Why does rising air form cloud?

Rising air expands and cools, and once it reaches the dew point the vapour condenses into droplets.

What does 100 per cent relative humidity mean?

The air holds as much vapour as it can at that temperature, so any more will condense.

S5 Geography Weather and Climate, Paper 1: starting with the lapse rate

2026-11-02

Paper 1 covers the lapse rate, relative humidity, weather against climate, the Hong Kong monsoon and heat island intensity, all figures built on 0.6 degree per 100 m.

Focus　Rate times height gives the temperature drop, humidity is actual over saturated, climate is a thirty year average and the winter monsoon comes from the northeast.

01　Paper details (check answers afterwards)

Item	Detail
Questions	10
Suggested time	25
Difficulty mix	Foundation 4 · Intermediate 3 · Challenge 2 · Error redo 1
Chapter	Chapter: S5 Geography: Weather and Climate
Level	S5

02　Questions (10 items)

FoundationAir at the foot of a hill is 28 degrees Celsius. If the temperature falls 0.6 degree per 100 m, what is it at 1500 m?
FoundationAir holds 12 grams of water vapour per cubic metre while saturation at that temperature is 24 grams. What is the relative humidity?
FoundationWhat is the difference between weather and climate?
FoundationWhich monsoon prevails in Hong Kong in winter and what weather does it bring?
IntermediateThe air is 30 degrees with a dew point of 20 degrees. If it cools 1 degree per 100 m, at what height does cloud form?
IntermediateA station records 28.5 degrees in its hottest month and 16.2 in its coldest. What is the annual range?
IntermediateAnnual rainfall is 2400 mm and 80 per cent falls from May to September. How much falls in the wet season?
ChallengeA summit is 15 degrees while the foot is 27 degrees, with a lapse rate of 0.6 degree per 100 m. How high is the hill?
ChallengeThe urban area reads 32.4 degrees and the countryside 29.1. What is the heat island intensity?
Error redoError: a student says Hong Kong has a humid southwest monsoon in winter. What is correct?

03　Answers and one-line notes

#	Answer	One-line note
1	19 degrees Celsius	Fifteen hundred metres is fifteen steps of 100 m, so 9 degrees are lost and 28 minus 9 is 19.
2	50 per cent	Relative humidity is actual vapour divided by saturation capacity times 100, and 12 over 24 is one half.
3	Weather is the short term state over days, climate is the long term average of thirty years or more	Weather changes from day to day, while climate is judged from averages and frequencies over thirty years or more.
4	The northeast monsoon from the continent, dry and cold	The winter monsoon blows from the continental interior, so it is dry and brings clear, cooler weather.
5	1000 m	Ten degrees must be lost to reach the dew point, and at one degree per 100 m that means 1000 m.
6	12.3 degrees Celsius	Annual range is the hottest month minus the coldest month, so 28.5 minus 16.2 is 12.3.
7	1920 mm	Two thousand four hundred times 0.8 is 1920, leaving only 480 mm for the other seven months.
8	2000 m	A difference of 12 degrees divided by 0.6 gives twenty steps of 100 m, which is 2000 m.
9	3.3 degrees Celsius	Heat island intensity is the urban minus rural temperature, so 32.4 minus 29.1 is 3.3.
10	The winter monsoon is northeast, dry and cold; the southwest monsoon belongs to summer	The direction is reversed: the winter monsoon comes from the northeast interior and only summer winds come from the southwest sea.

04　What to do after marking

After marking, redo only the wrong items and write down which step went wrong (formula, unit, or misread number).
Repeat the same item two days later; move to the next paper only when both attempts are correct.
Parents only need the answer and note columns; there is no need to explain every item.

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