Tiny smoke particles are suspended inside a transparent container filled with air (a smoke cell). A bright lamp shines light from the side. Looking through a microscope from above, small, bright, shimmering specks of light are seen to move around in a random, jerky manner. What are the moving specks of light?
air molecules being hit by other air molecules
smoke particles being hit by other smoke particles
air molecules being hit by smoke particles
smoke particles being hit by invisible air molecules
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.