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8 views

Show that the electric dipole term vanishes for a particular current

I'm interested to show that given a ring with radius a where there's a current $I_0 \cos \omega t$ ($I_0$ is a constant) there is no radiation due to the electric dipole term (appearing in the ...
3
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1answer
46 views

Eddy currents Vs. Inducing EMF in opposing the change?

In the following circuit there is a power supply applying a voltage(+$V$) to a circuit with resistance ($R$), current($I$) is now flowing in the circuit, and there is a movable part like so: The ...
2
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1answer
37 views

Will two opposing magnetic fields cancel out?

When a conductor induces eddy currents that creates a magnetic field opposing the change that created it, would the two fields at some point cancel out? Imagine the change to be so great, it ...
2
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4answers
219 views

Is Gauss' law valid for time-dependent electric fields?

The Maxwell's equation $\boldsymbol{\nabla}\cdot \textbf{E}(\textbf{r})=\frac{\rho(\textbf{r})}{\epsilon_0}$ is derived from the Gauss law in electrostatics (which is in turn derived from Coulomb's ...
4
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0answers
61 views

What empirical evidence is there for displacement current?

I wonder what more or less direct measurements of the displacement current exist. I know that the existence of em waves demonstrates its existence, though somewhat indirectly. I also know that there ...
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3answers
74 views

In terms of the Ampere-Maxwell law, why is $\vec {E}=0$ in a wire of a capacitor circuit?

I'm currently studying from "Introduction to Electromagnetics" by D.J. Griffiths. In the book the significance of the displacement current term is explained by looking a non-steady capacitor circuit ...
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1answer
35 views

Eddy currents on a conductors surface, and induced current flow in a circuit coexist?

The title seems confusing, because Eddy currents are induced currents... however, let me explain. Assume the following closed loop passing a uniform magnetic field like so: Now, this loop would ...
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0answers
15 views

Surface current density and infinite solenoid

I have an infinitely long cylinder with radius $R$ and axis lying on the $z-$axis, charged with volume density $\rho$ and surface density $\sigma$. The cylinder is spinning with angular velocity ...
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4answers
222 views

Method of calculating eddy currents of a conductor, is this correct?

I have a conductor with volume $V$, passing a magnetic field($B$) with velocity($v$): I'm trying to calculate the Eddy currents to figure out the magnitude of the drag force($F_d$) generated the ...
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0answers
30 views

Two equal charges accelerating parallel to each other

Let's say constant acceleration for simplicity. Ignore possible logistic concerns, such as what is accelerating them or how they stay in path. Lets just assume they are in a conduit made of a solid ...
0
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0answers
24 views

Magnetic field due to current carrying sheet

I have 2 infinite plates (x direction) with the width of A (y direction) and the distance between them is d (z direction). The current density is J on the first plate and -J on the second (the ...
0
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0answers
43 views

Is this a good explanation of electron mobility to the layman?

I'm writing an informative paper on graphene for my writing class (layman-oriented), and was describing electron mobility in very simplified terms. Let me know if anything is mistaken, badly ...
2
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1answer
79 views

Why do high voltage transmission line workers need a Faraday cage suit?

In this video the high voltage transmission line workers are wearing a Faraday cage suit. Why is this needed? Without the Faraday cage, the resistance of the human would be very high compared to the ...
0
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1answer
67 views

How is polarization vector in QFT related to polarization in classical electrodynamics?

As i know in classical electrodynamics polarization shows the orientation of the electric vector in a plane perpendicular to the direction of propagation of light. But in quantum field theory ...
0
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1answer
68 views

How do you take the derivative with respect to a rank two tensor?

I am learning classical field theory and am trying to find the momentum density of the electromagnetic lagrangian as part of an example of Noether's Theorem. The derivative I am encountering is: $$ ...
0
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0answers
30 views

What is the form of the skin effect in exponentially decreasing (or exponentially increasing) voltages?

I tried to replicate the standard derivation of the skin effect for exponentially shrinking or growing voltages (idealize the surface of the wire as a half-infinite volume of conductor) but I'm not ...
6
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1answer
108 views

Why can the Lorenz gauge condition always be fullfilled?

