d9

• Chris Nkinthorn, $\texttt{20190727}$

Prompt: Please discuss the reason(s) why radiation does require a participating medium for its transport.

Discussion: The transport of heat by radiation is fundamentally different from the conduction and convection as it is the only one of the three fundamental heat transfer (HT) mechanism that does not require a participating medium. Conduction and convection are the transport of heat due to molecular collisions, or of real particles with matter. Radiation is heat transfer because of the emission of electromagnetic waves due to discrete changes in the valence energy level of electrons. This distinction of heat energy being transported by electromagnetic waves separates radiation from the other forms of HT.

Response to: Joe Bostick

Great discussion! Thanks for bringing up the quantized nature of the emission of energy as EM waves. The postulation of discrete photons was the first step in the historical evolution of Stefan-Boltzmann's Law of Radiation as well as Planck's Law for radiant energy density.