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2
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3answers
46 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 ...
0
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0answers
22 views

Complete equations of motion in the scattering problem [on hold]

How to derive the complete equations of motion for an electron scattered by a proton using Lagrangian formalism?
1
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1answer
43 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
30 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
23 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 ...
1
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0answers
30 views

Electric field in a hollow object

I am currently visiting a course about electrodynamics. In my last lecture it was said that if a hollow sphere is inside of a bigger sphere, but only in the bigger sphere there are charges, the ...
2
votes
2answers
60 views

Classical Hall effect when current has neutral charge

Suppose I have a current of both negative and positive charges(I know that there is also current from only negative and only positive charges,I'm not confused) along an infinite wire of square ...
1
vote
1answer
34 views

Signs in derivation of capacitor discharge differential equation

In deriving the discharge current for a capacitor I have seen two different approaches: By Kirchhoff's law we have: $$ \begin{align} 0 &= I R + \frac{Q}{C}\\ \implies 0 &= \dot I R + ...
2
votes
1answer
39 views

Momentum carrying fields

Through some of my recent questions I have come to know of fields as an agent which can act as momentum . What is the correct physical picture that I should derive from statements like this ? Where ...
3
votes
6answers
649 views

Is electromagnetic vector field a sum of E and B?

I have a hard time to fully understand (classical) electromagnetic field theory with respect to Helmholtz's decomposition. Let me start from Helmholtz's theorem: Any vector field of class ...
0
votes
1answer
31 views

A static electron and a radiating electron

Let us consider an electron A, which is at rest in one frame of reference and another electron B which is accelerating in that frame of reference. Now the fields due to electron B are time varying . ...
2
votes
0answers
49 views

Motion of a charged particle in a “solid” charged sphere (accounting for radiation)

Consider a particle (point charge) with charge $q$ and mass $m$ that crosses into a uniformly charged sphere (with charge $Q$ and radius $R$). The trajectory of the particle is a diameter of the ...
0
votes
0answers
12 views

Electrodynamics of a single ion transport between a dielectric slab

I am trying to solve the mean passage time for a single solvated ion to diffuse through a pore. This pore is surrounded by the medium with a low dielectric permittivity, i.e. around 10. The solvent ...
1
vote
1answer
52 views

EM radiation explanation [duplicate]

Why is it so that a charged particle when accelerated radiates energy? I tried to think if it might be violating the law of conservation of energy but the energy transferred by the external agent may ...
4
votes
1answer
49 views

Does a magnetic field decrease or increase entropy?

My question is just the title: Does a magnetic field decrease or increase the entropy of a system? For example if we apply a magnetic filed to a substance, is the entropy decreased or increased?
-1
votes
2answers
84 views

Electric field 0 everywhere inside Gaussian surface

Gauss's Law shows that the electric field everywhere inside a spherical shell of uniform charge density is $0$. Suppose we have a surface which divides space into two disjoint regions (an interior and ...
0
votes
0answers
25 views

Interaction between charged particles as seen from two inertial frames of references

Let us consider two charged particles travelling at a uniform velocity, V, as seen from a frame of reference A . Now let us consider a frame of reference, B, which is also travelling at a uniform ...
0
votes
1answer
29 views

potential inside a cylindrical shell in terms of the surface potential?

Given a potential distribution $V(\phi)$ at the surface of an infinite cylindrical shell, is there an easy way to derive the potential inside the cylinder. No charges or currents anywhere.
1
vote
3answers
120 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 ...
2
votes
2answers
135 views

Magnetic field due to a charge having uniform velocity

Faraday's law states that "Any change in electric field induces a magnetic field and vice versa". I don't see exactly where these fields are induced, but I assume that these fields are induced at each ...
1
vote
1answer
275 views

What's the reason behind calling cathode rays tube by the name cathode?

I do believe that maybe due to the accumulation of negative electron on the metal surface so we called it cathode. But the thing is that we have studied that regardless of the polarity, the cathode ...
0
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0answers
42 views

What are some open problems in classical electrodynamics? [duplicate]

I am about to finish reading 'Introduction to Electrodynamics' by David Griffiths. Throughout the textbook, Griffiths makes frequent references to current literature (mostly articles from American ...
0
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0answers
22 views

Anyone know of a flow chart or list of common/useful consequences of Maxwell's equations?

I just recently started to appreciate the Maxwell equations. I had never really take the time to study them but I feel like I'm finally more familiar with them. I've noticed that it seems like a lot ...
1
vote
1answer
49 views

What are some practical things one can do with classical electrodynamics and QED?

Many basic types of physics have ready and obvious everyday applications. For instance, basic electromagnetism vector calculus can give great insights into how something as simple as a bar magnate ...
1
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0answers
28 views

Can a charge moving in an open trajectory qualify as current?

It is sometimes said that a point charge is equivalent to an electric current. If it were a steady current, I should be able to find it from Ampere’s law or Biot-Savart’s law. Even if the current is ...
6
votes
2answers
328 views

Evidence for electrodynamics in curved spacetime

Field theories in curved spacetime is usually formulated by integrating their Lagrangian over the curved spacetime. For example, for electrodynamics, we have the action $$ S = \int d^4x \left( ...
1
vote
0answers
43 views

Equivalence of integrals in Classical Electrodynamics

I have a technical question about a section from Jackson's Classical Electrodynamics 3rd ed. In chapter 14, Jackson derives an expression for $ \frac{d^2I}{d\omega d\Omega} $, the frequency spectrum ...
0
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0answers
40 views

A question about the chapter 6 of jackson?

