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.
|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-
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.
|Cells in Mixed Groupings||de-Broglie Hypothesis (Dual Nature of Matter)|
|Cells in Series and Parallel||Heisenberg Uncertainty Principle|
|Wheat Stone Bridge Principle||Spectrum and Types of Spectra|
|Kirchhoff’s Laws||Heat Transfer and Solar Energy-NIOS|