In the context of Einstein's photo-electric effect experiment, identify the correct statements among the following.
A. The energy of each photon is \( h\nu \), where \( \nu \) is the frequency
B. The work function is the minimum energy needed to remove an electron from the illuminated surface.
C. Kinetic energy of photoelectrons depends on frequency of light, not on its intensity.
D. The threshold frequency depends on intensity of incident light.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → A, B and C only
In Einstein’s photoelectric equation, \( K_{\max} = h\nu - \phi_0 \), light arrives as photons of energy \( h\nu \) and each electron absorbs a single photon.
(A) The energy of each photon is \( h\nu \), where \( \nu \) is the frequency — Correct. This is the quantum relation on which the photoelectric equation is built.
(B) The work function is the minimum energy needed to remove an electron from the illuminated surface. — Correct. It is the energy needed to free the least tightly bound electron; a photon with less energy cannot eject any electron.
(C) Kinetic energy of photoelectrons depends on frequency of light, not on its intensity. — Correct. The maximum kinetic energy \( h\nu - \phi_0 \) contains the frequency but not the intensity. A higher intensity only means more photons, so more electrons per second, each with the same maximum energy.
(D) The threshold frequency depends on intensity of incident light. — Incorrect. The threshold frequency is fixed by the work function of the metal alone.
\( \nu_0 = \phi_0/h \)
NCERT (2026-27):
Einstein’s Photoelectric Equation: Energy Quantum of Radiation – “… Each quantum of radiant energy has energy \( h\nu \), where h is Planck’s constant and \( \nu \) the frequency of light.”
Electron Emission – “… This minimum energy required by an electron to escape from the metal surface is called the work function of the metal.”
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 ….”