Combined Science Physics P2: Thermal Physics

Cambridge IGCSE Combined Science 0653 Physics P2 explains bulk thermal behaviour through particles. It covers states, particle motion, gas pressure, expansion, evaporation, conduction, convection, radiation and everyday consequences. Specific heat capacity is not part of this P2 syllabus boundary.

P2.1 States and the particle model

A solid has a fixed shape and volume. Its particles are close together in an ordered arrangement and vibrate about fixed positions. A liquid has a fixed volume but takes the shape of its container because close particles can move past one another. A gas has neither fixed shape nor fixed volume; its widely separated particles move rapidly and randomly.

Melting changes solid to liquid, freezing changes liquid to solid, boiling changes liquid to gas throughout the liquid, and condensation changes gas to liquid. Sublimation and deposition are not required in this syllabus section.

Simple particle diagrams must show differences in arrangement and separation, not different particle sizes. The same substance keeps the same particles when its state changes.

Particle motion and temperature

Raising temperature increases the average kinetic energy of the particles, so their random motion becomes faster. Lowering temperature reduces their average kinetic energy. Temperature is therefore connected to particle motion, but it is not the total energy stored by an entire sample.

For Supplement work, explain macroscopic properties using particle separation, motion and forces. A solid resists shape change because its particles remain in fixed relative positions. A liquid flows because particles can rearrange while staying close. A gas is easily compressed because there are large spaces between particles.