# 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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### Electromagnetic tensor in a FRW metric

In some papers [like https://arxiv.org/pdf/2204.06883.pdf, eq. (31) ], I see that the Electromagnetic tensor field, for a FRW metric (written in a conformal way) \begin{equation} ds^{2} = a^{2}(\tau) \...
87 views

### Are electric force and strong force equal in magnitude?

Should the electric force and the strong force be equal for a nuclei to be stable? Because if perhaps, the strong force is now more than that of the electric force, then shouldn't the nucleus collapse ...
37 views

### Resolving Faraday law vs. Stokes law for a long, time-varying current-carrying wire

A long wire carries a sinusoidally-time-varying current. What is the $E$ field around (not within) the wire? Assume quasi-stationary operation. Conflict: According to Faraday, the circulation of the ...
18 views

### Derivative of a real harmonic signal

simple question I can't figure out: $s(t) = A\cos(\omega t + \phi) = \mathfrak{R}[A e^{jwt}]$ is the temporal function of a real harmonic signal. I don't get how the derivative is still an imaginary ...
1 vote
24 views

### Can we interpret timelike, rest frame motion as velocity in the time direction? If so, does it cause charge to generate a ''$B$ field'' perp. to time?

For background: I've had courses on SR/GR from Hartle, E&M from Griffiths/Purcell, and know E/B fields are unified/transform with lorentz boost. My question is less about 'does SR account for E/B ...
1 vote
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### Why do the Feynman-Heaviside formulae for $\vec E, \vec B$ fields differ from the Lienard-Wiechert fields?

Why do the expressions for Feynman-Heaviside fields look completely different from the Lienard-Wiechart fields though both of which are fields due to a point charge moving along a specified trajectory?...
33 views

### Charge in crossed E and B-fields

This post describes the motion of a charge in crossed electric and magnetic fields as: $$x = r \cos ωt + \dfrac EB t\\ y = r \sin ωt\\$$ Can you please explain how these equations are derived. Why ...
45 views

### Gauss Law Difference between Griffiths and Jackson [closed]

As per Jackson, Gauss's Law is defined as: $$\nabla \cdot \vec E=4 \pi \rho/\epsilon$$ Now as per Griffiths, the same equation is defined as: $$\nabla \cdot \vec E= \rho/\epsilon$$ So the $\pi$ part ...
23 views

### Electric field from an oscillating electric dipole

In the case of two charged spheres connected by a wire and separated by a distance d, when we drive the charges back and forth in the wire (by applying an oscillating electric field), we then have a ...
8 views

### How to calculate decay in plasmonic wave amplitude travelling inside a metal-insulator-metal waveguide?

I'm working on a system of plasmonic resonators along a waveguide, to calculate the transmitance of the system I'm using a system of coupled differential equations (CMT), the system consists of 8 ...
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### What are the conditions for a glow discharge to occur vs an electric arc to occur in a glass tube?

After the invention of vacuum pumps, people experimented with running electricity in evacuated or partially evacuated glass tubes. In some sources people say this results in a glow discharge and in ...
61 views

1 vote
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### Does the force between two magnetic poles ever reach zero?

If we hold two magnetic like-poles together and start to move them away, would the repelling force reach absolute zero at certain point? In that scenario, as a layman, I think that there is something ...
78 views

### If magnetic field is a bivector, then what is the pole strength?

I have an intuition that magnetic fields are bivectors. While trying to derive some equations with bivectors, I arrived at this formula $$F=\frac{q_{m_a}q_{m_b}}{r^2}\hat r$$ So we have, $$F=q_mB$$ ...