Question

What relation between emissivity, e, and Absorptive Power, a, is given by Kirchhoff’s law?

(a) e < a

(b) e > a

(c) e = a

(d) no specific relation

I got this question in a national level competition.

My enquiry is from Black Body Radiation topic in chapter Quantum Physics of Engineering Physics I

Answer 1

The correct choice is (c) e = a

For explanation I would say: Kirchhoff’s law states that for any object the emissivity is always equal to absorptive power. For a black body, both of them are equal to one.