Actual 2024 AQA A-level PHYSICS 7408/2 Paper 2 Merged Question Paper + Mark
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IB/M/Jun24/7408/2
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Answer all questions in this section.
0 1 A room contains dry air at a temperature of 20.0 °C and a pressure of 105 kPa.
0 1 . 1 Show that the amount of air in each cubic metre is about 40 mol.
[1 mark]
0 1 . 2 The density of the dry air is 1.25 kg m−3
.
Calculate crms for the air molecules.
Give your answer to an appropriate number of significant figures.
[3 marks]
crms = m s−1
0 1 . 3 Calculate, in K, the change of temperature that will double crms for the air molecules.
[2 marks]
change of temperature = K
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IB/M/Jun24/7408/2
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0 1 box . 4 A room contains moist air at a temperature of 20 °C.
A dehumidifier cools and then condenses water vapour from the moist air.
The final temperature of the liquid water that collects in the dehumidifier is 10 °C.
Drier air leaves the dehumidifier at a temperature of 20 °C.
Table 1 compares the air flowing into and out from the dehumidifier.
Table 1
mass of water
mass of air
moist air flowing in 0.0057
drier air flowing out 0.0037
In one hour, a volume of 960 m3 of air flows through the dehumidifier.
Assume that the density of the air remains constant at 1.25 kg m−3
.
Determine how much heat energy is removed in one hour from the water vapour by
the dehumidifier.
 specific heat capacity of water vapour = 1860 J kg−1
 K−1
 specific latent heat of vaporisation of water = 2.3 × 106 J kg−1