Absorptivity is the fraction of incident radiation absorbed, while a black body absorbs and emits radiation across all wavelengths. Emissivity measures an object's radiant efficiency, and grey bodies partially absorb radiation at all wavelengths.
Absorptivity: Absorptivity, denoted as a(λ), is the fraction of incident radiation at a specific wavelength that is absorbed by a material.
Black Body: A black body is an object that absorbs all radiation falling on it, making it an ideal absorber and emitter of radiation at all wavelengths.
Emissivity: Emissivity, denoted as ε, is the efficiency of an object in radiating energy; black bodies have an emissivity of 1, whereas white bodies have an emissivity of 0.
Grey Body: A grey body is a material that absorbs all wavelengths of radiation but with an absorptivity less than 1, unlike a black body.
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