Answer: Is positive.
- A Is zero
- B Is positive
- C Is negative
- D Equals change in internal energy
Correct answer: B. Is positive
Explanation: Isothermal expansion: gas does positive work on surroundings (W > 0). Temperature stays constant so delta U = 0, Q = W.
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.