IGCSE Physics: Thermal Physics (Cambridge 0625)

This guide maps Topic 2 Thermal physics of Cambridge IGCSE Physics 0625 for the 2026–2028 examination series. Each sub-section below separates what every candidate must know (Core, examined at grades C–G) from what is required only at the Extended tier (Supplement, needed for grades A*–C).

Where this fits in 0625

Thermal physics is the second of the six 0625 topics, sitting between Motion, forces and energy and Waves. It leans directly on two ideas from Topic 1: pressure as force per unit area reappears when gas pressure is explained through particle collisions, and the concept of internal energy connects back to the energy-stores language introduced with work and power. It is also the topic where the particle picture of matter — which returns later in the course when radiation and states of matter are discussed — is set up properly, so gaps here tend to surface again in later topics.

Syllabus coverage

CAMBRIDGE IGCSE PHYSICS 0625 — TOPIC 2 THERMAL PHYSICS

• 2.1 Kinetic particle model of matter, in three parts. States of matter (2.1.1, Core) — the distinguishing properties of solids, liquids and gases, and the terms for changes of state (gas-to-solid and solid-to-gas transfers are not required). Particle model (2.1.2, Core) — particle arrangement, separation and motion in each state with simple particle diagrams; the link between particle motion and temperature, including absolute zero (−273 °C) as the lowest possible temperature where particles have least kinetic energy; gas pressure explained through particle collisions with surfaces; and the random motion of microscopic particles in suspension (Brownian motion) as evidence for the model. The Supplement adds explaining properties through the forces and distances between particles, treating pressure as the force per unit area created by colliding particles, and knowing that microscopic particles are moved by collisions with light, fast-moving molecules. Gases and the absolute scale of temperature (2.1.3, Core) — the qualitative effect on the pressure of a fixed mass of gas of changing temperature at constant volume or changing volume at constant temperature, and converting between kelvin and degrees Celsius with T (in K) = θ (in °C) + 273; the Supplement adds pV = constant for a fixed mass of gas at constant temperature, including its graph.
• 2.2 Thermal properties and temperature, in three parts. Thermal expansion (2.2.1, Core) — qualitative expansion of solids, liquids and gases at constant pressure, with everyday applications and consequences; the Supplement explains the relative order of magnitude of expansion of the three states through particle motion and arrangement. Specific heat capacity (2.2.2) — the Core asks only that a temperature rise increases an object’s internal energy; the Supplement defines specific heat capacity as energy per unit mass per unit temperature increase, uses c = ΔE/(mΔθ), links temperature rise to the average kinetic energy of the particles, and requires experiments to measure the specific heat capacity of a solid and of a liquid. Melting, boiling and evaporation (2.2.3, Core) — melting and boiling as energy input without temperature change, the melting and boiling temperatures of water at standard atmospheric pressure, condensation and solidification in particle terms, evaporation as the escape of more-energetic particles from a liquid surface, and the cooling effect of evaporation; the Supplement adds the differences between boiling and evaporation, how temperature, surface area and air movement affect evaporation, and explaining the cooling of an object in contact with an evaporating liquid.
• 2.3 Transfer of thermal energy, in four parts. Conduction (2.3.1, Core) — experiments demonstrating good and bad thermal conductors; the Supplement explains conduction in all solids through lattice vibrations plus free-electron movement in metals, explains why gases and most liquids conduct badly, and notes that many solids conduct better than insulators but less well than good conductors. Convection (2.3.2, Core) — convection as an important transfer method in liquids and gases, explained through density changes and shown by experiment. Radiation (2.3.3, Core) — thermal radiation as infrared emitted by all objects, requiring no medium, and the effect of surface colour (black or white) and texture (dull or shiny) on emission, absorption and reflection; the Supplement covers the balance of energy transfer at constant temperature, what happens when incoming and outgoing rates differ, how that balance controls the temperature of the Earth, experiments distinguishing good and bad emitters and absorbers, and how emission rate depends on surface temperature and surface area. Consequences of thermal energy transfer (2.3.4, Core) — everyday applications such as heating a kitchen pan and heating a room by convection; the Supplement examines applications where more than one transfer type matters at once, such as a wood or coal fire and a car radiator.

How to approach it

Almost every mark in this topic is earned by arguing from particles, so practise writing two-to-three-sentence explanations that name the arrangement, separation and motion of particles before drawing any conclusion — examiners reward the mechanism, not the bare fact. Keep the three transfer processes strictly separated: conduction needs particle contact, convection needs a fluid whose density can change, radiation needs nothing at all, and questions frequently describe a situation (a vacuum flask, a black car roof) and ask which process dominates. Extended candidates should give the equation work — c = ΔE/(mΔθ) and pV = constant — the same rehearsal as the Topic 1 equations, and be ready to describe the specific heat capacity experiments with the measurements taken and how the result is calculated. Finally, learn the evaporation–boiling distinctions as a table: where it happens, at what temperature, and how fast.

Official syllabus

Cambridge IGCSE Physics 0625 syllabus for 2026, 2027 and 2028 (Version 2, December 2025), Topic 2 verified against the PDF on 24 August 2026 — cambridgeinternational.org.