
#1
Nov413, 01:58 PM

P: 995

As far as I understand: In the Drude model we take the electron to be moving in a random direction after each collision (*), such that the mean velocity is simply the average of eEt/m, which is just eEτ/m, where τ is the relaxation time.
But Im very confused about this basic assumption (*), if the electron has a velocity in the direction of the field and suffers collision with another electron, it does not seem likely that the direction of the velocity of the 2 electrons after collision will be completely random. 



#2
Nov413, 02:33 PM

Thanks
P: 1,364

I wrote some details on this last winter for a class; see #7 in this thread:
http://www.physicsforums.com/showthread.php?t=712978 



#3
Nov513, 05:43 AM

P: 995

That was quite helpful. Now I don't suppose you could help me interpreting another
l) states that the equation for the displacement of a Fermi sphere is (all h's are hbars): h(d/dt + 1/τ)δk = F Now Newtons law for a completely free electron is: hdk/dt = F Why have they put in a δk, and how is the equation to be interpreted? Does it represent the motion of the Fermi sphere in steady state? 



#4
Nov513, 06:45 AM

Thanks
P: 1,364

Drude model
Probably the variation of k ...
You would get more attention by posting a new question. 


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