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 per second by the first sphere to that by the second is

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 ....... $W$.

If the temperature of the $Sun = 6000 \, K$,the radius of the Sun is $7.2 \times 10^{5} \, km$,the radius of the Earth is $6000 \, km$,and the distance between the Earth and the Sun is $15 \times 10^{7} \, km$,find the intensity of light on Earth.

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

Two spherical black bodies of radii $r_1$ and $r_2$ and with surface temperatures $T_1$ and $T_2$ respectively radiate the same power. Then the ratio of $r_1$ and $r_2$ will be:

At what temperature $T$ (in $K$) will a perfectly black body radiate energy at the rate of $5.67 \, W \, cm^{-2}$ (in $, K$)? Given Stefan's constant $\sigma = 5.67 \times 10^{-8} \, W \, m^{-2} K^{-4}$.