How to Revise Topic 2: Thermal Physics

Topic 2 is one of the shorter IGCSE Physics topics, but it contains several calculation-heavy subtopics that are frequently tested.

What Topic 2 covers

1. Kinetic particle model (states of matter, particle behaviour, Brownian motion)
2. Thermal properties and temperature (specific heat capacity, latent heat, heating/cooling curves)
3. Thermal energy transfers (conduction, convection, radiation, insulation)
4. Gases and the Kelvin scale (gas laws, absolute zero, Kelvin conversions)

Priority areas

Must-know calculations

• E = mc(change in T) for specific heat capacity
• E = mL for latent heat
• Temperature conversion: T(K) = T(degrees C) + 273
• Boyle’s Law: P1V1 = P2V2 (at constant temperature)
• Pressure Law: P1/T1 = P2/T2 (at constant volume, temperatures in Kelvin)

Must-know concepts

• Why temperature stays constant during a change of state (energy goes to breaking/forming bonds between particles, not increasing kinetic energy)
• The difference between evaporation and boiling
• How conduction, convection and radiation work at the particle level
• Why metals are good conductors (free electrons transfer kinetic energy)
• Why trapped air is a good insulator (prevents convection)
• Why dark, rough surfaces are better emitters and absorbers of radiation than light, shiny surfaces

Revision strategy for Topic 2

3-day intensive plan

• Day 1: Particle model (states, changes of state, Brownian motion). Specific heat capacity: learn the formula, practise 3 calculations, understand the experiment.
• Day 2: Latent heat: formula, heating/cooling curves, practise identifying the flat sections. Gas laws: learn Boyle’s and Pressure Law, practise calculations using Kelvin.
• Day 3: Thermal energy transfer: describe each method, explain in terms of particles, know examples and applications (vacuum flask, house insulation). Mixed past paper questions.

Common mistakes in Topic 2

• Using Celsius instead of Kelvin in gas law calculations (this gives wrong answers every time).
• Confusing specific heat capacity with specific latent heat (SHC involves a temperature change; latent heat involves a state change at constant temperature).
• Saying that heat “rises” (warm AIR rises due to convection; heat itself does not rise).
• Describing radiation as requiring a medium (radiation is the only method that works through a vacuum).
• Confusing evaporation and boiling (evaporation happens at any temperature from the surface only; boiling happens at a specific temperature throughout the liquid).

Self-test checklist

After revision, you should be able to:

• Describe the arrangement and motion of particles in solids, liquids and gases.
• Calculate energy using E = mc(delta T) and E = mL.
• Sketch and interpret heating/cooling curves.
• Convert between Celsius and Kelvin.
• Apply Boyle’s Law and the Pressure Law.
• Explain conduction, convection and radiation with particle-level detail.
• Describe how a vacuum flask reduces energy transfer.