Answer: Zero.
- A Maximum
- B Positive
- C Negative
- D Zero
Correct answer: D. Zero
Explanation: After a complete cycle, system returns to initial state. State function U depends only on state, so delta U = 0 for any cycle.
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.