In a cyclic process, work done by the system is

A metal sphere cools at a rate of $1.5^{\circ} \mathrm{C} / \mathrm{min}$ when its temperature is $80^{\circ} \mathrm{C}$. When the temperature of the sphere is $40^{\circ} \mathrm{C}$, its rate of cooling is $0.3^{\circ} \mathrm{C} / \mathrm{min}$. The temperature of the surrounding $\left(\theta_0\right)$ is

The change in the internal energy of the mass of gas, when the volume changes from V to 2 V at constant pressure P is $\left(\gamma=\frac{\mathrm{Cp}}{\mathrm{Cv}}\right)$

For a perfectly black body, coefficient of emission is