A Carnot heat engine has an efficiency of `10%`. If the same engine is worked backward to obtain a refrigerator, then find its coefficient of performance.

Options

A. 3
B. 5
C. 7
D. 9

Answer

D

Explanation

Efficiency of carnot engine is, `eta = 1 - (T_(2))/(T_(1))`
`0.1 = 1 - (T_(2))/(T_(1))`
`:. (T_(2))/(T_(1)) = 0.9`
Coefficient of perfomance (COP) of a refrigerator `= (T_(2))/(T_(1) - T_(2)) = (0.9T_(1))/(T_(1) - 0.9T_(1)) = 9`
`:. COP = 9`