If the ratio of specific heat of a gas at constant pressure to that at constant volume is γ, the change in internal energy of a mass of gas when the volume changes from V to 2V under constant pressure p is:

Two walls of thickness d1 and d2 and thermal conductivities k1 and k2 are in contact. In the steady-state, if the temperatures at the outer surfaces are T1 and T2, the temperature at the outer wall is: