Which statements about thermodynamic processes and heat engines is/are correct?
1. Work done in irreversible expansion is greater than in quasi-static expansion.
2. Efficiency of an ideal heat engine depends only reservoir temperatures.
3. Heat flows from cold to hot only with external work.
Show answer & explanation
Correct answer: B
Explanation
The correct answer is option 2 i.e. 2 and 3 only.
Statement 1 is false because work done in a quasi-static (reversible) expansion is always the maximum possible work; irreversible processes involve losses like friction.
Statement 2 is correct as the efficiency (η) of a Carnot engine is given by η = 1 - TL/TH, depending solely on absolute temperatures. Statement 3 is a direct consequence of the Second Law of Thermodynamics (Clausius Statement), asserting that heat cannot spontaneously flow from a colder to a hotter body without external work.