Physics 0625 · syllabus 2.3
Cambridge IGCSE Physics 0625 — Transfer of thermal energy topical past papers
How thermal energy moves by conduction, convection and infrared radiation, what makes good conductors, emitters and absorbers, and how this explains everyday designs.
- Questions
- 1,345
- Years
- 2009–2026
- With mark scheme
- 99%
- Questions 2022–2026
- 486
Anyone can browse these pages. Opening the questions and their mark schemes takes a free Momentum account.
What Transfer of thermal energy covers
Thermal energy moves from hotter places to colder ones in three ways. Conduction carries it through a material without the material itself moving: metals are good thermal conductors, while plastics, wood, glass and trapped air are poor conductors, or thermal insulators. Extended candidates explain why: in every solid, vibrating particles pass energy on to their neighbours through the lattice, and in metals free electrons also carry it quickly through the structure. Conduction is poor in gases, whose particles are far apart and collide only now and then, and in most liquids, whose particles are less tightly bound than in a solid and which have no free electrons.
Convection takes place in liquids and gases. A warmed part of the fluid expands, becomes less dense and rises, and cooler, denser fluid sinks to take its place, setting up a convection current. That is how a heater near the floor warms a whole room and how water in a pan heats from the bottom; a few crystals of coloured dye dropped into a beaker of water heated at one side make the current visible.
Thermal radiation is infrared radiation. Every object emits it, and it needs no medium, which is how the Sun's energy crosses space. Dull black surfaces are good emitters and good absorbers of infrared; light-coloured and shiny surfaces are poor emitters and poor absorbers, and reflect most of the infrared that reaches them. Extended candidates also know that an object stays at a constant temperature only when it gives out energy as fast as it receives it, that a hotter object or one with a larger surface area emits more, how this balance sets the Earth's temperature, how to compare emitters and absorbers by experiment, and how several transfers combine in a car radiator or a coal fire.
In the syllabus
The headings this topic has in the Cambridge International 2026–2028 syllabus, as the board prints them.
- 2.3 Transfer of thermal energy
What you should be able to do
- Describe experiments that show which materials are good thermal conductors and which are insulators
- Explain conduction with lattice vibrations and, in metals, free electrons, and why it is poor in gases and most liquids (Extended)
- Explain convection currents in terms of expansion and density, and describe an experiment that shows one
- Describe how a surface's colour and texture affect how well it emits, absorbs and reflects infrared
- Explain everyday examples such as a pan with a metal base and a room heated by convection, and, for Extended, a car radiator and a fire
- Explain how the balance between energy received and energy emitted sets the temperature of an object, including the Earth (Extended)
Key ideas
- Conduction: energy passed through a material by vibrating particles and, in metals, by free electrons
- Convection: warmer fluid expands, becomes less dense and rises; cooler, denser fluid sinks
- Radiation: infrared waves, given out by all objects and needing no medium
- Dull black surfaces: good emitters and absorbers; light, shiny surfaces: poor emitters and absorbers, good reflectors
- Constant temperature: energy received per second = energy emitted per second (Extended)
How Transfer of thermal energy has been examined
From 2022 to 2026, Transfer of thermal energy was on Paper 4 · Theory (Extended) in 14 of 14 exam series, worth about 16% of that paper’s marks.
| Paper | Questions | Share of marks | Series |
|---|---|---|---|
| Paper 1 · Multiple Choice (Core) | 187 | 15% | 14 of 14 |
| Paper 2 · Multiple Choice (Extended) | 180 | 14% | 14 of 14 |
| Paper 3 · Theory (Core) | 41 | 12% | 13 of 14 |
| Paper 4 · Theory (Extended) | 49 | 16% | 14 of 14 |
| Paper 6 · Alternative to Practical | 29 | 22% | 14 of 14 |
Momentum’s own count, over the questions in its bank for these years: a series is one exam session, every zone included, and a question filed under two chapters counts in both. Median marks per question: 1. The bank files this topic together with neighbouring ones, so these figures count every question in its chapters, including some on those topics.
Filed in Momentum under: Thermal Effects.
Mistakes that cost marks
- Writing 'heat rises' — warm fluid rises because it is less dense; it is the fluid that moves, carrying the energy with it
- Saying conduction or convection can cross a vacuum — both need particles; only radiation crosses empty space, as sunlight does
- Saying trapped air 'stops heat' — air is a poor conductor, and trapping it in small pockets prevents convection currents, so both transfers are reduced
- Saying cold flows into your hand from a metal bench — energy flows from your hand into the metal, which conducts it away quickly, so your hand cools
- Writing that particles travel from the hot end to the cold end in conduction — they vibrate about fixed positions and pass energy on; only the free electrons in metals move through the material
Exam technique
- Name the process first, then explain it step by step with particles or with density
- In comparison experiments, change only the material or the surface, keep everything else the same, and say what you measure, such as the temperature after a fixed time
- When more than one transfer is involved, as in a car radiator, name each process and say where it happens
- Use the words emitter, absorber and reflector rather than saying that a surface 'attracts heat'
Practising in Momentum
- Every question in a chapter as one list, from every paper and year in the bank, newest first or shuffled.
- Each question turns over to its own part of the mark scheme, where the board published one.
- Narrow by paper, year, session, zone and marks, and star the questions worth keeping.
- Pick chapters, a number of questions and a time, and the exam builder draws a mock to sit and mark.
Past-paper questions and mark schemes are the copyright of Cambridge International. Momentum shows them to signed-in learners for revision and does not publish them on these pages.