Davisson and Germer's Experiment and its Conclusion


We all know about atoms, particles, molecules these are some of the words which you all have heard at least once in your life but today we are going to dig a little deeper and will learn about matters,  particles and wave nature ? You must have been wondering just like me but then I did some research on this and got to know about one great experiment known as Davisson and Germer experiment and what conclusion does it derive which helps us in finding answer to our solution.


Davisson and Germer's experiment was performed by Clinton Davisson and Lester Germer. This experiment helps us to prove the wave nature of matter. This experiment has been performed between different voltages varying from 44V to 68V. This conclusion is noted that a strong peak of electron intensity is observed at 54V at angle 'Ө' = 50°

What is Davisson and Germer experiment ?

Davisson and Germer's Experiment setup
Davisson and Germer's Experiment setup

This experiment proves the wave nature of matter. Clinton Davisson and Lester Germer performed an experiment where they let filament beam fall on nickel crystal, due to this electrons scatter which then is collected with help of a moving collector. This moving collector is connected with a galvanometer which shows the current produce.

With the help of this data, matter travels in a wave nature is proved.

Wave nature of matter:

I have been mentioning the wave nature of matter a lot more! Most of you must have knowledge about it but if you don't, no need to worry I got you covered.

details of wave
Wave

So basically, wave nature of matter means that all the electron particles behave like a wave. According to de Broglie's all the particle when they are in motion possesses wave characteristics. This is what you mean by wave nature of matter.

de Broglie's hypothesis:

de Broglie's hypothesis says that all the matter has both, particles and wave nature in them. Now, this is called a hypothesis because there were no certain practical proof there.

de Broglie's hypothesis equation is,


where 'λ' = wavelength, 'p' = momentum of wave and 'h' is the planks constant.

Setup of Davisson and Germer experiment:

 Experiment set up consists of :

Davisson and Germer's Experiment setup
Davisson and Germer's Experiment setup

  • Evacuated chamber: So that electrons can move freely without air resistance.
  • Electron gun: It comprises of tungsten filament coated with barium oxide which is heated at low voltage, due to this it can be used to emit electrons.
  • Battery: As high voltage supply used to accelerate electron
  • Cylinder with a fine hole connected with a battery: This is connected to a battery to accelerate the electron and due to the hole in cylinder sprays electron in form of a beam.
  • Nickle target: Electron beam falls on it and spreads.
  • Movable detector: To detect the electron's intensity once it falls on nickel and spreads.
  • Galvanometer: It is used to measure small current which created when an electron hits the detector. The amount of current produced shows us the intensity of electron at a particular area.

Working of Davisson and Germer experiment:


This whole setup is in the evacuated chamber so that electrons can move freely and there is no air resistance. Electron gun with tungsten filament is heated with low voltage and this is used to emit electrons. Electrons emitted by the filament are accelerated to the desired velocity with the help of high voltage power by applying suitable voltage.

This emitted electron is made to pass the cylinder with a fine hole, this cylinder is connected with high voltage supply so when electrons get inside them they get accelerated and due to the fine hole, they come out in the form of a beam.

This beam is made to fall on nickel crystal and due to this electron gets scattered in all the direction. This is where movable detectors come into play. The intensity of the scattered beam is measured by a movable detector with the help of a galvanometer connected to it.

If the intensity of the electron is high then current produced will be high. So, the intensity of the electron is proportional to the deflection in a galvanometer.

Conclusion of Davisson and Germer experiment:

By moving the detector on a circular scale, the intensity of the electron is measured at different angle  'Ө'.

'Ө' is the angle between the incident and the scattered electron beam. This variation of the intensity (I) of the electron and angle 'Ө' is measured at different voltages.

This experiment has been performed between different voltages varying from 44V to 68V. This conclusion is noted that a strong peak of electron intensity is observed at 54V at angle 'Ө' = 50°

Wave nature relation with Davisson and Germer experiment:

This experiment helps us to prove the wave theory of light, but how?

The appearance of the peak in a particular direction of 'Ө' = 50° and voltage = 54V is due to the interference of electron scattered from different layers of nickel crystal.

With the help of electron diffraction method (used to find the wavelength of electron wave) the measurement of matter wave was found to be 0.165nm. 

The de Broglie's wavelength λ associated with electron emitted from 54V is given by:




Conclusion:

Davisson and Germer's experiment proves De Broglie's hypothesis (matter has wave nature as well) by proving that wavelength λ for an electron at 54V is 0.167nm theoretically and practically as well.

This experiment helps us and proves the theoretical method by showing us practical proof.

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