Pollen grains suspended in water are observed under a microscope. They are seen to move around in a random, jerky, continuous motion.
What is the cause of this motion?
Convection currents in the water created by the warmth of the light source.
Continuous bombardment of the pollen grains by fast-moving, invisible water molecules.
Active self-propulsion of the pollen grains through the liquid.
Mutual gravitational or electrostatic attraction between neighboring pollen grains.
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.