We changed our privacy policy. Read more.

Questions tagged [electromagnetism]

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.

3,617 questions with no upvoted or accepted answers
Filter by
Sorted by
Tagged with
21
votes
0answers
587 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 ...
12
votes
2answers
992 views

Could the Faraday's rotating wire experiment be explained without using Lorentz force?

I read Faraday's rotating wire experiment which resulted in the invention of the homopolar motor. He was clever enough to think it that way and make the wire rotate around one of the poles of the ...
11
votes
0answers
2k views

Average force between two parallel finite wires with AC

Imagine 2 parallel antennas (wires) of equal length (a) with a distance r between them. Both have AC currents with identical sine wave forms (equal frequencies and amplitudes) . They are also in-...
10
votes
0answers
435 views

Special conformal transformations and image charges

Let us consider a grounded conducting sphere with radius $r$ and a point charge $e$ at a distance $R>r$ from the center of the sphere. For simplicity, we can choose the sphere to be centered at the ...
10
votes
1answer
1k views

Question about superconductivity

A long cylinder of radius $R$ is made from two different material. Its radius $r<r_0$ $(r_0<R)$ part is a material with superconducting transition temperature $T_1$, and its $r_0<r<R$ ...
9
votes
0answers
132 views

Do radio beams self-focus in the interstellar medium?

Summary: In a plasma, electromagnetic waves create a ponderomotive force that pushes electrons and ions out of the way. Thus, in an intense laser beam, electrons tends to move away from the areas ...
9
votes
0answers
2k views

What is "spin-orbit torque?"

I am trying really hard to understand the concept of spin-orbit torque. It is a new-ish discovery in the field of spintronics and has many applications for magnetic devices. The information that has ...
9
votes
1answer
768 views

Boundary conditions on current carrying wire

I'm trying to simulate by finite elements method Maxwell equations for a current carrying wire. My 3d geometry consists of a cylinder and a box containing it. I will use a mixed formulation and ...
9
votes
0answers
436 views

Does a rotating magnetic monopole have electric and magnetic moment in classical view?

Would a rotating sphere of magnetic monopole charge have electric moment ? In a duality transformation $E\rightarrow B\cdot c$ etc. how is the magnetic moment translated $m = I\cdot S $ ? $M_{el} = \...
8
votes
0answers
181 views

Has the Helmholtz decomposition of the $\mathbf{E}$ field from the Liénard–Wiechert potentials been worked out?

If you look at Maxwell's equations for $\mathbf{E}(\mathbf{x},t)$ they split neatly into two categories. They are: \begin{align} \nabla\cdot\mathbf{E}(\mathbf{x},t)&=\frac{\rho(\mathbf{x},t)}{\...
8
votes
2answers
780 views

Non-Relativistic Electron Hamiltonian

I have determined a Hamiltonian for an electron using an appropriate Lagrangian of the form $$ L=\frac{1}{2m}\left(m\overrightarrow{v}+\frac{q}{c}\overrightarrow{A}\right)^2-\frac{q^2}{2mc^2}\...
7
votes
0answers
68 views

Electron in rotating frame

Suppose there is a stationary electron in an inertial frame $S$. Then there is only a static Coulomb field relative to $S$. However, according to a rotating frame $S'$, whose angular velocity relative ...
7
votes
0answers
70 views

Is the magnetic field at the centroid of a closed loop connected at two different points to a battery always zero?

Given a closed 2-dimensional conducting loop, the terminals of a battery are connected at any two points on the loop (but not the same point). As an example, consider a circle of radius $R$; the two ...
7
votes
0answers
80 views

What would Maxwell's equations look like in a universe which followed Galilean transformations?

I was wondering how the electromagnetic force would behave in a Gallilean transformation universe. Would the magnetic force be non-existent? We know that Gallilean transformations are Lorentz ...
7
votes
0answers
333 views

Solving Maxwell equations on curved spacetime

I have difficulties to understand how to solve the Maxwell equations on curved spacetime. I want to solve the equations in the weak regime $g_{\mu\nu}=\eta_{\mu\nu}+h{\mu\nu},~ h_{\mu\nu}\ll 1$ ...
7
votes
1answer
731 views

Photons and Electric Current

I am trying to understand how photons as the force carrier for the electromagnetic force (or field) manifest themselves in a flow of electric charge, i.e. an electric current. Both standard (...
7
votes
1answer
255 views

Is electricity perpetual in a superconductor system?

