Chapter 19 - Heat Engines and Refrigerators - Exercises and Problems - Page 550: 23

a) $ \eta = 0.25 =25\%$ b) $T_C = 231.75^oC$

a) We have $W = Q_H -Q_C $ $ 200J = Q_H - 600J$ $Q_H = 800J$ Now, $ \eta = \frac{W}{Q_H} = \frac{200}{800}$ $ \eta = 0.25 =25\%$ b) Now, $ \eta = 1- \frac{T_C}{T_H}$ $ 0.25 =1- \frac{T_C}{(400+273)K}$ $ T_C = 0.75* 673K = 504.75K$ $T_C = 231.75^oC$