JEE · NEET Previous Year Question
Even Carnot engine cannot give 100% efficiency because we cannot
Topic: NEET PYQ
Answer: C. Full step-by-step solution below.
- APrevent radiation
- BFind ideal sources
- CReach absolute zero temperature
- DEliminate friction
Correct answer: C
Solution
(c) The efficiency of Carnot engine is,where, is the temperature of the source and that of sink.
Since,
So,
To obtain efficiency (i.e., ), must be zero that is, if a sink at absolute zero would be available, all the heat taken from the source would have been converted into work. The temperature of sink means a negative temperature on the absolute scale at which the efficiency of engine is greater than unity. This would be a violation of the 2 nd law of thermodynamics. Hence, a negative temperature on the absolute scale is impossible. Hence, we cannot reach absolute zero temperature.
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