This is what explained in answer for part b of exercise of 6.1 of Jackson. This represents a plane traveling in the positive x direction and a plane traveling in the negative x direction, both ...
0
votes
0answers
32 views

Deriving Lorentz force on a point charge moving perpendicular to external magnetic field using Maxwell stress tensor?

I heard that when we use Maxwell stress tensor to derive Lorentz force on a point charge moving perpendicular to external magnetic field, the result is not $qvB$ but $\frac{2}{3}qvB$. This should be ...
1
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0answers
37 views

Help understanding electromagnetism integral from exercise in MTW? [closed]

I was skimming through Misner, Thorne and Wheeler's book Gravitation looking for exercises to challenge myself with and came across the following exercise on page 178: Verify that the variational ...
2
votes
1answer
93 views

Why is there no induced electric field in the experiment (Faraday's Law)

Below are three circuit diagrams for each of Faraday's experiments that allowed Faraday to come up with Faraday's Law. In Griffiths' Introduction to Electrodynamics Griffiths states (on page 302 of ...
0
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0answers
45 views

Time reversed Abraham-Lorentz reaction force

The Abraham-Lorentz radiation reaction force on a charged particle is given by: $$\mathbf{F_{rad}} = \frac{q^2}{6\pi\epsilon_0c^3}\mathbf{\dot{a}}$$ I understand the situation where one fires a ...
1
vote
2answers
80 views

Why does the classical electrodynamics Lagrangian density equation have a “field” term and an “interaction” term?

On Wikipedia's page on classical electrodynamics, they state the Lagrangian density equation as follows \begin{equation} \mathcal{L} = \mathcal{L}_{\text{field}} + \mathcal{L}_{\text{int}} = ...
2
votes
1answer
117 views

Falling charged objects: energy conservation paradox?

Imagine that we start with two oppositely charged objects on the ground, separated by a distance $d$, with charges $+q$, $-q$ and masses $m$. We raise them both up to a height $h$. In doing so we ...
5
votes
1answer
97 views

Time reversal in classical electrodynamics

It is known that classical electrodynamics is time reversal invariant if one assumes that the transformation laws under such operation are $$\mathbf E(t,\mathbf x)\mapsto\mathbf E(-t,\mathbf x)$$ ...
3
votes
1answer
483 views

Width of a photon. And its length

Everyone is always talking about photon's wavelength. But what about its dimensions? What is length and width of it? And does it even have a point to think about such things? Or those dimensions are ...
0
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0answers
23 views

Charge movement in a rotating EM field (relativistic)

I have this problem let's see if anyone can help me advance a little. (No need to say that if my approach is ridiculous or too hard and anyone knows a better solution, I would like to know it). I ...
0
votes
1answer
40 views

Plasma frequency

I have a neutral plasma and I need to solve Maxwell equations given the charge and current densities on the plasma. In order to do it I need to know the electrical permittivity $\varepsilon$, I've ...
9
votes
2answers
128 views

Is the electromagnetic mass real?

In his Lectures on Physics vol II Ch.28-2 Feynman calculates the field momentum of a moving charged sphere with charge $q$, radius $a$ and velocity $\mathbf{v}$. He finds that the total momentum in ...
0
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0answers
10 views

Force on a small conductor in an EM wave

What forces act on a small, flat conductor subjected to electromagnetic radiation, if the conductor is much smaller than the wavelength? My guess is that the magnetic field component of the wave ...
1
vote
2answers
99 views

Energy conservation in electrodynamic system?

Consider two charged particles initially at rest in the configuration below. Let us assume the following: Starting at time $t=0$, we apply a constant force $f$ to the the bottom particle so that ...
1
vote
1answer
22 views

Non-constant potential distribution

I know that given a static charge distribution, the closed loop integral of the electric field is zero. But what if the charges are moving, i.e, the potential at a point a changing. Is the line ...
0
votes
0answers
40 views

Electric and Magnetic Field Created by Moving Electron

From a classical perspective, what are the electric and magnetic fields created by a single electron, initially located at the origin and moving along the $x$ axis with velocity $v \ll c$? I'm ...
0
votes
1answer
69 views

Momentum around an accelerated electron

Assume that an electron is accelerated along the +x-axis. The electron will radiate electromagnetic energy and momentum in every direction. But it seems to me that the EM momentum it radiates in ...
0
votes
0answers
27 views

Electromagnetic induction inside cylinder

Suppose we have a hollow cylinder whose walls conduct some alternating current. We also have a round wire inside cylinder with same axis as that of cylinder so my question is that can there be ...
2
votes
1answer
169 views

Poisson's equation for time dependent charge

Is Poisson's equation valid for a time dependent charge density? I think Poisson's equation is valid just for electrostatic fields. But I saw a paper that's used this equation for time dependent ...
1
vote
1answer
102 views

Why doesn't magnetic forces on current carrying wire depends on relative velocity?

We know that magnetic field arises due to relative velocity of charged particle . Electrons in wire move at very slow drift velocity but relativistic variation of magnetic field doesn't seem to apply ...
1
vote
2answers
76 views

Can magnetic force do work? [duplicate]

I have been told numerous times that magnetic force do no work at all but I have some trouble digesting this fact. Now suppose we have two straight wire with some current, they certainly can feel ...
1
vote
1answer
57 views

Induced electric field due to a moving wire

An infinite wire carrying a constant current $I$ in the $\hat{z}$ direction is moving in the $y$ direction at a constant speed $v$. Find the electric field, in the quasistatic approximation, at the ...
0
votes
2answers
61 views

Could we describe acids and bases using electromagnetism?

Why don't we use Maxwell's equations in acids and base theory? Surely the interaction between two charged species is readily described by this. The theory I have so far come across is HASB theory. ...