Question 18. Emissivity of perfectly black body is (a) 1 (b) 2 (c) 5 (d) 0 Answer
Correct option is B) Emissivity of a perfect black body is always 1. The best absorber is defined as the object which can absorb all the electromagnetic radiations falling upon it. The black body is not only a perfect absorber but it is also the best in emitting radiation. Also, a black bosy in thermal equlibrium has emissivity, ϵ=1
