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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68 views

Why monopole does not radiate energy in electodynamics?

Why there is no monopole radiation in Electromagnetic field? I read somewhere that it is impossible because it violates charge conservation. I don't understand how? How charge conservation gets ...
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3answers
67 views

Potential due to a continuous charge distribution on ring

Derive the formula for the potential at point $P(0,0,z)$ directly above the center of a ring of charge with radius $R$ and uniform charge density $\lambda$. My attempt: Since $$\lambda= ...
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0answers
17 views

Effective magnetic moment

How can one calculate effect moment from susceptibility (SI*10^6) versus temperature (K) graph? What is the typical range of effect moment for ferromagnets?
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1answer
105 views

Why can we detect a magnetic field, but not an electric field around an AC current?

Consider a wire through which an AC current is passing. Because of the AC current there is an alternating magnetic field present around the wire and because of the alternating magnetic field there ...
0
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1answer
48 views

Question about one of the problems of the Bohr model

This is probably extremely basic physics that I don't know, but I'm still going to ask: Say in hydrogen, according to the Bohr model the electron is "really" orbiting the proton, and as a consequence ...
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1answer
34 views

Electric field of a finite, conducting plate

let's assume a finite, conducting plate of dimension: 10m x 10m x 1m. I want to determine the electric field at the middle of one of the plates 10m x 10m surfaces. Using Gauss's law one finds the ...
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1answer
40 views

Field and Charge densities in two dimensional corners and along edges

In jackson's book, we can derive the equation as following. $\sigma(\rho)=\epsilon_{0}E_{\phi}(\rho, 0)\approx-\frac{\epsilon\pi a_{1}}{\beta}\rho^{(\pi/\beta)-1}---(2.75)$ My question is there are ...
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2answers
57 views

Equivalent formulas for electric current density

I am reading an article that states that the "ratio of current to the area for a given surface is known as current density" and is defined as $J = \frac{I}{A}$ where $I$ is the current and $A$ is ...
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1answer
44 views

Superconducting electromagnets?

Is it true that superconducting electromagnets don't need any power? So... energy to created a magnetic field via a superconductor would be zero? Since resistance is zero, does that also mean that ...
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2answers
28 views

Explain the concept of “accumulated momentum” for an electron

I need someone to help me understand this equation: $ \Delta p = qEt$ where $q$ is the charge, $E$ is the electric field and $t$ is in seconds. I thought that we were supposed to write momentum in ...
4
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3answers
142 views

Deriving Heaviside-Feynman formula for the electric field of an arbitrarily moving charge from Lienard-Wiechert potential

I've been trying to derive this (which Feynman warns takes a lot of work) for a couple of days now, without success. My current best derivation which however doesn't give the right answer is: First, ...
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0answers
74 views

Problem in Classical electrodynamics Jackson

There are two problems. On page 35, Jackson try to use scalar potential that satisfy the poisson's equation. But, i completely lost the step.    ...
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0answers
33 views

Electrodynamics boundary conditions with complex $\epsilon$ and $\mu$

I wonder if the usual derivation for boundary conditions at an interface given in EMT textbooks hold for complex permittivity and/or permeability? Do the fields carry phase information themselves(i.e. ...
2
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1answer
69 views

Lagrangian density for the electromagnetic field

I want to know how the Lagrangian density for the electromagnetic field is written in the following form:
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1answer
57 views
1
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1answer
60 views

Show that $\mathbf{A}$ is a valid vector potential [closed]

Is $$\mathbf{A} = -\frac{1}{2}\mathbf{r \times B}$$ a valid vector potential in the Coulomb gauge? Here's my work so far. Using the identity for the curl of a cross product I get ...
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0answers
26 views

Magnetic field of a living human [duplicate]

Is it true that a human body is like a bar magnet? Say our head is north pole while the legs are south pole, or vice versa? If so, can we confirm it by experiment say with the 360 Pro compass etc?
3
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4answers
139 views

Apparent Contradiction with Faraday's Law

Say we have a non-uniform magnetic field that is static in time. Specifically, let's make it: $\overrightarrow{B}(x,y,z) = x \hat{z} $ Now say we have a metal loop in the xy plane which has a ...
0
votes
1answer
81 views

Electromagnetic induction creates a current with a Lorentz force?

