In this physics video lecture for iitjee, we are going to discuss photoelectric effect. The topic covered in the above IIT JEE video is photoelectric emission.

So what is photoelectric emission? It is when a light of appropriate frequency on a metal surface, emission of electrons takes place and these electrons are called photoelectrons. This frequency should be greater than the threshold frequency. So how does an electron come out? It happens when a photon of appropriate frequency falls on the metal surface, electron emission takes place and these electrons are called photoelectrons. The two important things that we must learn from this jee physics video are here,

  1. The electrons absorb a photon and thus gains kinetic energy. The electron cannot absorb the photon completely. If the electron is attached to some metal then it gains or absorbs the kinetic energy of the photon completely.
  2. If the electron stops, it emits its energy in the form of a photon. This phenomenon is known as the breaking effect.

The photon has linear momentum. The free electron cannot absorb the total energy of the photon because linear momentum and energy cannot be conserved all together. An electron can gain infinite energy.

Just when the photon falls on the metals surface, this photon is absorbed by any of the electrons immediately.  The energy of the photon is ‘hν’ which is given by the Planck’s law. One electron cannot absorb more than one photon. This is because the electron doest get a chance to absorb a second photon, as the number of photon is less when compared to the number of electrons.  Once the electron has absorbed the photon it comes out of the metal surface immediately without any time lag. The time of emission is about 10-8 seconds.

The photoelectric effect was first seen by Hertz in the year 1887. Then Leonard saw it experimentally. And this was explained by Einstein and he received the Nobel Prize in 1930.