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Even Carnot engine cannot give 100% effi...

Even Carnot engine cannot give `100%` efficiency because we cannot

A

prevent radiation

B

find ideal sources

C

reach absolute zero temperature

D

eliminate friction

Text Solution

Verified by Experts

The correct Answer is:
C
The efficiency of Carnot engine is `eta=1-(T_2"/"1T_1)`
Where,`T_1` is the temperature of the source and `T_2` that of sink.
Since, ` (T_2)/(T_1)=(Q_2)/(Q_1)`
So, `et=1 -(Q_2)/(Q_1)`
To obtain 100% efficiency (i.e.,`eta=1),Q_2` must be zero i.e., 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 2nd law of thermodynamics. Hence, a negative temperature on the absolute scale is impossible. Hence, we cannot reach absolute zero temperature.
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