2.3Thermal Physics

Transfer of Thermal Energy — Cambridge IGCSE Physics 0625 Revision Notes & Topical Questions

20 min read 32 parts Lesson 26 of 45 Unit quiz

📚 Cambridge IGCSE Physics 0625 Hub / Topical Revision

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Lesson summary

2.3 Transfer of Thermal Energy (Part 1) — IGCSE PHYSICS notes: Distinguish good conductors from insulators using simple demonstrations and explain conduction in solids by lattice vibrations and free electrons.Good thermal conductors — they transfer thermal energy quickly.Aluminiu…

Bad conductors (thermal insulators)
Observation
Explanation
Definition
Best conductors
Everyday insulators

Part 1 of 7Conductors and insulators

Conductors and insulators

Good thermal conductors

Good thermal conductors they transfer thermal energy quickly.
Aluminium pans and copper wire are examples.

Bad conductors (thermal insulators)

Bad conductors (thermal insulators) they transfer thermal energy poorly.
A wool blanket or layers of cardboard or paper are examples.

Key idea

Key idea the more thermal energy a material takes away, the cooler the contact feels, and the more it holds in, the warmer it feels.

Part 2 of 7Demonstration 1: tiles and rug

Choose a tiled or stone floor with a thick rug or towel lying on it for several hours, so both are at the same temperature.

Stand with one bare foot on the tiles and the other on the rug.

Compare how warm each feels.

Observation

Observation the tiles feel cold and the rug feels warm, although they are at the same temperature.

Explanation

Explanation tiles are good conductors and carry thermal energy away from the foot, while the rug is an insulator and takes very little.

Part 3 of 7Demonstration 2: wood and metal rod

Wrap paper tightly round a rod that is half wood and half metal.

Heat the paper at the join with a gentle flame, turning the rod.

Stop when the paper is discoloured, then unwrap it.

Observation

Observation the paper is undamaged over the metal and charred over the wood.

Explanation

Explanation the metal conducts energy away from the paper along its length, so the paper stays cool, while the wood does not.

Part 4 of 7Demonstration 3: comparing metals

Arrange strips of different metals of equal width and length around a central point.

Stick a ball bearing at the same distance on each strip using a little wax.

Turn the strips upside down and heat the centre gently.

Time how long the wax takes to melt and each ball bearing to fall.

Result

Result the better the conductor, the shorter the time for the ball to drop.

Fair test

Fair test only the material should differ between strips.

Part 5 of 7How conduction works in solids

Definition

Definition thermal conduction is the transfer of thermal energy through a material by lattice vibrations and, in metals, by free (delocalised) electrons.
It is the main method of thermal transfer in solids.

Lattice vibrations

Lattice vibrations in all solids, atoms at the hotter end vibrate more and bump into neighbours.
The collisions pass on energy from atom to atom until thermal equilibrium is reached.

Free electrons

Free electrons in metals, vibrating atoms also transfer energy to free electrons.
The electrons travel far through the metal and collide with distant atoms, so energy moves much faster.

Best conductors

Best conductors metals, because they have many free electrons.

Part 6 of 7More key facts: Demonstrating Conduction and Conduction in Solids

Everyday insulators

Everyday insulators wool, wood, plastic, trapped air and fibreglass slow thermal transfer.

Everyday conductors

Everyday conductors copper, aluminium and steel are used where fast transfer is wanted.

Relative conduction

Relative conduction a better conductor melts the wax and drops the ball bearing sooner.

Temperature feel

Temperature feel touch senses the rate of energy loss from your skin, not the temperature of the object.

Final temperature

Final temperature all objects in the same room eventually reach the same temperature, whatever their conductivity.

Part 7 of 7More from the specification

1Convection currents in fluids

Convection currents in fluids heated liquid or gases expand and become less dense, rising upward to establish continuous circulatory convection currents.

2Thermal radiation and surface properties

Thermal radiation and surface properties hot objects emit infrared radiation, with matte black surface finishes emitting and absorbing radiant heat most effectively.

3Domestic room radiator thermal heating

Domestic room radiator thermal heating room radiator units warm circulating air by conduction,
- while buoyant air convection currents distribute warmth throughout buildings.

4Thermal conduction mechanism

Thermal conduction occurs through particle collisions in liquids and insulators,
and is substantially accelerated in metals by free conduction electron diffusion.

5Thermal convection currents

Convection occurs in fluidsheating causes thermal expansion and lower fluid density,
causing hot fluid to rise while cooler, denser fluid sinks to replace it.

6Infrared thermal radiation

Thermal radiation consists of electromagnetic infrared waves requiring no medium;
- dull, dark surfaces are the best absorbers and emitters,
while shiny silver surfaces reflect radiation.

7Absorbed

Taken in by an object, with light energy transferred to thermal energy.

8Greenhouse effect

Warming of the Earth because gases absorb and re-emit its infrared radiation

9Convection current

Circulating flow of fluid caused by density differences

10Potassium permanganate

A purple compound used to show convection currents in water.

11Radiation

Transfer by electromagnetic waves, requiring no medium

12Convection

Transfer of thermal energy by the movement of a heated fluid

13Liquid

State with a fixed volume that takes the shape of its container.

14Infrared

The part of the electromagnetic spectrum emitted by warm objects.

Key terms

Term	Meaning
Thermal conductor	A material that transfers thermal energy quickly.
Thermal insulator	A material that transfers thermal energy slowly.
Conduction	Transfer of thermal energy through a material by vibrating particles and free electrons.
Free (delocalised) electron	An electron in a metal that can move through the material.
Lattice	The regular arrangement of atoms in a solid.
Thermal equilibrium	A state with no net transfer of thermal energy and equal temperature.

Avoid these mistakes

Saying the tiles are colder — they are the same temperature but conduct heat away faster.

Thinking cold flows into the foot — thermal energy flows out of the foot.

Using "electrons vibrate" — electrons move and atoms vibrate.

Forgetting to keep size, shape and start distance equal in the metal strip experiment.

Last updated: 18 October 2026