The figure shows the experimental set-up for the photoelectric effect. Light from the source S passes through the window W and falls on the photosensitive plate C (emitter). The emitted electrons are collected by the plate A (collector). The battery keeps a potential difference between C and A, and this can be varied.
Light of a fixed frequency above the threshold frequency falls on C, and A is kept at a fixed positive potential with respect to C. The photocurrent is directly proportional to
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → the intensity of the light
The photocurrent is the flow of photoelectrons from C to A. Here the frequency and the potential of A are both kept fixed. So the current depends only on how many electrons come out of C each second. More intense light brings more photons each second, so more electrons are emitted.
Option (1) the frequency of the light — Incorrect. The frequency is fixed here. Above the threshold, a change in frequency does not change how many electrons come out each second.
Option (2) the intensity of the light — Correct. At a fixed frequency and a fixed potential, the number of photoelectrons per second, and so the current, rises in direct proportion to the intensity.
Option (3) the work function of C — Incorrect. The work function is a fixed property of the metal C. It decides the threshold frequency, and the light is already above it.
Option (4) the potential of A — Incorrect. The potential of A is held fixed in this set-up. A quantity that does not change cannot be what the current changes with here.
NCERT (2026-27):
Effect of intensity of light on photocurrent – “Keeping the frequency of the incident radiation and the potential fixed, the intensity of light is varied and the resulting photoelectric current is measured each time. It is found that the photocurrent increases linearly with intensity of incident light …”