Energy Transfers
3 marks · NormalExplain why a house with thick loft insulation and double glazing loses less heat in winter, referring to conduction, convection and radiation.
Explain how each method of heat transfer is reduced by these features.
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Loft insulation has trapped air, which is a poor conductor and so reduces heat loss by conduction through the roof. It also stops convection currents from forming in the loft space. The reflective side of insulation reduces heat loss by radiation. Double glazing reduces conduction (two layers with air in between) and prevents convection currents between two panes. The special glass also reflects infrared radiation back inside.
Must show: Conduction: thick insulation and glass are poor conductors; Convection: trapped air stops currents; Radiation: reflective surfaces reflect infrared
Common mistakes: Only discussing one method
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Marking points
B1 · 1 mark · Mentions conduction reduced by poor conductors (air/insulation/double glass).
B1 · 1 mark · Mentions convection prevented by trapping air or filling gaps.
B1 · 1 mark · Mentions radiation reduced by reflective surfaces (foil/glass).
Worked solution
Conduction: Thick insulation and the air gap in double glazing are poor thermal conductors, so less heat travels through them. Convection: The trapped air in insulation and between double glazing stops air from circulating, so convection currents cannot take heat from inside to outside. Radiation: Foil-backed insulation and some glass types reflect infrared radiation back inside, reducing heat loss by radiation.