this effectively means that only frequencies ν ≤ T1011 will be emitted, which
fits with the common experience that a black surface heated by the highfrequency
light from the Sun, will not itself shine like the Sun, but radiate
only lower frequencies. We refer to kT
h
as the cut-off frequency, in the sense
that frequencies ν > kT
h will be radiated subject to strong damping. We see
that the cut-off frequency scales with T, which is Wien’s Displacement Law.
In other words, the cut-off distance in terms of wave-length scales with 1
T
as
shown in Fig. 4.1.
Below we shall for simplicity leave out the constant of proportionality in
(4.1) and write Rν(T) ∼ T ν2
θ(ν, T) expressing the dependence on T and
ν, with ∼ denoting proportionality. But it is important to note that the
constant γ =
2k
c
2
is very small: With k ≈ 10−23 J/K and c ≈ 3 × 108 m/s, we
have γ ≈ 10−40. In particular, γν2