Find the radiant energy emitted per second in $Js^{-1}$ by a lamp filament at $2000 K$. The surface area is $5.0 \times 10^{-5} m^{2}$,the relative emissivity is $0.85$,and $\sigma = 5.7 \times 10^{-8} W m^{-2} K^{-4}$.

If the temperature of a perfectly black body is increased by $50\%$,find the percentage increase in the amount of radiation emitted from its surface.

$A$ black body at temperature $127^{\circ} C$ radiates heat at the rate of $5 \ cal / cm^2 \ s$. At a temperature $927^{\circ} C$,its rate of emission in units of $cal / cm^2 \ s$ will be

The temperature of a piece of iron is $27^{\circ}C$ and it is radiating energy at the rate of $Q \text{ kW m}^{-2}$. If its temperature is raised to $151^{\circ}C$,the rate of radiation of energy will become approximately ....... $Q \text{ kW m}^{-2}$.

$A$ black metal foil is warmed by radiation from a small sphere at temperature $T$ and at a distance $d$. It is found that the power received by the foil is $P$. If both the temperature and distance are doubled,the power received by the foil will be:

Two black bodies at temperatures $327^{\circ} C$ and $427^{\circ} C$ are kept in an evacuated chamber at $27^{\circ} C$. The ratio of their rates of loss of heat are :