Why is the Lorenz gauge condition always possible for classical electromagnetic fields? So far I can only understand the following: If we perform a gauge transformation $A\mapsto ...
0
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1answer
23 views

Induced current in a loop due to varying flux

Suppose you have a loop of wire beside a infinite long wire carrying a current I. The current in the infinite wire is given by: $$I(t) = I_0(1-e^{(-\alpha t)})$$ Where $\alpha$ is a constant and $I_0$ ...
2
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0answers
42 views

Torque on a wire loop from straight wire [closed]

I need to show that the torque on this wire loop is $$N = \frac{\mu_0}{\pi} 2abdII' \frac{(b^2+d^2)\sin(\theta)}{b^4+d^4-2b^2d^2\cos(2\theta)}$$ The where $\theta$, is the angle between the loop ...
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3answers
133 views

Tricks for evaluating tensor contractions with Levi-Civita symbol

I am trying to evaluate the Lorentz invariant $\epsilon^{\alpha\beta\gamma\delta}F_{\alpha\beta}F_{\gamma\delta}$, where $F_{\mu\nu}$ is the electromagnetic field tensor, $$ F_{\mu\nu} = ...
0
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1answer
74 views

The image current due to moving charges and a current carrying thin wire

Suppose we have a plane conductor and positive charged particles of mass m are moving parallel to the plane conductor at a distance d. The trajectory can be assumed to be straight. An image current ...
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0answers
37 views

Why wouldn't any Emission Theory work?

http://www.pitt.edu/~jdnorton/teaching/HPS_0410/chapters/origins_pathway/#Emission Here, at the Emission theories of light, I loved the discussed theory. There seems to be a contradiction right ...
2
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1answer
65 views

If time-like paths are geodesics, what physical principle applies to space-like intervals?

If I have a number of particles interacting with one another locally, then the center of mass of the system moves along a geodesic. Taking this further with the particles interacting via an EM field, ...
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1answer
35 views

Magnetic flux from an infinit wire through a Square loop [closed]

Okay so I need to solve this exercise. I know that the magnitic field from an infinit wire is given by: $ \vec{B} = \frac{\mu_0I}{2\pi r} \hat{\phi}$, And that I must do an intergral looking ...
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0answers
53 views

Is Jefimenko's assertion regarding E and B fields a physical fact? [duplicate]

Standard textbooks says: "Time varying Electric field and magnetic field produce each other". But Oleg Jefimenko says NO to this. Who is correct: standard textbooks OR Jefimenko ? Both can not be ...
2
votes
1answer
93 views

Is it true that the self-force prevents a classical particle from falling into a Coulomb potential? What is the physical explanation of this result? [closed]

In 1943 CJ Eliezer published a paper claiming that the self-force prevents a zero angular momentum particle from ever reaching the center of an attractive Coulomb potential (and what's more that it ...
0
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1answer
61 views

What is space charge and how to calculate it?

I want to clarify the meaning of space charge. What I know is that the space charge is the total charge in a small region in space. I really confuse this in the ion beam context. Many text book says ...
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0answers
52 views

Meissner effect and levitation

In a field less than critical field, decreasing the temperature below the critical temperature will eliminate the magnetic field inside a superconductor and increase the magnetic field around it. ...
2
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0answers
72 views

Perpetual motion in electric dipole restricted to a circular path with a charge at the centre

This problem is from Griffith's Introduction to Electrodynamics (4th Ed.), Problem 4.31. A point charge $Q$ is "nailed down" on a table. Around it, at radius $R$, is a frictionless circular ...
2
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1answer
39 views

Point charges in a sphere

If we put N point charges (with charge +q) in a sphere with radius R and the charges can move freely in the sphere but can't get out of it, where will the charges go to and what will be the ...
2
votes
1answer
46 views

Are energy and momentum separable for EM waves

Everywhere I get to read statements like EM radiations and EM fields carry "energy as well as momentum " . I wonder if energy and momentum are inalienable . Is it possible for a field to carry only ...
0
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1answer
49 views

Aharonov-Bohm experiment: A possible way to understand potentials?

I'm posting this question as a function of an another question I found here: What is potential energy truly? The answer of WetSavannaAnimal aka Rod Vance. As I understand the hole point is to see ...
2
votes
1answer
57 views

Time changing potential gives rise to “force”?

