Which of the following graphs correctly represents the relation between $\ln E$ and $\ln T$, where $E$ is the amount of radiation emitted per unit time from unit area of a body and $T$ is the absolute temperature?

Spheres $P$ and $Q$ are uniformly constructed from the same material,which is a good conductor of heat,and the radius of $Q$ is thrice the radius of $P$. The rate of fall of temperature of $P$ is $x$ times that of $Q$ when both are at the same surface temperature. The value of $x$ is:

Two spherical black bodies have radii $r_1$ and $r_2$. Their surface temperatures are $T_1$ and $T_2$. If they radiate the same power,then $\frac{r_2}{r_1}$ is:

Two bodies $A$ and $B$ have emissivities of $0.01$ and $0.81$ respectively. The outer surface areas of both bodies are the same. Both bodies emit total radiant power at the same rate. The wavelength $\lambda_B$ corresponding to the maximum spectral radiance for body $B$ is $1.0 \mu m$. If the temperature of body $A$ is $5802 \ K$,then the temperature of body $B$ is .... $K$.

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.

The unit of Stefan's constant is: