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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.
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How to generate a EM wave with E-field parallel to the direction of propagation? [closed]
I guess this is not possible in the far field. But I would like to know how to do that in the near field, say at 50cm for frequencies below 1GHz say.
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3
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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 …
- 497
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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 …
- 497
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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 …
- 497
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0
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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
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1
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32
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Dielectric polarization - should not the dimensions of the polarised dielectric increase in ...
In the classical model for polarization, if a dielectric is placed in a an electrical field (assumed to be static for the sake of simplicity), the trajectory of the electrons inside the atoms of the d …
- 497
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 …
- 497
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1
answer
207
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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 …
- 497
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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
-1
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1
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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 …
- 497
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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
3
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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
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0
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65
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Magnetic field lines of a toroid magnet
I am not sure what are the magnetic field lines of a torroid magnet like this one:
In particular, at the center of the magnet, is the field null or is it maximal?
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Which of these magnets should have the strongest strength at 10cm?
Basically, I need to generate the strongest possible field at 10 cm from a circular magnet, in its central axis.
I hesitate about what buying.
For example, the following magnet has a large diameter of …
- 497
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5
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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 …
- 497