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Results tagged with electromagnetism
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user 219091
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.
4
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1
answer
300
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Deducing the Heaviside-Feynman formulae from Jefimenko's equations
I've tried to deduce the one point charge Heaviside–Feynman formula from the Jefimenko's equations.
This should be possible, by replacing the densities with Dirac deltas, somehow, but I failed.
Could …
CommunityBot
- 1
4
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5
answers
386
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How does the Poynting vector know who is the primary and who is the secondary of a transformer?
I've read in several places that the Poynting vector is directed from the primary to the secondary of a transformer (we assume here that the primary is the winding that provide the AC energy, while th …
- 3,001
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0
answers
26
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Maximum principle for the potential inside a non uniform isotropic dielectric
If a dielectric is isotropic and uniform, then assuming it carries no free charge, we know that the potential $V$ inside the dielectric is harmonic: $\Delta V = 0$. Hence the maximum principle holds i …
- 497
0
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1
answer
48
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Is the magnetic field outside a solenoid almost null for AC current?
Despite an answer to this thread, I'm not so sure the magnetic flux outside an infinite ideal solenoid is null whenever the current is AC. I've seen no real proof of that, and the Biot-Savart law whic …
- 3,137
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votes
1
answer
75
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In a ion source, how do we make the ions get out of the cavity?
Ion sources are devices that allow creating ion beams (e.g. argon ions) and to project them outside the device, for example to be further processed by a particle accelerator, or to irradiate materials …
- 497
0
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0
answers
30
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Coupling ion ray with a EM wave and penetration depth
Ion sources are devices that allow creating ion beams (e.g. argon ions) and to project them outside the device, for example to be further processed by a particle accelerator, or to irradiate materials …
- 497
-1
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1
answer
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Apparent contradiction in Ampere law for a solenoid
This picture in Wikipedia is supposed to explain the solenoid formula for the magnetic field $$B l= \mu_0 N I$$
(assuming steady currents).
But this would be true if one consider only the part of the …
- 4,936
1
vote
How does the Poynting vector know who is the primary and who is the secondary of a transformer?
Building on the excellent answer of HTNW (and also thanks to the comments of Ján Lalinský), I wish to elaborate a bit about inverting the primary and the secondary.
It is true that the primary and the …
- 497
5
votes
2
answers
87
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Relativistic momentum of the E.M field vs Poynting momentum questions
I come somehow to the following thoughts:
The energy of the EM field is $$\mathcal{E} = {\epsilon_0\over 2} (E^2 + c^2 B^2).$$
Associate to $\mathcal E$ the relativistic mass $$m_r = {\mathcal{E}\over …
- 213k
0
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Electric potential vs electromagnetic potential questions
Building on the answer of Ján Lalinský and on further research, I add here my own answer to the question.
question 1: It turns out that the electric potential $V$ measured at some point of the wires i …
- 497
4
votes
2
answers
190
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Electric potential vs electromagnetic potential questions
On the other hand, in electromagnetism are defined the scalar potential $\varphi$ and the vector potential $\mathbf A$, and there holds everywhere inside and outside the wires$$\nabla \varphi = - {\mathbf …
- 497
1
vote
2
answers
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Apparent instantaneous EM propagation paradox in two concentric solenoids [duplicate]
Assume there are two solenoids $S_1$ and $S_2$ sharing the same axis, one of radius $R_1$ and the other of radius $R_2 > R_1$ resp.
For the sake of simplicity, I will assume that $S_2$ reduces to a si …
- 6,783
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1
answer
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Electromagnetic wave in vacuum - Do we have always ${\bf E}\cdot {\bf B} = 0$ and $E = cB$?
In vacuum, but not necessarily into free space, e.g. inside a waveguide, does a EM wave always fulfill the relations
$${\bf E}\cdot {\bf B} = 0, \quad E = cB,$$
with $\bf E$ and $\bf B$ the electric a …
- 1,830
1
vote
3
answers
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Oscillation coil: where is the electric field?
Let assume a simple RF coil fed with an alternating current at RF frequencies, say 100MHz.
I believe that no one doubts that the coil will radiate RF energy in the form of radio waves.
A radio wave is …
- 65.1k
3
votes
3
answers
493
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Floating potential of a conductor near another conductor with known potential with respect t...
Electrostatics textbooks delight at computing the electric field or the potential created by a known distribution of charge, ignoring the fact that this is rather a non practical question. In practica …
