Which of the following statements are correct?
A. In a photon-particle collision number of photons are conserved.
B. The photoelectric current is directly proportional to the intensity of incident light.
C. The photoelectric emission is an instantaneous process.
D. Maximum kinetic energy of photoelectrons depend on the intensity of incident radiation.
E. The threshold frequency is different for different metals.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → B, C and E only
Each statement is checked against the experimental facts of the photoelectric effect and the photon picture of light.
(A) In a photon-particle collision number of photons are conserved — Incorrect. Total energy and total momentum are conserved in such a collision, but photons can be absorbed or created, so their number is not conserved.
(B) The photoelectric current is directly proportional to the intensity of incident light — Correct. For light of a given frequency above the threshold, a higher intensity means more photons per second, so more electrons are emitted per second.
(C) The photoelectric emission is an instantaneous process — Correct. There is no measurable time lag between the arrival of the light and the emission, even for very weak light.
(D) Maximum kinetic energy of photoelectrons depend on the intensity of incident radiation — Incorrect. \( K_{\max} = h\nu - \phi_0 \) depends on the frequency and on the metal, not on the intensity.
(E) The threshold frequency is different for different metals — Correct. The threshold frequency is \( \nu_0 = \phi_0/h \), and the work function \( \phi_0 \) is a property of the metal.
NCERT (2026-27):
Particle Nature of Light: The Photon – “… (v) In a photon-particle collision (such as photon-electron collision), the total energy and total momentum are conserved. However, the number of photons may not be conserved in a collision.”
Effect of Frequency of Incident Radiation on Stopping Potential – “… This minimum, cut-off frequency ν0, is called the threshold frequency. It is different for different metals. … (i) For a given photosensitive material and frequency of incident radiation (above the threshold frequency), the photoelectric current is directly proportional to the intensity of incident light (Fig. 11.2). … Above the threshold frequency, the stopping potential or equivalently the maximum kinetic energy of the emitted photoelectrons increases linearly with the frequency of the incident radiation, but is independent of its intensity (Fig. 11.5). (iv) The photoelectric emission is an instantaneous process without any apparent time lag (~10–9s or less), even when the incident radiation is made exceedingly dim.”