solution for Prelim II

# solution for Prelim II - Cornell University College of...

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2 Problem 1 (30 points) For each of the following statements or equations, say whether it is true or false and provide one sentence of explanation. For example: Statement: For an ideal gas undergoing a process, pv k = constant . Answer: In general this is false. However, it is true for an isentropic process when the specific heats can be considered to be constant. 1) A closed system in communication with a single heat reservoir cannot do work on the surroundings. A) False. It is the case, however, that the system cannot execute a cycle and do work. 2) For a closed system executing a cycle in communication with two heat reservoirs, it is possible to effect a heat transfer Q H > 0 to the high temperature reservoir, while the system receives work W , with W = 1/2Q H . True, for 1 2 / CH TT . The least work possible is for a reversible cycle, for which (1 / ) C H H W T T Q  . 3) A power cycle operating between thermal reservoirs o 800 H TC and o 200 C can have an efficiency of 60%. False. The maximum possible efficiency is 1 / 1 (200 273) / (800 273) 56%   . 4) For a closed system executing a reversible process, the entropy does not change. False. The entropy can change due to heat transfer.
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solution for Prelim II - Cornell University College of...

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