Brownian motion can be observed under a microscope when looking at tiny pollen grains suspended in calm water.
What is the primary cause of the continuous, random movement of these pollen grains?
The pollen grains are constantly bombarded by fast-moving water molecules.
Convection currents in the water carry the pollen grains in random directions.
The pollen grains have different densities and rise or sink at different rates.
The pollen grains collide with the glass slide holding the water droplet.
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.