Question

$T_{2}.V_{1}^{\gamma - 1} = T_{3}.V_{2}^{\gamma - 1} $$${\text{and }T_{1}.V_{1}^{\gamma - 1} = T_{4}.V_{2}^{\gamma - 1} }{\therefore\frac{T_{2}}{T_{1}} = \frac{T_{3}}{T_{4}} \Rightarrow \frac{T_{2} - T_{1}}{T_{1}} = \frac{T_{3} - T_{4}}{T_{3}}}$$

$\eta = 1 - \frac{\left| q_{rej} \right|}{q_{abs}} = 1 - \frac{n.C_{V,m}\left( T_{3} - T_{4} \right)}{n.C_{V,m}\left( T_{2} - T_{1} \right)} = 1 - \frac{T_{4}}{T_{1}}$

$= 1 - \left( \frac{V_{1}}{V_{2}} \right)^{\gamma - 1} = 1 - \left( \frac{1}{10} \right)^{\frac{7}{5} - 1} = - 0.6$