Conduction
Follow thermal energy through materials, compare evidence and design a fair investigation.
Core: experiments comparing conductors and insulators. Supplement / Extended: particle mechanisms and intermediate conductors. This is Cambridge IGCSE, separate from Egyptian Baccalaureate / Thanaweya Amma and not Year 3.
Core 2.3.1.1 · Supplement 2.3.1.2–4 · PDF pp.188–193 / printed pp.180–185.
Energy moves; the spoon does not flow
Conduction transfers thermal energy from a hotter region towards a colder region without bulk movement of the material. A spoon can stay still while its handle warms. Do not imagine 'cold' travelling into the hot end.
Worked example
A rod has one end at 80 °C and the other at 25 °C. The net energy transfer is towards the 25 °C end. At equal temperatures there is no net transfer between the ends, even though particles still move.
Think first: Does conduction require the whole object to move?
No. Energy is passed through the material. Bulk motion of a liquid or gas carrying energy is convection, our next lesson.
Which rod transfers energy more readily?
Predict, then inspect the pin evidence
Core. Which material will have the earliest pin fall at the same marker distance in this illustrative matched experiment? Make a prediction before using the time control. These are recorded model observations, not a calculated heat-flow simulation.
Copper: 0 of 3 pins fallen · Iron: 0 of 3 pins fallen · Glass: 0 of 3 pins fallen
| Material | At 2 cm | At 4 cm | At 6 cm |
|---|---|---|---|
| Copper | 20 | 50 | 90 |
| Iron | 60 | 120 | 180 |
| Glass | Not within 180 s | Not within 180 s | Not within 180 s |
This table deliberately stays visible as study evidence. Prediction feedback is unscored and nothing is saved beyond this page session.
Worked method: six distinct marking points
Describe a teacher-supervised comparison of copper and iron using wax markers. Make the method, fair test, safety and conclusion explicit.
- Use metal rods, matched pins and small dabs of the same wax; fix each rod securely. [1 mark]
- Keep rod dimensions and marker distances equal. [1 mark]
- Start at the same temperature; apply matched heating to corresponding ends and start timing. [1 mark]
- Record when each corresponding pin falls and repeat after cooling/resetting the apparatus. [1 mark]
- Use eye protection, heatproof supports and tongs; let rods cool before handling. [1 mark]
- A consistently shorter fall time supports better conduction in this matched setup. Do not infer an exact conductivity ratio from these times. [1 mark]
These suggested marks belong to this original task, not an official Cambridge mark scheme. A real investigation needs teacher-approved apparatus and risk assessment; this screen activity is not a home heating instruction.
Is it a fair test of material?
Rod dimensions, marker distance, wax, initial temperature and heating are matched. Only material changes.
Changing comparison clears the prediction. No lasting score is stored.
A smaller temperature decrease supports better insulation
| Time / min | Wool | Paper | No covering |
|---|---|---|---|
| 0 | 70 | 70 | 70 |
| 5 | 65 | 61 | 56 |
| 10 | 61 | 55 | 46 |
| 15 | 58 | 50 | 40 |
Worked comparison: decrease, not final value
Wool: 70 − 58 = 12 °C. Paper: 70 − 50 = 20 °C. No covering: 70 − 40 = 30 °C. Wool’s water cooled 18 °C less than the uncovered water. This is a difference between decreases, not a percentage and not proof that conduction is the only transfer mechanism.
Keep water amount, mug/lid design, starting temperature, layer thickness, exposed area, room conditions and timing matched. Use safely warm water under supervision; hot water can scald. Do not compare a thick wool layer with a thin paper layer and claim to have isolated material alone.
Practise, then explain
Four multiple-choice questions, three numerical data-reading responses and seven written tasks. Practical comparisons are Core; the particle mechanisms and intermediate conductors are Supplement / Extended. Numerical answers are checked automatically; written answers use a self-assessment guide. The suggested marks are for this original practice, not an official Cambridge mark scheme.
Practice stays only while this page is open. Refreshing or leaving clears these responses. Copy useful written work into your notes before leaving.
One end of a stationary rod is at 80 °C and the other is at 25 °C. Which statement describes conduction?
Optional hint
Think about what is transferred, and whether the whole rod travels.
Source clarifications and safe limits
The original PDF is unchanged. We retain its wax-and-pin comparison and Figure 26.1’s equal-distance markers, but use original explicitly illustrative timings. Pin-fall timing is qualitative evidence, affected by heating contact, heat capacity, dimensions and wax as well as conduction; it does not directly give a conductivity ratio.
The source describes gas collisions as rare. At everyday pressures collisions are frequent: low density, separated particles and no solid lattice help explain poor conduction. Most liquids have close particles, so do not copy the gas-spacing explanation into a liquid answer. The syllabus’s lattice-vibration model describes energy transfer in solids; real non-crystalline solids need not have a perfectly regular lattice.
The source’s covered-mug comparison concerns overall cooling, not conduction alone. Trapped air reduces conduction and also restricts bulk air movement. A wooden handle reduces risk but can still get dangerously hot. Do not touch heated rods or spoons to test conduction, heat glass with a flame, or improvise this experiment at home. Any physical demonstration needs teacher-approved equipment and supervision.
Source alignment: supplied Physics-0625 Volume A, PDF pp.188–193 / printed pp.180–185, Figure 26.1; official Cambridge 2026–2028 syllabus, section 2.3.1. Original teaching, model data and questions. Source-download access is unchanged.