A black body is one which neither reflects nor transmits but absorbs the whole of the heat radiation incident on it. The absorptive power of a perfect black body is unity.
When a black body is heated to a high temperature, it emits radiations of all possible wavelengths within a certain wavelength range. The radiations emitted by a black body are called full or black body radiations.
Blackbody radiator is any object that is a perfect emitter and a perfect absorber of radiation.
Anybody at any temperature above absolute zero will radiate to some extent, the intensity and frequency distribution of the radiation depending on the detailed structure of the body. To begin analyzing heat radiation, we need to be specific about the body doing the radiating: The simplest possible case is an idealized body which is a perfect absorber, and therefore also (from the above argument) a perfect emitter. For obvious reasons, this is called a “black body”.
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