Question

Volume versus temperature graph of two moles of helium gas is as shown in figure. The ratio of heat absorbed and the work done by the gas in process `1-2` is

A. `3`
B. `5/2`
C. `5/3`
D. `7/2`

Answer 1

Correct Answer - B
`V-T` graph is a straight line passing through origin.
Hence, `V propT` or `P prop` constant
`:. Delta Q = nC_(p)Delta T` and `Delta U = nC_(v)Delta T`
Also `Delta W = Delta Q-Delta U = mu(C_(p)-C_(v))Delta T`
`:. (Delta Q)/(DeltaW) = (nC_(p)DeltaT)/(n(C_p-C_v)DeltaT) = (C_p)/(C_(p)-C_(v)) = (1)/(1-(C_v)/(C_P))`
`(C_v)/(C_p) = 3/5` for helium gas. Hence `(DeltaQ)/(DeltaW) = 1/(1-3//5) = 5/2`.