An ideal Carnot's engine whose efficiency 40% receives heat of 500K. If the efficiency is to be 50% then the temperature of sink will be

Options

A. 600 K
B. 700 K
C. 800 K
D. 900 K

Answer

B

Explanation

As the resistance of the rheostate decreases, overall resistance of the circuit decreases there for current through the cell will increase. Resulting in decrease in terminal voltage = E - ir across the cell. Due to this. Current through constant resistor `R=(E-ir)/(R)` will decrease.