PHYS 445 Lecture 24  Density of states
24  1
© 2001 by David Boal, Simon Fraser University.
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Lecture 24  Density of states
What's Important:
•
density of states in phase space
Text
: Reif
Counting quantum states
Some time back, we said that we needed to introduce a "density of states" factor in
order to convert a sum over discrete states into an integral over continuum states:
Σ
r
exp(
r
)
→
∫
d
3
q
d
3
p
exp(
).
Similarly, we have now evaluated the number distributions for photons, BE and FD
systems, as a function of
r
and
N
.
But what is
N
for a box of photons?
We now address these issues with a digression into quantum mechanics.
The "old"
quantum theory will be used, based upon de Broglie's idea that a particle has wave
characteristics by virtue of its momentum:
=
h
/
p
(verified by neutron scattering)
Suppose that we place a number of particles with their associated waves in a cubic
box with perfectly reflecting walls.
If there are interactions among the particles, then
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 Spring '08
 DavidBoal
 Physics, NZ, Emax, David Boal

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