In a demonstration of Brownian motion, smoke particles suspended in air are observed under a microscope. Bright specks of light are seen moving in a random, zigzag path.
Which statement best explains this observation?
Convection currents in the air cause the smoke particles to move in different directions.
The smoke particles are bombarded by much smaller, fast-moving air molecules that cannot be seen.
The smoke particles are hit by larger, slower-moving dust particles.
The smoke particles move continuously to avoid collisions with 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.