Question

Assertion :A body that is good radiator is also a good absorber of radiation at a given wavelength. Reason: According to Kirchoff's law the absorptivity of a body is equal to its emissivity at a given wavelength.

• 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 C Assertion is correct but Reason is incorrect

According to Kirchoff's law
$\frac{e_{\lambda }}{a_{\lambda }}=E_{\lambda }$
Here, $E_{\lambda }$ is emissivity of black body which is constant, so, $e_{\lambda }\propto a_{\lambda }$. It means good emitter are good absorber of radiation.