When dust particles collide randomly in a beam of Sunlight, the phenomenon observed is known as

Step 1: Analyze the question The question describes dust particles moving and colliding randomly in a beam of sunlight. The key ideas are random motion and collision of particles.

Step 2: Explain the concepts

• Brownian movement: The continuous, random, zigzag motion of colloidal or microscopic particles. It happens because the particles are bombarded by the fast-moving molecules of the surrounding medium (air or liquid). It was first observed by Robert Brown with pollen grains in water.
• Dialysis: Separation of colloids from dissolved ions or molecules using a semi-permeable membrane.
• Diffusion: The spread of particles from a region of high concentration to one of low concentration.
• Osmosis: Movement of solvent through a semi-permeable membrane from a dilute to a concentrated solution.
• Tyndall effect: The scattering of light by colloidal particles, which makes the path of a light beam visible.

Step 3: Apply to the question Dust in a sunbeam shows two things:

1. The beam becomes visible because the dust scatters light. This is the Tyndall effect.
2. The particles are seen moving about randomly and colliding. This is Brownian movement.

The question asks specifically about the random collision/movement of the particles, not the visibility of the beam. So the phenomenon is Brownian movement.

Be careful with option E. The Tyndall effect explains why the beam can be seen, but it does not describe random particle motion.

Answer: A. Brownian movement

Exam tip: Match the keyword to the phenomenon:

• "Random / zigzag motion" → Brownian movement
• "Light scattering / beam visible" → Tyndall effect
• "Semi-permeable membrane" → Osmosis or dialysis

Keep it up, you're doing well!