Diffusion of light in the atmosphere takes place due to

Question

UnlockIAS · Accepted Answer

Correct — B, Dust particles. Diffusion (scattering) of light in the atmosphere is caused mainly by the fine dust and suspended particulate matter (aerosols) floating in the air. When sunlight strikes these tiny particles it is scattered in all directions — the Tyndall effect — which is why daylight reaches us as soft, diffuse illumination and why a dusty beam of light becomes visible. Among the given options, dust particles are the principal scatterers.

Why the other options are wrong — (a) Wrong — CO2 is only a trace atmospheric gas; while air molecules do scatter light (Rayleigh scattering), CO2 specifically is not the cause of the general diffusion of light and is not the intended answer.  (c) Wrong — helium is an inert gas present in minute amounts; it plays no significant role in scattering sunlight.  (d) Wrong — water vapour can absorb light and, as droplets, scatter it, but the everyday diffusion of light in the atmosphere is attributed mainly to suspended dust and particulate matter, not water vapour.

Concept: When light passes through a medium containing fine suspended particles, it is redirected in many directions — a process called scattering or diffusion of light. Larger suspended particles such as atmospheric dust and aerosols produce the Tyndall effect, scattering light broadly across the spectrum and making beams visible and daylight diffuse. (Very small air molecules cause wavelength-dependent Rayleigh scattering, which makes the sky blue — but the general diffusion of light in this question is attributed to dust particles.)

State PCS 2021 Q25 — Science & Technology PYQ with Answer

State PCS 2021 Q25 — Science & Technology PYQ with Answer