Brownian motion is the random, jerky movement of microscopic particles suspended in a fluid (such as pollen grains in water or smoke particles in air).
Which statement correctly explains why Brownian motion occurs?
The suspended particles are bombarded in a random manner by the much smaller, fast-moving molecules of the fluid.
Convection currents in the fluid cause the suspended particles to drift in random directions.
Electrostatic forces of attraction and repulsion between the suspended particles cause them to move.
The suspended particles are alive and move around under their own power.
151 exam-style questions on CIE IGCSE Physics 2.1.2a Particle structure and motion in solids, liquids and gases. Each one has a worked solution and a mark scheme showing where the marks go.