Answer: Work output / Heat input.
- A Work output / Heat input
- B Heat output / Heat input
- C Heat input / Work output
- D Work output / Heat rejected
Correct answer: A. Work output / Heat input
Explanation: Efficiency = W/Q<sub>in</sub> = work output / heat absorbed from hot source.
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.