from Per Oni in #15:
"That book was written in 1975 and is generally accepted as a brilliant piece of work. However I do accept that the differences between Fermi speed, thermal velocity, drift speed, signal speed are never well explained anywhere."
I include a pdf version of an article (Conduction.pdf) that gives a nice summary of Drude and Sommerfeld models (unfortunately original online link no longer works). Note it makes the point that the net result gives the same overall figure for conductivity (but very different results for other parameters of interest). That's probably what Mermin meant by classical models working so well. https://www.physicsforums.com/attachment.php?attachmentid=38139&stc=1&d=1313832109
from harrylin in #17:
"Thank you - that little piece of information had not reached me!"
Your welcome Harald.
from Mr.GaGa in #18:
"I read
http://en.wikipedia.org/wiki/Drift_velocity and the velocity of charge(electron) is very slow. Actually, it is the electromagnetic fiel in conductors to transimit energy and signal whose velocity is much faster than light in vacuum. In particular, it is infinity according to the reference (Energy transport faster than light in good conductors, arXiv:/1101.1840v2). Really?"
How that article got published in a peer-reviewed journal is beyond me. No way can be true. For a near monochromatic wave propogating in a hollow waveguide for instance, the phase velocity v
p (speed a crest moves at) exceeds c, but the signal velocity v
s (speed an actual signal moves at) is correspondingly less according to v
pv
s = c
2. When dispersion is high this relation gets a bit fuzzy and the peak value of a pulse can, within the pulse envelope and over a limited duration, move faster than c, but never can the pulse leading edge exceed c, no matter what. See eg
http://en.wikipedia.org/wiki/Superluminal_motion [oops - better one at http://en.wikipedia.org/wiki/Faster-than-light]
Finally, wondering why I have received just one email notification on this thread since my last entry #6! And yes, my settings are still set for automatic 'instant' notification.