In the context of the Photoelectric effect, identify the statements which support quantum nature of light.
(A) The electric charge of photoelectrons is quantized
(B) The maximum kinetic energy of photoelectrons depends on the frequency of the incident light, but is independent of its intensity
(C) The photoelectric emission is an instantaneous process without any apparent time lag, even when the incident radiation is made exceedingly dim
(D) There is a minimum frequency of light below which no photoelectrons are emitted
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → (B), (C) and (D) only
In Einstein's photoelectric equation light comes in packets (photons) of energy \( h\nu \), and one photon gives all its energy to one electron. A statement supports the quantum nature of light only if it can be explained by this and not by the wave picture.
(A) The electric charge of photoelectrons is quantized — Incorrect. This is a property of electric charge, not of light, so it says nothing about the nature of light.
(B) The maximum kinetic energy of photoelectrons depends on the frequency of the incident light, but is independent of its intensity — Correct. \( K_{\max} = h\nu - \phi_0 \) depends only on the photon energy; a wave would carry more energy with greater intensity.
(C) The photoelectric emission is an instantaneous process without any apparent time lag, even when the incident radiation is made exceedingly dim — Correct. One photon ejects one electron at once, whereas a wave would need time to build up the energy.
(D) There is a minimum frequency of light below which no photoelectrons are emitted — Correct. A photon must carry at least the work function, \( h\nu_0 = \phi_0 \), whatever the intensity.
NCERT (2026-27):
Effect of Frequency of Incident Radiation on Stopping Potential – “… (iii) For a given photosensitive material, there exists a certain minimum cut-off frequency of the incident radiation, called the threshold frequency, below which no emission of photoelectrons takes place, no matter how intense the incident light is. 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.”