynamics and electromagnetism

I've been reading a set of notes (Chapter 13 of Caltech Ph 136 notes from 2004, by Blandford and Thorne) that draw an analogy between fluid dynamics and electromagnetism, identifying the magnetic ...
2
votes
2answers
184 views

$E,H,\rho,\vec{j}$ intensive? $B,D,\Phi,\vec{A}$ extensive? Why not $ DdE,BdH ,\Phi\delta\rho,\vec{A}\cdot \delta \vec{j}$ as infinitesimal work?

$u$ is the e&m field energy $\frac{\partial u}{\partial t}=H\cdot \frac{\partial B}{\partial t}+E\cdot \frac{\partial D}{\partial t}$ Compared with thermo physics: $PdV,TdS,\mu dN$ ...
2
votes
1answer
260 views

Jiles-Atherton model of hysteresis

In my quest for finding a good algorithm to draw hysteresis curve,I have found Jiles-Atherton model which seems to be a rather new model. But I have trouble understanding some of the ...
3
votes
4answers
745 views

Electromagnetic factors affecting inertial mass of a body affect its gravitational mass or not?

We can see that when a charge sphere is at rest & we are to put it in motion with any desired velocity than we will have to apply the same force for a longer time as if it were applied to the ...
0
votes
2answers
3k views

Landau Levels and Magnetic length

I am looking into Landau Levels and keep coming across a magnetic length defined as follows for a 2D system: $l_B=\sqrt{\frac{\hbar c}{e B}}$ I have seen numerous sources say this is: $l_B\approx ...
1
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0answers
715 views

Hysteresis Curve and how to implement it using Preisach model or other models

As a homework I need to draw a hysteresis curve (preferably an interactive one) using Matlab or any other programming language. The problem is I have trouble finding a good algorithm to do so. I need ...
3
votes
1answer
757 views

What does “optical conductivity” mean?

Does it just mean "AC electric conductivity"? If so, why have a special name for it, and why mention optical specifically? The wikipedia page on it is very sparse. This (warning, PDF) document just ...
0
votes
1answer
90 views

Electric field and magnetic field question here?

Are the energy of the electric field and the energy of the magnetic field concentrated on their sources OR are they scattered in the environment where the fields arent zero? Can you base your answer ...
-1
votes
1answer
274 views

Application of Displacement Current

I'm reasonably happy with the derivation and results of displacement current, however, I'd like to be aware of a few practical applications of this idea. So far, the only one I'm aware of is when ...
2
votes
2answers
113 views

What is $\epsilon_\infty$ in this equation and why can it be neglected in the IR?

I'm reading this paper (warning, PDF) and they mention that the complex permittivity $\epsilon$ and complex conductivity $\sigma$ are related through the equation $$\epsilon - \epsilon_\infty = (4\pi ...
1
vote
0answers
44 views

Could a strong AC electric field adversely affect the capacity of a lithium battery?

I run some battery powered test equipment in close proximity (~10cm) to a conductor carrying 25kV (50Hz AC). I find the battery life is much shorter than expected, having checked the current ...
3
votes
1answer
134 views

Solving non-linear ODE for divalent solution at a 1-D surface boudary

I am trying to solve the following equation for a positively charged plane with charge density $\sigma$ at $z = 0$. $$ \phi''(z)=-\frac{e}{\epsilon \epsilon_0} \big(z_+n_{+} e^{-\beta z_+ ...
42
votes
7answers
20k views

Does electricity flow on the surface of a wire or in the interior?

I was having a conversation with my father and father-in-law, both of whom are in electric related work, and we came to a point where none of us knew how to proceed. I was under the impression that ...
4
votes
1answer
400 views

DC current in ideal conductor and skin effect?

I know that the skin depth derived for AC current goes as $$\delta \propto \sqrt{\frac{1}{\omega \sigma}}$$ where $\omega$ is the angular frequency of the field and $\sigma$ is the conductivty. Now: ...
3
votes
2answers
101 views

Associated Legendre Integer Giving Full Asimuthal Range and Physical Interpretation of $l(l+1)$

In separating the Laplacian in spherical coordinates, one arrives at the associated Legendre equation (ALE). Write the ALE as $$\frac{1}{\sin \theta} \frac{\partial }{\partial \theta}(\sin \theta ...
0
votes
2answers
146 views

Inductor's energy

I have some knowledge about LC circuits, like I know Maxwell's equations, the differential equations of circuit oscillator and so on. I am armed with equations to solve physical problems involving ...
2
votes
1answer
81 views

How is “Band Intensity” related to absorption coefficient

I am interested in the linear absorption of 762nm light near a transition of molecular oxygen. I need to find some experimental numbers that will tell us how far the 762nm light will propagate before ...
0
votes
1answer
182 views

Transverse part of a current

I am reading Many particle physics (3rd edition by Mahan). On page 51, there is a current of the form $$\vec{j}(\vec{r})=\vec{J}_0e^{i\vec{k}\cdot\vec{r}}$$, the transverse part of it is: ...
1
vote
1answer
2k views

Would two Neodymium magnets stick together with twice the power?

Assume I use a coil to create B-flux and put ONE Neodymium cylinder magnet (1" diameter & 0.25" thick) close to the flux, it would create 10 lbs of force. Does that mean that putting TWO cylinder ...
3
votes
1answer
320 views

Understanding Poynting's Theorem intuitively

I understand that, broadly speaking, Poynting's theorem is a statement of conservation of energy. Energy density of a volume of current and charge decreases proportionally to work done on charges ...
1
vote
1answer
97 views

Calculate energy from vacuum electromagnetic-field action

I'm reading Rubakov's "Classical Theory of Gauge Fields", and I'm having a little bit of trouble with problem 7, p 15: Using an expression of the type $E = \int d^{3} x \frac{\delta L}{\delta ...
0
votes
0answers
175 views

Determining the path of a particle in a velocity selector

I am wondering how you can determine the path of a particle in a velocity selector provided its velocity doesn't equal $ \frac{E}{B} $. I understand that the equation is derived from this force ...
1
vote
2answers
316 views

Faraday's law and “infinite induction”

I may have confused after thinking too much about Faraday's law. If an emf is induced in a circuit due to some changing magnetic field, the induced current will be in a direction such that the ...
2
votes
1answer
225 views

Walter Lewin's lecture on Faraday's law

In Walter Lewin's lecture on Faraday's law, he does a demonstration with a solenoid where he shows that current is induced in a loop that surrounds the solenoid as the magnetic flux is changing. He ...