Answer: Conservation of energy.
- A Entropy always increases
- B Conservation of energy
- C Heat flows from cold to hot
- D Temperature is absolute
Correct answer: B. Conservation of energy
Explanation: The first law is conservation of energy: delta U = Q - W (internal energy change = heat added - work done by system).
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.