Supplement 2.1: Absorption, Emission and Reflection
A complete depiction of the exchange of radiation between the black and the white body is represented in the following graph. Besides absorption and emission it considers reflection of the radiation on the surface of the bodies as well. The radiative properties of the inner walls of the cavity are still not considered.
Two bodies in a thermal equilibrium in an isolated cavity. The arrows represent different radiative fluxes each. The letters r, e and a on the short arrows stand for reflected, emitted and absorbed.
In a thermal equilibrium, emitted and reflected radiation of one body would come to the same as the incoming radiation of the other body. Absorbed and emitted radiation of each body are the same following to Kirchhoff's law. In order to clarify these balances there are lines of dots in the graphics.
Task: From imbalance to equilibrium
