Lecture5-6Notes - R. A. Harris Identical Particles CHEM...

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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 self-evident 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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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.

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Lecture5-6Notes - R. A. Harris Identical Particles CHEM...

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