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The efficiency of an ideal heat engine working between the freezing point and boiling point of water, is

1. 26.8%
2. 20%
3. 12.5%
4. 6.25%

Correct answer: 26.8%

Solution

The efficiency of an ideal heat engine is given by η = 1 - (T_c/T_h), where T_c and T_h are the absolute temperatures of the cold and hot reservoirs, respectively. Converting the freezing point (0°C) and boiling point (100°C) to Kelvin, T_c = 273 K and T_h = 373 K. Substituting, η = 1 - (273/373) ≈ 0.268 or 26.8%.

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