Choose the phenomenon from the following, which shows that light is a transverse wave.
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → Polarisation
A wave can be polarised only if its vibrations are perpendicular to the direction of travel, because only then can they be confined to one plane. Longitudinal waves vibrate along the direction of travel and have no such choice of plane.
So polarisation is the phenomenon that shows light is a transverse wave.
Option (1) Diffraction — Incorrect. Diffraction happens for all waves; sound, a longitudinal wave, also diffracts round obstacles.
Option (2) Interference — Incorrect. Interference shows the wave nature of light, but longitudinal waves such as sound interfere too.
Option (3) Reflection — Incorrect. Reflection is shown by every kind of wave (an echo is reflected sound) and even by particles.
Option (4) Polarisation — Correct. Only transverse waves can be polarised, so polarisation of light proves it is transverse.
Note: A similar question was also asked in CUET (UG) 2025 on 14-05-2025 (Slot 1).
NCERT (2026-27):
Polarisation – “… Light waves are transverse in nature; i.e., the electric field associated with a propagating light wave is always at right angles to the direction of propagation of the wave. This can be easily demonstrated using a simple polaroid.”