# 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.

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### 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 ...
2answers
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### 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 ...
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### Do the Planck voltage and the Planck current have a natural physical interpretation in classical general relativity?

Most Planck units are a product of powers of all three of $\hbar$, $c$, and $G$, so we will not be able to fully understand their physical significance until we have a full theory of quantum gravity. ...
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### 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-...
2answers
1k views

### Biot-Savart law from Ampère's with multivariate calculus

Let us assume the validity of Ampère's circuital law $$\oint_{\gamma}\mathbf{B}\cdot d\mathbf{x}=\mu_0 I_{\text{linked}}$$where $\mathbf{B}$ is the magnetic field, $\gamma$ a closed path linking the ...
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### 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 ...
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### Does a classical charge naturally have spin in a non-flat FLRW universe?

I was recently reading a paper https://arxiv.org/abs/0912.0225 which describes Coulomb's law in a closed universe. I've seen the argument from several sources that the total electric charge in a ...
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### 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 ...
1answer
541 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 ...
1answer
173 views

### Can light (electromagnetic radiation) cause electromagnetic induction in a wire?

Can light, as an electromagnetic wave, cause electromagnetic induction in a wire by passing near the wire? Does a moving electromagnetic wave cause a varying magnetic field in the region near the wire?...
0answers
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### 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 ...
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### Landau quantization: degeneracy of first level

In some books the degeneracy of one Landau level in a two-dimensional gas of free electrons is calculated in the following way: Note: The electron spin is not considered. Number of states of a free ...
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153 views

### Why isn't cosmic microwave background radiation on Earth drowned out by thermal noise

The Penzias/Wilson experiment, which detected the CMB, doesn't sound feasible given thermal noise. When Penzias and Wilson reduced their data they found a low, steady, mysterious noise that ...
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139 views

### Can the Hall effect drive a current?

In the Hall Effect current is passed through a wide strip of metal in a perpendicular magnetic field. Since (some of) the negative charges in the metal move but the positive ones stay put, the ...