 channel for physics. Please subscribe my channel. Hello everyone and welcome back to another episode of physics partner. Today we are going to demonstrate the Frank Hertz experiment. The Frank Hertz experiment was the first electrical measurement to clearly show the quantum nature of atom and thus transformed our understanding of the world. It was presented on 24 April 1940 to the German physical society in a paper by James Frank and Gustav Hertz. Frank Hertz experiment is demonstrated the existence of excited states in mercury at helping to confirm the quantum theory which predicted the electrons occupied only discrete quantized energy states. This experiment support Bohr model of atom. Now have a look on the apparatus using this experiment. It consists of a tube containing low pressure gas fitted with three electrons. Cathode for electron emission, a mesh grid for the acceleration of electrons and a collecting plate. With the help of thermonic emissions electrons are emitted by a heated cathode and then accelerated towards a grid. You can see here in this demonstration they accelerated towards a grid which is at positive potential relative to the cathode. The collecting plate is at the lower potential and it's negative with respect to mesh grid. If electrons have sufficient energy on reaching the grid some will pass through the grid and reaching collecting plate and it will be measured at current by the emitter. You can see here a sensitive emitter is attached here which can measure the current. You can see here electrons which do not have sufficient energy on the reaching the grid will be slowed down and will fall back to the grid. The experiment results confirm the existing of discrete energy levels. As long as electrons collision is elastic the electrons will not lose energy on colliding the gas molecules in tube. You can see on the screen as the accelerating potential increases the current also increases but as the accelerating potential reaches a particular value it reached to 4.9 that is particular value for mercury. So you can see each electron pauses that much of potential and now the collision between in elastic as the result the energy level of electrons bound to the atom is raised. Now the electron almost loses that energy and major current drops. You observed that when the accelerating voltage reaches 4.9 electron volt the lowest energy required by the mercury atom for excitation the current drops sharply. This drop is due to inelastic collision. So you can observe very clearly when the accelerating voltage reaches 4.9 electron volt the lowest energy required by the mercury atom for excitation the current drops sharply. This drop is due to inelastic collision between the accelerated electrons and electrons in the mercury atom. The sudden onset suggests that the mercury electrons cannot accept energy until it reaches the threshold to elevate them to an excited state. Collected current drops at multiples of 4.9 electron volt at 9.8 volt which electrons get sufficient energy to participate in to inelastic collision. The excite to mercury atoms and no energy will be left. The process will repeat for each interval of 4.9 electron volt. Now let's talk about the results that we can conclude from Frank Hurd's experiment. Basically this experiment confirmed the existence of quantum theory. The energy states in an atom seems to be an abstract concept until the experiment was conducted. It confirmed the presence of energy state in the atom like mercury and neon. In this video we showed mercury only. The quantum theory stated that these electrons in an atom exist in the discrete and quantized state. It was observed during the experiment that the current drops suddenly at some specific value. Indicating the changes in the energy of electrons. The overall presentation of this phenomenon on CRO showed several bumps which increasing and decreasing value of current. This was helpful to interpret the quantized level of energy. So that's all for today. I hope you enjoyed the video. I hope it helps you to understand the Frank Hurd experiment. So thank you very much for your listening and take care of yourself and see you in the next video. Goodbye.