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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.
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Key Terms: Davisson germer experiment, Electron diffraction, Wave Particle Duality, Quantum Mechanics, Power supply, Voltage, Electron, Wave nature
Setup of Davisson Germer Experiment
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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:
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Davisson Germer Experiment Observations
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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
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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.
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Previous Year Questions
- If its disintegration constant is 3.7×104sec−1,3.7×104sec−1, the mass of X is…. [AP EAPCET 1998]
- The emission of photoelectrons is directly proportional to…. [NEET 1997]
- The de-Broglie wavelength associated with the electrons would be… [NEET 2011]
- By photoelectric effect, Einstein proved…. [NEET 2000]
- The energy of most energetic photoelectron is…. [JIPMER 1999]
- When monochromatic radiation of intensity II falls on a metal surface…. [NEET 2010]
- An example for the best source of monochromatic light is... [JKCET 2019]
Sample Questions
Ques. In an Energy Quantum of Radiation, what do you understand by Einstein's Photoelectric Equation? (3 marks)
Ans. Albert Einstein in 1905 projected a fundamental picture of quanta of radiation or electromagnetic radiation that defines the photoelectric effect. Here each radiant energy has energy ‘hv’ under this proposal. Here h indicates Planck's constant and v indicates the frequency of light.
Ideally, the quantum of energy of radiation or ‘hv’ is absorbed by an electron under the photoelectric effect. Here an electron with maximum kinetic energy will be ‘
’ if the quantum energy which was absorbed by the electrons surpasses the defined minimum energy which is required for the escape of the electron from the metal surface.
Here, as the work function depends on the material's nature and hence the value of a selective material's work function will be constant.
Ques. What Does the Wave Nature of Matter explain to us? (3 marks)
Ans. Ideally, the wave nature of light can be shown as a phenomenon related to interference, polarization, and diffraction. While one can find that in a Compton effect and photoelectric effect the radiations act as photons which are also known as a bunch of particles. Here the photons get changed since the momentum transfer also gets affected.
In the hypothesis of De Broglie, he answered whether a particle of nature exhibits the wave character or not. And this is possible only if the radiation contains dual wave particles. He attributes a matter with a wave-like character. The matter will show some similar characters only if the dual nature is seen in terms of radiation.
According to De Broglie, a wavelength ‘λ’ is linked with the momentum of a particle which is represented by ‘p’. This would give us λ = h/p = h/(m v). Here m represents the mass of the particle and v represents the speed.
Ques. How can intensity variation of scattered electrons be obtained? (1 mark)
Ans. The variation of the intensity (I) of the scattered electrons can be obtained by changing the angle of scattering θ.
Ques. How can we change the accelerated voltage? (1 mark)
Ans. The accelerated voltage can be varied from 44 V to 68 V by changing the accelerating potential difference.
Ques. What is the use of a Photoelectric Cell? (3 marks)
Ans. A photoelectric cell usually has a technical application. Due to the electrical properties of photoelectric cells, these devices get affected by lights. With this, even the light energy is also converted into electricity directly with the help of the photovoltaic effect. This is ideally a chemical and physical phenomenon. Here, the electrical characteristics which include voltage, resistance, and current show different features when they come in contact with light.
In motion films, a photocell is used in producing sound and hence it is also termed an electric eye. These photocells are also used in scanning and telecasting scenes from a television camera. This device is used to detect some minute holes in the metal sheets in some industries for the need of construction.
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