$A$ sphere is at temperature $600 \text{ K}$. In an external environment of $200 \text{ K}$, its cooling rate is $R$. When the temperature of the sphere falls to $400 \text{ K}$, then the cooling rate $R'$ will become:

$A$ black body at $227^o C$ radiates heat at the rate of $7 \; cal/cm^2 s$. At a temperature of $727^o C$,the rate of heat radiated in the same units will be:

An object is at a temperature of $400^{\circ}C$. At what temperature would it radiate energy twice as fast? The temperature of the surroundings may be assumed to be negligible.

$A$ star $(P)$ behaves like a perfectly black body emitting radiant energy at temperature $T$. Another star $(Q)$ also behaves like a perfectly black body emitting radiant energy at temperature $T/4$ and has a radius eight times the radius of star $(P)$. The ratio of radiant energy emitted by $(P)$ to that by $(Q)$ is

The rate of radiation of a black body at $0^{\circ} C$ is $E \text{ J}s^{-1}$. The rate of radiation of the black body at $273^{\circ} C$ will be

The area of a hole of a heat furnace is $10^{-4} \ m^2$. It radiates $1.58 \times 10^5 \ \text{calories}$ of heat per hour. If the emissivity of the furnace is $0.80$, then its temperature is ....... $K$.