The ratio of the pressure power to the absorption power of all substances for a particular wavelength is the same at given temperature. The ratio is known as

Options

A. the emissive power of a perfectly black body
B. the emissive power of any type of body
C. the Stefan's constant
D. the Wien's law

Answer

A

Explanation

According to Kirchoff's law,
`(e_(lambda)/a_(lambda))_("Any body") = (e_(lambda)/a_(lambda))_("Perfectly black body") = E_(lambda)`
where `E_(lambda)` is emissive power of a perfectly black body.