6,129 reputation
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location Massachusetts
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visits member for 3 years, 1 month
seen 10 hours ago

Aug
8
answered What's the electric field intensity inside parallel-plate capacitor filled with water?
Aug
7
answered What voltages are used to “safely” shock someone (as in a carnival game)
Aug
3
comment Particle as a representation of the Lorentz group
For good discussion, see Weinberg, The Quantum Theory of Fields, Volume 1, Chapter 2 appendix A and B.
Aug
2
answered Electrial Conductivity of Thin Metal Films
Aug
2
comment total noise power of a resistor (all frequencies)
This related question has a nice discussion. The answer cites a "classic" 1946 paper by Robert Dicke (free link , official link). The discrepancy between 3D mode density and 1D mode density helps explain some facts in antenna theory, particularly the fact that antennas larger than 1 square wavelength have to have a narrow acceptance angle.
Aug
2
comment total noise power of a resistor (all frequencies)
Thanks, that's what I was looking for. Maybe there is no universal official name for the constant, but "one-dimensional analogue of the Stefan-Boltzmann constant" is pretty good. Since the oscillations in a wire or resistor are stuck in one dimension, there are many fewer high-energy modes, so extra temperature does not as dramatically grow the total power. That makes sense.
Aug
1
comment Electrial Conductivity of Thin Metal Films
How thin? Few atoms? Few million atoms?
Aug
1
accepted total noise power of a resistor (all frequencies)
Aug
1
awarded  Enthusiast
Jul
28
comment Polarization true or false: Repeating circular filters is different from repeating linear filters?
@straups -- thanks, I corrected.
Jul
28
revised Polarization true or false: Repeating circular filters is different from repeating linear filters?
correct error, thanks straups
Jul
27
comment Advice on classes: Theoretical Mechanics vs E&M II
Three classes of Griffiths is enough for a lifetime? Personally, I would say a whole lifetime of Griffiths is not enough for a lifetime. How I love it!
Jul
27
asked total noise power of a resistor (all frequencies)
Jul
27
revised Polarization true or false: Repeating circular filters is different from repeating linear filters?
added 214 characters in body
Jul
27
answered Polarization true or false: Repeating circular filters is different from repeating linear filters?
Jul
27
comment Electromagnetic wave reflection vs. light reflection
"ionosphere has a different refractive index" is correct, not hand-waving. Higher conductivity means larger imaginary part of refractive index - link.
Jul
25
comment Is it theoretically possible to reach 0 kelvin?
the problem is that the words "stand perfectly still" is ambiguous. If you had said WHY it is impossible to "stand perfectly still" then it would have helped us understand what you meant by "stand perfectly still". It seems my first guess at what you meant was wrong. I updated my answer.
Jul
25
revised Is it theoretically possible to reach 0 kelvin?
update
Jul
25
comment Is it theoretically possible to reach 0 kelvin?
@Arnold Neumaier - I am saying something much simpler than you think. When you hear the words "standing still" you interpret it as "RMS velocity is zero". When I hear the words "standing still" I interpret it as "staying in the same state as a function of time." Under my interpretation (but not yours), a ground-state particle is "standing still". I don't know which interpretation had in mind when he asked the question.
Jul
25
comment Is it theoretically possible to reach 0 kelvin?
If a particle is in the ground state of a quantum oscillator, the mean square velocity is positive. But I think a reasonable person could argue that the particle was "standing still", in the sense of not changing over time.