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 on reservoir temperatures. 3. Heat flows from cold to hot only with external work.
2 and 3 only
Statement 1 — FALSE. For a gas expanding between the same two states, the work done is maximum in a quasi-static (reversible) process and less in an irreversible expansion. So work in irreversible expansion is smaller, not greater.
Statement 2 — TRUE. The efficiency of an ideal (Carnot) heat engine is \(\eta = 1 - \dfrac{T_C}{T_H}\), which depends only on the absolute temperatures of the cold (\(T_C\)) and hot (\(T_H\)) reservoirs.
Statement 3 — TRUE. By the Second Law of Thermodynamics (Clausius statement), heat cannot flow spontaneously from a colder body to a hotter body; transfer in that direction requires external work, as in a refrigerator or heat pump.
Hence statements 2 and 3 are correct → option B.
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In summer season, the top and outer surface of the house are painted white because:
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A body in motion essentially acquires
A. Kinetic energy
B. Potential energy
C. Mechanical energy
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