When an ideal diatomic gas undergoes adiabatic expansion, if the increase in its volume is $0.5 \%$, then the change in the pressure of the gas is

To increase the rms speed of gas molecules by $25 \%$, the percentage increase in absolute temperature of the gas is to be

A rectangular slab consists of two cubes of copper and brass of equal sides having thermal conductivities in the ratio $4: 1$. If the free face of brass is at $0^{\circ} \mathrm{C}$ and that of copper is at $100^{\circ} \mathrm{C}$, then the temperature of their interface is

The efficiency of a Carnot's heat engine is $\frac{1}{3}$. If the temperature of the source is decreased by $50^{\circ} \mathrm{C}$ and the temperature of the sink is increased by $25^{\circ} \mathrm{C}$, the efficiency of the engine becomes $\frac{3}{16}$. The initial temperature of the sink is