The induced electromotive force (emf) and thus current in a circuit is equal to the time rate of change of magnetic flux link with the circuit. The direction of the induced emf or the current is such ...
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1answer
48 views

if light is electromagnetic then can light produce electricity or attract metals

what I mean to say is that if light is electromagnetic in nature then shouldn't it show electric or magnetic properties on matters? Like if light falls on a metal it should produce current due to ...
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0answers
35 views

Would a portable superconducting coil “battery” be impractical due to magnetism?

I'm working on a science fiction story idea, and trying to make sure I get all of the physics right. One of the concepts I'm using is superconducting coils as "batteries," because they can store huge ...
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0answers
17 views

Does Dowell's Method of determining losses include winding losses?

Dowell's Method of determining losses uses the DC resistance of the portion of wire in the equation, however does this give the total resistance of the wire? Or only the resistance due to the ...
0
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2answers
32 views

Isn't the inductor equation negative?

The inductor "resists" change in current. So say you measure the voltage across the inductor from point A to point B - the current is flowing in from A towards B. Now say the current is increasing. ...
5
votes
1answer
79 views

Can an analog to the Meissner Effect be proposed for matter and gravitational fields?

In the study of electromagnetic fields and quantum electrodynamics we observe and theorize on the behavior of superconductivity and the Meissner effect. Has an analog of these behaviors been proposed ...
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0answers
25 views

Calculating Velocity in motional EMF

To calulate motional $\epsilon$, we use the following formula: $\epsilon$ = $-vBL$ What is the proper formula from what is below to calulate the velocity of a conductor moving in a magnetic field? ...
7
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2answers
509 views

Why are EM waves transverse?

I was reading Griffiths' Introduction to Electrodynamics, specifically the section on plane waves. I can see that if we want a transverse wave traveling in the $z$ direction that we are only going to ...
2
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0answers
68 views

Odd experiment results (electromagnetics)

Okay, a bit of background. So I'm working on a linear accelerator (you might know it as a Gauss rifle), and I had worked through the equations I thought I needed (Magnetic force, displacement, etc.) ...
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0answers
17 views

Longitudinal dielectric wave does it exist in charge free region?

can we transmit energy through Longitudinal dielectric wave when the surrounding is charge free. Please give me a good link about L.M.D. I a beginner about this topic.
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2answers
95 views

What does a relativistically moving capacitor “look” like? [duplicate]

Suppose I have a parallel plate capacitor with a vacuum between the plates, a voltage $V$ across them and a capacitance of $C$. What will this arrangement look like to an observer in a uniformly ...
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1answer
26 views

why an immersion lens is called so in Ion Optics?

In Ion Optics, an immersion lens is composed of two planar apertured electrodes. My question is why it is called an 'Immersion" lens? I know that an Einzel lense has three or more electrodes. But ...
0
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1answer
97 views

Description of the motion of the COM of a system of charged particles moving in a magnetic field

I recently came across a problem where an electrically neutral particle is at rest in a uniform magnetic field. The particle now splits into two charged particles of equal mass $m$; charge and mass ...
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2answers
89 views

Is this an example of Parity violation? [duplicate]

I always hear about parity violation in high energy physics, but what about examples in classical physics? Say we have a wire carrying current in the $+x$ direction, thus generating a magnetic field ...
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1answer
37 views

What is the dormant common ground between harmonic mechanical oscilators and electromagnetical ones?

When I learnt electromagnetic oscillators I couldn't help but notice that it has many common stuff with mechanical ones. I know that it had to have sinusoidal equations. I (firstly, without ...
0
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3answers
115 views

How does an electron undergoing uniform circular motion exactly lose energy?

