Correct option (a) Both A and R are true and R is the correct explanation of A
Explanation :
When we heat the gas at constant volume, the heat is supplied to raise the temperature of gas only. When we heat the gas at constant pressure, the volume of the gas apart from temperature of the gas rises. When the gas expands, it does some external work for increasing the volume. So in this case, the heat is supplied.
(a) to raise the temperature of the gas.
(b) to do the mechanical work for expansion.
As a result more amount of heat is required to increase the temperature of the gas through the same amount when the pressure is kept constant. Hence Cp is always greater than the value of Cv.
