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GATE 2023 CH – Question 28

Thermodynamics · Laws of thermodynamics, open and closed systems, entropy and chemical potential · 1 mark · Multiple select

Consider a system where a Carnot engine is operating between a source and a sink. Which of the following statements about this system is/are NOT correct?

  1. This engine is reversible.
  2. The engine efficiency is independent of the source and sink temperatures.
  3. This engine has the highest efficiency among all engines that operate between the same source and sink.
  4. The total entropy of this system increases at the completion of each cycle of the engine.

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Show answer and explanation

Correct answer: (B) The engine efficiency is independent of the source and sink temperatures.; (D) The total entropy of this system increases at the completion of each cycle of the engine.

Explanation

A Carnot engine is reversible (A is correct) and it has the highest possible efficiency between two given reservoirs (C is correct). Its efficiency $1 - \frac{T_{sink}}{T_{source}}$ depends on the two temperatures, so B is not correct. For a reversible cycle the total entropy of the engine and the reservoirs stays constant, so D is not correct.