Tiny pollen grains suspended in water are observed under a microscope. The pollen grains are seen to move in a random, jerky manner.
What is the reason for this observation?
Convection currents are carrying the pollen grains.
The pollen grains are being bombarded by much smaller, fast-moving water molecules.
The pollen grains are alive and moving on their own.
Mutual electrostatic repulsion between the pollen grains forces them to move.
321 exam-style questions on CIE IGCSE Physics 2.1 Kinetic particle model of matter, covering 2.1.1 States of matter and changes of state, 2.1.2a Particle structure and motion in solids, liquids and gases, 2.1.2b Gas pressure and particle collisions, 2.1.2c Brownian motion, 2.1.3a The absolute scale of temperature, and 2.1.3b Pressure, volume and temperature of a gas. Each one has a worked solution and a mark scheme showing where the marks go.