Derive the Einstein’s photoelectric equation.

According to Einstein, light of frequency  consists of a shower of photons, is of energy . When a photon of light of frequency  is incident on a metal, a part of the energy acquired by the electron is used to pull out the electron from the surface of the metal and the rest of it is utilized in imparting K.E. to the emitted electron.

Let,  be the energy spent in extracting the electron from the emitter and  the K.E. of the photo-electron.

Then,                          

This relation is known as Einstein’s Photoelectric Equation. If,  is the threshold frequency, then, 

Where,  is the maximum velocity acquired by the electron.