A student uses a microscope to observe pollen grains suspended in water. Under the microscope, the pollen grains are seen to move in a random, jerky, zigzag path.
Why do the pollen grains move randomly?
They are collided with by invisible, rapidly moving water molecules.
They are tiny living organisms that can swim through the water.
They are carried by convection currents caused by the illumination light.
They suffer from mutual repulsion due to electrostatic charges.
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.