Astrophysics (Index)About

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, the reflection of any color implies incomplete absorption, and by Kirchhoff's law its emission would be reduced by the same ratio. It also explains why lightweight emergency blankets are made reflective even though absorbing any incident EMR would seem to be helpful.


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

Referenced by pages:
gray body

Index