When 2 moles of a monoatomic gas expands adiabatically from a temperature of $80^{\circ} \mathrm{C}$ to $50^{\circ} \mathrm{C}$, the work done is $W$. The work done when 3 moles of a diatomic gas expands adiabatically from $50^{\circ} \mathrm{C}$ to $20^{\circ} \mathrm{C}$, is

A gas absorbs 18 J of heat and work done on the gas is 12 J . Then, the change in internal energy of the gas

If the ratio of the absolute temperature of the sink and source of a Carnot engine is changed from $2: 3$ to $3: 4$, the efficiency of the engine change by