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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What is the difference between Right Hand Palm Rule, Fleming's Right Hand Thumb Rule and Fleming's Left Hand Thumb Rule?

I dont understand in what scenarios are the three rules applied and are any two of them similar or are they all different?
2
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2answers
57 views

Magnetic Levitation : Confusion with Lenz's Law

Considering the above diagram, I am failing to see why the aluminium ring floats upwards rather than oscillates. I understand Faraday's law, but I am struggling with Lenz's law - as there is an ...
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2answers
50 views

Derivatives of Fields in E&M

In QED the field strength tensor $F_{\mu\nu}$ is given by the commutator of the covariant derivatives $$D_\mu=\partial_\mu-ieA_\mu$$ where $A_\mu$ is the gauge field. Explicitly we have ...
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1answer
44 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?

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 ...
2
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1answer
53 views

Magnetic monopoles and special relativity

I was thinking about magnetism as a product of special relativity and the result of this approach to the magnetic monopoles. So if magnetism is a product of electricity(like electricity from another ...
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0answers
71 views

Bar magnet dropped through coil

If you have drop a bar magnet through a coil so that it goes all the way through I was told the graph of emf induced in the coil vs time looks something like this: (emf induced is on y axis, time ...
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1answer
26 views

Faraday and Lenz's laws

in my revision guide it gives the equation for Faraday's law as $$\text{induced emf} = N\frac{\Delta \phi}{\Delta t}$$ while the one for Lenz's law is given $$\text{induced ...
2
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1answer
27 views

Calculating the potential of 2 spherical perfect conductors with the image method

I am searching for a way to calculate the potential on the surface of two perfect conductors that are spheres. I am not sure my method is correct. Here is a diagram of what I am studying : They ...
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2answers
63 views

Conducting rod moving through magnetic field

If a conducting rod moves through a magnetic field which way do its electrons move? In my revision guide it shows the following picture (more or less, but the following is my drawing of it -- I ...
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1answer
28 views

Interacting magnetic fields

Is there a reason why two magnetic fields perpendicular to each other do not interact? If they are parallel or at a non-90 degree angle they interact. Is it because magnetic field lines can be viwed ...
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0answers
20 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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1answer
38 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 ...
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0answers
11 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 ...
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1answer
29 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
29 views

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

Suppose we have a row of $5$ electromagnets, with a copper wire connecting them. Is it possible to create magnetic field in the $4^{th}$ magnet without affecting the $1^{st}$,$2^{nd}$,$3^{rd}$ and ...
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1answer
47 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
46 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
31 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
35 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
79 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
103 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
46 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 ...
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0answers
27 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 ...
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1answer
77 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
37 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
30 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 ...
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0answers
26 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
105 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 ...
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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
25 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
53 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
44 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
20 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 ...
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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
45 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 [closed]

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
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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, ...
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0answers
45 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 ...