 the unique channel for physics. Please subscribe my channel. Hello and welcome back to another episode of physics partner. Today we are going to discuss photoelectric effect. What is photoelectric effect? When light is incident on the metal surface electrons are emitted from it. This phenomenon is called photoelectric effect photo because of photons of light and electric because the movement of electrons in electric current. The electrons emitted from the metal surface are called photoelectrons and the electric current produced by the photoelectrons is called photoelectric current. Let's make a historical review. Henrich Rodolf Hertz, a German physicist developed the photoelectric effect in 1887. 1902, German physicist Philipp Linnard established the connection between light and electricity. Hence it's called photoelectric. Albert Einstein was the first to successfully explain the laws of the photoelectric effect after years of research in this field. Light, Einstein said, is a beam of particles whose energies are related to their frequencies according to Planck's formula. When that beam is directed at a metal, the photons collide with the atoms. If a photon's frequency is sufficient to knock off an electron, the collision produces the photoelectric effect. Let's see what is the reason behind it. When photons, the light, hit the metal surface with the frequency greater than the threshold frequency, the electrons in the material get sufficient energy and emitted from the metal surface. These electrons are actually the valence electron which are lightly packed with the nucleus. The photoelectric effect experiment cannot be explained using the wave model of light. Let's perform a virtual experiment to verify photoelectric effect. You can see I have a material here, cesium and we have a galvanometer. We can see the current produced because of the effect of light and you can see there is no electron flowing right now because as you already studied that the frequency should be more than the frequency of threshold. So, let us increase the frequency and let's see the effect. So, when we increase the frequency, you can see the changes and after crossing the threshold, you can see the electrons are start flowing. So, it means the photoelectric effect started when the frequency is crossing the threshold frequency. You can see the voltage is produced here and you can see, let's change the material and try other materials with higher threshold. So, just remember that that is on the green light with the frequency of 477 THz, photoelectric effect started. Let me try and make another material with higher threshold. So, let's take sodium. Let's take sodium. Let's try with sodium. So, I am going to increase the frequency and I reach to the green, but still there is no photoelectric effect. As I told you the for sodium, the material sodium is different with cesium. So, the threshold frequency will be different. So, if I increase more frequency, still there is no photoelectric effect started, but now afterwards at the frequency of 573 THz, you can see the photoelectric effect the electrons are producing because of the effect of light. So, it means photoelectric effect for different elements depend on the different threshold frequency. Let's see how electromagnetic effect is applied in our daily life. There are so many applications of photoelectric effect. So, it is used in synatomography. It is used in traffic signals. It is used to switch off and switch on street lights automatically. It is used in burglar alarms. So, thank you very much for your watching and listening. I hope you enjoyed the video. I hope this is very useful for you. So, see you in the next video. Take care of yourself. Goodbye.