A Carnot engine works between a source at 500 kelvin and a sink at 300 kelvin. Its efficiency is
- A.40 per cent
- B.60 per cent
- C.20 per cent
- D.About 66.7 per cent
Correct answer
Explanation
The correct answer is A, 40 per cent. The efficiency of an ideal Carnot engine is one minus the ratio of the sink temperature to the source temperature, both in kelvin. Here the ratio is 300 divided by 500, that is 0.6, and one minus 0.6 is 0.4, which is 40 per cent.
Option B, 60 per cent, is the ratio itself rather than the efficiency, the answer of a candidate who forgets to subtract from one. Option C, 20 per cent, comes from dividing the difference of the two temperatures by their sum, which is not the formula. Option D, about 66.7 per cent, comes from dividing the source by the sink, again a misuse of the formula. Note also that the temperatures must be in kelvin; using degrees Celsius in this formula gives a wrong answer every time.
Read the full article: Heat and Thermodynamics: Laws, Latent Heat and Transfer
Practice Questions
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- A.Calorie
- B.Joule
- C.Kelvin
- D.Watt
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- C.100 degrees Celsius
- D.Minus 4 degrees Celsius
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- B.540 calories per gram
- C.336 calories per gram
- D.2260 calories per gram
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- B.Radiation only
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