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CHEM 120A
Spring 2005
Lectures 5,6
R. A. Harris
Identical Particles
Identical particles are particles that are the same in certain basic qualities. We shall
give a more precise definition later on. Here, we assume a selfevident definition.
Superposition gives rise to another level of difference beyond that which occurs with
respect to single particles, one that has nothing to do with the interaction between
particles. As with single particles, we'll construct a
gedanken
apparatus to exhibit the
effects of identity.
As before, we'll consider an oversimplified situation. We consider two sources. They
shall both emit particles at a uniform rate towards a screen, x. We place two detectors
behind the screen. We count the coincidences, or number of counts at x
1
and x
2
. This is
similar to what was done in the last section, but the coincidences are at two screens. We
could make generalizations to include time as well. We equally well could consider a
large number of particles from each source at one time as long as the particles don’t
interact, etc.
Here is the apparatus:
x
x
1
, D(x
1
)
x
2
, D(x
2
)
Source a
Source b
First consider classical particles. There are four probabilities: P
a
(x
1
) is the
probability of finding a particle at x
1
which has been emitted from source a; P
a
(x
2
) is the
probability of finding a particle at x
2
which has been emitted from source a; P
b
(x
1
) is the
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View Full Document probability of finding a particle at x
1
which has been emitted from source b; and P
b
(x
2
) is
the probability of finding a particle at x
2
which has been emitted from source b.
x
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This note was uploaded on 09/29/2009 for the course CHEM 120A taught by Professor Whaley during the Spring '07 term at University of California, Berkeley.
 Spring '07
 Whaley
 Physical chemistry, pH

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