question_answer

Sketch a graph between frequency of incident radiations and stopping potential for a given photosensitive material. What information can be obtained from the value of intercept on the potential axis? A source of light of frequency greater than the threshold frequency is placed at a distance of 1 m from the cathode of a photo-cell. The stopping potential is found to be V. If the distance of the light source from the cathode is reduced, explain giving reasons, what change will you observe in the (i) photoelectric current, (ii) stopping potential ?   

Answer:

                The graph between frequency of incident radiation and stopping potential for a given photo- sensitive surface is shown in Fig. From the value of the intercept on the potential axis, we can determine the work function \[{{W}_{0}}\] as follows: As           \[e{{V}_{0}}=hv-{{W}_{0}}\] or            \[{{V}_{0}}=\left( \frac{h}{e} \right)v-\frac{{{W}_{0}}}{e}\]          \[\therefore \] Intercept on the potential axis \[=-\frac{{{W}_{0}}}{e}\] Work function, \[{{W}_{0}}=e\times \] Magnitude of intercept on the potential axis. If the distance of the light source from the cathode is reduced, then (i) the photoelectric current increases because the intensity of incident radiation increases, and (ii) the stopping potential \[{{V}_{0}}\] remains the same because it is independent of the intensity.