Davisson and Germer Experiment
The first experimental proof of the wave nature of electron was demonstrated in 1927 by two American physicists C.J Davison and L.H Germer. The basis of their experiment was that since the wavelength of an electron is of the order of spacing of atoms of a crystal, a beam of electrons shoes diffraction effects when incident on a crystal.
Experiment setup of Davisson Germer Experiment: The experimental arrangement of Davisson Germer experiment is discussed below:
- An electron gun was taken, which comprised of a tungsten filament F, coated with barium oxide and heated by a low voltage power supply.
- Electrons emitted from this electron gun were accelerated to a desired velocity by applying suitable potential difference from a high voltage power supply.
- These emitted electrons were made to pass through a cylinder perforated with fine holes along its axis, thus producing a fine collimated beam.
- This beam produced from the cylinder is made to fall on the surface of a nickel crystal. This leads to scattering of electrons in various directions.
- The intensity of the beam of electrons is measured by the electron detector which is connected to a sensitive galvanometer, (to record the current) and can be moved on a circular scale.
- The intensity of the scattered electron beam is measured for different values of angle of scattering, θ (angle between the incident and the scattered electron beams) by moving the detector on the circular scale at different positions.
Observations of Davisson Germer Experiment: Observations of Davisson Germer experiment are listed below:
- By varying accelerating potential difference, we finally obtained the variation of the intensity (I) of the scattered electrons with the angle of scattering, θ. The accelerated voltage was varied from 44V to 68 V.
- A strong peak was noticed in the intensity (I) of the scattered electron for an accelerating voltage of 54V at a scattering angle θ = 50°.
- This peak can be explained as a result of the constructive interference of electrons scattered from different layers of the regularly spaced atoms of the crystals.
- The wavelength of matter waves was calculated with the help of electron diffraction, which measured to be 0.165 nm.
Co-relating Davisson Germer experiment and De Broglie relation: According to de Broglie, wavelength λ associated with electrons is given by λ = h /p.
λ = 1.227/√54 = 0.167nm.
Thus, Davisson Germer experiment confirms the wave nature of electrons and the de Broglie relation.