The absorption coefficient value of a perfect black body is

If $e_\lambda$ and $a_\lambda$ are the emissive power and absorptive power of a body respectively,and $E_\lambda$ is the emissive power of a perfectly black body,what is the relation according to Kirchhoff's law?

$A$ spherical body of emissivity $e = 0.6$ placed inside a perfect black body is maintained at temperature $T$. The energy radiated per second by the body will be:

$A$ thermopile bolometer is used to detect:

$A$ body is said to be opaque to the radiation if ($a$,$r$,and $t$ are the coefficients of absorption,reflection,and transmission,respectively).

Which of the following is best close to an ideal black body?