2.3.1Thermal Physics
Demonstrating Conduction — Cambridge IGCSE Physics 0625 Revision Notes & Topical Questions
5 min read 9 parts Lesson 30 of 45 1 quiz
Lesson summary
2.3.1 Demonstrating Conduction — IGCSE PHYSICS notes: Describe experiments that compare how well materials conduct thermal energy and interpret the results.Good conductors — transfer thermal energy quickly, for example an aluminium pan or copper wireInsulators — bad conductors th…
- Detecting transfer
- Observation
- Conclusion
- Independent variable
- Control variables
- Results table
Part 1 of 7Good and bad conductors
Good conductors
- Good conductors transfer thermal energy quickly, for example an aluminium pan or copper wire
Insulators
- Insulators bad conductors that transfer it slowly, for example a wool blanket or paper
Detecting transfer
- Detecting transfer energy cannot be seen, so a change at the far end is observed
- Wax melting
- A pin falling
- A temperature rise
Part 2 of 7Tiles and rug
Tiles and rug
Leave a thick rug or towel on a tiled floor 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 both are at the same temperature
Explanation
- Tiles are good conductors and take energy away from the foot
- The rug is an insulator and takes very little energy from the foot
Part 3 of 7Wood and metal rod
Wood and metal rod
Wrap paper tightly round a rod made of half wood and half metal.
Heat the paper at the join with a gentle flame, turning the rod.
Stop when the paper is clearly discoloured and unwrap it.
Observation
- Observation paper is charred on the wood but undamaged on the metal
Explanation
- Metal conducts energy away along its length so the paper stays cool
- Wood is an insulator so the paper gets hot enough to burn
Part 4 of 7Comparing metals
1
Arrange strips of equal width and length around a central heated point.
2
Stick a ball bearing with wax at equal distances from the centre on each strip.
3
Heat the centre gently with a candle.
4
Time how long each bearing takes to fall as the wax melts.
- Result
- the better conductor makes the wax melt in a shorter time
Part 5 of 7Water and ice
Set-up
- Set-up ice wrapped in wire gauze at the bottom of a test tube of cold water, heated near the top
Observation
- Observation the top water boils while the ice stays solid for several minutes
Conclusion
- Conclusion water is a poor conductor, and hot water stays at the top because it is less dense
Part 6 of 7Fair test and results
Independent variable
- Independent variable material of the rod
Dependent variable
- Dependent variable time for the wax to melt or final temperature
Control variables
- Control variables length, thickness, starting temperature, heat source and distance of the wax
Results table
- Results table material, time in seconds and rank
- Plot temperature against time for each rod on the same axes
- The steepest curve is the best conductor
Safety
- Safety tie back hair, keep flames away from flammables and use tongs for hot rods
Part 7 of 7More from the specification
More from the specification
Thermal Conduction and Convection
- Thermal energy transfers through solids primarily by conduction via lattice vibrations and free electron diffusion,
- whereas in liquid and gases heating occurs primarily by bulk fluid movement called convection.
Thermal Radiation and Infrared Waves
- All matter above absolute zero emits thermal radiation as electromagnetic waves in the infrared region, transferring energy across a vacuum without requiring a material medium.
Surface Emission and Absorption Characteristics
- A dull, matte black surface is both the best absorber and the best emitter of infrared radiation,
- whereas a shiny white or silver surface reflects most radiation and emits very poorly.
Domestic Radiators and Terrestrial Energy Transfer
- Despite their name, a domestic radiator transfers heat to a room predominantly by setting up convection currents in the air,
- while thermal radiation from the Sun warms the Earth surface.
Greenhouse effect
- Warming of the Earth because gases absorb and re-emit its infrared radiation
Convection current
- Circulating flow of fluid caused by density differences
Thermal equilibrium
- Constant temperature because energy is absorbed and lost at equal rates
Potassium permanganate
- A purple compound used to show convection currents in water.
Radiation
- Transfer by electromagnetic waves, requiring no medium
Convection
- Transfer of thermal energy by the movement of a heated fluid
Liquid
- State with a fixed volume that takes the shape of its container.
Infrared
- The part of the electromagnetic spectrum emitted by warm objects.
Electron
- Negatively charged particle in an atom.
Absorbed
- Taken in by an object, with light energy transferred to thermal energy.
Lattice
- The regular arrangement of atoms in a solid.
Vibration
- A repeated backwards and forwards movement.
Key terms
| Term | Meaning |
|---|---|
| Thermal conductor | Material that transfers thermal energy quickly |
| Thermal insulator | Material that transfers thermal energy slowly |
| Thermal equilibrium | State in which two objects are at the same temperature |
| Fair test | Only one variable changed while others are controlled |
Avoid these mistakes
1
Thinking the tiles are colder than the rug — both are at the same temperature, tiles simply conduct energy away faster.
2
Thinking paper next to metal burns first — metal conducts energy away so the paper stays cool.
3
Not controlling length and thickness of the rods — the test is then unfair.
4
Claiming a numerical conductivity from a ranking test — it only ranks the materials.
Marked practiceQuizzes for this lesson
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