Tiny pollen grains suspended in water are viewed under a microscope. The pollen grains are observed to move in a random, jerky manner. Which statement correctly explains this observation?
The water is composed of much smaller, fast-moving molecules that are constantly and randomly colliding with the pollen grains.
Convection currents in the water are carrying the pollen grains in random directions.
The pollen grains are living organisms that are actively swimming through the water.
The temperature of the water is steadily increasing, causing the grains to expand.
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.