According to Kirchhoff's law of thermal radiation, for an opaque object in thermodynamic equilibrium, its emissivity is equal to its absorptivity. This means a material that is a good absorber of heat radiation is also a good emitter of heat radiation at the same temperature and wavelength.
Good absorbers of heat are
Asked in WBPSC CS Prelims 2019 · Topic: Heat and Thermodynamics (Blackbody Radiation and Laws (Stefan-Boltzmann, Wien's Displacement))
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