Q.

During an adiabatic process, if the pressure of a gas is found to be proportional to the cube of its absolute temperature, then the ratio of CPCV for the gas is                          [2024]

1 32  
2 75  
3 53  
4 97  

Ans.

(1) 

         P=T3⇒PT-3= constant

        ∵ PVT=nR= constant from ideal gas equation ⇒T=PVnR

         P(PVnR)-3= constant ⇒P-2V-3=constant

        ⇒PV3/2= constant                                   ... (1)

         ∴ Process equation for adiabatic process is 

          PVγ= constant                                           ... (2)

         Comparing equation (1) and (2)

         ⇒CPCV=γ=32