I wonder if electricity consumption happen according to the Law of conservation of energy and Joule effect, in a regular circuit certain amount of energy is transformed into heat by components ...
7
votes
0answers
400 views

1-form formulation of quantized electromagnetism

In a perpetual round of reformulations, I've put quantized electromagnetism into a 1-form notation. I'm looking for references that do anything similar, both to avoid reinventing the wheel and perhaps ...
7
votes
3answers
268 views

Why do clothes produce sounds after being in front of a computer for a long time?

Quite often, after sitting in front of the computer not moving a whole lot for a long time my upper body clothes (usually sweaters) make soft crackling sounds when moving or specially when taking them ...
7
votes
1answer
791 views

Hidden momentum

I'm trying to learn about hidden momentum. After reading what I could find with a google search, I understand that it is equal to the momentum carried by radiation, calculated with the Poynting vector....
6
votes
0answers
98 views

What developments have been made in this unsolved problem?

I found this section in The Feynman Lectures Vol. 1 page (28-2). I was curious on where we stand to solve this question as of today? Any information/links on developments will be helpful. \begin{...
6
votes
0answers
272 views

Trouble with Classical Derivation of Cherenkov Radiation Mechanism -- Magnetic Field Intensity

I've been going through a translation of Frank and Tamm's original theory on Cherenkov radiation published by Jelley in 1958, and the bottom line is that I'm stuck on one of the intuitive leaps that ...
6
votes
2answers
1k views

How does a electric quadrupole oscillate?

I know that in static a electric quadrupole is made of two positive charges and two negative charges, distributed as in the following figure: What I don't understand is when it oscillates and ...
6
votes
1answer
1k views

Current geometry and Ampere's law

Under the right circumstances, Ampere's law $\oint \vec H\cdot d\vec \ell=I_{encl}$ can be used to deduce the field $\vec H$ at a point from the current enclosed by the circuit which produces $\vec H$....
6
votes
1answer
774 views

Divergent self-energy of point charges in Classical Electrodynamics

Assuming the electron to be a classical point particle, if one calculates the self-energy one finds $$U=-\frac{e^2}{8\pi\epsilon_0r}$$ which diverges as $r\rightarrow 0$. Therefore, the measured mass ...
6
votes
0answers
214 views

Are there yet Optical Magnetic Mirrors (OMMs) which reflect via interaction with the magnetic field?

update 2021: As the question has remained unanswered for five years and the field of optical metamaterials has advanced, I think this question can be revisited. The most familiar mirror relies on ...
6
votes
1answer
689 views

Maxwell stress tensor at material boundaries

I am trying to grasp the meaning of the Maxwell Stress tensor $T_i^j$ at material boundaries. Concretely, I am trying to calculate the force between two waveguides. The results are given in an article ...
6
votes
0answers
175 views

Experiments or phenomenon to falsify the existence of monopoles?

This is a related, but opposite question to this one I have heard about a lot of things regarding elementary and GUT magnetic monopoles, as well the quasiparticle monopoles in spin ice Since there's ...
6
votes
0answers
223 views

Is there any antenna with a single null?

If we designate the origin (the reference point from which all displacement vectors are measured) $\vec{0}$, and If we consider a sphere $\mathbb{B}\left(\vec{0},\mathcal{R}\right)$ of radius $\...
6
votes
0answers
7k views

How to calculate the magnetic dipole moment of a bar magnet?

I want to calculate the force between two magnets. In a previous Phys.SE question, I was told that I needed to use the dipole-dipole interaction, but that equation depends on $m$, the magnetic dipole ...
6
votes
1answer
14k views

Force from solenoid

I'd like to approximate the force from a solenoid, or at the very least find a formula which is proportional to the force so that I can experimentally find the constant for my particular case. ...
5
votes
0answers
56 views

Relation between the electric and magnetic fields for an arbitrary electromagnetic wave

When solving the wave equation for electromagnetic waves, $$ \nabla^{2} \mathbf{E}=\mu_{0} \varepsilon_{0} \frac{\partial^{2} \mathbf{E}}{\partial t^{2}}, \quad \nabla^{2} \mathbf{B}=\mu_{0} \...
5
votes
0answers
125 views

An equivalence principle for gauge theories

In GR there is the equivalence principal, stating that in an arbitrary gravitational field, no local non-gravitational experiment can distinguish a freely falling, non-rotating system from a uniformly ...
5
votes
0answers
60 views

