Question
The efficiency of heat engine cannot be $100\%$. Explain?
✓
Answer
The efficiency of heat engine is given by, $\eta=1-\frac{\text{Q}_2}{\text{Q}_1}$ $\text{Q}_2=$ Heat rejected to the sink, $\text{Q}_1=$ Heat absorbed from the source $\eta=1$ or 100% if and only if $Q_2 = 0$ This cannot happen because if $Q_2 = 0$, then the temperature of the working substance will go on increasing. A stage will come when the temperature of the working substance becomes equal to the temperature of the source. In this situation, there is no transfer of heat from source to the working substance. Hence, we will not get the output.
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