Question

If between wavelength $\lambda$ and $\lambda +d\lambda ,e_{\lambda }$ and $a_{\lambda }$ be the emissive and absorption powers of a body and $E_{\lambda }$ be the emissive power of a perfectly black body, then according to Kirchoff's law, which is true?

• A. $e_{\lambda }=a_{\lambda }=E_{\lambda }$
• B. $e_{\lambda }{E}_{\lambda }=a_{\lambda }$
• C. $e_{\lambda }=a_{\lambda }{E}_{\lambda }$
• D. $e_{\lambda }{a}_{\lambda }{E}_{\lambda }=constant$

Answer 1

The correct option is C $e_{\lambda }=a_{\lambda }{E}_{\lambda }$

According to $Kirchof{f}^{\prime }slaw$, the ratio of $emissivepower$ to $absorptivepower$ is the same for all bodies is equal to the $emissive$ power of a perfectly black body i.e., $e_{\lambda }=a_{\lambda }{E}_{\lambda }$ .