A Carnot engine whose low temperature reservoir is at `7^(@)C` has an efficiency of `50%`. It is desired to increase the efficiency to `70%` By low many degrees should the temperature of the high temperature reservoir be increased

Options

A. 840 K
B. 280 K
C. 560 K
D. 380 K

Answer

D

Explanation

`eta=(T_(1)-T_2)/(T_(1)) implies 1/2 =(T_1-(273+7))/(T_(1)) implies T_1 = 560K`
Now, `eta.=(T_1-T_2)/(T_1) implies 0.7 =(T_1-(273+7))/(T_1)`
`implies T_1 =933 K`
Increase is temperature
`Delta T`=933-560=373K=380K (approx.).