Question

For a perfectly black body, coefficient of emission is ______.

Options

• zero

• unity

• less than one (non-zero)

• infinity

Answer 1

For a perfectly black body, coefficient of emission is unity.

Explanation:

A perfectly black body is an ideal emitter that absorbs all incident radiation completely, so by definition its coefficient of emission (emissivity) equals 1 (unity), the maximum possible value, since emissivity is the ratio of radiation emitted by a body to that emitted by a perfect black body at the same temperature.