Question

A carnot engine is operating between 100 degree Celsius and 50 degree Celsius. Its efficiency will be:

13.40%

(B) 15.20% (C) 50%

100%​

Answer 1

Answer:

100%

Explanation:

The easy way to think about it is that you have a rich energy source at 100°C, and you have extracted some of that energy as work when you took it down to 60°C, but in fact you could have tried to take it all the way down to Absolute Zero. That is, you extracted the proportion (T[hot]-T[cold]) / (T[hot]-T[abszero])

This expression in fact works for T[hot] and T[cold] expressed in any temperature scale, including Celsius (where T[abszero]=(-273)), Fahrenheit (where T[abszero]=(-460)) and Kelvin (where T[abszero]=0).

(Incidentally, I said "you could have tried to take it all the way down to Absolute Zero" because the third law of thermodynamics then says you can never quite do this.)