O-LevelPhysicsThermal Physics5054/21 · Oct/Nov 2015 · Q26 Marks

Fig. 2.1 shows a freezer for keeping food frozen. [Figure 2.1]

(a)The outside surface of a freezer is painted white. Explain one advantage of having the outside surface of the freezer painted white.[2]
(b)(i)The lid of the freezer is closed and air at room temperature is trapped inside the freezer. The freezer is switched on. State and explain, using ideas about molecules, what happens to the pressure of the air in the freezer, as it cools.[3]
(b)(ii)When the freezer reaches its operating temperature, it is more difficult to open the lid. Explain why.[1]

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Mark scheme

Marking points from the official mark scheme (Oct/Nov 2015). The mark or mark type is shown in brackets.

[1] poor absorber/good reflector of (infra-red) radiation
[1] less thermal energy absorbed
[1] (pressure/it) decreases
[1] molecules slow down
[1] less frequent/less violent (molecular) collisions with wall
[1] (pressure difference causes) a downward force on lid or pressure outside > pressure inside

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