Defined absorptive power of a body .What is the absorptive power of a perfect black body?

Explanation

Absorptive power of a body is defined as the ratio of energy absorbed by the body within the wave length range of `lambda` and `lambda+d lambda` to the total energy flux following on the body.
absorptive power,
`a_(lambda) = ("Energy flux absorbed in certain time")/("Total energy flux incident on the body in the same time")`