A heat engine operates between a high temperature reservoir at T_H and a low temperature reservoir at T_L.Its efficiency is given by 1 - T_L/T_H: A)only if the working substance is an ideal gas B)only if the engine is reversible C)only if the engine is quasi-static D)only if the engine operates on a Stirling cycle E)no matter what characteristics the engine has

Question

Quizplus · Accepted Answer

The efficiency of a heat engine is given by 1 - Tl/Th, where Tl is the temperature of the low temperature reservoir and Th is the temperature of the high temperature reservoir. This formula applies to all heat engines, but its validity depends on the assumptions made about the engine. If the engine is reversible, then the formula gives the maximum possible efficiency. If the engine is not reversible, then the efficiency will be less than the maximum. Since the formula is valid for all heat engines, choice (A) is incorrect. Since the formula is valid for both quasi-static and non-quasi-static engines, choice (C) is incorrect. Since the formula applies to all heat engines, choice (D) is incorrect. Therefore, the best choice is (B), only if the engine is reversible.

A Heat Engine Operates Between a High Temperature Reservoir at TH

A Heat Engine Operates Between a High Temperature Reservoir at T_H