$A$ black body at a temperature of $227^{\circ} C$ radiates heat energy at the rate of $5 \ cal/cm^{2}-s$. At a temperature of $727^{\circ} C$,the rate of heat radiated per unit area in $cal/cm^{2}-s$ will be:

Two spheres $S_{1}$ and $S_{2}$ have radii $R$ and $3R$ and temperatures $T$ and $T/3$ respectively. If they are coated with a material of the same emissivity, and the rate of radiation of $S_{1}$ is $E$, then the rate of radiation of $S_{2}$ is:

The unit of Stefan-Boltzmann's constant $(\sigma)$ is:

The total radiant energy per unit area,normal to the direction of incidence,received at a distance $R$ from the centre of a star of radius $r$,whose outer surface radiates as a black body at a temperature $T \ K$ is given by

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

The ratio of radiant energies radiated per unit surface area by two bodies is $16 : 1$. The temperature of the hotter body is $1000 \ K$. Then,the temperature of the colder body will be ....... $K$.