1. 1
   A homeowner in a cold climate compares two identical exterior walls: one made of solid brick, and one made of brick with a layer of foam cavity-wall insulation added.

   (a)

   A homeowner in a cold climate notices that a wall made of solid brick loses heat faster than an identical wall with a layer of foam insulation added inside a cavity. What does this tell us about the thermal conductivity of the foam insulation compared with brick?

   [1 mark]

   • AThe foam has a lower thermal conductivity than brick
   • BThe foam has a higher thermal conductivity than brick
   • CThe foam and brick have the same thermal conductivity
   • DThermal conductivity cannot be compared between different materials

   (b)

   Which statement correctly describes the relationship between wall thickness and the rate of energy transfer by conduction through the wall, for two walls of the same material?

   [1 mark]

   • AA thicker wall of the same material transfers energy at a faster rate
   • BA thicker wall of the same material transfers energy at a slower rate
   • CWall thickness has no effect on the rate of energy transfer
   • DA thicker wall transfers energy only by convection, not conduction

   (c)

   Explain why the wall with foam cavity-wall insulation loses thermal energy from the house at a slower rate than the solid brick wall, referring to thermal conductivity in your answer.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A family fits a thick layer of loft (roof space) insulation made of mineral wool above their ceiling, in a house that previously had no loft insulation.

   (a)

   What is the main purpose of this insulation?

   [1 mark]

   • ATo increase the rate of energy transfer from the house to the loft space
   • BTo increase the electrical resistance of the ceiling
   • CTo reduce the rate of energy transfer from the house to the loft space and outside
   • DTo reflect visible light back into the rooms below

   (b)

   Mineral wool loft insulation works partly by trapping pockets of air within its fibres. Why does this help reduce energy transfer out of the house?

   [1 mark]

   • ATrapped air is an excellent electrical conductor
   • BTrapped air chemically reacts with the mineral wool to release cooling gases
   • CTrapped air increases the density of the insulation, blocking sound instead of heat
   • DTrapped air is a poor conductor of thermal energy, and being trapped it also reduces energy transfer by convection

   (c)

   The family's energy supplier estimates that, before insulating, the house loses thermal energy through the loft at a rate of 900 J/s, and after insulating this falls to 300 J/s. Calculate the amount of thermal energy saved through the loft over a 24 hour period as a result of adding the insulation.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A property developer is renovating an old cottage that has solid stone walls and single-glazed windows, and wants to reduce the rate of thermal energy loss from the building. The developer is choosing between two wall insulation boards: Board P (50 mm thick, thermal conductivity 0.025 W/m°C) and Board Q (30 mm thick, thermal conductivity 0.020 W/m°C).

   (a)

   A property developer is renovating an old cottage with solid stone walls and single-glazed windows. Explain, referring to thermal conductivity and thickness, two reasons why the cottage currently loses thermal energy at a high rate, and suggest one renovation the developer could make to reduce each energy loss.

   [3 marks]

   (b)

   The developer is choosing between two brands of wall insulation board to fit inside the stone walls. Board P has a thickness of 50 mm and a thermal conductivity of 0.025 W/m°C. Board Q has a thickness of 30 mm and a thermal conductivity of 0.020 W/m°C. Explain which board would be more effective at reducing the rate of energy transfer through the wall, considering both thickness and thermal conductivity.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A local council must choose one energy-efficiency upgrade (cavity wall insulation, loft insulation, or double glazing) to fund for a row of 1930s terraced houses with uninsulated cavity walls, no loft insulation, and single-glazed windows.

   (a)

   A local council is deciding how to spend a limited energy-efficiency grant on a row of 1930s terraced houses. The houses currently have uninsulated cavity walls, no loft insulation, and single-glazed windows. The council can only afford to fund one of the following upgrades per house: cavity wall insulation, loft insulation, or double glazing. Using the ideas of thermal conductivity, insulation thickness, and rate of energy transfer, evaluate which single upgrade is likely to provide the greatest reduction in energy loss for these houses, and explain your reasoning.

   [6 marks]

   (b)

   After the council's upgrade programme, residents report lower heating bills but some residents in houses that received only double glazing say they still feel cold in winter and their bills have not fallen by very much. Explain, using your understanding of energy transfer and insulation, why these residents may have seen a smaller improvement compared with residents who received loft or cavity wall insulation, and suggest what further work the council could consider funding in future to address this.

   [6 marks]

   Total for question 4: 12 marks

End of questions