Imagine a charged particle inside a Faraday cage (i.e. charge on outside, zero electric field inside, but non-zero electric potential on the inside). Suppose the charge distributed on the outside of ...
6
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3answers
97 views

Why isn't it obvious that a particle doesn't interact with its own field, classically?

The Wheeler-Feynman absorber theory or any other theory that tries to avoid the notion of field as an independent degree of freedom has always been concerned about infinite self energy of a charged ...
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1answer
41 views

Question regarding charge and acceleration

From a stationary charge electrostatic fields arise. From a moving charge, magnetostatic fields arise. From an accelerating charge, EM waves arise. So i wonder -- what about a non-constantly ...
0
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0answers
49 views

Direct interaction theory

I got to know about a kind of theory or formulation of EM which doesn't have the idea of fields in it. In that theory I guess field isn't that which mediates the force between two charged particles. ...
4
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4answers
211 views

A current through a wire produces a magnetic field around it. Is the reverse possible?

If somehow a magnetic field around a wire can be made to exist that is identical to the magnetic field produced when a current passes through the wire, will a current be produced in the wire?A thought ...
1
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2answers
77 views

What actually is a continuous charge distribution? [closed]

I am well aware of the maths of how to do all sorts of calculations using continuous charge distributions (like volume, space, and, line charge distributions) but when I think about it I couldn't get ...
3
votes
1answer
198 views

Charged particle under a uniform electric field

Suppose a charge particle $q$ starts to move without initial velocity under the influence of a uniform electric field $E$ pointing in the positive $x$ direction. Express its position vector in ...
3
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1answer
123 views

Induced magnetic field produces electric field and vice versa forever!

So here are the two of Maxwell's laws that I am interested in: So we have the simple circuit (from google): So, before the system goes into steady-state we know that charge slowly accumulates on ...
0
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0answers
15 views

Can TEM waves have constant offsets - that is, mean of non-zero in context of Poynting's theorem?

Suppose the electromagnetic wave and the corresponding magnetic field wave are TEM waves. Can such waves have overall mean of non-zero? (so DC offset) If they do, what do they mean in context of ...
0
votes
1answer
72 views

What do we mean with magnetic monopole and dipole?

What do we mean with magnetic monopole and dipole? I can not find a way to relate magnetic monopoles and dipoles with electric ones. I do not understand their outcomes. Also,what is their role in ...
1
vote
1answer
63 views

Induced potential difference paradox

So,i was studying from some lecture notes from MIT's open course program,and i stumbled across this example The example says:The solenoid is so long that its external magnetic field is negligible. ...
1
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2answers
81 views

Induced emf problem

This is not homework question,just a thought experiment about a general question i have about induction. Let's suppose that we have a closed circuit with only two resistors in series.We also have a ...
0
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1answer
38 views

How is the field of a non-moving charge static if field changes propagate only at the speed of light?

Let us consider a charged particle which is static with respect to a frame of reference $A$. Now suppose that I accelerate the charged particle to a speed $v$. Now when I accelerated it to a speed ...
2
votes
2answers
62 views

Can an electron borrow momentum from its field?

Let us consider a charged particle moving with uniform velocity $v$. We know that the EM field due to it has some momentum too. If the mass of the particle is $M$, then the momentum of the particle is ...
2
votes
3answers
66 views

movement of particles in electric field

I am confused about a homework problem. Let's assume we have two electrically charged particles of which we know the charge and mass respectively. Let's say that at first they are fixed at some ...
1
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1answer
87 views

The interaction of a charged particle with its own field

I have seen other questions regarding the mentioned topic. I want an answer to be different in some ways from the answers that were posted in response to the related questions. What exactly are ...
1
vote
1answer
44 views

Ampere's law, do I include the electric field causing the current?

Let's say I have a long, straight wire with a time varying current, $I$ through it. Now if I take a circular Amperian path around this loop wire (and concentric with it) there is both a current $I$ ...
0
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2answers
24 views

Different kinds of time varying EM fields and difference in the way they transfer energy

Instead of broadening up the scope of answer , I would like to divide this question into two parts without any introduction . 1) Do all the time varying EM fields have the ability to transfer energy ...