Question

Which of the following shows Brownian motion?

• A. Movement of dust particles in a ray of sunlight
• B. Movement of ants on the ground
• C. Motion of an oil drop in water
• D. Movement of molten wax after melting of a candle

Answer 1

The correct option is A Movement of dust particles in a ray of sunlight

Movement of dust particles in a ray of sunlight is an example for Brownian motion. The particles in the ray of sunlight move in a zig-zag manner due to the intermixing of dust particles which are in continuous motion with the particles of air.
Oil is insoluble in water, hence it would move only on the top layer of water, not in a random motion. Hence the motion is not a Brownian motion.
Movement of ants and wax is not the random motion of particles suspended in a fluid, hence not under Brownian motion.