Question:
For a perfectly black body, coefficient of emission is
For a perfectly black body, coefficient of emission is
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Black body = Perfect Absorber = Perfect Emitter. In physics, "Unity" always means exactly 1.
Updated On: May 14, 2026
- zero.
- unity.
- less than one (non-zero).
- infinity.
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The Correct Option is B
Solution and Explanation
Step 1: Concept
Kirchhoff's law of thermal radiation states that at a given temperature, the emissivity ($\epsilon$) of a body is equal to its absorptivity ($a$).
Step 2: Meaning
A perfectly black body is an ideal surface that absorbs all incident radiation, meaning its coefficient of absorption $a = 1$.
Step 3: Analysis
Since for a perfectly black body $a = 1$, and by Kirchhoff's law $\epsilon = a$, the coefficient of emission (emissivity) must also be 1.
Step 4: Conclusion
The coefficient of emission is unity. Final Answer: (B)
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