SAT Subject Physics Practice Question 137: Answer and Explanation

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Question: 137

10. Of the following, which is the best description of the second law of thermodynamics?

A. The total energy of the universe is a constant.
B. The efficiency of a heat engine can never be greater than 50 percent.
C. The amount of heat required to vaporize a liquid is greater than the amount of heat required to melt a solid of the same substance.
D. The entropy of the universe is always increasing.
E. As the altitude increases, the boiling point of water decreases.

Correct Answer: D

Explanation:

A is the first law of thermodynamics. C and E are true, but they are not equivalent to the second law of thermodynamics. B is false, but if it read, “The efficiency of a heat engine can never be equal to 100 percent,” then it would be equivalent to the Second Law. D is one of the several equivalent forms of the second law of thermodynamics.

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