Davisson–Germer experiment:
The Davisson–Germer experiment was a physics experiment conducted in 1927 which confirmed the de Broglie hypothesis, which says that particles of matter (such as electrons) have wave properties. This demonstration of wave-particle duality was important historically in the establishment of quantum mechanics and of the Schrödinger equation.
[edit] History
In 1924 Louis de Broglie presented his thesis concerning the wave-particle, proposing the idea that all matter displayed the wave-particle duality of photons.[1] According to de Broglie, for all matter and for radiation alike, the energy E of the particle was related to the frequency of its associated wave ν, by the Planck relation
and that the momentum of the particle p was related to its wavelength λ by what is now know as the de Broglie relation
where h is Planck's constant.
In 1926, upon knowing the preliminary results of Davisson and Germer, Walter Elsasser remarked that the wave-like nature of matter might be investigated by electron scattering experiments on crystalline solids, as the wave-like nature of X-rays was confirmed through X-ray scattering experiments on crystalline solids.[1][2]
In 1927 at Bell Labs, Clinton Davisson and Lester Germer fired slow moving electrons at a crystalline nickel target.[3] The angular dependence of the reflected electron intensity was measured, and was determined to have the same diffraction pattern as those predicted by Bragg for X-rays. This was also replicated by George Paget Thomson.[1]
The experiment confirmed the de Broglie hypothesis – matter displayed wave-like behaviour. This, in combination with Arthur Compton's experiment, established the wave particle duality hypothesis, which was a fundamental step in quantum theory.
[edit] Experiment
The Davisson–Germer consisted of firing an electron beam from an electron gun on a nickel crystal at normal incidence (i.e. perpendicular to the surface of the crystal). The electron gun consisted of a heated filament that released thermally excited electrons, which were then accelerated through a potential difference V (giving them a kinetic energy of eV (e is the charge of an electron)). An electron detector was placed at an angle θ = 50° and measured the number of electrons that were scattered at that particular angle.[1]
According to the de Broglie relation, a beam of 54 eV had a wavelenth of 0.165 nm. This matched the predictions of Bragg's law
for n = 1, θ = 50°, and for the spacing of the crystalline planes of nickel (d = 0.091 nm) obtained from previous X-ray scattering experiments on crystalline nickel.[1]
[edit] See also
[edit] References
- ^ a b c d e R. Eisberg, R. Resnick (1985). "Chapter 3 – de Broglie's Postulate—Wavelike Properties of Particles", Quantum Physics: of Atoms, Molecules, Solids, Nuclei, and Particles, 2nd Edition, John Wiley & Sons. ISBN 0-471-87373-X.
- ^ H. Rubin. "Walter m. Elsasser". National Academies Press. Retrieved on 2008-08-26.
- ^ C.Davisson, L.H. Germer (1927). "Reflection of electrons by a crystal of nickel". Nature Vol. 119: 558–560. doi:10.1038/119558a0.
[edit] External links
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