Question

A Carnot engine, whose sink is at 300 K, has an efficiency of 40%. By how much the source temperature should be changed so as to increase the efficiency to 60% ?

• A. 250K increase
• B. 250 K decrease
• C. 325 K increase
• D. 325 K decrease

Answer 1

Answer: (A)

250K increase

Efficiency of a carnot engine$\left(\eta \right)=1-\frac{T_c}{T_h}$
$0.4=1-\frac{300}{T_h}$
$T_h=\frac{300}{0.6}=500K$
For the efficiency to be 0.6;
$0.6=1-\frac{300}{T_h}$
$T_h=\frac{300}{0.4}=750K$
Change in temperature$=750-500=250K$
Option A.