Question

The thermal efficiency of a heat engine is 25%. If in one cycle the heat absorbed from the hot reservoir is 50000 J, what is the heat rejected to the cold reservoir in one cycle?

Answer 1

Data: η = 25 % = 0.25, Q_H = 50000 J

η = `W/(Q_H)`

∴ W = ηQ_H

= (0.25) (50000) = 12500 J

Also, W = Q_H − |Q_C|

∴ |Q_C| =  Q_H − W

= (50000 − 12500)

= 37500 J

This is the heat rejected to the cold reservoir in one cycle.

[Note: Q_C = − 37500 J]