We now study the relation between the frequency \(\nu \) of the incident radiation and the stopping potential V₀. We suitably adjust the same intensity of light radiation at various frequencies and study the variation of photocurrent with collector plate potential. The resulting variation is shown in figure (a). We obtain different values of stopping potential but the same value of the saturation current for incident radiation of different frequencies. The energy of the emitted electrons depends on the frequency of the incident radiations. The stopping potential is more negative for higher frequencies of incident radiation. Note from the figure that the stopping potentials are in the order V₀₃ > V₀₂ > V₀₁ if the frequencies are in the order \(\nu \)₃ > \(\nu \)₂ > \(\nu \)₁. This implies that greater the frequency of incident light, greater is the maximum kinetic energy of the photoelectrons. Consequently, we need greater retarding potential to stop them completely. If we plot a graph between the frequency of incident radiation and the corresponding stopping potential for different metals we get a straight line, as shown in figure (b).
The graph shows that
(i) The stopping potential V₀ varies linearly with the frequency of incident radiation for a given photosensitive material.
(ii) There exists a certain minimum cut-off frequency \(\nu \)₀ for which the stopping potential is zero.

                                               (a)   

                                              (b)

Why the saturation current  is same for varying frequency in figure (a)?

All of the above.

Saturation current depends upon the intensity of the incident light which is constant during this case which explains its same value for varying frequencies. Moreover, intensity of light is inversely proportional to the square of the distance between the source and collector. So, saturation current also depends upon the distance.