Question

For any material, if R, T and A represent the reflection coefficient, transparent coefficient and absorption coefficient respectively, then, for a blackbody which one of the following is true ?

• A. \(R = 1, T = 0, A = 0 \)
• B. \(R = 1, T = 1, A = 0 \)
• C. \(R = 0, T = 1, A = 1 \)
• D. \(R = 0, T = 0, A = 1 \)
• E. \(R = 0, T = 1, A = 0 \)

Hint:

A blackbody appears "black" because it reflects nothing ($R=0$) and transmits nothing ($T=0$), capturing all light that hits it.

Answer 1

The Correct Option is D

Concept: For any surface, the incident radiation is distributed among reflection, absorption, and transmission: \[ A + R + T = 1 \] where \(A\) is absorptance, \(R\) is reflectance, and \(T\) is transmittance.

Step 1: Apply the definition of a blackbody.
By definition, a blackbody is a perfect absorber of all incident radiation, regardless of wavelength or angle. Therefore, the absorption coefficient \(A = 1\).

Step 2: Evaluate other coefficients.
If all radiation is absorbed (\(A = 1\)), there is no energy left to be reflected or transmitted. Thus, \(R = 0\) and \(T = 0\).