whenever a light of high frequency strikes a metal surface then outer electron of that metal gets ejected .This phenomenon is known as photoelectric effect and the electrons emitted is known as photoelectrons.
Let us a take a evacuated tube consisting of a two electrode anode and cathode connected to a variable voltage . when a light falls of sufficient frequecy falls on cathode electrons are emitted and it is attracted towards poitive terminal i.e anode .If both the electrodes are externally connected current flows through it and it is called photo electric current.
This photoelectric current depends on following condition.
1)if we increase the intensity of incident light i.e increase the number of photons per unit area more electron get emitted due to more collision of photons withelectron of that anode.2)If we make the anode more positive more emitted electron from cathode gets attracted towards anode, so more is the current.3)if we increase the frequency of the incident light (i.e energy) more is the energy of the emitted electron and it moves easily towards the anode due to its K.E and more is the current.
Now if we make the anode negative then ejected eletron gets repelled but the emitted electron with sufficent energy overcome this rpulsion and make its way towards anode and reach there.IF we make the anode more negative then for some particular negative voltage on this anode no electron can reach it due to repulsion.This negative voltage is known as stopping potenial
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