$A$ solid sphere at a temperature $T \ K$ is cut into two hemispheres. The ratio of energies radiated by one hemisphere to the whole sphere per second is

State and explain the Stefan-Boltzmann law.

The temperature of a spherical black body is inversely proportional to its radius. If its radius is doubled,then the power radiating from it will be

$A$ black body of surface area $10 \ cm^2$ is heated to $127^{\circ}C$ and is suspended in a room at temperature $27^{\circ}C$. The initial rate of loss of heat from the body at the room temperature will be ...... $W$.

If the temperature of a hot body is increased by $50 \%$,then the increase in the quantity of emitted heat radiation will be approximately (in $\%$)

The 'Kangri' is an earthen pot used to stay warm in Kashmir during the winter months. Assume that the 'Kangri' is spherical and of surface area $7 \times 10^{-2} \,m^{2}$. It contains $300 \,g$ of a mixture of coal,wood,and leaves with a calorific value of $30 \,kJ/g$ (and provides heat with $10 \%$ efficiency). The surface temperature of the 'Kangri' is $60^{\circ}C$ and the room temperature is $0^{\circ}C$. Then,a reasonable estimate for the duration $t$ (in $h$) that the 'Kangri' heat will last is (take the 'Kangri' to be a black body).