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Deduce Eisenstein's photoelectric equation

According to Einstein, one photo electron is emitted from a metal of one photon of suitable frequency is incident on the metal. Suppose a photon of suitable frequency ƒ (greater than the threshold frequency for the metal) is incident on the metal. The energy hƒ of the photon is spent in two ways:

1. A part of photon energy is used in liberating the least tightly bound electron from the metal surface which is equal to the work function (W₀) of the metal.
2. The rest of the energy of photon appears as maximum kinetic energy of the emitted electron.

Mathematically, we have,                   
The above equation is known as Einstein's photoelectric equation.