TABLE OF CONTENTS In Chapter 2 we saw that classical mechanics was incapable of explaining the optical spectra emitted by atoms, or even the existence of atoms. Bohr developed a model for the atom of hydrogen by assuming the quantization of the electromagnetic field, which was an introduction to wave or quantum mechanics. Quantum mechanics is a more precise approach to describe nearly all physical phenomena which reduces to classical mechanics in the limit where the masses and energies of the particles are large or macroscopic.
In this section, we will illustrate the success of quantum mechanics through the historically important examples of blackbody radiation, wave-particle duality, the photoelectric effect, and the Davisson and Germer experiment.
As introduced in Chapter 2, a blackbody is an ideal source of electromagnetic radiation and the radiated power dependence was depicted as a function of wavelength in Fig. 2.3 for several temperatures of the blackbody.
When the temperature of the body is at or below room temperature, the radiation is mostly in the infrared spectral region, i.e. not detectable by the human eye. When the temperature is raised, the emission power increases and its peak shifts toward shorter wavelengths as shown in Fig. 2.3. Several attempts to explain this observed blackbody spectrum were made using classical mechanics in the latter half of the 19 th century, and one of the most successful ones was proposed by Rayleigh and Jeans.
In their classical model, a solid at thermal equilibrium is...
