Question

Helium gas is subjected to a polytropic process in which the heat supplied to the gas is four times the work done by it. The molar heat capacity of the gas for the process is: (R is universal gas constant)
A. `R//2`
B. `R`
C. `2//R`
D. `3//R`

Answer 1

Correct Answer - C
Given `Delta Q = 4 Delta W`
But, `DeltaW = DeltaU = DeltaQ`
`:. DeltaU = 3DeltaW = 3/4 DeltaQ`
`implies nC_(v)DeltaT = 3/4 n CDeltaT or, C = 4/3 C_(v) = 4/3[(3R)/(2)] = 2R`.