At a certain temperature for a given wavelength,the ratio of the emissive power of a body to the emissive power of a black body in the same circumstances is known as:

Out of the following, which statement is $NOT$ true about black body radiation?

If $e_\lambda$ and $a_\lambda$ are the emissive power and absorptive power of a body respectively,and $E_\lambda$ is the emissive power of a perfectly black body,what is the relation according to Kirchhoff's law?

The sun radiates electromagnetic energy at the rate of $3.9 \times 10^{26} \ W$. Its radius is $6.96 \times 10^8 \ m$. The intensity of sunlight at the solar surface will be (in $W/m^2$):

$A$ sphere,a cube,and a thin circular plate,all made of the same material and having the same mass,are initially heated to a temperature of $1000^{\circ}C$. Which one of these will cool first?

Heat energy is incident on the surface of a material at the rate of $1000 \ J \ min^{-1}$. If the coefficient of absorption is $0.8$ and the coefficient of reflection is $0.1$,then the amount of heat energy transmitted through the material in $5$ minutes is: (in $J$)