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.
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.