A Carnot engine operates between reservoirs at 600 K and 300 K. Its maximum possible efficiency is
Correct answer: B. 50 per cent
- A. 20 per cent
- B. 50 per cent
- C. 75 per cent
- D. 100 per cent
Explanation
Carnot efficiency is 1 minus the ratio of the cold to the hot absolute temperature, which is 1 minus 300 over 600, giving 0.5 or 50 per cent. The temperatures must be in kelvin for this to work; using degrees Celsius gives nonsense. No real engine between the same two reservoirs can beat this figure.
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About First Law of Thermodynamics
The first law relates heat supplied, work done and the change in internal energy through energy conservation. Problems use sign conventions and apply the law to isothermal, adiabatic, isobaric and isochoric processes. Internal energy is a state function, while heat and work depend on the path followed.
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