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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35 views

What is the gravitational effect inside a electromagnetic shield due to an external electromagnetic field?

I am new in General Relativity. I know that electromagnetic field (or, the electromagnetic energy tensor, $T^{ik}=1/4\pi[1/4F_{mn}F^{mn}g^{ik}-F^i_lF^{lk}]$) can affect gravitation. Now if we take a ...
1
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0answers
9 views

Second-order correction in Quantum-Confined Stark effect

In the wikipedia article, there is a second-order correction in the Quantum-Confined Stark Effect. I could not understand how it was solved. I did not understand the meaning of 2(0) and 1(0) and how I ...
0
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1answer
26 views

Does heating an electromagnet cause change in its magnetic field?

Does heating an electromagnet cause change in its magnetic field as well and vice versa?
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1answer
22 views

Is it possible to pass electric current through magnet without affecting it?

Suppose we a row of 5 electromagnets, with a copper wire connecting them. Is it possible to create magnetic field in the 4th magnet without affecting the 1st,2nd,3rd and 5th magnet by passing electric ...
0
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1answer
46 views

Cryptic remark in physics revision guide

I am currently revising for my AP physics and I couldn't understand one of the end-of-section summary notes. It says: "Remember that the direction of magnetic field is from North to South, and that ...
3
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1answer
42 views

Do the relations between E/B and D/H contain higher order multipole terms?

Jackson writes in section 1.4 (third edition) that \begin{align*} D_\alpha &= \epsilon_0 E_\alpha + \left(P_\alpha - \sum_\beta \frac{\partial Q'_{\alpha\beta}}{\partial x_\beta} + \ldots \right) ...
2
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1answer
30 views

Do changing magnetic fields always produce solenoidal electric fields?

Since the curl of E is the time derivative of B, $\nabla \times \vec{E} = -\frac{\partial B}{\partial t}$ Do changing magnetic fields always produce solenoidal electric fields? For instance a ...
2
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2answers
64 views

Transition from 4-potential to E and B [on hold]

In my lecture notes there is a step that i cannot follow: $$\frac{i}{2}[\gamma^{\mu},\gamma^{\nu}] (\partial_{\mu}A_{\nu}-\partial_{\nu}A_{\mu})=: \sigma^{\mu\nu}F_{\mu\nu}=i\vec{\alpha} ...
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2answers
33 views

Magnet gyroscopic force spin

I was wondering whether a magnet exerts any measurable gyroscopic effects. I understand that magnetism is caused by alignment of spins of electrons which have angular momentum. (I realise that that ...
2
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3answers
72 views

Electric field or static electric field around a plugged-in lamp cord (when lamp is not turned on)?

When an electrical cord from, say, a lamp, is plugged into an AC wall socket, I'm aware that an electric field forms around the entire length of the cord and even before the lamp switch is flipped on. ...
3
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4answers
100 views

What is the meaning of EM field having curl?

We know that the "sourceful" fields like gravity or electric static field due to charge are all curl=0. But both E/M fields have curl and they mutually "curling" into each other, making them kind of ...
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1answer
21 views

Faraday's Law: Current loop and proton

A single circular loop of wire with radius R carries a large clockwise current I(loop)=I0, which constrains a proton of mass M and charge e to travel in a small circle of radius r at constant speed ...
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0answers
44 views

Direction of emf and it's physical sense?

I have a situation where there exist a time varying magnetic field and a circular loop place perpendicular to it. Let us assume that the magnetic field is $\vec B=\frac{B_0 t}{\tau}$ . I tried to ...
1
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0answers
26 views

Is there an electric field in the direction of a uniform current?

In an infinite plane where uniform current is passing through,is there any electric field? Because i know that charge produces an electric field but in a uniform current and because it is an infinite ...
1
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1answer
75 views

Poincaré' lemma and EM potential $A^{\mu}$

My lecturer said that given the sourceless Maxwell's equations $$ \partial_{\mu}\, ^ *F^{\mu\nu} = 0 $$, we can find a solution $$ F^{\mu\nu} = \partial_{\mu}A_{\nu} - \partial_{\nu}A_{\mu},$$ that ...
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0answers
36 views

Solutions to Dirac equation in 2+1 D [on hold]

