Answer the following questions related to thermal radiation without performing detailed numerical calculations.
a. (a) State Stefan–Boltzmann law for thermal radiation from a perfect blackbody.
b. (b) Explain, on the basis of this law, why the brightness of an electric heating coil increases rapidly when its temperature is raised by a modest amount.
c. (c) Distinguish between a perfect blackbody and a real body with regard to (i) absorptive power and (ii) emissivity.