In an experiment to observe Brownian motion, tiny pollen grains are suspended in water and viewed through a microscope. The pollen grains are seen to undergo continuous, erratic, and random movements.
Which of the following statements correctly explains this observation?
Water molecules have much larger masses than pollen grains and they move in random directions.
Water molecules move at much higher average speeds than pollen grains and collide with them from random directions.
Water molecules move at much higher average speeds than pollen grains and they all move in a single, coordinated direction.
Water molecules have comparable masses to pollen grains and move in fixed, vibrational paths.
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.