All Questions
70
questions
26
votes
2
answers
7k
views
Is it (practically) possible for a large building to be a Faraday cage?
In my sophomore year of high school, my P.E. teachers kept on complaining about how phones didn't have a network connection in our gym, regardless of model, service provider, etc. A couple of feet ...
7
votes
3
answers
346
views
Why do clothes produce sounds after being in front of a computer for a long time?
Quite often, after sitting in front of the computer not moving a whole lot for a long time my upper body clothes (usually sweaters) make soft crackling sounds when moving or specially when taking them ...
- 171
6
votes
3
answers
2k
views
Feynman on Inverse Square Law of EM Radiation
I've been reading through (and listening to) a collection of lectures form Richard Feynman's Lectures on Physics. In lecture #2, titled "Basic Physics", he makes the following statement:
Although ...
5
votes
1
answer
271
views
Earnshaw Theorem for ionic solids
Is a single molecule of sodium chloride (say) or a cluster of molecules of NaCl unstable, although macroscopically NaCl is in fact, stable?
How can I reason this based on Earnshaw's theorem?
- 113
4
votes
1
answer
639
views
Why is the susceptibility $\chi(t)$ real?
So my question is quite simple I suppose, and perhaps trivial. It is known that the frequency domain susceptbility $\chi(\omega)$ is complex, and that the two parts can be related with the Kramers-...
- 1,521
3
votes
1
answer
1k
views
Why would a rotating charged sphere not have time varying electric field?
I have seen Gauss Law being used for a uniformly charged hollow sphere rotating with $\omega$. How is that valid to use Gauss law since it is an electrostatic law and if it is valid, why do we get a ...
user56199
3
votes
0
answers
162
views
Is frictional heat just electromagnetic interactions creating infrared radiation?
Example: Rub your index finger on a sheet of paper and you will feel that it will get noticeably hotter
Is the reason you feel this increase in heat (technically an increase in kinetic energy of the ...
- 283
2
votes
4
answers
764
views
Is the vacuum permittivity a result of defining other units first?
From Coulomb's law
$$F=\frac{1}{4\pi\epsilon_0}\frac{q_1q_2}{r^2}$$
If instead we defined the charge of a coulomb to be $\sqrt{\epsilon_0}$ times it is now, the force would be exactly the ...
- 191
2
votes
2
answers
154
views
Should static electricity affect a Crookes radiometer?
I've been playing around with a Crookes radiometer for fun and I happened across something I can't figure out.
I know the fundamentals of the radiometer (e.g. partial vacuum, thermodynamics, etc.), ...
- 121
2
votes
3
answers
138
views
Radiations in static fields by poynting Vector
Why is the Poynting vector $\vec S=\frac{1}{\mu_0}(\vec E\times \vec B)$ not able to produce radiation when fields are static?
- 193
2
votes
0
answers
70
views
A travelling field; Feynman lectures on Physics Volume 2
In Feynman's Lectures on Physics, volume 2, Chapter 18 (18-5), we look at the creation of a electromagnetic field, due to a moving infinite sheet of charge,
By looking at the Maxwell equations ...
- 455
2
votes
3
answers
1k
views
How do near-field EM fields change to far-field EM waves at an antenna
What is the mechanism by which the near-field non-traveling electromagnetic fields in the vicinity of an antenna are changed into the far-field electromagnetic waves traveling at the speed of light? ...
- 249
1
vote
1
answer
15k
views
Why the electric bulb turns on almost instantly when the switch is closed? [duplicate]
The electron drift speed is estimated to be very low.How could there is current almost the instant a circuit is closed??
By the discussions it is known that The information about beginning of the ...
- 5,819
1
vote
2
answers
66
views
Why magnetic and electric field static
When charge moves at a constant speed, it is said that it produces static magnetic and electric field.
Why static ? If it moves, at every points, electric field and magnetic field change as they are ...
1
vote
1
answer
383
views
Are electric field lines always perpendicular to a conductor's surface?
I know that in a conductor body, in an electrostatic situation (Where $\vec E=0$ in the interior), the E field must be perpendicular to the surface outside because it is solely generated by electric ...
user336281