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Kirchhoff's law of thermal radiation

(for an object in thermodynamic equilibrium, emissivity equals absorptance)

Kirchhoff's law of thermal radiation states that for an object in thermodynamic equilibrium, emissivity and absorptance (aka absorptivity) at any specific wavelength are the same. This explains why the black body concept specifies black: "black" means no reflection and reflection of any color implies incomplete absorption, and by Kirchhoff's law its emission is likewise reduced. It also explains why lightweight "emergency blankets" are made reflective even though absorbing any incident EMR might seem to be helpful.


(physics,EMR)
Further reading:
http://en.wikipedia.org/wiki/Kirchhoff%27s_law_of_thermal_radiation

Referenced by pages:
gray body

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