If the incident radiation of same frequency but different intensity \( I_1 \), \( I_2 \) and \( I_3 \) falls on the plates, variation of photo electric current with collector plate potential is shown in figure with different intensities.
Which is correct?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → \( I_3 \gt I_2 \gt I_1 \)
For radiation of a given frequency, the number of photoelectrons emitted per second is proportional to the intensity of the radiation. When the collector is positive enough, all these electrons are collected and the current reaches its saturation value, so
\( \displaystyle i_{\text{saturation}} \propto I \)
The frequency is the same for all three curves, so the maximum kinetic energy of the photoelectrons is the same and all the curves meet the potential axis at one stopping potential; only their saturation levels differ.
The curve with the highest saturation current belongs to the highest intensity. In the figure the saturation currents decrease from the \( I_3 \) curve to the \( I_2 \) curve to the \( I_1 \) curve, so
\( \displaystyle I_3 \gt I_2 \gt I_1 \)
NCERT (2026-27):
Effect of Potential on Photoelectric Current – “… We can now repeat this experiment with incident radiation of the same frequency but of higher intensity I2 and I3 (I3 > I2 > I1). We note that the saturation currents are now found to be at higher values. This shows that more electrons are being emitted per second, proportional to the intensity of incident radiation.”