O-LevelPhysicsThermal Physics5054/22 · Oct/Nov 2023 · Q55 Marks

Fig. 5.1 shows a device that cools the air in a room by evaporation. [Figure 5.1] Water drips from the container into the sponge block and keeps it wet. Air flows in through one grille and out through the other. As the air flows through the wet sponge block, the water in the sponge block evaporates.

(a)(i)When the water evaporates, the temperature of water remaining in the sponge block decreases. Explain, in terms of the movement of particles, why this decrease in temperature occurs.[2]
(a)(ii)Explain why energy is needed when the water evaporates.[1]
(b)State two ways in which evaporation differs from boiling. 1 2[2]

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Mark scheme

Marking points from the official mark scheme (Oct/Nov 2023). The mark or mark type is shown in brackets.

[1] faster-moving particles and (more likely to) escape (from the water)
[1] remaining particles have less (average) kinetic energy / move more slowly (on average)
[1] (work is done) moving particles apart (against the forces of attraction) or (energy needed) to supply the latent heat
[2] any two from: no bubbles formed or occurs only at the surface occurs at any temperature is affected by exposed surface area / moving air over surface / temperature

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