Question

The absorptivity for a black body is

• A. \(0\)
• B. \(1\)
• C. \(0.8\)
• D. \(0.95\)

Hint:

A black body is a perfect absorber, so its absorptivity is \(1\).

Answer 1

The Correct Option is B

A black body is an ideal body. It absorbs all radiation falling on it. Absorptivity is defined as: \[ \alpha=\frac{\text{radiation absorbed}}{\text{radiation incident}} \] For a black body, all incident radiation is absorbed. So: \[ \text{radiation absorbed}=\text{radiation incident} \] Therefore: \[ \alpha=1 \] A perfect reflector would have absorptivity zero. But a black body is a perfect absorber. Hence, the absorptivity of a black body is: \[ 1 \]