How black body absorbs light? I learn that black body absorbs light, but couldn't get the mechanism behind it. I wish I could get help.
 A: Consider a hollow insulated body with a very small hole, a ray is passed in it. The body is made in such a way that the possibility of that ray to get out of that body is almost zero. So this body completely absorbs that ray.
Reference
A: In physics one should have clearly defined terms.
Black body radiation is a mathematical model where a function can describe the effects of radiation for an object that radiates off , after absorbing, any radiation that falls on it:

"Blackbody radiation" or "cavity radiation" refers to an object or system which absorbs all radiation incident upon it and re-radiates energy which is characteristic of this radiating system only, not dependent upon the type of radiation which is incident upon it. The radiated energy can be considered to be produced by standing wave or resonant modes of the cavity which is radiating. 

This is one of the lynch pins of quantum mechanics, because classical electrodynamics, as can be seen in the link, diverges for high radiation frequencies, and only the quantization hypothesis allows for a fit with the data. This is where photons and the energy they carry, proportional to their frequency, first appear.
It so happens that all solid bodies ot a given temperature, even though composed of complex quantum mechanical entities, fit this spectrum  approximately. See the radiation from the sun for an approximate fit , and the microwave background radiation which fits the formula perfectly. 
Now, black colored items are seen by our eyes as black because they absorb all visible frequencies. This does not mean that they absorb the invisible to our eyes also, as the spectrum of radiation is enormous, and the material  may be reflecting a lot of frequencies, but our eyes would not preceive it. 
