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JEE Main 2023 (12 Apr, Shift 1) · Heat Engines, Refrigerators & Second Law

Heat Engines, Refrigerators & Second Law question from JEE Main 2023 (12 Apr, Shift 1)

Q25JEE Main 2023 · 12 APR · SHIFT 1Medium

Heat Engines, Refrigerators & Second Law

An engine operating between the boiling and freezing points of water will have

A. efficiency more than 27%.

B. efficiency less than the efficiency of a Carnot engine operating between the same two temperatures.

C. efficiency equal to 27%27\%

D. efficiency less than 27%27\%

Choose the correct answer from the options given below:

Show answer and solution

Answer: (b)

  1. Carnot efficiency between 373 K and 273 K: ηC=1−273373=100373≈26.8%≈27%\eta_C = 1 - \frac{273}{373} = \frac{100}{373} \approx 26.8\% \approx 27\%.
  2. A: false, no engine can exceed the Carnot efficiency (about 27%).
  3. B: true, a real engine is less efficient than a Carnot engine between the same temperatures.
  4. C: false and D: true, since a real engine has η<ηC≈27%\eta < \eta_C \approx 27\%.
  5. So the answer is (b) B and D only.
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