Correct Option
The correct option isScattering of light by suspended particles
Explanation
The phenomenon described is known as the Tyndall Effect. It is caused by the scattering of light by particles in a colloid or a fine suspension (such as dust in the air).
Option Analysis:
- Total internal reflection is Incorrect: Total Internal Reflection occurs when light travels from an optically denser medium to a rarer medium at an angle exceeding the critical angle. It explains phenomena like mirages and the working of optical fibers, not the visibility of a light beam in air.
- Scattering of light by suspended particles is Correct: Suspended dust particles in the room intercept the incoming sunlight and scatter it in various directions. This scattered light reaches the observer's eyes, rendering the path of the beam visible. This is the defining characteristic of the Tyndall Effect.
- Atmospheric refraction is Incorrect: Atmospheric Refraction refers to the bending of light as it passes through atmospheric layers of varying densities. It is responsible for the twinkling of stars and the advanced sunrise/delayed sunset, but not the illumination of a light path.
- Dispersion of light is Incorrect: Dispersion is the separation of white light into its constituent colors (spectrum) due to varying refractive indices for different wavelengths (e.g., formation of a rainbow).
Key Takeaway:
The visibility of a light beam's path in a medium containing suspended particles is primarily due to the scattering of light (Tyndall Effect).