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Entropy in heat flow

Page history last edited by Joe Redish 6 years, 1 month ago

7.3.1.P3

 

1. Suppose we have two identical boxes of matter, A and B, that are in thermal contact but cannot exchange materials. They come to thermal equilibrium. System 1 consists of box A alone, while system 2 consists of both boxes A and B. What can you say about the entropy of the two systems?

 

A. The entropy of system 2 is twice as high as that of system 1.

B. The entropy of system 2 is a lot more than twice as high compared to system 1.

C. The number of microstates of system 2 is twice as high as those of system 1.

D. The number of microstates of system 2 is a lot more than twice as high as those of system 1.

E. You can’t tell anything about the comparative entropy of the two systems without more information.

 

2. Two rooms of a cabin are kept at different temperatures, as shown. If 5 J of energy pass through the interior wall from room 2 to room 1, the exchange is too small to change the temperature of either room by a measurable amount. S1 and S2 are the entropies of the two rooms. If only this exchange occurs

 

  1. S1 and S2 decrease by equal amounts.
  2. S1 and S2 decrease by unequal amounts.
  3. S1 increases, but S2 decreases by more.
  4. S1 increases and S2 decreases, but S1 increases by more. 
  5. S2 increases, but S1 decreases by more.
  6. S2 increases and S1 decreases, but S2 increases by more. 
  7. S1 increases and S2 decreases by equal amounts.
 

 

 

3.  Suppose a small amount of heat Q flows from a system A at high temperature (350K) to a system B at low temperature (250K). If Q = 0.5 J, mA = 1.2 kg, and mB = 0.6 kg, what will the total entropy change of the system be as a result?

 

 

 

Ben Geller 2/18/13

 

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