Einstein Photoelectric Equation

Class XII - Physics

Einstein Photoelectric Equation :-

According to Einstein, whenever light of suitable frequency falls on the metal surface the energy of the photon
(light wave) is used to extract the electrons from the surface of the metal and rest of the energy of photon is used to emit kinetic energy of electrons.

                The energy of photon used to extract electrons is known as work function. It is denoted by w₀.

Mathematically,

According to Einstein Photoelectric equation,

Energy of Photon             =             Work function   +             Kinetic energy……. (i)

Here,

Energy of Photon             =             hf

Work function (w₀)         =             hf₀

1.   f₀ is the threshold frequency that is needed for the extraction of the electrons from the metal surface.

2.   'h' is plank's constant.

Kinetic energy (K.E)        =             ½ mv_max²

Then, equation (i) can be written as,

Energy of photon                             =             w₀           +             K.E.

or,                          hf                      =             hf₀          +             ½ mv_max²

or,                          hf – hf₀              =             ½ mv_max²

So,                          h(f-f₀)               =             ½ mv_max²