 Namaste. Hello everybody. This is Dr. Mrs. Preeti Sunil Joshi, Assistant Professor from Department of Humanities and Sciences, Balchan Institute of Technology, Solapur. I welcome you in this session, which is related to Davison Germer experiment. At the end of this session, students will learn about Davison Germer experiment and articulate the evidence supporting the claim that a wave model of matter is appropriate to explain the diffraction of matter given under certain conditions. This video includes the contents as the concept related with the Davison Germer experiment, the experimental setup, working, investigations and analysis related with the experiment. In 1924, Louis de Broglie postulated that all forms of matter have both particle and wave characteristics. According to this hypothesis, electrons just like light have a dual particle and wave nature. Waves exhibit diffraction. If the de Broglie hypothesis is valid, then the matter waves should exhibit diffraction effects. Davison is observed when the wavelength is comparable to the size of the object which causes diffraction. Two American physicists Davison and Germer were the first to experimentally prove the wave nature of material particles and verified the de Broglie equation. De Broglie argued the dual nature of matter back in 1924, but it was only later that Davison and Germer experiment verified the results. The results established the first experimental proof of quantum mechanics. In 1927, Davison and Germer observed the diffraction of an electron beam incident on a nickel crystal. The experiment by Davison and Germer provides the experimental proof of the concept of wave nature of material particles. The experimental arrangement of Davison and Germer experiment is as shown in the figure. The apparatus consists of an electron gun which is used to produce the collimated beam of electrons and anode A is connected to a variable voltage source accelerated the electrons. The energy of the electrons can be computed from the accelerating potential. These electrons were scattered by a nickel crystal located at C. The crystal can be rotated on the axis. The number of electrons scattered by the crystal in different directions was measured with the help of the detector D which can be moved on a scale. Now working, an electron beam is generated from a hot tungsten filament F and an anode A connected to a variable voltage source accelerates the electrons. The energy of the electrons can be computed from the accelerating potential V which is applied between the filament F and anode A. The electrons emerge through an opening in the anode and fall normally on the surface of a nickel crystal C. These electrons were scattered by a nickel crystal located at C. The crystal can be rotated on the axis. The detector D measures the number of electrons scattered by the crystal in different directions. The detector could be moved on a graduated semicircular scale and thus the intensity of the scattered electron beam was determined as a function of the scattering angle phi. If I do shine the electron beam on a nickel target what should actually happen? What is predicted was they should scatter randomly with random intensities. What was found actually here that at certain angles between the incident beam and the scattered beam the intensity was extremely high and at certain angles the intensity was extremely low and this could only happen that the electrons that are scattered by different layers are constructively interfering at certain angles and it is destructively interfering in certain angles. So the analysis of this experiment was done by the investigations as the current was measured to various positions of the detector. The detector current is directly proportional to the intensity of the diffracted beam and lastly the polar graphs were obtained for different voltages. Davison and Germer plotted a graph taking angle between the incident and scattered direction of the electron beam that is phi along y-axis and the intensity of the scattered beam at different values of the accelerated potentials along x-axis. The nature of the graph is as shown here. It was found that at 40 volt the graph is smooth. Then a hump appears in polar curve when 44 volt electrons were incident on the crystal. The hump grew in size with increasing voltage in the graph develops a peak at 50 degree and the peak becomes more pronounced for a voltage 54 volt. It is observed that the electrons scattered more than 50 degree with the direction of the incident beam. The maximum is the indication that the electrons are being diffracted. This peak indicated the wave behavior of the electrons. The basic thought behind the Davison-Germer experiment was that the waves reflected from two different atomic layers on a nickel crystal will have a fixed phase difference. After reflection these waves will interfere either constructively or destructively hence producing a diffraction pattern. In the Davison and Germer experiment electrons are used. These electrons formed a diffraction pattern. The dual nature of matter was thus verified. It may be interpreted that the rows of the atoms at the surface of the nickel crystal act like rulings of a natural diffraction grating and the de Broglie waves associated with the electrons underwent diffraction. When they were incident on the crystal the hump produced at 50 degree as shown in the figure then corresponds to the first order diffraction maxima. So, Bragg's law applicable for x-ray diffraction by the crystals would be valid for electron wave diffraction also. Now this figure shows the atomic planes and the incident and scattered beams. The interplanar spacing is obtained from x-ray diffraction and it is to be d is equal to 0.91 angstrom unit. From figure it is seen that the glancing angle theta is equal to 65 degree. So, if we calculate the wavelength by Bragg's equation that is lambda is equal to 2 d sin theta the wavelength comes to be 1.65 angstrom unit and if by de Broglie equation the wavelength of the electron wave is calculated from the accelerating potential v then by the equation lambda is equal to h upon under root 2m into e into v the wavelength comes to be 1.66 angstrom unit. It is seen that the values obtained experimentally using Bragg's equation and de Broglie equation agreed well. Therefore, Davison-Germain experiment gave conclusion evidence that electrons exhibit it is seen that the values obtained experimentally using Bragg's equation and de Broglie equation agreed well. Therefore, Davison-Germain experiment gave conclusion evidence that electrons exhibit diffraction property. Students, now pause the video and try to answer these questions. Check for the correct answers. Now, let us come to the summary of this session. The Davison-Germain experiment demonstrated the wave nature of the electron confirming the earlier hypothesis of de Broglie. Putting wave particle duality on a firm experimental footing it represented a major step forward in the development of quantum mechanics. The Bragg's law for diffraction had been applied to x-ray diffraction but this was the first application to particle waves. These are the references. Thank you.