Part 1 of 4Conduction
Heat travels through solids by passing energy from particle to particle.
Mechanism
- Particles at the hot end vibrate more strongly and pass energy on to their neighbours.
Metals
- Metals conduct well because free electrons carry energy quickly through the material.
Insulators
- Materials such as wood, plastic and trapped air conduct poorly and are used to reduce heat loss.
Where it happens
- Conduction is mainly in solids, since the particles are close together and in contact.
Everyday example
- A metal spoon left in a hot drink soon feels hot at the handle because conduction carries energy along it.
Part 2 of 4Convection and Radiation
Fluids transfer heat by moving, and radiation needs no material at all.
Convection
- When a fluid is heated it expands, becomes less dense and rises, while cooler denser fluid sinks to replace it.
Convection currents
- This circulation sets up convection currents, which warm a room from a radiator.
Radiation
- Hot objects give out infrared radiation, which can travel through a vacuum.
Surfaces
- Dark matt surfaces absorb and emit radiation well, while light shiny surfaces reflect it.
Sea breezes
- Warm air rising over hot land draws in cooler air from the sea, producing a convection current we feel as a breeze.
Emitters and absorbers
- A black teapot cools faster than a shiny one because dark surfaces are better at giving out radiation.
| Method | Needs particles? | Typical situation |
|---|---|---|
| Conduction | Yes, solids | A spoon warming in hot soup |
| Convection | Yes, fluids | Hot air rising from a radiator |
| Radiation | No | Heat from the Sun reaching Earth |
Part 3 of 4Reducing Heat Loss
Several methods target each type of heat transfer.
Reducing Heat Loss
Loft insulation
- Fibre layers trap air, which is a poor conductor, reducing conduction through the roof.
Cavity walls
- Foam or a gap in the wall limits convection and conduction between inside and outside.
Double glazing
- Two panes with a gap between them reduce conduction and convection through the window.
Vacuum flask
- A shiny, vacuum-filled gap stops conduction and convection, and reflects radiation back.
Draught proofing
- Sealing gaps around doors and windows stops warm air leaking out, reducing heat loss by convection.
Thermal imaging
- Infrared cameras show where a house loses most heat, helping owners decide where insulation is needed.
Part 4 of 4Exam Checklist & Tips
4.1.4 – Key Points for the Exam
- Conduction Transfer of heat through a material by vibrating particles and electrons.
- Convection Transfer of heat in a fluid by the movement of warmer, less dense regions.
- Radiation Transfer of heat as infrared waves, which needs no medium.
- Insulator A material that conducts heat poorly.
Common Mistakes
- Saying that heat rises; it is warm fluid that rises because it is less dense.
- Claiming convection can happen in a solid.
- Forgetting that radiation can pass through a vacuum.
- Stating that a shiny surface is a good emitter of radiation when it is a poor one.