Effect of Intensity of Incident Radiation

The electrode C i.e. collecting electrode is made positive with respect to D. Keeping the frequency of light and the potentials fixed, the intensity (amount of energy falling per unit area per second) of incident light is varied and the photoelectric current (i) is measured in ammeter. The photoelectric current is directly proportional to the intensity of light. The photoelectric current gives an account of number of photoelectrons ejected per sec.

Effect of p.d. between C & D

Keeping the intensity and frequency of light constant, the positive potential of C is increased gradually. The photoelectric current increases with increase in voltage (accelerating voltage) till, for a certain positive potential of plate C, the current becomes maximum beyond which it does not increase for any increase in the accelerating voltage. This maximum value of the current is called as saturation current.

• Make the potential of C as zero and make it increasingly negative. The photoelectric current decrease as the potential is made increasingly negative (retarding potential), till for a sharply defined negative potential V_c of C, the current becomes zero. The retarding potential for which the photoelectric current becomes zero is called as cut-off or stopping potential (V_c).

When light of same frequency is used at higher intensity, the value of saturation current is found to be greater, but the stopping potential remains the same. Hence the stopping potential is independent of intensity of incident light of same frequency.