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.

wave nature of electrons has been established experimentally by Davison and Germer - Experimental Verification of Wave Nature of Electron

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°.

Polar graphs are then plotted between the intensity of scattered electrons and latitude angle Φ - Experimental Verification of Wave Nature of Electron

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.

From simple geometry, and for Φ = 50°.
θ + Φ + θ = 180°
⇒ 2θ + Φ = 180°
⇒ 2θ = (180° – Φ)
⇒ 2θ = (180° – 50°) = 130°
⇒ θ = 65°

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

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

2d Sinθ = nλ
⇒ 2d Sinθ = 1 x λ
⇒ 2 x 0.91 x Sin 65° = λ
⇒ λ = 1.65 Å

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

wavelength of wave associated with electron - Experimental Verification of Wave Nature of Electron

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.


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