The graph showing the variation of photoelectric current (i) with the intensity (Iν) of incident light of frequency ν (above the threshold frequency) on a metallic plate is
Answer & explanation
Correct answer: option 2
The correct answer is Option (2)
Above the threshold frequency, each photon that is absorbed can eject one electron, and emission is instantaneous. The number of photons per second is proportional to the intensity, so the number of photoelectrons per second, and hence the photoelectric current, is directly proportional to the intensity:
\( i \propto I_\nu \)
The graph is a straight line through the origin: no light gives no current, and there is no minimum intensity for emission.
Why the other options are incorrect
Option (1) — Incorrect. This graph shows a current even at zero intensity, which is impossible: without photons no electrons are emitted.
Option (3) — Incorrect. This graph needs a minimum intensity before any current flows; for frequencies above the threshold, even very weak light causes emission.
Option (4) — Incorrect. The current is not an irregular function of intensity; it increases linearly.
Note: A similar question was also asked in CUET (UG) 2023 on 15-06-2023 (Slot 2).
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 as shown graphically in Fig. 11.2.”
