Brownian motion can be observed by looking at tiny pollen grains suspended in water under a microscope. What causes the pollen grains to move in a random, jerky path?
Direct collisions between the pollen grains themselves.
Convection currents arising inside the water container.
Constant bombardment of the pollen grains by much smaller, rapidly moving water molecules.
Electrostatic forces of attraction and repulsion between the pollen grains.
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.