We can integrate this over frequency to get the total power radiated per unit area.
R(T) =
π^2 c
60( ̄hc)^3k^4 T^4 = (5. 67 × 10 −^8 W/m^2 /◦K^4 ) T^4
See Example 2.6.1:What is the temperature at the solar surface? Use both the the intensity of
radiation on earth and that the spectrum peaks about 500 nm to get answers.*
See Example 2.6.2:The cosmic microwave background is black body radiation with a temperature
of 2.7 degrees. For what frequency (and what wavelength) does the intensity peak?*
2.2 The Photoelectric Effect
The Photoelectric Effect shows that Plank’s hypothesis, used to fitthe Black Body data, is actually
correct for EM radiation. Einstein went further and proposed, in 1905, that light was made up of
particles with energy related to the frequency of the light,E=hν. (He got his Nobel prize for the
Photoelectric effect, not for Special or General Relativity.)