Question

The absorption coefficient value of a perfect black body is

• A. zero
• B. \(<1 \)
• C. \(>1 \)
• D. \( 1 \)

Hint:

A perfect black body is also an ideal emitter. According to Kirchhoff's law of thermal radiation, for an object in thermal equilibrium, the emissivity and the absorptivity are equal.

Answer 1

The Correct Option is D

The absorption coefficient \( \alpha \) of a material is a measure of how much radiation it absorbs compared to how much it reflects or transmits. A perfect black body is an idealized physical body that absorbs all incident electromagnetic radiation, regardless of frequency or angle of incidence. Thus, the absorption coefficient of a perfect black body is: \[ \alpha = 1 \] This means it absorbs all incident radiation and does not reflect or transmit any, making it a perfect absorber.