Matching Optical Effects with Physical Phenomena of Light

To determine the correct matching between the optical effects in List-I and the underlying physical phenomena in List-II, we analyze each entry individually:

1. (P) Colorful sky in north polar region (Aurora Borealis):

   • Mechanism: Charged particles (protons and electrons) originating from solar wind enter Earth's magnetosphere and collide with gases in the upper atmosphere.
   • Phenomenon: The excitation and subsequent de-excitation of oxygen and nitrogen atoms emit light of characteristic wavelengths (aurora).
   • Therefore, $\text{P} \rightarrow 5$ (Emission of radiation from oxygen and nitrogen atoms excited by charged particles).

2. (Q) Partially polarized sun light:

   • Mechanism: As unpolarized sunlight passes through Earth's atmosphere, it interacts with air molecules.
   • Phenomenon: Rayleigh scattering by atmospheric molecules scatters the electric field components unequally depending on the viewing angle, resulting in partially polarized light in the sky.
   • Therefore, $\text{Q} \rightarrow 4$ (Scattering of light by molecules in the atmosphere).

3. (R) Rainbow:

   • Mechanism: Sunlight enters spherical water droplets, bends due to refraction, separates into its constituent colors due to dispersion, and undergoes reflection inside the droplet before emerging.
   • Phenomenon: Dispersion and reflection inside water drops.
   • Therefore, $\text{R} \rightarrow 1$ (Dispersion and reflection).

4. (S) Dark and bright fringes:

   • Mechanism: When light encounters obstacles, apertures, or multiple coherent paths, wave properties lead to constructive and destructive superposition.
   • Phenomenon: Diffraction and interference produce alternate dark and bright fringes on an observation screen.
   • Therefore, $\text{S} \rightarrow 3$ (Diffraction).

Comparing with the options: $\text{P} \rightarrow 5, \quad \text{Q} \rightarrow 4, \quad \text{R} \rightarrow 1, \quad \text{S} \rightarrow 3$

This corresponds to Option A.