Question

A carnot engine absorbs $760kJ$ heat from a source at $380K$. It rejects
(I) $650kJ$,
(II) $560kJ$
of heat to sink at $280K.$ State which of these represent a reversible and irreversible cycle.

• A. I - Reversible , II - Irreversible
• B. I - Reversible, II - Reversible
• C. I - Irreversible, II - Irreversible
• D. I - Irreversible, II - Reversible

Answer 1

The correct option is D I - Irreversible, II - Reversible

$\text{Efficiency of carnot engine}\left(\eta \right)=\frac{Q_h-Q_c}{Q_h}=\frac{T_h-T_c}{T_h}$
According to given data,
${\eta }_{rev}=\frac{380-280}{380}=0.2631$

For cycle I :
${\eta }_1=\frac{760-650}{760}=0.1447$
$\because {\eta }_1<{\eta }_{rev}$
Hence cycle is irreversible.

For cycle II :
${\eta }_2=\frac{760-560}{760}=0.2631$
$\because {\eta }_2={\eta }_{rev}$
Hence the cycle is reversible.