. State Kirchhoff's law of radiation and prove it theoretically
According to Kirchoff’s law of radiation the emissivity of the radiating body is equal to absorptivity. Mathematically it is written as a = e.
2. Proving it theoretically : Consider an ordinary body A and a perfectly black body B of the same dimension suspended in a uniform temperature. At thermal equilibrium both the bodies will have the same temperature.
Let E = emissive power of ordinary body A
According to kirchoff’s law of radiation a = e.