Physics for Scientists and Engineers: A Strategic Approach with Modern Physics (3rd Edition)

Published by Pearson
ISBN 10: 0321740904
ISBN 13: 978-0-32174-090-8

Chapter 19 - Heat Engines and Refrigerators - Exercises and Problems - Page 550: 24

Answer

a) $ \eta =0.4 =40\%$ b) $P_H =400W$ c) $P_C = 666.67W$

Work Step by Step

a) We have $\eta = 1-\frac{T_C}{T_H}$ $\eta =1- \frac{300}{500}$ $ \eta =0.4 =40\%$ b)For carnot engine we have $\frac{Q_H}{Q_C} =\frac{T_H}{T_C}$ $\frac{Q_H}{Q_C} =\frac{500K}{300K}$ $ Q_H = 5/3Q_C$ Now $ \eta =\frac{W}{Q_H}$ Dividing numerator and denominator on right side by $t$, we get $0.4 = P_{out}/P_H$ where $P_H$ is rate of heat input $ P_H = 0.4* P_{out}$ $P_H = 0.4* 1000W$ $P_H =400W$ c) For carnot engine we have $\frac{Q_H}{Q_C} =\frac{T_H}{T_C}$ $\frac{Q_H}{Q_C} =\frac{500K}{300K}$ $ Q_H = 5/3Q_C$ Dividing both sides by $t$ we get $P_H = 0.6 * P_C$ where $P_C $ is rate of heat output $ 400W = 0.6 * P_C$ $P_C = 666.67W$
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