One of the main reasons for the failure of the Rutherford model of atomic structure, it is famously stated, is that the electron undergoing circular orbit loses energy since due to its centripetal ...
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0answers
15 views

Mechanism of Current flow in Metals [duplicate]

I do not fully understand the mechanism of current flow in conductors. It cannot be that a current starts only when an electron from one terminal of the electric supply physically reaches the other ...
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1answer
40 views

Change in line density of electrons

We're proving that electricity and magnetism are essentially two manifestations of the same underlying phenomenon by using the toy example of a positive charge moving parallel to an infinitely long ...
0
votes
1answer
29 views

Dependence of the Capacitance on the Material and Geometry of the Plates

I have two questions concerning capacitors: 1) We know that the capacitance of a capacitor also depend on the dielectric material inside as $C=$ $\dfrac{K \epsilon_0 A}{d}$ But what if the ...
3
votes
1answer
58 views

Effect of Motion on Capacitors

What will happen if a capacitor is accelerated or rotated very very fast? Will its capacitance decrease? Will one of the plates be able to hold the electrons which is providing the Potential ...
3
votes
1answer
104 views

Vector fields and tensors in E&M

I'm confused by a very basic property of electric fields. The electric field is a vector field. Vectors are tensors. Wikipedia has the following statement in the article about the electromagnetic ...
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0answers
38 views

Induced emf in a circular conducting wheel

Consider a conducting wheel with $N \in \mathbb{N}$ spokes which is completely in a homogenous magnetic field $\vec{B}$ perpendicular to the wheel plane. ...
0
votes
1answer
37 views

Help understanding this differential equation of a varying electromagnetic field [closed]

I'm reading some lecture notes (we're studying blackbody radiation and are approaching Planck's formula) but I'm struggling to understand exactly what's being said. So the lecture notes read as ...
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0answers
38 views

Velocities of waves (such as visible light, and radio)

The speed of light in a vacuum is a constant 299,792,458 m/s. In water, it is much slower. Does this happen to such waves as radio, or X-ray? (Would say, a 3 meter wavelength travel slower in air than ...
2
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2answers
54 views

$ε_0$ affects electric field intensity, but $μ_0$ doesn't affect magnetic field intensity?

I'll be honest: this question is actually a homework problem. I've spent the past hour going through Google and several textbooks trying to answer the question "Why does $ϵ_0$ affect electric field ...
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0answers
40 views

Electrical Resistance of Spherical, Contacting Colloids

So, I work a lot with Magneto-Rheological (MR) fluids - which are essentially electrolyte solutions with suspended, paramagnetic colloids/particles. Once a magnetic field is applied to such a fluid, ...
1
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1answer
116 views

Derivation of Maxwell stress tensor from EM Lagrangian

From Noether's theorem applied to fields we can get the general expression for the stress-energy-momentum tensor for some fields: $$T^{\mu}_{\;\nu} = \sum_{i} (\frac{\partial \mathcal{L}}{\partial ...
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1answer
37 views

Does magnitude of a charge influence magnitude of force that individual charge exerts on another charge [closed]

two point charges, q1 and q2, are placed 0.3m apart on the x-axis, as shown in the figure above. Charge q1 has a value of -3 nano Coulomb and q2 has a value of +4.8 x10^-8 C. The net electric field ...
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0answers
70 views

Electrical field of the coil

Take the case of two coils, first one connected to alternating current supply, and the second one connected to load. First coil creates magnetic field, and electric field is reduced by anti-emf ...
7
votes
0answers
88 views

Electric charges on compact four-manifolds

Textbook wisdom in electromagnetism tells you that there is no total electric charge on a compact manifold. For example, consider space-time of the form $\mathbb{R} \times M_3$ where the first factor ...
2
votes
1answer
20 views

What happens when a force is applied to a flux pinned superconductor?

When a force is applied to a superconductor to move it in a direction that it resists because it is flux pinned, where does the additional energy used to overcome the flux pinning resistance go? E.g. ...
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1answer
30 views

How can we derive that an accelerated charge particle will radiate EMWs?

All the properties of the electromagnetic entity is said to be fully described by the four golden rules of Electromagnetism : The Maxwell's Equations.How can we derive that a charged particle will ...