# A homeowner installs cavity wall insulation in their house. Explain how cavity wall insulation reduces the rate at which heat energy is lost through the walls.

> OCR GCSE Physics A: Gateway Science (J249) — P7 Energy · Explain · 4 marks

> A homeowner notices that their heating bill is very high in winter. They decide to have cavity wall insulation fitted, where a fibreglass material is injected to fill the air gap between the inner and outer walls.

## Mark scheme (4 marks)

1. Without insulation, air in the cavity allows convection currents to form
2. The insulating material fills the cavity and prevents convection currents from forming
3. The insulating material is a poor conductor of heat / has low thermal conductivity
4. This reduces the rate of energy transfer to the surroundings, so less energy is wasted / the system is more efficient

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