The Davission-Germer experiment was conducted by Clinton Davission and Lester Germer, American physicists, in the years 1923-1927, which theorized the de Broglie hypothesis.
De Broglie said that as light has a dual nature of being a wave and a particle, it must also have the characteristics of both. This establishes that the wavelength is inversely proportional to the momentum of a particle.
The experiment verified the de Broglie hypothesis, established the wave-particle duality and also established Schrodinger equation along with quantum mechanics.
The electron gun was taken with a tungsten filament, coated with barium oxide and that got heated by a voltage supply of low power. By applying potential difference from a higher voltage supply, the electrons emitted from the gun were accelerated to a desired velocity. The emitted electrons passed through a cylinder which was perforated with fine holes along its axis, producing a collimated beam. Scattering of electrons takes place when the beam produced is made to fall on a nickel surface. Voltage accelerated the electrons from a heated filament and the electrons struck the surface of a nickel metal.
The electron beam which was directed at the nickel crystal could be also rotated to observe the angular dependence of scattered electrons. Faraday box or electron detector, was mounted on an arc owing to the fact that it could be rotated to observe electrons as various different angles.
To their surprise, there was a peak in the intensity of the scattered electronic beam as certain angles. The peak indicated the wave behaviour of the electrons. This was interpreted by the Bragg’s law for giving values for the lattice spacing in nickel crystal.
The intensity of the scattered electron beam was measured for the different values by moving the detector on that circular scale at various positions.
THE OBSERVATIONS OF THE EXPERIMENT
- Accelerating the potential difference, results in obtaining the variation of intensity of scattered electrons along with their angle of scattering. The accelerated voltage varies from 44V to 68V.
- The strong peak noticed was in the accelerating voltage of 54V at an angle of 50̊.
- The peak is explained as a result of constructive interference of scattering of electrons from different layers of regularly spaced atoms of crystals.
- The electron diffraction helped in calculation of wavelength of matter which was 0.165nm.
The relationship can be established using the Bragg’s law, kinetic energy of the accelerated electrons and the deBroglie wavelength-
Electron wavelength= Bragg law= deBroglie relationship= acceleration though the voltage V