Name and explain the phenomenon of light due to which the path of a beam of light becomes visible when it enters a smoke filled room through a small hole. Also state the dependence of colour of the light we receive on the size of the particle of the medium through which the beam of light passes.
Generated by claude-sonnet-4-6 · 2026-06-15 06:54 · grounding rag
Model Answer
Tyndall Effect: When a beam of light passes through a smoke-filled room through a small hole, its path becomes visible due to scattering of light by colloidal particles. This phenomenon is called the Tyndall Effect. The smoke particles (colloidal size) scatter the light falling on them, making the beam's path visible to an observer on the side.
Dependence of colour on particle size:
- Very fine (small) particles scatter mainly blue light (shorter wavelengths).
- Particles of larger size scatter light of longer wavelengths (like red/yellow).
- If particles are very large, the scattered light may appear white.
Source: Chapter 10, Section 10.6.1 Tyndall Effect
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Explanation
- The question has two parts — name + explain the phenomenon (2 marks) and state colour dependence (1 mark). Allocate your writing accordingly.
- Always name the phenomenon first (Tyndall Effect), then explain it using key terms: scattering, colloidal particles, beam visibility.
- For colour dependence, examiners expect the three-point progression: fine particles → blue; larger particles → longer wavelengths; very large → white. Don't skip any.
- Avoid mixing up scattering with refraction or reflection — these are common errors.