1.7 Thermal conductivity and insulation
9 exam questions worth 21 marks. Write your answer, open the mark scheme, then give yourself the marks you earned. Your answers are saved on this device.
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Name a material that is a good thermal conductor.
Mark scheme
any metal, e.g. copper / aluminium / iron
Model answer
Copper (or any other metal).
Explain why a thick wall transfers energy more slowly than a thin wall made of the same material.
Mark scheme
rate of energy transfer decreases as thickness increases (1); energy has further to travel / more particles to pass through (1)
Model answer
A thicker wall means the energy has a greater distance to travel through the material, so the rate of transfer is lower.
Explain how loft insulation reduces energy loss from a house.
Mark scheme
insulation (e.g. fibreglass) has a low thermal conductivity (1); traps air which is a poor conductor (1); reduces conduction / stops convection through the roof (1)
Model answer
Loft insulation such as fibreglass has a low thermal conductivity. It traps air, which is a poor conductor, so less energy is conducted through the roof.
Double glazing has a gap between two panes of glass. Explain why this reduces the energy transferred through the window.
Mark scheme
the gap contains air / a vacuum (1); air is a poor conductor / a vacuum cannot conduct (1)
Model answer
The gap contains air, which is a poor conductor, or a vacuum, which cannot conduct, so the rate of conduction is low.
Cavity wall insulation costs £540 to install and saves £90 each year on heating bills. Calculate the payback time.
Mark scheme
540 / 90 (1); 6 years (1)
Model answer
payback time = 540 ÷ 90 = 6 years.
Two houses are the same size. House A has walls of low thermal conductivity. House B has walls of high thermal conductivity. Which house will cool down faster on a cold night? Explain your answer.
Mark scheme
house B (1); energy is transferred faster / more quickly through walls of higher thermal conductivity (1)
Model answer
House B, because its walls have a higher thermal conductivity so energy is transferred through them faster.
Draught-proofing costs £120 to install and saves £60 each year on heating bills. Calculate the payback time.
Mark scheme
payback time = cost ÷ saving per year = 120 ÷ 60 (1); 2 years (1)
Model answer
Payback time = 120 / 60 = 2 years.
Explain, in terms of particles, why metals are better thermal conductors than plastics.
Mark scheme
metals have free / delocalised electrons (1); which move through the metal and carry energy quickly (1); plastics have no free electrons so energy is only passed on by vibrations of particles (slower) (1)
Model answer
Metals contain free electrons, which move through the metal and carry energy quickly. Plastics have no free electrons, so energy is passed on only by particles vibrating and colliding, which is slower.
A homeowner can choose between loft insulation, costing £300 and saving £100 a year, and double glazing, costing £4000 and saving £80 a year. Evaluate the two options.
Mark scheme
loft insulation payback = 300 ÷ 100 = 3 years (1); double glazing payback = 4000 ÷ 80 = 50 years (1); loft insulation pays for itself much sooner / is better value (1); double glazing may have other benefits (noise reduction, comfort) (1)
Model answer
The loft insulation has a payback time of 3 years and the double glazing 50 years. The loft insulation is much better value for saving money. Double glazing could still be chosen for other benefits, such as less noise.
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