A heat engine executes one complete cycle. The change in entropy of the engine (just the engine, not the external thermal reservoirs) is:
A
zero
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B
greater than zero
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C
less than zero
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D
depends on the type of engine
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Solution
The correct option is A
zero
In one complete cycle, the engine returns to its original state. So all macroscopic variables (N, V, T, S etc) must return to their original state and the change is zero. Remember, even though heat is a path variable, the entropy S is a state variable, hence this stamen will be true even for an irreversible process.