Experimental Verification of Wave Nature of Electron

Wave Nature of Electron (Prove by Davison and Germer Experiment):

The wave nature of electrons has been established experimentally by Davison and Germer in 1927.

The apparatus consists of a Filament ‘F’ made up of Tungsten, which on heating with a low tension battery (L.T.) emits a large number of electrons. ‘A’ is an anode with a fine hole. The beam of electrons emitted from the cathode is allowed to pass through the hole in the anode. ‘N’ is a nickel crystal cut along a cubical diagonal. ‘D’ is an electron detector. It can be rotated on the circular scale and is connected to a sensitive galvanometer, which records current.

Working- A fine beam of electrons is made to fall on a nickel crystal. The incident electrons are then scattered in different directions by the atoms of nickel crystal. By rotating the electron detector on a circular scale, the intensity of the scattered beam is measured at different latitude angle Φ.

Polar graphs are then plotted between the intensity of scattered electrons and latitude angle Φ for different accelerating voltages from 44 volts to 68 volts. The graphs show that there is a sharp bump when the accelerating voltage is 54 volts and Φ = 50°.

The appearance of a bump in a particular direction is due to the constructive interference of electrons scattered from nickel crystal. This establishes the wave nature of electrons.

Also, for nickel crystal, the interatomic separation d = 0.91 Å.

According to Brag’s Law, and for 1st order diffraction maxima (n=1)

According to de Broglie hypothesis, the wavelength of wave associated with electron is given by-

This shows that there is close agreement between an estimated value and experimental value. This proves the existence of de Broglie waves for the electrons in motion.