Questions tagged [electromagnetism]
The classical theory of electric and magnetic fields, both in the static and dynamic case. It 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 ...
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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 waveforms (equal frequencies and amplitudes). They are also in phase ...
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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 centered at the ...
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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 ...
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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 $g_{\mu\nu}=\eta_{\mu\nu}+h{\mu\nu},~ h_{\mu\nu}\ll 1$ ...
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Boundary conditions on current carrying wire
I'm trying to simulate Maxwell equations by finite elements method for a current carrying wire. My 3d geometry consists of a cylinder and a box containing it. I will use a mixed formulation and ...
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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} = \...
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QED lagrangian: gauge fixing term
I have a question about the structure of the QED lagrangian, in particular the free photon lagrangian which is contained in it. My premise is: I only know how to exploit canonical quantization in ...
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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)}{\...
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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 \...
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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 ...
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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 ...
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Should the energy-momentum tensor be invariant under gauge transformations?
For example, consider the electromagnetic theory given by
\begin{align}
I=-\frac{1}{4}\int d^4x\, F_{\mu\nu}F^{\mu\nu},
\end{align}
where $F_{\mu\nu}=\partial_\mu A_\nu-\partial_\nu A_\mu$. The action ...
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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 ...
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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 $\vec H$....
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