Davisson and Germer Experiment: Setup, Observations & De Broglie's Relation

Davisson Germer Experiment verified the de Broglie relationship and proved the wave nature of electrons. Many scientists who proposed their initial atomic models could only explain the particle nature of electrons but failed to explain the properties related to their wave nature. However, in 1927 two scientists named C.J. Davisson and L.H. Germer carried out an experiment which was popularly known as Davisson Germer’s experiment explaining the wave nature of electrons through electron diffraction. The results of the experiment established the first experimental proof of quantum mechanics.  

Key Terms: Davisson germer experiment, Electron diffraction, Wave Particle Duality, Quantum Mechanics, Power supply, Voltage, Electron, Wave nature

Setup of Davisson Germer Experiment

[Click Here for Sample Questions]

The main parts of the experimental setup of Davisson Germer Experiment are electron gun, electrostatic particle accelerator, collimator, target, and detector. The Davisson Germer experiment setup is discussed below:

• An electron gun with a tungsten filament F was coated with barium oxide and then heated through a low voltage power supply.
• The electron gun emits electrons while applying suitable potential differences from a high voltage power supply.
• These electrons are then again accelerated to a particular velocity.
• The electrons were then made to pass through the axis of a perforated cylinder with fine holes. It, therefore, produces a fine collimated beam.
• When the beams from the cylinder are made to fall on the Nickel crystal surface, the electrons will get scattered in different directions.
• The beam of electrons produced will have a certain amount of intensity. An electron detector is used to measure the intensity of electrons.
• The electron detector is moved on a circular scale after connecting it to a sensitive galvanometer to record the current.
• The intensity of the scattered electron beam is measured for different values of the angle of scattering. 
• This is done by moving the electron detector in the circular scale at different positions, by changing the angle θ (i.e angle between the incident and the scattered electron beams). 

The video below explains this:

Davisson and Germer Experiment Detailed Video Explanation:

Also Read:

Davisson Germer Experiment Observations

[Click Here for Previous Year Questions]

Some of the observations which are obtained from the Davisson Germer experiment are:

• By changing the angle of scattering, represented by θ, we can get the variation of intensity (I) of the scattered electrons.
• The accelerated voltage can change from 44 V to 68 V by varying the accelerating potential difference.
• A strong peak in the intensity of electrons can be observed with an accelerating voltage of 54 V and a scattering angle θ = 50º of an electron.
• This peak in intensity was a result of the constructive interference of the electrons that are scattered from different layers of the regularly spaced atoms of the crystals.
• The wavelength of matter waves was determined as 0.165 nm with the help of electron diffraction.

Relation between Davisson Germer Experiment & de Broglie Equation

[Click Here for Sample Questions]

According to de Broglie equation,

\(\lambda = h/p = {1.227 \over \sqrt V} nm\\ \lambda = {1.227 \over \sqrt 54} nm\\ = 0.167 nm \)

Where, λ is the wavelength associated with electrons

Therefore, the Davisson Germer experiment confirms the de Broglie relation and the wave nature of electrons.

Importance of Davisson Germer Experiment

• The Davisson Germer Experiment illustrated the wave nature of electrons, in continuation of the theorem of De-Broglie.
• This experiment gave the confirmation to wave-particle quality.
• It is an apparatus built up for the purpose of measuring the energies of electrons scattered from the surface of the metal.

Things to Remember

• Davisson Germer’s experiment explained the wave nature of electrons through electron diffraction.
• The variation of the intensity (I) of the scattered electrons can be obtained by changing the angle of scattering θ.
• The accelerated voltage can be varied from 44 V to 68 V by changing the accelerating potential difference.
• The Davisson Germer Experiment illustrated the wave nature of electrons, in continuation of the theorem of De-Broglie.

Also Read:

Previous Year Questions

1. If its disintegration constant is 3.7×10⁴sec⁻¹,3.7×10⁴sec−1, the mass of X is…. [AP EAPCET 1998]
2. The emission of photoelectrons is directly proportional to…. [NEET 1997]
3. The de-Broglie wavelength associated with the electrons would be… [NEET 2011]
4. By photoelectric effect, Einstein proved…. [NEET 2000]
5. The energy of most energetic photoelectron is…. [JIPMER 1999]
6. When monochromatic radiation of intensity II falls on a metal surface…. [NEET 2010]
7. An example for the best source of monochromatic light is... [JKCET 2019]