Hello I solved the Dirac equation in 2+1 D taking two different gamma matrix representations. rep.A: $$\gamma^0=\sigma^3, \qquad\gamma^1=i\sigma^1, \qquad\gamma^2=i\sigma^2.$$ rep.B: ...
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0answers
26 views

Is it possible to defy the earths magnetic field, allowing you to hover? [duplicate]

I am just trying to figure out that if you can defy the Earths magnetic field, allowing you to hover. Some friends and I have theorized that if you put on heavy-weight magnets, and add an electronic ...
2
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1answer
34 views

Difference between electric and magnetic field (relating to EEG & MEG)

I study cognitive neuroscience and I periodically run into physics related questions in the context of neuroimaging technologies. My question specifically refers to electric and magnetic fields that ...
3
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1answer
37 views

Could the 4 Forces Split Off or “Decay” into Other Forces in the Distant Future? [duplicate]

From my basic understanding of popular-level physics articles and books and such, the 4 forces (Electromagnetism, Gravity, Strong and Weak Force) used to be 1 force in the early universe, then split ...
3
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1answer
29 views

What's the difference between “Ohmic dissipation”, “Joule heating”, “ion drag” and “resistive heating”?

The following terms are sometimes used to refer to ... more or less ... the same thing by different people and in different contexts (electronic circuits vs. plasma physics, etc.): Ohmic ...
0
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0answers
25 views

How to find the terminal angular velocity of the given figure? [on hold]

I have posted the picture of question, can someone please tell how to do it ?
2
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0answers
93 views

What exactly is NASA's proposed mechanism for “propellantless” “EM Drive” propulsion? [duplicate]

Of course, this question runs perilously close to this site's prohibition against discussing non-mainstream physics. However, the accepted answer in meta about what is acceptable and what is not ...
1
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1answer
13 views

Do electric sinusidal waves rotate 45 degrees too when light pass through a hollow cylindrical magnet or just the sinusoidal magnetic waves do that?

Do electric sinusoidal waves rotate 45 degrees too when light pass through a hollow cylindrical magnet or just the sinusoidal magnetic waves do that?
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0answers
20 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. ...
1
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0answers
13 views

AC current through induction on both sides

When you rotate a coil in a magnetic field one side cuts downwards the other cuts upwards. When you move a piece of wire up and down you get an AC current or pdf which you can see on a voltmeter as ...
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1answer
51 views

Light - What is it? [on hold]

First of all, please excuse my bad english. I am from Germany. I am interested in, what light really is. I know, there is a range in the spectrum, and this range is visible. This is defined as light. ...
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5answers
2k views

Is current in superconductors infinite? If they have 0 resistance then I (V/R) should be infinite?

I learned many years ago that according to Ohm's law, current is equal to voltage divided by resistance. Now if superconductors have zero resistance then the current should be infinite. Moreover the ...
0
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1answer
21 views

Calculating potential difference for fraction of loop with induced current

Given a circular wire loop of radius r, resistance R enclosing a magnetic field perpendicular to the plane of the loop that increases with time ($B=\alpha t$), I have calculated the induced current ...
2
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1answer
43 views

Planck's postulate for oscillators or for light?

I know that Planck originally postulated that the energy of an oscillator in a black body was quantised to $E=nh\nu$ but did he know at the time that this meant the energy of light was also quantised ...
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0answers
19 views

Ground State energy as a function of $N$ and $B$, $E_0(N,B)$

The one-particle Hamiltonian is given by: $$\hat{H}=\frac{1}{2m}\left(p+\frac{e}{c}A\right)^2$$ where $p=\hbar\vec{k}$ with $e > 0$ and vector potential $A=(0,x,0)B$, such $B=\triangledown ...
0
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0answers
24 views

Polarisation states in 1d?

I am working through a derivation of the spectral energy density in a 1d cavity. The derivation says that the number of modes (per unit volume) in a frequency interval $dv$ is given by: $$g(\nu)d\nu ...
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0answers
27 views

Can we use the geomagnetic field to power something? [duplicate]

My question might sound idiotic, but I could not help it: Can we harness the earth's geomagnetic field to repel another magnet in such a way that we can get some motion out of it?
2
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0answers
43 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 ...
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1answer
42 views

Applying Schrodinger equation to find the energies of a free electron model in a metal [on hold]

The one-particle Hamiltonian is given by $$\hat{H}=\frac{1}{2m}\left(p+\frac{e}{c}A\right)$$ with $e > 0$ and vector potential $A=(0,x,0)B$, such $B=\triangledown \times A=(0,0,B)$ Question: "I ...
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0answers
13 views

electromagnetic losses at conductor interface at high frequencies??

