Two different adiabatic paths for the same gas intersect two isothermals at as shown in the P −V diagram (Fig). Then
The two adiabatic paths ad and bc for the gas intersect the two isothermals ab and cd
at temperatures (see Fig.). Since points a and d lie on the same adiabatic path,
we have
[1]
Since points b and c also lie on the same adiabatic path,
[2]
From (1) and (2), we get