Contents
Part 2 of 3
Brownian motion
identify
Try it yourself
A drop of muddy river water is sealed under a thin cover slip and watched through a microscope for 20 minutes. Tiny particles of clay are seen in it. Which row describes what the clay particles do?
identify: name or select.
| Row | Path of each clay particle | Neighbouring clay particles | After 20 minutes |
|---|---|---|---|
| A | a random zig-zag | each moves in its own way | still jiggling |
| B | a random zig-zag | all move the same way together | still jiggling |
| C | a smooth, straight drift | each moves in its own way | they have stopped |
| D | a regular back-and-forth | all move the same way together | still jiggling |
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Scope and sources
Cambridge IGCSE Physics 0625 · 2026–2028 v2 · Original learning materials.
The distinguishing properties of solids, liquids and gases and the terms for the changes of state (2.1.1.1, 2.1.1.2); the arrangement, separation and motion of particles in each state, with simple particle diagrams (2.1.2.1); the motion of particles and temperature, with absolute zero, −273 °C, where the particles have least kinetic energy (2.1.2.2); the random motion of microscopic particles in a suspension as evidence for the kinetic particle model (2.1.2.4) and its explanation by random collisions (2.1.2.5); how forces and distances between particles and their motion affect the properties of solids, liquids and gases (2.1.2.6); microscopic particles moved by collisions with light, fast-moving molecules, and the terms atoms or molecules as distinct from microscopic particles (2.1.2.8). Gas pressure and the kelvin scale are in the module on gas pressure; melting, boiling and evaporation in their own module.
Apparatus, amounts and times in the experiment are illustrative. Real practical work follows a teacher-approved safety method.
Official Cambridge syllabus