User:Arjen Dijksman/QO

1. Blackbody radiation

Rayleigh’s way : Assumed that every spectral mode k of the electromagnetic field contributes to an average energy k_B.T. For higher k, there are more and more modes in which the field may oscillate --> enormous energy contents of the field for high k --> doesn’t fit for high k.

Planck’s way: Field is described in the same way but energy exchange can only occur in finite packets proportional to k (=hbar k.c). Population of successive energy levels are related by thermal Boltzmann factor.

Einstein’s way: The quanta of electromagnetic energy are particles. There may occur three processes: -	absorption -	spontaneous emission -	stimulated emission

Bose’s way: Gas of lightquanta

Ex 1 Average number of photons per mode for sunlight in the visible range

Ex 2 Ratio between stimulated emission and spontaneous emission

Ex 3 CMB

Ex 4 Heat capacity and Debye formula