The temperature of a lamp filament is $2100 \ K$ and its surface area is $4 \times 10^{-4} \ m^2$. If the emissivity of the filament is $0.453$,then the power of the lamp will be ....... $W$.

The temperatures of two bodies $A$ and $B$ are respectively $727^{\circ}C$ and $327^{\circ}C$. The ratio $H_A:H_B$ of the rates of heat radiated by them is

Two black spheres $P$ and $Q$ have radii in the ratio $4:3$. The wavelengths of maximum intensity of radiation are in the ratio $4:5$ respectively. The ratio of radiated power by $P$ to $Q$ is

At $273^{\circ} C$,the emissive power of a perfectly black body is $R$. Its emissive power at $0^{\circ} C$ is:

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

$A$ black rectangular surface of area $A$ emits energy $E$ per unit time at $27^{\circ}C$. If length and breadth are reduced to $(1/4)^{th}$ of their initial values and the temperature is raised to $327^{\circ}C$, then the energy emitted per unit time becomes: