$A$ rectangular black body of temperature $127^{\circ} C$ has surface area $4 \ cm \times 2 \ cm$ and rate of radiation is $E$. If its temperature is increased by $400^{\circ} C$ and surface area is reduced to half of the initial value,then the rate of radiation is:

$A$ metal ball of surface area $200 \; cm^2$ and temperature $527^{\circ}C$ is surrounded by a vessel at $27^{\circ}C$. If the emissivity of the metal is $0.4$,then the rate of loss of heat from the ball is approximately .......... $J/s$. $(\sigma = 5.67 \times 10^{-8} \; J/(m^2 \cdot s \cdot K^4))$

The original temperature of a black body is $727^{\circ}C$. The temperature at which this black body must be raised so as to double the total radiant energy is ....... $K$.

Two spheres of same material and radii $5 \ m$ and $2 \ m$ are at temperatures $200 \ K$ and $250 \ K$ respectively. The ratio of energies radiated by them per second is

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

$A$ black body radiates energy at the rate of $E \ W/m^2$ at a high temperature $T \ K$. When the temperature is reduced to $\frac{T}{2} \ K$,the radiant energy will be