O-LevelPhysicsThermal Physics5054/22 · Oct/Nov 2020 · Q37 Marks

Fig. 3.1 shows a hot water tank that contains two electric heaters X and Y. [Figure 3.1] Heater X is used during the daytime but heater Y is only used at night when electricity is cheaper.

(a)The tank is full of cold water and X is switched on. The temperature of all the water above X increases very quickly but the temperature of the water below X increases much more slowly.
(a)(i)Explain the process that causes the water above X to increase in temperature.[3]
(a)(ii)Heater Y remains switched off. Explain why the temperature of the water below heater X increases much more slowly than the temperature of the water above heater X.[2]
(b)The hot water tank is covered in a thick layer of insulating material. The material is a plastic that contains a large number of small pockets of trapped air. Explain why this material is a good insulator.[2]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2020). The mark or mark type is shown in brackets.

[1] (a)(i) water expands (as it is heated) or molecules move apart
[1] (a)(i) density (of heated water) decreases or (heated water) rises
[1] (a)(i) it rises and the cold water falls or convection current established
[1] (a)(ii) water (below X) heated by conduction or no convection occurs
[1] (a)(ii) water is a poor conductor
[1] (b) air/plastic is a poor/slow (thermal) conductor
[1] (b) trapping the air prevents convection (in air) or no free electrons (in plastic)

On Oracle Prep you can write or photograph your own answer and have it marked by AI against this mark scheme, with feedback on what you missed.