Calculate the radiation power for a sphere whose temperature is $227^{\circ} C$,radius is $2\, m$,and emissivity is $0.8$ (in $W$).

$A$ 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 ...... $W$.

$A$ black rectangular surface of area '$A$' emits energy '$E$' per second at $27^{\circ} C$. If length and breadth are reduced to $\frac{1}{3}$ of their initial values and the temperature is raised to $327^{\circ} C$,then the energy emitted per second becomes:

The outer surface of a star in the form of a sphere radiates heat as a black body at temperature $T$. The total radiant energy per unit area,normal to the direction of incidence,received at a distance $R$ from the center of a star of radius $r$ is $(R > r)$ ($\sigma =$ Stefan's constant).

If the temperature of a body is increased from $-73^{\circ}C$ to $327^{\circ}C$,the ratio of its emissive power will be ...

Two spheres of the same material have radii $1 \ m$ and $4 \ m$ and temperatures $4000 \ K$ and $2000 \ K$ respectively. The ratio of the energy radiated by them is .....