445lec9 - PHYS 445 Lecture 9 Temperature and specific heat...

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9 - 1 © 2001 by David Boal, Simon Fraser University. All rights reserved; further resale or copying is strictly prohibited. Lecture 9 - Temperature and specific heat What's Important: thermal equilibrium temperature zeroth law of thermodynamics equipartition theorem specific heat of an ideal gas Text : Reif Approach to equilibrium (thermal) Let's return to the problem of two systems A and A' being brought into thermal (but not mechanical) contact. Notes : After contact, averages are made over the energies because the systems can exchange energy. The most probable energies are very close to the average energies. By conservation of energy: E f + E ' f = E i + E ' i Note that no averages need be performed over the initial states, as they are in isolation and their energies are constant. Defining Q as the energy absorbed by A , (and Q' by A' ) then Q = E f - E i = E ' i - E ' f = - Q ' or Q + Q' = 0. (9.1) What about the entropy? Recall that the probability in the combined system is given by P ( E ) = const • ( E ) ' ( E' ) The probability of being in the final state is always greater than, or equal to, the probability of being in the initial state, reflecting the number of accessible states: (after) ln f ( E f ) + ln ' f ( E' f ) ln i ( E i ) + ln ' i ( E' i ) (before) But we know that entropy is related to by S = k B ln
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445lec9 - PHYS 445 Lecture 9 Temperature and specific heat...

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