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⎠ (1.15) Planck’s law of black body radiation was in agreement with experimental observations. The
maximum intensity of radiation can be easily deduced from Eq. (1.15) and it occurs at the
wavelengths given by Wien’s law
λ max T = const. = 2880 µm K . (1.16) This law predicts that the maximum intensity shifts to the blue spectral region as the temperature
of the black body is increased. The energy of the black body radiation at the intensity maximum
is given by Emax = h c / λmax and Emax equals about five times the thermal energy, that is
Emax = 4.98 kT. Several black body radiation spectra are shown in Fig. 1.2.
Planck’s postulate of discrete, allowed energies of atomic oscillators as well as of forbidden,
or disallowed energies marks the historical origin of quantum mechanics. It took scientists
several decades to come to a complete understanding of quantum mechanics. In the following,
the basic postulates of quantum mechanics will be summarized and their implications will be
discussed. Exercise. The color of hot objects. If an object gets sufficiently hot, it appears to the human eye,
to glow in the red region of the visible spectrum. Assume that the emission spectrum of the hot
object peaks at a wavelength of 650 nm. Calculate the temperature of the object.
As the temperature of the object is increased further, the glow changes from the reddish to a
yellowish color. At even higher temperatures, the light emitted by the object changes to a white
glow. Explain these experimental observations based on the black body radiation. © E. F. Schubert 5...
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This note was uploaded on 02/05/2013 for the course CHEM 131A taught by Professor Rentzepis during the Fall '12 term at UC Irvine.
- Fall '12