Question

A Carnot engine, having an efficiency of $\frac{1}{10}$ as heat engine, is used as a refrigerator. If the workdone on the system is $10J$, the amount of energy absorbed from the reservoir at lower temperature is

• A. $99J$
• B. $90J$
• C. $1J$
• D. $100J$

Answer 1

The correct option is B $90J$

Efficiency of Carnot Cycle:

$\eta =\frac{W}{Q_H}$

Also, $Q_H=Q_C+W$

As efficiency is $10$% and $W=10J$

Therefore; $0.1=\frac{10}{Q_H}\Rightarrow Q_H=100J{Q}_c=Q_H-W=90J\left(reservoiratlowertemperature\right)$