Two Ideas Leading to Quantum Mechanics

In the previous section, we pointed out that the interpretation of atomic line spectra posed a difficult problem for classical physics and that Bohr had some success in explaining the emission spectrum for the hydrogen atom. However, because his model was not correct, he was unable to explain all features of the hydrogen emission spectrum and could not explain the spectra of multielectron atoms at all. A decade or so after Bohr s work on hydrogen, two landmark ideas stimulated a new approach to quantum mechanics. Those ideas are considered in this section and the new quantum mechanics— wave mechanics—in the next. 

To explain the photoelectric effect, Einstein suggested that light has particle-like properties, which are displayed through photons. Other phenomena, however, such as the dispersion of light into a spectrum by a prism, are best understood in terms of the wave theory of light. Light, then, appears to have a dual nature. 

In 1924, Louis de Broglie, considering the nature of light and matter, offered a startling proposition Small particles of matter may at times display wave-like properties. 

De Broglie argued that the relationship p = h/X, derived by Einstein for the momentum of a photon (see Are You Wondering 8-2), should also apply to particles of matter. Lor a particle of mass m moving with speed u, the momentum is p = mu, and so the relationship p = h/X can be written in the form 

De Broglie conceived of the wave-particle duality of small particles while working on his doctorate degree. He was awarded the Nobel Prize in physics 1929 for this work. 

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