Answer: Hot to cold body.
- A Cold to hot body
- B Hot to cold body
- C Either direction
- D Only at phase changes
Correct answer: B. Hot to cold body
Explanation: Second law: heat flows spontaneously from higher temperature (hot) to lower temperature (cold).
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.