The area of the hole of a heat furnace is $10^{-4} \ m^2$. It radiates $1.58 \times 10^5 \ cal$ of heat per hour. If the emissivity of the furnace is $0.80$,then its temperature is .......... $K$.

The energy spectrum of a black body has maximum energy at a wavelength of $\lambda_0$. Now, the temperature of the black body is increased such that the maximum energy is obtained at a wavelength of $3\lambda_0/4$. By what factor will the power radiated by the black body increase?

If the temperature of the sun (black body) is doubled,the rate of energy received on earth will be increased by a factor of

$A$ black body radiates heat energy at the rate of $2 \times 10^5 \, J/s \cdot m^2$ at a temperature of $127 \, ^\circ C$. The temperature of the black body at which the rate becomes $32 \times 10^5 \, J/s \cdot m^2$ is ....... $^\circ C$.

The temperature of a black body reduces to half of its initial value. By what fraction will the amount of radiation emitted reduce?

Find the rate of radiation emitted per unit area per unit time by a black body at a temperature of $10^{3} \ K$ (in $J \ m^{-2} \ s^{-1}$).