Reversibility of light rays, Faraday effect and Fermat's principle

I am currently having some struggle to understand the connection between the following three concepts in optics: Law of Reversibility (Geometrical Optics): The direction of light rays does not matter ...
5
votes
0answers
113 views

Maxwell's Equations In Curved Spacetime Derived Via ADM Formalism VS Differential Forms Discrepancy

I' m trying to understand how the electromagnetic potential for diagonal Bianchi IX models when an electromagnetic field is aligned with one of the three axis is computed. The metric in question is \...
5
votes
1answer
328 views

Can we talk about velocity field and acceleration field in 1D?

It's well know that a charged particle radiate when it is accelerated. We can rely on two different formulas. The first one it's from Jefimenkos : $$\mathbf{E}(\mathbf{r}, t) = \frac{1}{4 \pi \...
5
votes
0answers
192 views

Electromagnetic Unruh effect?

The Unruh temperature is given by $$T=\frac{\hbar\ a}{2\pi c k_B}.$$ If we have an electron field with charge $e$ and mass $m_e$ acted on by an electromagnetic field $\vec{E}$ then very naively maybe ...
5
votes
0answers
136 views

Can a bulk crystal have a spontaneous quadrupole moment?

Crystals of polar space groups e.g. ferroelectrics can have a spontaneous electric dipole moment. Is it possible for a crystal to have a spontaneous electric quadrupole moment (and higher order terms ...
5
votes
0answers
178 views

Is there an equation of state for a non-ideal Fermi gas?

For a gas of self-interacting electrons (i.e. a non-ideal Fermi gas), is there is there any sense in trying to define an equation of state? If so, what is the equation of state for a gas of electrons? ...
5
votes
0answers
1k views

Why not use the Weyl gauge?

In E&M in Minkowski space, the Lorenz and Coulomb gauges are typically used since they make things vastly simpler. On a curved background, Maxwell's equations (without sources) can be written as: ...
5
votes
0answers
489 views

Hamiltonian formulation of the semiclassical Model of electrons

I'm currently reading the book Solid State Physics by Neil W. Ashcroft and N. David Mermin. In Chapter 12 they introduce the "Semiclassical Model of Electron Dynamics". In short: After having solved ...
5
votes
0answers
813 views

Do divergence and curl of Lorentz force have some physical meaning?

Time ago I started thinking about this: if we take the well known Lorentz Force expression, namely $$\mathbf{F} = q\left(\mathbf{E} + \mathbf{v}\times\mathbf{B}\right)$$ and we operate $\nabla\cdot \...
5
votes
0answers
149 views

How can one confirm creation of magnetic graphene?

Recently my high school physics teacher contacted me looking for an expert to ask about this situation. I am paraphrasing his correspondence below: I just had a a student accidentally create magnetic ...
5
votes
0answers
219 views

MRI and precession

A lot of explanations of the quantum mechanics of MRI discuss the precession of a proton in an external magnetic field, for example here: http://www.physicscentral.com/explore/action/mri.cfm Doing ...
5
votes
0answers
381 views

Ohm's Law for Accelerated Conductors

My questions are about the Ohm's law for a moving conductor in a stationary magnetic field. As we know this law is stated based on following relation with respect to the fixed frame of reference ...
5
votes
0answers
92 views

Spin-dependence of the directionality of dipole radiation

I am interested in understanding how and whether the transformation properties of a (classical or quantum) field under rotations or boosts relate in a simple way to the directional dependence of the ...
5
votes
1answer
4k views

Equivalence between a charged rotating cylinder and a solenoid

Suppose we have a cylindrical shell of radius $r$ with surface charge density $\sigma$. Then we start rotating the cylinder at an angular speed $\Omega$. You can show that in this case the surface ...
5
votes
0answers
158 views

Is the search for a Simple-group-based Electro-Weak theory over?

Just wondering: We know that, in its current form of the $SU(2)_L\times U(1)$, the electroweak theroy rides a wave of huge success. However, is it not possible that the correct simple group ...
5
votes
1answer
651 views

Why do diamagnetic substances align perpendicular to the field

My textbook says that Diamagnetic substances align their longest axis perpendicular to the field in uniform magnetic field while paramagnetic substances align their longest axis parallel to the field. ...

1
2 3 4 5
73