1. Planck's primary assumption was that the
oscillators
representing the walls of the cavity had various
natrural
frequencies (f), but could only have energies in
integer
multiples of hf. He did not quantize the radiation
field.
2. It was Einstein, in 1905, who derived a variety of
results from the assumption that hf referred to the
radiation field.
For example, that the statistical behavior of the
radiation field in a volume Vo was similar to that of
N gas molecules in that the probablility of finding
the energy E in a sub-volume v, was given by (v/Vo)^N
,where
N = E/hf .