How does heat move by conduction, convection and radiation, and how can we reduce unwanted heat loss?
Heat transfer by conduction, convection and infrared radiation, the role of surface colour, and methods of reducing unwanted energy transfers.
A CCEA GCSE Physics answer on heat transfer by conduction, convection and infrared radiation, how surface colour affects emission and absorption, and how insulation reduces unwanted energy transfers from buildings.
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What this dot point is asking
CCEA wants you to describe the three ways heat is transferred (conduction, convection and infrared radiation), explain each at the particle level, describe how surface colour affects radiation, and explain methods of reducing unwanted energy transfers such as insulating a house.
The answer
Conduction
Non-metals such as wood, plastic and gases are poor conductors (good insulators) because they have no free electrons and, in gases, the particles are far apart.
Convection
Radiators heat a room by warming the air, which rises and circulates; sea breezes form from convection currents in the atmosphere.
Radiation
Reducing unwanted heat transfer
Homes lose heat through the roof, walls and windows by all three methods. Insulation works by trapping air (a poor conductor that cannot form convection currents) or by reflecting radiation:
- Loft insulation and cavity wall insulation trap air to reduce conduction and convection.
- Double glazing traps gas or a vacuum between two panes.
- Draught excluders stop convection through gaps.
- Reflective foil behind radiators reflects infrared back into the room.
Worked example: choosing a vacuum flask
Examples in context
Example 1. A metal spoon in soup. The handle of a metal spoon left in hot soup soon feels hot because metals conduct heat quickly through free electrons; a wooden spoon stays cool because wood is a poor conductor.
Example 2. Hot air balloons. A burner heats the air inside the balloon; the warm air becomes less dense and rises, a large-scale use of convection to lift the balloon.
Try this
Q1. Name the method of heat transfer that can occur through a vacuum. [1 mark]
- Cue. Infrared radiation.
Q2. Explain why a gas is a poor conductor of heat. [2 marks]
- Cue. Its particles are far apart and there are no free electrons to carry energy.
Q3. State one way to reduce heat loss from a house and explain how it works. [2 marks]
- Cue. Loft insulation traps air, reducing conduction and convection through the roof.
Exam-style practice questions
Practice questions written in the style of CCEA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
CCEA style4 marksExplain, in terms of particles, why metals are good conductors of heat but trapped air is a good insulator.Show worked answer →
In a metal, heat is conducted by vibrating particles passing on energy and, mainly, by free (delocalised) electrons that move through the metal carrying energy quickly from the hot region to the cold region.
Air is a gas, so its particles are far apart and there are no free electrons. When the air is trapped (so it cannot form convection currents) it transfers very little heat, making it a good insulator.
Markers reward: metals conduct via free electrons (and vibrations); air particles far apart, no free electrons; trapped air prevents convection, so a good insulator.
CCEA style4 marksA house loses heat through its roof, walls and windows. Describe two methods of reducing this heat loss and explain how each one works.Show worked answer →
Loft insulation: a thick layer of fibre traps air in the roof space. Trapped air reduces conduction and prevents convection currents, cutting heat loss upward through the roof.
Double glazing: two panes of glass with a gap (air or a vacuum) between them. The trapped gas or vacuum reduces conduction and convection through the window.
Other valid answers: cavity wall insulation; draught excluders; reflective foil behind radiators (reduces radiation losses).
Markers reward two valid methods, each with a correct explanation linking trapped air or reflection to reduced conduction, convection or radiation.
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Sources & how we know this
- CCEA GCSE Physics specification — CCEA (2017)