In the photoelectric effect, the intensity of the incident light decides which of the following?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → the number of the photoelectrons
Option (1) the kinetic energy of the photoelectrons — Incorrect. The maximum kinetic energy \( K_{\mathrm{max}}=h\nu-\phi_0 \) is fixed by the frequency and the metal. It does not depend on the intensity.
Option (2) the momentum of the photoelectrons — Incorrect. The momentum of a photoelectron goes with its kinetic energy, which the intensity does not change.
Option (3) the number of the photoelectrons — Correct. The intensity is proportional to the number of photons falling per unit area per unit time. More photons means more electrons absorbing them, so more photoelectrons come out (for \( \nu\gt\nu_0 \)).
Option (4) the energy of each photon — Incorrect. Each photon has energy \( E=h\nu \), set by the frequency alone. A higher intensity only increases the number of photons.
NCERT (2026-27):
Einstein’s Photoelectric Equation: Energy Quantum of Radiation – “… In this picture, intensity of radiation as noted above, is proportional to the number of energy quanta per unit area per unit time. The greater the number of energy quanta available, the greater is the number of electrons absorbing the energy quanta and greater, therefore, is the number of electrons coming out of the metal (for ν > ν0).”