Skin depth effect reminder When an electromagnetic wave arrives at a conductor interface of conductivity $\sigma$ , most of it is reflected back. Only a small fraction penetrates as an evanescent ...
2
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1answer
24 views

A Method of Images Problem from Electrodynamics (Cylindrical Surfaces)

This problem is from Introduction to Electrodynamics 4th Edition , Griffiths, problem 3.12 Two long, straight copper pipes, each of radius $R$, are held a distance $2d$ apart. One is at potential ...
3
votes
1answer
43 views

Why do I see different color sparks from the 2 pins when I plug an appliance in a socket?

I plugged in the charger of my laptop into a socket, which I have done a lot of times but this time, I noticed a strange thing. When the contact was made between the pins of charger and the socket, ...
0
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0answers
43 views

Electrostatics and relativity [closed]

How to get the "d‘Alembertian acting on four vector A=-four vector j" from Poission's electric static equation by Lorentz transformation?
2
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3answers
56 views

Electromagnets, and how $H$ is the thing we set on the dial

Let's say that I have an electromagnet, consisting of Helmholtz coils with an iron core. David Griffiths, in his "Introduction to Electricity & Magnetism" text claims that $H$ is what we set, by ...
0
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0answers
23 views

Can anyone list all the ways the gravitational force interacts with the electromagnetic at our energy scale? [closed]

Apart from weight does the gravitational force manifest itself in our world in any other way?also, are these two different questions?
2
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2answers
60 views

How does electromagnetic radiation affect the velocity of a charged particle?

I've heard that the acceleration of a charged particle releases electromagnetic waves. So let's say there is a charged electron moving forwards in a region with a downwards magnetic field. If the ...
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votes
1answer
24 views

Induction Oscillation [closed]

A bar (m=100g, l=10cm) is moving in a constant magnetic field $B$ as shown above. The resistor $R$ is $1\Omega$. The bar is attached to a spring with spring constant $10N/m$, can you derive ...
0
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0answers
8 views

Triodes: Why do mesh fineness and radius of the grid affect amplification factor?

My basic understanding is that a grid which is much closer to the cathode than the anode will be more able to create a repulsive electric field than the anode's attractive field, thus current can be ...
0
votes
1answer
46 views

The Aesthetics of impossible or unreal physical phenomena [closed]

I know this may not be a typical question for the Physics board. I am a MA Design student working on a project to illustrate experiments on speculative/fictional physical events. My final work will ...
0
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0answers
17 views

Finite Value of Cross Section of (Scattering/Absorption) of Localized Surface Plasmon at Resonance

According to textbook written by Stefan A. Maier, ch.5, p.70, cross section of scattering and absorption are defined as: $$C_{sca}=\frac{8\pi}{3}k^4a^6 ...
0
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0answers
28 views

Gravitoelectromagnetism or graviton thory to derive equivelent formulas to relativity theory [closed]

Is it possible to change the definitions of an event happening (which currently in relativistic theory is defined by the moment you see* something - the time light took to travel to you) such that ...
3
votes
1answer
62 views

How much external field have to be applied to saturate a Mu metal shield till magnetization?

My main goal is to magnetize and demagnetize a Mu metal shield. Till now I am using a Helmholtz coils setup and I can generate 10 mT applying 2 A DC. I am using a DRV425 fluxgate and a hall probe ...
2
votes
1answer
29 views

Force on a moving charge in relative frame

Consider a particle of charge $q$ moving at velocity, $v$, enters a magnetic field $B$ which is perpendicular to its motion. Now consider two observers, one stationary and the other moving at the ...
0
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1answer
27 views

Does a correct application of the Lorentz force to find induced emf need resistance?

The emf between two points is defined as the work done per unit charge on the charge when moved (along a given and stated path) between those two points. To find the emf due to a magnetic field the ...
0
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2answers
53 views

How come the length of a wire does not affects on the circuit current?

Today we started learning about the electromagnetic induction. Out teacher gave us the following explanation: Suppose we have a conduction frame inside a magnetic field $\vec{B}$ going towards the ...