In the above figure the variation of photoelectric current with collector plate potential is given. Choose the correct statements.
(A) The saturation current is constant for different frequencies of incident radiations.
(B) The intensity of the incident radiations is same for different frequencies.
(C) The stopping potential increases with the increase in frequency of incident radiations.
(D) The saturation current increases with the frequency of radiation.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → (A), (B) and (C) only
The graph shows three curves for frequencies \( \nu_3 \gt \nu_2 \gt \nu_1 \). All three rise to the same saturation current, but each is cut off at a different stopping potential.
(A) The saturation current is constant for different frequencies of incident radiations. — Correct. The three curves level off at the same height.
(B) The intensity of the incident radiations is same for different frequencies. — Correct. Saturation current is proportional to the number of photoelectrons emitted per second, which depends on the intensity. Equal saturation currents mean the intensity is the same for all three frequencies.
(C) The stopping potential increases with the increase in frequency of incident radiations. — Correct. By Einstein’s photoelectric equation, a higher frequency gives a larger maximum kinetic energy, so a larger retarding potential is needed; the graph shows \( V_{03} \gt V_{02} \gt V_{01} \) for \( \nu_3 \gt \nu_2 \gt \nu_1 \).
\( \displaystyle eV_0 = h\nu - \phi_0 \)
(D) The saturation current increases with the frequency of radiation. — Incorrect. The curves for different frequencies reach the same saturation current; frequency changes the stopping potential, not the saturation current.
NCERT (2026-27):
Effect of Frequency of Incident Radiation on Stopping Potential – “… We suitably adjust the same intensity of light radiation at various frequencies and study the variation of photocurrent with collector plate potential. The resulting variation is shown in Fig. 11.4. We obtain different values of stopping potential but the same value of the saturation current for incident radiation of different frequencies. … This implies that greater the frequency of incident light, greater is the maximum kinetic energy of the photoelectrons. Consequently, we need greater retarding potential to stop them completely.”
