AQA · GCSE · Physics
Course version: 8463 · Version from Sept 2016
Students should be able to describe how the rate of cooling of a building…
Full specification wording
Energy transfers in a system: Students should be able to describe how the rate of cooling of a building is affected by the thickness and thermal conductivity of its walls.
A building cools because energy passes out through the walls, roof and windows by conduction, and the rate of that loss depends on two properties of the walls.
Checked against the AQA 8463 specification (opens in a new tab) on .
- Point 7 of 8
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
A building cools because energy passes out through the walls, roof and windows by conduction, and the rate of that loss depends on two properties of the walls. Thermal conductivity comes first: brick and glass conduct more readily than foam, mineral wool or trapped air, so filling a cavity with foam lowers the rate of cooling. Thickness comes second: for the same material, a thicker wall means a lower rate of energy transfer, which is why loft insulation is sold by depth and why the standard practical compares thicknesses of the same material. The two work together, so a thin layer of a poor conductor can outperform a thick layer of a good one. The consequence is practical: the building stays warmer for longer and needs less heating.
What earns the marks
- Stating that a thicker wall gives a lower rate of energy transfer.
- Stating that a lower thermal conductivity gives a lower rate of energy transfer.
- Linking the lower rate to a slower fall in the temperature inside the building.
- Supporting the conclusion with data, such as a longer time for the same temperature drop.
Common mistakes and how to put them right
Claiming thick insulation stops cooling completely rather than slowing it.
Changing both thickness and material in an argument, so neither effect is isolated.
Saying the thicker wall keeps more heat in, without mentioning the rate of energy transfer.
Assuming a material feels warm because it produces energy rather than because it conducts poorly.
Exam tips
- Answer in terms of rate of cooling, since higher and lower rate are the phrases the mark scheme uses.
- Where a graph is given, quote a pair of readings to support the conclusion rather than describing the shape.
- Keep conduction and radiation separate; wall colour and shininess belong to the radiation questions.
Try the lesson
The start of the Energy transfers in a system: Students should be able to describe how the rate of cooling of a building is affected by the thickness and thermal conductivity of its walls. lesson, made from checked teaching notes for this specification point.
Have a go first
A house has walls made from a material with a low thermal conductivity. What effect does this have on the rate at which the house cools down?
Listen
A building cools because energy passes out through the walls, roof and windows by conduction, and the rate of that loss depends on two properties of the walls. Thermal conductivity comes first: brick and glass conduct more readily than foam, mineral wool or trapped air, so filling a cavity with foam lowers the rate of cooling. Thickness comes second: for the same material, a thicker wall means a lower rate of energy transfer, which is why loft insulation is sold by depth and why the standard practical compares thicknesses of the same material. The two work together, so a thin layer of a poor conductor can outperform a thick layer of a good one. The consequence is practical: the building stays warmer for longer and needs less heating. A strong answer earns marks for these points. stating that a thicker wall gives a lower rate of energy transfer. stating that a lower thermal conductivity gives a lower rate of energy transfer. linking the lower rate to a slower fall in the temperature inside the building. supporting the conclusion with data, such as a longer time for the same temperature drop. Exam tip: Answer in terms of rate of cooling, since higher and lower rate are the phrases the mark scheme uses.
Key words
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rate of cooling
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wall thickness
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thermal conductivity
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data-supported conclusions
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See every definition
- rate of cooling
- How quickly a building loses energy and its inside temperature falls, which is lower when the walls conduct less readily.
- wall thickness
- For the same material, a thicker wall means a lower rate of energy transfer, so the building cools more slowly.
- thermal conductivity
- A property of a material: brick and glass conduct more readily than foam, mineral wool or trapped air, so a lower value gives a lower rate of energy transfer.
- data-supported conclusions
- Conclusions backed by data, such as a longer time for the same temperature drop.
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