. D AVISSON AND G ERMER E XPERIMENT The wave nature of electrons was first experimentally verified by C.J. Davisson and L.H. Germer in and independently by G.P.
Thomson, in , who observed diffraction effects with beams of electrons scattered by crystals. Davisson and Thomson shared the Nobel Prize in for their experimental discovery of diffraction of electrons by crystals. The experimental arrange- ment used by Davisson and Germer is schematically shown in Fig. .
. It consists of an electron gun which comprises of a tungsten filament F, coated with barium oxide and heated by a low voltage power supply (L.T. or battery). Electrons emitted by the filament are accelerated to a desired velocity FIGURE .
Davisson-Germer electron diffraction arrangement. E XAMPLE . E XAMPLE . by applying suitable potential/voltage from a high voltage power supply (H.T.
or battery). They are made to pass through a cylinder with fine holes along its axis, producing a fine collimated beam. The beam is made to fall on the surface of a nickel crystal. The electrons are scattered in all directions by the atoms of the crystal.
The intensity of the electron beam, scattered in a given direction, is measured by the electron detector (collector). The detector can be moved on a circular scale and is connected to a sensitive galvanometer, which records the current. The deflection of the galvanometer is proportional to the intensity of the electron beam entering the collector. The apparatus is enclosed in an evacuated chamber.
By moving the detector on the circular scale at different positions, the intensity of the scattered electron beam is measured for different values of angle of scattering which is the angle between the incident and the scattered electron beams. The variation of the intensity ( I ) of the scattered electrons with the angle of scattering is obtained for different accelerating voltages. The experiment was performed by varying the accelarating voltage from V to V. It was noticed that a strong peak appeared in the intensity ( I ) of the scattered electron for an accelarating