Which of the following phenomena proved that the photon has particle nature?
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → Photoelectric effect
A phenomenon shows particle nature only if it needs light to arrive in discrete packets of energy \( h\nu \); phenomena explained by superposing waves show wave nature.
Option (1) Interference — Incorrect. Interference is explained by the superposition of waves, so it supports the wave nature of light.
Option (2) Diffraction — Incorrect. Diffraction is the bending of waves round edges, again a wave effect.
Option (3) Polarization — Incorrect. Polarization shows that light waves are transverse; it is a wave property.
Option (4) Photoelectric effect — Correct. The instantaneous emission, the threshold frequency and the maximum kinetic energy independent of intensity are explained only if light comes as photons of energy \( h\nu \) (Einstein's photoelectric equation).
Note: A similar question was also asked in CUET (UG) 2023 on 25-05-2023 (Slot 3) and on 23-05-2023 (Slot 3).
NCERT (2026-27):
Einstein’s Photoelectric Equation: Energy Quantum of Radiation – “… Photoelectric effect thus gave evidence to the strange fact that light in interaction with matter behaved as if it was made of quanta or packets of energy, each of energy hν.”
Particle Nature of Light: The Photon – “… A definite value of energy as well as momentum is a strong sign that the light quantum can be associated with a particle. This particle was later named photon.”