Question

Define 'emissive power' and coefficient of emission of a body.

Answer 1

Emissive power of a body at a given temperature is the quantity of radiant energy emitted by the body per unit time per unit surface area of the body at that temperature.
If '$Q$' is the amount of radiant energy emitted, '$A$' is the surface area of the body and '$t$ ' is the time for which body radiates energy, then the emissive power is
$E=\frac{Q}{At}$
Coefficient of emission of a body is the ratio of the emissive power of the body at a given temperature to the emissive power of a perfectly black body at the same temperature.
Coefficient of emission, $e=\frac{E}{E_b}$