Tiny smoke particles are suspended in air inside a closed container. When viewed under a microscope, the smoke particles are observed to move in a random, irregular zigzag fashion.
What causes this random movement?
The smoke particles are being bombarded by larger, invisible air molecules.
The smoke particles are being bombarded by smaller, invisible air molecules moving at high speed.
The air molecules and smoke particles are at different temperatures, creating heat currents.
The smoke particles are repulsed by electrostatic forces between each other.
151 exam-style questions on CIE IGCSE Physics 2.1.2a Particle structure and motion in solids, liquids and gases. Each one has a worked solution and a mark scheme showing where the marks go.