Question

Assertion :The absorbance of a perfect black body is unity. Reason: A perfect black body when heated emits radiations of all possible wavelengths at that temperature.

• A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
• B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
• C. Assertion is correct but Reason is incorrect
• D. Both Assertion and Reason are incorrect

Answer 1

The correct option is B Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion

Radiation moves through space in straight lines, or beams, and only substances in sight of a radiating body can intercept radiation from that body. The fraction of the radiation is called the reflectivity, r. The fraction that is absorbed is called the absorptivity, a. The fraction that is transmitted is called the transmissivity, t.

The sum of these fractions must be unity, r+a+t=1.

The maximum possible absorptivity is unity, attained only if the body absorbs all radiation incident upon it and reflects or transmits none. A body that absorbs all incident radiation is called a black body.

A perfectly black body heated emits radiations of all possible wavelengths at a particular temperature due to black body radiation.