Question

Which of the following law states that "good absorbers of heat are good emitters"?

• A. Stefan's law
• B. Kirchhoff's law
• C. Planck's law
• D. Wien's law

Answer 1

The correct option is B Kirchhoff's law

Kirchhoff's law states that, the ratio of emissive power to the absorptive power corresponding to a particular wavelength and at a given temperature is constant for all bodies:

$e_{\lambda }/a_{\lambda }=constant=E_{\lambda }$

where $E_{\lambda }=$ emissive power of a perfect black body corresponding to same wavelength and temperature, it is clear from above relation that if $a_{\lambda }$ (absorptive power) is large for a body, $e_{\lambda }$ (emissivetive power) will also be large to keep the ratio constant i.e. good absorbers are good emitters.