Answer: Q cold /W.
- A W/Q<sub>cold</sub>
- B Q<sub>cold</sub>/W
- C Q<sub>hot</sub>/W
- D W/Q<sub>hot</sub>
Correct answer: B. Q<sub>cold</sub>/W
Explanation: COP = Q<sub>cold</sub>/W (heat removed from cold reservoir per unit work done). A good refrigerator has high COP.
The Carnot cycle alternates two isothermal steps (heat absorbed at TH, released at TC) with two adiabatic steps (no heat exchange); the enclosed loop area equals the net work output, and η = 1−TC/TH is the maximum possible efficiency between those two temperatures.
Concept context
Laws of thermodynamics, heat engines, entropy, and gas processes.