Small smoke particles are suspended in air. When viewed with a microscope under a bright light, the smoke particles can be seen to be moving about irregularly and continuously.
What causes this movement?
The smoke particles are being bombarded by the heavier particles of the air.
The smoke particles are being bombarded by the lighter particles of the air.
The temperature of the air is higher than that of the smoke particles.
The temperature of the air is lower than that of the smoke particles.
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.