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 $\sigma = 5.7 \times 10^{-8} W m^{-2} K^{-4}$.

Three very large plates of the same area are kept parallel and close to each other. They are considered as ideal black surfaces and have very high thermal conductivity. The first and third plates are maintained at temperatures $2T$ and $3T$ respectively. The temperature of the middle (i.e.,second) plate under steady-state condition is

$A$ black rectangular surface of area $A$ emits energy $E$ per second at $27^{\circ}C$. If the length and breadth are reduced to half of their initial values and the temperature is raised to $327^{\circ}C$, then the energy emitted per second becomes: (in $E$)

$A$ body radiates energy at a rate of $5 \ W$ at a temperature of $127^{\circ}C$. If the temperature is increased to $927^{\circ}C$,then it radiates energy at the rate of ...... $W$.

The ratio of the energy of emitted radiation of a black body at $27^{\circ}C$ and $927^{\circ}C$ is:

$A$ black sphere has radius $R$ whose rate of radiation is $E$ at temperature $T$. If the radius is made $R/3$ and the temperature $3T$,the rate of radiation will be: