NCERT Solutions Class 9 Social Science Chapter 3 Atmosphere and Climate

F R E E S T U D Y M AT E R I A L F O R E V E R Y S T U D E N T

CLASS 9 · SOCIAL SCIENCE

NCERT Solutions

Chapter 3: Atmosphere and
Climate

NCERT Textbook — Understanding Society: India And Beyond

BOOK PAGES SECTIONS QUESTIONS MEDIUM

39 – 59 15 40 English

Solutions, notes, sample papers & more at 67 pages

Class 9 Social Science Chapter 3 Atmosphere and Climate AglaSem · NCERT Solutions

CLASS 9 · SOCIAL SCIENCE · UNDERSTANDING SOCIETY: INDIA AND BEYOND

NCERT Solutions — Chapter 3: Atmosphere and Climate
Complete NCERT Solutions for Class 9 Social Science Chapter 3 Atmosphere and Climate from Understanding
Society: India and Beyond, Grade 9 Part 1. Every question the chapter prints is answered — The Big Questions,
all three THINK ABOUT IT boxes, LET'S RECALL, all three LET'S EXPLORE boxes, LET'S ANALYSE, the
Classroom Discussion on the Punjab floods, the Before we move on… recap and all of Questions and
activities including the full Table 3.3 data exercise — with the mechanism explained layer by layer, the
climate graphs drawn, and every figure recomputed from the book's own tables.

TEXTBOOK BOOK PAGES

Understanding Society: India and Beyond (Class 39 – 59
9)

SECTIONS QUESTIONS

15 40

MEDIUM

English

The Big Questions — Page 39
Chapter opening

THE BIG QUESTIONS

Q1 What is the composition of the atmosphere?

The atmosphere is a mixture of gases, not a single gas. Two gases do almost all of it —
nitrogen (78%) and oxygen (21%) — and everything else shares the last 1%. On top of this
mixture the air also carries water vapour and tiny dust particles.

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Class 9 Social Science Chapter 3 Atmosphere and Climate AglaSem · NCERT Solutions

What Fig. 3.2 prints
Nitrogen 78%

Oxygen 21%

Argon 0.93%

Dry air Carbon dioxide 0.04%
100%
Others 0.03%

Total 100.00%

Water vapour (0.1–0.4%) and dust are
extra, on top of this dry-air mixture.

Fig. A — The composition of the atmosphere, drawn from the figures printed in Fig. 3.2. Nitrogen and
oxygen together make 99% of dry air; everything else shares the last 1%.

Add up what Fig. 3.2 prints:
78 + 21 = 99% — nitrogen and oxygen alone

0.93 (argon) + 0.04 (carbon dioxide) + 0.03 (others) = 1.00%

99 + 1 = 100% — the pie is complete

Water vapour is counted separately, and it is the one part of the mixture that keeps changing:
the chapter says it generally ranges from 0.1 per cent to 0.4 per cent. That is a fourfold swing,
and it matters far more than its small size suggests, because water vapour is what makes
clouds and precipitation possible.
The other gases named in the chapter — beyond argon and carbon dioxide — are helium,
neon, krypton, xenon, ozone and hydrogen. They are present, but in very small quantities.

Why the proportions are not the same everywhere: the chapter says plainly that
the composition of the atmosphere also varies with altitude. Gravity holds the
heavier gases close to the surface, so the air thins out as you rise, and by the
exosphere only the lightest gases — helium and hydrogen — are left, and even
those float away into space. So the 78:21 figures describe the air near the ground,
which is where we live and where the weather happens.

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Class 9 Social Science Chapter 3 Atmosphere and Climate AglaSem · NCERT Solutions

Did you know? Carbon dioxide is only 0.04% of the air — four parts in ten thousand.
Yet this tiny share is the gas at the centre of the climate change discussion later in
the chapter, because it traps heat. Small in quantity does not mean small in effect.

Q2 How do the different layers of the atmosphere affect the planet Earth?

Each layer does a different job for the Earth, and the reason each layer can do that job is the
way its temperature changes with altitude. That is exactly how the layers are defined — the
chapter says they are marked out on the basis of changes in temperature and density with
increasing altitude.

The red line = temperature
(Fig. 3.3 gives no scale — only the direction of change)

EXOSPHERE

100

THERMOSPHERE
▶ rises
Gas molecules absorb X-rays and
short-wave ultraviolet from the Sun.
80 Mesopause

MESOSPHERE ◀ falls
No ozone and no heat from the
Height (km)

surface, so the air cools again.
50 Stratopause

STRATOSPHERE ▶ rises
Ozone here absorbs the Sun's
ultraviolet rays and warms the air.

12 Tropopause
TROPOSPHERE ◀ falls
Warmed from below by the Earth's
0
surface, so it cools as you go up.
Heights are the chapter's own: troposphere about 12 km, stratosphere to 50 km,
mesosphere to 80 km, thermosphere 80–700 km. The scale is broken above 100 km.

Fig. C — The layers of the atmosphere and how temperature behaves in each. The red line follows Fig.
3.3 of the book: it falls in the troposphere, rises in the stratosphere, falls in the mesosphere and rises
steeply in the thermosphere.

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Class 9 Social Science Chapter 3 Atmosphere and Climate
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LAYER EXTENT WHAT IT DOES FOR THE EARTH

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Class 9 Social Science Chapter 3 Atmosphere and Climate AglaSem · NCERT Solutions

Q3 What is the mechanism of monsoon?

The mechanism is a seasonal reversal of the wind, and it is driven by one simple fact: land
heats up and cools down faster than the sea. The chapter's own definition in the margin says
it exactly — monsoon refers to the seasonal reversal in the wind direction during a year.

South-west (summer) monsoon North-east (winter) monsoon
June – September October – February

RAIN

moist winds cold, dry winds

L H H L

LAND SEA LAND SEA

Land heats faster than the ocean, so a low-pressure Land cools faster than the ocean, so high pressure
area forms over India while the cooler sea keeps high sits over India and low pressure over the sea. Wind
pressure. Wind blows sea → land, and brings rain. blows land → sea, and is cold and dry.
But over the Bay of Bengal it picks up moisture and
rains on Tamil Nadu, Andhra Pradesh and Karnataka.

Wind always blows from HIGH pressure to LOW pressure. That single rule reverses
the wind twice a year — and that reversal is what we call the monsoon.

Fig. E — The mechanism of the monsoon. The same rule — wind blows from high pressure to low
pressure — produces opposite winds in summer and winter, because land heats and cools faster than
the sea.

Step by step, in summer (the south-west monsoon, June to September):

1. During summer the landmass of India heats up faster than the surrounding oceans.
2. Hot air over the land expands and rises, leaving a low-pressure area over the Indian
subcontinent.
3. The Indian Ocean stays relatively cooler, so the air over it is heavier and sinks — a high-
pressure area.
4. Winds move from high pressure to low pressure. So moist winds blow from the ocean
towards the land, across the Indian Ocean, the Arabian Sea and the Bay of Bengal.
5. These winds are loaded with water vapour picked up over the sea. When they rise over the
land and the hills, that vapour condenses and falls as rain. This monsoon accounts for most
of the rainfall in the country throughout the year.

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Class 9 Social Science Chapter 3 Atmosphere and Climate AglaSem · NCERT Solutions

In winter (the north-east monsoon, October to February) everything reverses: the Indian
landmass now cools faster than the surrounding oceans, so high pressure sits over the land
and low pressure over the seas. The wind therefore blows from land to sea — cold and dry,
bringing no rain to most of India. The exception is important: when these winds cross the Bay
of Bengal they pick up moisture, and they rain on the eastern coast — especially Tamil Nadu,
Andhra Pradesh and parts of Karnataka.

Why land and sea heat so differently: this is the single fact the whole monsoon
rests on. Water needs far more heat to warm up than soil and rock do, and the sea
also mixes its heat down through a great depth, while the land can only heat its thin
top layer. So in summer the land races ahead of the sea in temperature, and in
winter it falls behind. The pressure difference that follows is what turns the wind
around — twice every year.

Where the name comes from: the Arab traders sailing to India named this reversal
monsoon, from the Arabic word mausim, which literally means season. Sailors were
the first to notice it, because in the age of sailing ships they were completely at the
mercy of the winds — and a wind that reverses on schedule is a wind you can plan a
voyage around.

Q4 How can we reduce our carbon footprint?

By cutting the greenhouse gases our daily choices release. A carbon footprint is defined in the
chapter as the total amount of greenhouse gases released into the atmosphere as a result
of human activities, such as energy use, transportation, or the production of goods and
services — so those three are exactly where the reductions have to come from.
The chapter's four collective actions:

Reducing carbon footprints — the everyday choices below.
Using renewable energy — solar and wind instead of burning fossil fuels.
Protecting forests — trees absorb carbon dioxide, and deforestation is named as one of the
main causes of climate change.
Adopting sustainable lifestyles — using less, and using it longer.

What that means for a student, taken from the four habits the LET'S EXPLORE box asks
you to score:

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Class 9 Social Science Chapter 3 Atmosphere and Climate AglaSem · NCERT Solutions

AREA THE HIGH-IMPACT HABIT THE LOW-IMPACT HABIT TO
MOVE TO

Transport Travelling by private car even for short Walk or cycle for short trips; use public
distances; taking flights more than twice a transport or carpool for longer ones
year

Electricity Leaving lights and fans on frequently Switch off every appliance when it is not
in use

Water Long showers, running taps, several buckets Use water judiciously — one bucket for a
for a bath bath

Waste and Throwing away plastic and not recycling Reuse, recycle and avoid single-use
plastics plastics

Why saving electricity and water counts as saving carbon: most of the electricity
we use is still generated by burning fossil fuels, so a fan left running is coal burnt
somewhere and carbon dioxide added to the atmosphere. Water is the same story
once removed — it has to be pumped, treated and delivered, and all of that runs on
energy. This is why the chapter can put transport, electricity, water and plastic in one
scorecard: they all end at the same place, the greenhouse gases in the air.

The chapter's own closing line is worth keeping: 'Every small step counts, and
every human being plays a vital role in shaping a healthier and greener future.' One
student's saved bucket of water is small; a class of forty doing it every day for a year
is not.

In-text Questions — Page 39
The chapter's opening paragraph

Q1 What do you see when you look up in the sky?

Floating clouds, the sunshine, and — even if you cannot see it — a breeze you can feel on your
face. The chapter's point is that these three are not separate things you happen to notice. All of
them are the result of one thing: the blanket of air surrounding the Earth, called the
atmosphere.

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Class 9 Social Science Chapter 3 Atmosphere and Climate AglaSem · NCERT Solutions

WHAT YOU WHAT IT ACTUALLY IS
NOTICE

Clouds Water vapour from the atmosphere that has condensed — and almost all of it sits in the
lowest layer, the troposphere

Sunshine Sunlight that has passed through the atmosphere, with the harmful radiation, including
ultraviolet, filtered out on the way

A breeze Air on the move — wind, flowing from a high-pressure area towards a low-pressure area

Why we cannot see the atmosphere itself: the gases that make it up — nitrogen,
oxygen, argon — are colourless and transparent. We only ever see what the
atmosphere does: the clouds it forms, the light it lets through, the dust it carries, the
blue it scatters. That is why the sky looks empty and yet nothing about the sky is
empty.

THINK ABOUT IT — Page 39
A world with no atmosphere

THINK ABOUT IT

Q1 Can you imagine what would happen if there were no atmosphere? Discuss your
thoughts with your friends and teachers.

Life on the Earth would end. The way to answer this question is not to guess, but to take each
job the chapter says the atmosphere does and remove it — the consequence follows from the
job.

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Class 9 Social Science Chapter 3 Atmosphere and Climate
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WHAT THE ATMOSPHERE DOES (PAGE 39) WHAT WOULD HAPPEN WITHOUT IT

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Class 9 Social Science Chapter 3 Atmosphere and Climate AglaSem · NCERT Solutions

Composition of the Atmosphere

LET'S RECALL

Q1 How is nitrogen useful for plants? Remember that you learnt this in the chapter
'The Invisible Living World: Beyond Our Naked Eyes', in your Grade 8 Science
textbook.

Nitrogen is the raw material plants need to build proteins — and therefore to build leaves,
stems, roots and seeds. It is also part of chlorophyll, the green pigment that lets a plant make
its own food. Without nitrogen a plant stays stunted and yellow.
But there is a problem, and it is the point of the question. Nitrogen makes up 78% of the air
— the single most abundant gas around us — and yet plants cannot use it straight from the
air. The nitrogen in the atmosphere is locked in a very tightly bound form that roots cannot
absorb.
The solution comes from the invisible living world. Certain nitrogen-fixing bacteria —
Rhizobium living in the root nodules of leguminous plants such as gram, peas, beans and
groundnut, and free-living bacteria in the soil — convert atmospheric nitrogen into nitrogen
compounds the plant roots can take up. Lightning does a small share of the same work. This
is why the chapter you read in Grade 8 Science put nitrogen under the invisible living world: the
bacteria are the link between the air and the plant.

Why this connects back to Chapter 3: it shows that the composition of the
atmosphere is not just a list of percentages to memorise. The 78% nitrogen figure is
the reservoir that every protein in every living body is ultimately drawn from —
through bacteria, into plants, and then into the animals and people who eat them.

Try this: this is also why farmers in India rotate a cereal such as wheat or rice with a
pulse such as gram or moong. The pulse crop, with its Rhizobium nodules, puts
nitrogen back into the soil for the cereal that follows — a very old Indian practice
with a very modern explanation.

In-text Questions — Page 43

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Class 9 Social Science Chapter 3 Atmosphere and Climate AglaSem · NCERT Solutions

Weather and Climate

Q1 'Is it going to rain today?' 'Will it be bright and sunny today?' How often do you find
yourself wondering about these questions when you want to go out and play?

Almost every day — and that is precisely the chapter's point. Both questions are about today, so
both of them are questions about weather, not climate.

WEATHER CLIMATE

Time scale Hour-to-hour and day-to-day An extended period — usually thirty years
or more

Area One place, right now A large area, averaged

How much it varies Can change significantly from day Changes only slowly, over decades
to day

The question it 'Should I carry an umbrella this 'Which crops can be grown in this region?'
answers afternoon?'

Notice how much weather decides for us in a single day. The chapter puts it in terms of
mood and plans: hot or humid weather may make one irritable, while pleasant or breezy
weather may make one cheerful, or even plan for an outing. Whether the cricket match
happens, whether the clothes dry, whether the school trip goes ahead — all of it turns on the
weather of that one day.

Why the two must not be mixed up: one unusually cold day in Chennai does not
make Chennai's climate cold, and one dry July does not make India's climate dry.
Climate is an average over a long period, so it survives odd days; weather is what
any single day actually does. That is also why a single flood or heatwave cannot by
itself prove climate change — the argument has to be made from the long-run
pattern.

THINK ABOUT IT — Page 45

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Class 9 Social Science Chapter 3 Atmosphere and Climate AglaSem · NCERT Solutions

Wind

THINK ABOUT IT

Q1 You might have noticed that sometimes the wind is so strong that it is difficult to
walk against it. Can you think of some other times when strong winds have caused
problems for you?

Yes — and Table 3.1 lets you name the strength as well as the problem, because it pairs each
wind speed with the effects you would actually see.

WIND SPEED PROBLEMS IT CAUSES, FROM TABLE 3.1 AND EVERYDAY LIFE
(KM/HR)

Calm 0–1 No problem at all — smoke rises straight up. But on a hot, still day there is no
breeze to cool you either

Light 6 – 11 Leaves rustle and you can feel it on your face. Loose papers and homework sheets
breeze blow off the desk

Strong 39 – 49 Umbrellas are difficult to use and large branches sway — this is the wind that
breeze turns an umbrella inside out on the way to school, and makes cycling into it hard
work

Storm 103 – 117 Very rarely experienced, and usually accompanied by widespread damage —
uprooted trees, blown-off roofs, snapped power lines, cancelled trains and flights

Everyday examples worth mentioning in your discussion: dust blown into the eyes on a
windy afternoon; washing pulled off the line; a badminton or cricket match spoiled because the
ball keeps drifting; kites cut loose or torn on Makar Sankranti; a power cut after a storm brings
down a line; and — as the chapter says at the start of the Wind section — trees uprooted
during a storm.

Why walking into wind is so much harder than walking with it: the wind pushes
on the whole front of your body, and that push grows very steeply as the wind
speeds up — a strong breeze of 45 km/hr does not push twice as hard as one of 22
km/hr, but far more. That is why the jump from a light breeze (6–11 km/hr) to a
storm (103–117 km/hr) in Table 3.1 is not a jump from 'noticeable' to 'annoying' but
from 'leaves rustle' to 'widespread damage'.

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Class 9 Social Science Chapter 3 Atmosphere and Climate AglaSem · NCERT Solutions

Check it yourself: notice how Table 3.1 leaves gaps — nothing is listed between 1
and 6, between 11 and 39, or between 49 and 103 km/hr. Those gaps are the missing
categories the next LET'S EXPLORE box asks you to find.

LET'S EXPLORE — Page 46
Table 3.1, Wind speeds and their common effects

LET'S EXPLORE

Q1 Find out other categories of wind based on speed and their common effects, and
share your findings in class.

How to do this task. Table 3.1 in your book prints only four of the categories — Calm, Light
breeze, Strong breeze and Storm — and if you look at the speed column you can see the gaps
for yourself.

Table 3.1 covers 0–1 · 6–11 · 39–49 · 103–117 km/hr

Missing bands: 2–5, 12–38, 50–102 and everything above 117

So there are several categories still to be found, mostly in the middle of the range.

Where to look: the full scale Table 3.1 is drawn from is the Beaufort wind scale, which the
India Meteorological Department also uses. Good sources are the IMD website
(mausam.imd.gov.in), a school atlas, the encyclopedia section of your library, or the daily
weather bulletin in the newspaper, which often names the wind category for the day.
What a good answer must contain — for every category you find, give three things, exactly as
Table 3.1 does: (i) the name, (ii) the speed range in km/hr, and (iii) the common effects you
could actually observe. Effects are what make the scale usable without any instrument.
Sample answer:

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Class 9 Social Science Chapter 3 Atmosphere and Climate
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WIND SPEED COMMON EFFECTS YOU CAN OBSERVE

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Light air 2–5 Smoke drifts sideways instead of rising straight up; a wind vane

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Gentle breeze 12 – 19 Leaves and small twigs move constantly; a light flag is lifted; kites

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Moderate breeze 20 – 28
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Fresh breeze 29 – 38 Small trees in leaf begin to sway; small waves form on a pond or
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Near gale 50 – 61 Whole trees in motion; walking against the wind becomes

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Gale Twigs break off trees; walking is difficult; progress on a cycle is
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Strong gale Slight structural damage — roof tiles and tin sheets are blown off

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Tip.cfor sharing in class: present it as one continuous ladder
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Why a scale of effects was invented at all: before instruments were common,
sailors and farmers still needed to report wind strength. So the scale was built out of
things anyone could see — smoke, leaves, branches, umbrellas, waves. It is a
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reminder that careful observation can be turned into reliable data, which is exactly
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LET'S ANALYSE — Page 47
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Class 9 Social Science Chapter 3 Atmosphere and Climate AglaSem · NCERT Solutions

Watching the weather change over two weeks

LET'S ANALYSE

Q1 Note down the weather report from a local newspaper for two weeks and observe
the changes occurring in the weather.

Method. Take the weather box from the same newspaper at the same time every day for
fourteen days — the same source each day, so the readings are comparable. Copy out the five
elements of weather the chapter has just taught you, because those are what the report
actually prints.

COLUMN TO KEEP WHAT TO WRITE IN IT

Date Day 1 to Day 14

Maximum and minimum temperature (°C) Both numbers — the difference between them is the day's range

Humidity (%) Usually given for morning and evening

Rainfall (mm) Write 0 on a dry day, not a blank — a zero is a reading too

Wind Direction it blows from, and speed in km/hr

Sky condition Clear, partly cloudy, overcast, foggy

What a good answer must contain. The table alone is not the answer — the observations you
draw from it are. Look for, and write down:

The highest and lowest maximum temperature of the fortnight, and the difference between
them.
Whether temperature fell on the days it rained — the chapter says rain lowers the
temperature of a place, so this is a claim you can test yourself.
Whether high humidity went with cloudy or rainy days, and low humidity with clear ones.
Whether the sky was cloudy and wet when pressure was low and clear and sunny when it
was high — again, the chapter's own claim on page 45.
Whether the wind blew from roughly the same direction for most days. A steady direction
over a fortnight is a hint of the season's prevailing wind.

Sample answer: 'Over the fourteen days the maximum temperature ranged from 31°C to 38°C,
a spread of 7°C. It rained on three days — Days 4, 5 and 11. On each of those days the
maximum was 3 to 4°C lower than on the day before, and the morning humidity rose above
80%, while on the clear days it stayed near 55%. The sky was overcast on all three rainy days and
clear on the eight hottest days. The wind blew from the south-west on eleven of the fourteen

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Class 9 Social Science Chapter 3 Atmosphere and Climate AglaSem · NCERT Solutions

days. Conclusion: weather changed a great deal from day to day, exactly as the chapter says,
but the changes were not random — temperature, humidity, cloud and rain moved together,
and the steady south-westerly wind showed that the whole fortnight belonged to one season.'

Why two weeks, and why this is not a study of climate: fourteen days is long
enough to show that weather varies day to day, but nowhere near long enough to
say anything about climate — for that the chapter requires thirty years or more.
Your fortnight is a sample of weather; it becomes evidence about climate only when
thousands of such fortnights are averaged, which is what Table 3.3 later in the
chapter actually shows.

THINK ABOUT IT — Page 48
Traditional Indian seasons (Table 3.2)

THINK ABOUT IT

Q1 Hindustani Classical music associates certain rāgas with specific seasons. Find out
which rāgas are connected to each season with the help of your elders and
teachers.

Method. This is a find-out question, so the answer must come from people and from listening,
not from memory. Ask a music teacher, a grandparent, or anyone in your family who sings or
plays; listen to recordings and note what the announcer or sleeve notes say about the season;
and match what you learn to the six ṛtus of Table 3.2, so that your answer sits inside the
chapter's own framework.
What a good answer must contain: (i) the season in the ṛtu system and its months, (ii) the
name of the rāga, and (iii) one line on why the two are linked — the mood the rāga creates
and the weather that mood belongs to. A list of names with nothing else is not an answer.
Sample answer:

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ṚTU MONTHS RĀGAS TRADITIONALLY THE LINK
(TABLE ASSOCIATED
3.2)

Vasanta March – April Basant, Bahār, Hindol Spring rāgas, sung at Holi and at the
turn of the season — bright and
playful, like the flowering of the trees

Grīṣhma May – June Deepak, Marwa, Sarang Rāgas of heat and of the long, glaring
afternoon; Sarang is a midday rāga of
the hot season

Varṣhā July – August Miyān kī Malhār, Megh, The rain rāgas — the whole Malhār
Megh Malhār, Gaud Malhār family belongs to the monsoon, and
the very word megh means cloud

Śharad September – Bhūpālī, Jaunpurī, Pahāḍī Clear, calm rāgas for the bright skies
October after the monsoon has withdrawn

Hemanta November – Bhairav, Todi Grave morning rāgas that suit the
December cool, misty early winter

Śhiśhira January – Bhairavī, Māl kauns Deep, still rāgas of the coldest weeks
February of the year

Why music and season were tied together at all: before printed calendars and
forecasts, the year was lived through what could be sensed — heat, rain, cold,
flowering, harvest. Music was one of the ways that experience was organised and
remembered. Kālidāsa traces the path of the monsoon clouds in the Meghadūtam,
Varāhamihira predicts rainfall by the nakṣhatras in the Bṛihatsaṁhitā, and singers
gave each ṛtu its own rāga — three different ways of doing the same thing, which is
paying close attention to the seasons.

Note for your class discussion: the associations are a living tradition, not a fixed
rule, so different gharānās and different regions will give you slightly different lists.
Record whom you asked along with what they told you — that difference is itself an
interesting finding, and it is also good practice for handling sources.

LET'S EXPLORE — Page 52

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Monsoon

LET'S EXPLORE

Q1 Describe in your own words how monsoon affects the lives of the people around
you.

Method. This must be written about your own place, so gather it first: ask a farmer, a vegetable
seller, a mason or a rickshaw driver what changes for them when the rains come and when they
fail; notice what changes in your own house and school; and then organise what you hear under
the headings the chapter itself gives — agriculture, water supply, daily life, transport,
festivals, employment, and the two risks, floods and droughts.
What a good answer must contain: not a general essay on the monsoon, but named, local,
concrete detail — which crop is sown when the rains arrive, which road floods, which festival
falls in the rainy months, whose work stops and whose work starts. A good answer also gives
both sides: the chapter is clear that a good monsoon brings food and water, while excessive
rainfall causes floods and a weak monsoon causes drought.

AREA OF LIFE WHAT TO LOOK FOR AROUND YOU
(FROM PAGE 52)

Agriculture Farmers rely on rain for sowing and growing crops. Which crop is sown with the first
showers? What happens to it if the rain is late?

Water supply A good monsoon means sufficient food production and water supply in rivers,
reservoirs and wells. Does your locality's well, tank or tap improve after the rains?

Daily life and transport Waterlogged roads, delayed buses, missed school days, umbrellas and raincoats,
leaking roofs being repaired before June

Festivals Which festivals in your region fall in the rainy months, and how are they tied to the
rain or the harvest that follows?

Employment Especially in rural areas — farm work rises when the rains come; building work and
brick-making often stop

Floods and droughts Has your area seen either? The Punjab floods of 2025, later in this chapter, are the
book's own example

Sample answer: 'In our village the whole year is arranged around the monsoon. From the
middle of June people watch the sky every evening, and as soon as the first heavy showers fall
the fields are ploughed and paddy is transplanted; the men who had gone to work in the town
come back for the sowing. Our well, which is nearly dry by May, fills again by the end of July, and
the tank at the edge of the village holds water for the cattle until winter. School becomes harder
in these months — the road to it is unmetalled and turns to mud, and on two or three days each

Page 18 of 67

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July we cannot go at all. My mother says a good monsoon means the price of vegetables stays
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CAUSE NAMED THE ACTION THAT WHY IT WORKS
IN THE ANSWERS IT
CHAPTER

Burning of fossil Use renewable energy — solar, Burning coal, oil and gas is what releases carbon
fuels wind — and cut wasteful energy dioxide in the first place; renewable sources
use release none while generating

Deforestation Protect forests and plant trees Trees absorb carbon dioxide as they grow, so a
standing forest is a store of carbon; cutting it
releases that store

Industrial pollution Cleaner industrial processes; Every manufactured object carries the
buy less, reuse and recycle more greenhouse gases released in making it — the
chapter counts 'the production of goods and
services' inside the carbon footprint

Our own daily Reduce the carbon footprint — These are the choices a student actually
habits walk or cycle, switch off controls, and they are exactly what the LET'S
appliances, save water, refuse EXPLORE scorecard measures
single-use plastic

Why the word 'collective' is doing real work in that sentence: the greenhouse
gases mix through the whole atmosphere, so it makes no difference where they
were released — a tonne of carbon dioxide from any country warms the same
planet. That is why no single person, city or country can solve it alone, and also why
no one is excused from acting. The chapter puts both halves together: 'Every small
step counts, and every human being plays a vital role.'

Do not lose sight of who is hit hardest. The chapter says climate change 'has great
impact on almost all sections of the population including women and children', and
that it threatens 'human health, agriculture, and livelihoods' — not only ecosystems.
The reason to act is not abstract.

LET'S EXPLORE — Pages 53–54

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My Carbon Footprint

LET'S EXPLORE

Q1 Step 1: My Daily Habits — Tick the options that best describe you. A. Transport; B.
Electricity Use; C. Water Use; D. Waste and Plastics.

How to do this honestly. Tick the option that describes what you actually did last week, not
what you intend to do. The whole exercise only works if the ticks are truthful — an activity that
flatters you teaches you nothing.
The four sections, with the impact level the book assigns to each choice:

HABIT LOW IMPACT MEDIUM IMPACT HIGH IMPACT VERY HIGH
IMPACT

A. Transport I usually walk / use I use public transport I travel by private I take flights
a cycle / carpool car even for short more than twice
distances a year

B. Electricity I always switch off I sometimes forget to I leave lights and —
Use appliances when switch them off fans on frequently
not in use

C. Water Use I use water I sometimes waste I rarely think about —
judiciously — one water (running tap, saving water
bucket for a bath long showers)

D. Waste and I reuse, recycle and I sometimes use I often throw away —
Plastics avoid single-use disposable plastics plastic and do not
plastics recycle

Why these four and not others: look back at the definition of carbon footprint in
the margin — 'greenhouse gases released… as a result of human activities, such as
energy use, transportation, or the production of goods and services'. Transport
is the second of those; electricity is the first; plastic and waste are the third, since
every plastic bottle carries the fuel burnt to make it. Water belongs there too,
because water has to be pumped, treated and delivered, and all of that runs on
energy.

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Check it yourself: tick your row for a normal school week, then repeat the exercise
for a holiday week. Most students find their transport score is quite different —
which tells you that a footprint is not a fixed personal number but a record of
choices, and choices can change.

Q2 Step 2: Score Yourself — Low impact choices = 1 point; Medium impact choices = 2
points; High impact choices = 3 points; Very high impact choices = 4 points. Now add
up your total score: ______ points.

Work out the range first, so you know what your total means. There are four sections — A,
B, C and D — and you tick one option in each, so you add four numbers.

Lowest possible score = 1 + 1 + 1 + 1 = 4 points (every choice low impact)
Highest possible score = 4 + 3 + 3 + 3 = 13 points

(only Transport has a 'very high impact' option, worth 4; the other three stop at 3)

Midpoint of the scale = (4 + 13) ÷ 2 = 8.5 points

So read your total like this:

TOTAL WHAT IT MEANS
SCORE

4–6 A small carbon footprint. Your habits are already close to what the chapter recommends — keep
them, and help others change theirs

7–9 A middling footprint. Usually one or two sections are pulling the total up; find which, and start
there

10 – 13 A large footprint. The good news is that a large score is the easiest to reduce, because the high-
impact habits are the ones with the most room to change

Sample answer: 'I ticked public transport / carpool for transport (2), I sometimes forget to switch
off appliances for electricity (2), I use water judiciously for water (1) and I sometimes use disposable
plastics for waste (2). My total is 2 + 2 + 1 + 2 = 7 points out of a possible 13. My water habit is
already at the lowest impact; the three points I can most easily save are in electricity and
plastics.'

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Tip: the useful number is not the total but which section scored highest. A total
tells you how you are doing; the section tells you what to do next.

Q3 Step 3: My Climate Action Pledge — Think about two simple changes you can make
to reduce your score, and write them down below.

What makes a good pledge — three tests. It must be specific (a named action, not 'I will save
energy'), repeatable (something you will do every day or every week, not once), and yours to
control (a change you can make without needing anyone else's permission). Then check it
against the scorecard: a good pledge should move one of your four ticks down by at least one
impact level.
Sample answer:

1. Pledge 1 — Transport: 'From Monday I will walk or cycle to school and to the shops within
two kilometres of my house, instead of asking to be dropped by car. I will keep a note on the
calendar of the days I manage it.' Effect on my score: Transport moves from high impact (3
points) to low impact (1 point) — a saving of 2 points.
2. Pledge 2 — Electricity: 'I will switch off the fan and lights every time I leave my room, and I
will check the whole house before I go to bed.' Effect on my score: Electricity moves from
medium impact (2 points) to low impact (1 point) — a saving of 1 point.

Score before the pledge = 7 points

Saving from Pledge 1 = 3 − 1 = 2 points
Saving from Pledge 2 = 2 − 1 = 1 point

New score = 7 − 2 − 1 = 4 points — the lowest the scorecard allows

Why two small pledges beat one grand one: the chapter's whole argument is that
this is a problem of collective and everyday action — 'every small step counts'. A
promise to do something dramatic once is a single event; a habit repeated three
hundred times a year is what actually changes a footprint. And a habit you keep is
worth more than an ambition you abandon in a fortnight.

Try this in class: add up the whole class's saving. If forty students each save 2
points' worth of car journeys, the class as a group has made a change no single
pledge could — which is exactly what the word 'collective' in the chapter means.

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Punjab Floods 2025: A Case Study
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The fair conclusion: nature decided that there would be a flood; human decisions
decided how severe it was. The chapter's own summing-up says the same thing —
'All these factors together increased the damage caused by the floods' — and it ends
by underlining 'the urgent need for improved flood management and preparedness'.
That last phrase is the giveaway: you can only 'manage' and 'prepare for' the part
that is in human hands.

For your discussion: avoid the two easy extremes — 'it was just nature, nothing
could be done' and 'it was entirely man-made'. Both are wrong, and the interesting
argument lies between them: which single human cause, if fixed, would have saved
the most? Different groups in the class will pick embankments, floodplain building,
desilting or early warning, and each can be defended from the chapter's own list.

Q2 Do you think better planning could have reduced the damage? How?

Yes — and the way to prove it is to take each human-made cause the chapter lists and ask
what planning would have done differently. That turns an opinion into an argument.

HUMAN-MADE WHAT BETTER PLANNING WOULD DAMAGE IT WOULD HAVE
CAUSE HAVE DONE REDUCED

Weak and old Inspect and strengthen the embankments before Fewer breaches, so villages and
dhūsī bāndh the monsoon each year, and repair the weak fields behind the embankment
stretches first stay dry

Houses and farms Mark and enforce a floodplain zone where Far fewer houses flooded; people
too close to the building is not allowed, and leave the river its are not living in the path of the
rivers natural spreading room water in the first place

Silt collected in Regular desilting of river channels and The river carries more water
rivers and dams reservoirs, so they can hold and carry the water within its banks before it
they were designed for overflows

Late or unclear A clear early-warning system — SMS alerts, Lives saved, cattle and grain
flood warnings sirens, announcements in the local language — moved in time, families evacuated
with named routes and identified relief camps calmly

Planning would also have helped with what came after. The chapter lists the effects: people
in relief camps, paddy fields under water, poultry and dairy farms destroyed, roads and bridges
damaged, and murky standing water causing waterborne diseases and sanitation

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concerns. Pre-positioned relief supplies, pumps ready to drain standing water, and stocks of
chlorine tablets and medicines would have cut every one of those.

Why prevention is worth more than relief: once the water is in the village,
everything you can do is expensive and partial — boats, camps, compensation,
rebuilding. Everything on the planning list above is done in the dry season, at a small
fraction of the cost, and it works for every flood, not just one. That is the reasoning
behind the chapter's closing phrase, 'the urgent need for improved flood
management and preparedness'.

Note the honest limit: planning reduces damage; it does not abolish floods. Rain
that falls on Punjab, Himachal Pradesh and Jammu & Kashmir at the same time, onto
rivers already running high, will flood something. The goal is to decide where it
floods — into designed spillways and empty floodplains rather than into villages.

Q3 What are the guidelines for the management of floods according to the National
Disaster Management Authority (NDMA)?

Method — this is a find-out question. The chapter does not print the NDMA guidelines, so do
not invent them. Go to the source: the NDMA's own website (ndma.gov.in), which publishes its
National Disaster Management Guidelines: Management of Floods, and its public 'Do's and Don'ts'
for floods. Your school library, the district disaster management authority, or a local Civil
Defence volunteer are good second sources. Quote the source you used.
What a good answer must contain: the NDMA's approach is organised around the disaster
management cycle — what is done before, during and after a flood — so arrange your findings
under those three heads rather than as one long list, and give a concrete example of each.
Sample answer (check each point against the NDMA website before you submit it):

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STAGE WHAT THE GUIDELINES COVER

Before — Flood-risk mapping and floodplain zoning so that building is regulated in flood-prone land;
prevention and maintaining and strengthening embankments; desilting rivers and reservoirs; catchment-
mitigation area treatment and afforestation upstream; flood-resistant design for roads, bridges and
public buildings

Before — A flood forecasting and early-warning system with warnings issued in the local language
preparedness and reaching the last village; district disaster management plans; identified relief camps
and evacuation routes; mock drills; trained community volunteers and Aapda Mitra-type
schemes; school and community awareness programmes

During — Evacuation of people and livestock; search and rescue by the NDRF and state forces;
response emergency shelter, safe drinking water, food and medical aid; keeping communication lines
open; a single incident command so agencies do not work at cross-purposes

After — recovery Draining standing water and disinfecting sources to prevent waterborne disease; damage
and rehabilitation assessment and relief for crops, cattle and houses; repairing roads, bridges and
embankments; and 'building back better', so that what is rebuilt is safer than what was lost

Why the guidelines are organised as a cycle: because the four human-made
causes of the Punjab floods sit at different points in it. Weak embankments and
building on the floodplain are prevention failures; silted rivers are a mitigation
failure; late and unclear warnings are a preparedness failure; and the disease from
standing water is a recovery problem. Reading the case study against the cycle
shows exactly where the system needs strengthening — which is what a guideline is
for.

Q4 What role can students/youth play in helping with disaster preparedness?

A large one — because most of preparedness is knowledge, organisation and
communication, and students are good at all three. Rescue is a job for trained professionals;
getting information to people before the water rises is not.

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ROLE WHAT IT LOOKS LIKE IN PRACTICE

Learn first Know your own area's risk — which stretch of the river overflows, which lanes flood first,
where the nearest relief camp and high ground are. Learn basic first aid and how to switch off
the electricity mains safely

Make a family Prepare an emergency kit — documents in a plastic folder, torch, dry food, drinking water,
plan matches, medicines — and agree where the family will meet if it has to leave. One of the
Punjab causes was people being unprepared; a plan fixes exactly that

Spread The chapter says warnings 'came late or were not clearly communicated'. Students can carry
warnings an official alert to elderly neighbours and to families without phones, and explain it in the
local language

Run awareness Posters, wall newspapers, a street play, a class assembly on flood do's and don'ts — the
in school chapter's own Questions and activities in Chapter 2 used exactly this method

Take part in School evacuation drills, NCC, NSS, Scouts and Guides, Junior Red Cross and Civil Defence
drills programmes; help mark evacuation routes and check that exits are clear

Help after the Collect clothes, books and dry rations; help younger children catch up on missed school; assist
flood in awareness on boiling drinking water, so that waterborne disease does not follow the flood

Protect the Tree planting, keeping drains and canals free of plastic waste, and not encroaching on
environment riverbanks — small acts that reduce the flood itself, not only its damage

Why students matter more than their age suggests: information moves through
a village along family lines, and every student is a link in several of them at once —
home, neighbours, school. A student who understands what a flood warning means
can explain it to a grandmother who cannot read the SMS, and to a younger brother
who will remember the drill. Preparedness is not one heroic act; it is many people
knowing what to do before it happens.

Do not overreach. A good answer should say clearly what students should not do:
never enter floodwater, never attempt a rescue, never go near broken electric lines,
and never spread an unverified warning on social media — a false alarm destroys
trust in the real one.

Before we move on … — Pages 56–57

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The chapter's recap points, expanded
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COMPONENT SHARE WHAT IT DOES

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Why the same air both supports life and makes weather: because the two jobs
are done by different parts of the mixture. Life depends on the steady 99% —
nitrogen and oxygen, in proportions that barely change. Weather depends on the
part that does change: water vapour swinging between 0.1% and 0.4%, and the dust
it condenses on. A constant gas cannot produce a variable sky; a variable one can.

Q2 The atmosphere is made up of different layers, namely the Troposphere,
Stratosphere, Mesosphere, Thermosphere, and Exosphere, which are divided based
on changes in temperature and air density as we go higher above the Earth's
surface.

What this recap means, expanded. The five layers are not five different substances — the air is
much the same mixture throughout the lower layers. What changes is temperature and
density, and it is those two changes that draw the boundaries.

LAYER EXTENDS THICKNESS TEMPERATURE ITS LANDMARK
TO WITH ALTITUDE FEATURE

Troposphere about 12 12 km Falls Nearly all weather; most
km water vapour and clouds;
the air we breathe

Stratosphere 50 km 38 km Rises The ozone layer;
aeroplanes fly here

Mesosphere 80 km 30 km Falls Meteorites burn up

Thermosphere 700 km 620 km Rises very rapidly Ionosphere reflects radio
waves; auroras

Exosphere fades into — — Very thin air; helium and
space hydrogen escape

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Class 9 Social Science Chapter 3 Atmosphere and Climate AglaSem · NCERT Solutions

Work out the thicknesses from the chapter's own heights:

Troposphere = 12 − 0 = 12 km

Stratosphere = 50 − 12 = 38 km

Mesosphere = 80 − 50 = 30 km

Thermosphere = 700 − 80 = 620 km

So the troposphere is only 12 km of the roughly 700 km measured here — about 1.7% of the

height — and yet nearly all the weather happens inside it.

The three boundaries have names of their own, and each marks the point where the
temperature stops going one way and turns the other: the tropopause (troposphere /
stratosphere), the stratopause (stratosphere / mesosphere) and the mesopause (mesosphere /
thermosphere).

Why density is the second criterion, and why it behaves more simply than
temperature: density just falls, all the way up, without reversing — the chapter says
it is highest near the Earth's surface and decreases with altitude. That is gravity:
the air near the ground is squeezed by the weight of all the air above it, and there is
less and less weight above you as you rise. Temperature, by contrast, reverses four
times, because it depends on where the heating comes from in each layer. Two
different rules, two different patterns — and together they cut the atmosphere into
five.

Q3 Weather refers to the daily atmospheric conditions, while climate is the average
weather of a place over a long period of time.

What this recap means, expanded. Same atmosphere, same five elements — the difference is
entirely one of time and area.

Page 31 of 67

Class 9 Social Science Chapter 3 Atmosphere and Climate AglaSem · NCERT Solutions

WEATHER CLIMATE

Definition in The hour-to-hour and day-to-day The sum total of weather conditions and
the chapter conditions of the atmosphere variations over a large area for an extended
period, usually thirty years or more

Area A single place A large region

How it changes Can vary significantly from day to Changes only over decades
day

Example from 'Is it going to rain today?' — and the 'The climate of India can be broadly classified as
this chapter two-week newspaper record in LET'S tropical monsoon' — and the averages in Table
ANALYSE 3.3

Both are built from the same five elements, which the chapter lists as the major ones that
impact human life: temperature, precipitation, humidity, wind and atmospheric pressure.
Read those five for today and you have described the weather; average them over thirty years
and you have described the climate.

Why thirty years, and not three or three hundred: a short record is dominated by
chance — one freak year would tilt the whole average. Thirty years is long enough
for the good monsoons and the failed ones to balance out, so that what is left is the
genuine character of the place. That is why every number in Table 3.3 is called an
average monthly figure: no single January in Delhi was exactly 14.4°C, but the typical
one is.

Where this matters most: climate change is defined in this chapter as a long-term
change in weather patterns. It can only be detected by comparing one long average
with another — never by pointing at a single hot day or a single flood.

Q4 India has a tropical monsoon climate, and the Indian Meteorological Department
(IMD) divides the year into four main seasons, namely—Winter, Summer, Monsoon,
and Post-monsoon.

What this recap means, expanded. 'Tropical monsoon' is a two-word description doing two
jobs: tropical because most of India lies in the torrid zone, between the Tropic of Cancer and
the equator, where insolation is high and temperatures stay warm; monsoon because the rain is
delivered by a wind that reverses with the seasons.

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Class 9 Social Science Chapter 3 Atmosphere and Climate AglaSem · NCERT Solutions

SEASON MONTHS WHAT THE CHAPTER SAYS ABOUT IT

Winter December to early Coldest months are December and January. Average temperature
April in the north-west about 10–15°C, rising towards the equator to 20–
25°C in mainland India's south-east

Summer or pre- April to June (to Hottest month is April in western and southern regions, May in the
monsoon July in north- north. Average across most of inland India 32–40°C
western India)

Monsoon or June to September Dominated by the humid south-west summer monsoon, which
rainy (advancing sweeps across the country in late May or early June. Rain begins to
monsoon) recede from north India at the beginning of October, and South
India typically receives more rainfall during this time

Post-monsoon October to In north-western India, October and November are usually
(retreating December cloudless
monsoon)

Two additions the chapter makes to this four-fold scheme:

The Himalayan states, being more temperate, experience two additional seasons —
autumn and spring.
Traditionally India recognises six seasons (ṛtus) of about two months each — Vasanta,
Grīṣhma, Varṣhā, Śharad, Hemanta, Śhiśhira — based on the astronomical division of the
twelve months into six parts, and reflected in the arrangement of months in the traditional
Indian calendar (Table 3.2).

Page 33 of 67

as e
Class 9 Social Science Chapter 3 Atmosphere and Climate
a g l AglaSem · NCERT Solutions

co m
e m.
m l as
.co a g
Low angle of incoming sunlight

se m
g l a
a
Arctic Circle
60° N

com
30° N Tropic of Cancer

m . ag
Sun's rays

e
Sunlight strikes

a s
Equator

agl
most directly

30° S Tropic of Capricorn

co m
m.
60° S
Antarctic Circle

m as e
.co a g l
m
ase
Low angle of incoming sunlight

agl Because the Earth is a sphere, the Sun's rays strike the equator head-on but reach the poles at a low angle,
spread over a much larger area. That is why insolation — and so temperature — decreases from the equator to the poles.

m a s
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North Pole

em
Frigid Zone

a s
Arctic Circle 66½°N

ag l North Temperate Zone

Tropic of Cancer 23½°N

co m
Torrid Zone

.
Equator 0°

e m
as
Torrid Zone

m l
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Tropic of Capricorn 23½°S

m
ase
South Temperate Zone

agl
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Frigid Zone

South Pole
se m
com g l a
. a
The five temperature zones: one torrid zone between the two tropics, a temperate zone on each side of it,

m
ase
and a frigid zone beyond each polar circle.

agl
Fig. 3.6, page 44 — temperature zones of the Earth. The Sun's rays strike the equator head-on and
the poles at a low angle, which is why the Earth is divided into one torrid, two temperate and two

co m
.
frigid zones.

se m
o m l a
g because insolation
m .cWhy the temperature figures rise as you move south:
a
as e
agl
decreases from the equator towards the poles. The north-west of India is furthest
.c
m
from the equator, so its winter average is 10–15°C; the south-east is nearest, so the

m a s e
co agl
same months there average 20–25°C. The same rule that sorts the Earth into torrid,

m .
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temperate and frigid zones (Fig. 3.6) is at work inside India itself — and Table 3.3
shows it station by station.
g l as
a

co m
m .
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.co


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Class 9 Social Science Chapter 3 Atmosphere and Climate AglaSem · NCERT Solutions

Did you know? The interest in measuring the monsoon is very old in India.
Kauṭilya's Arthaśhāstra records scientific measurements of rainfall and their use in
managing revenue and relief; Kṛiṣhiparāśhara predicted rain from the positions of
the Moon and the Sun, and Varāhamihira's Bṛihatsaṁhitā from the lunar mansions
(nakṣhatras). Today the same task is carried out by the IMD, the National Monsoon
Mission and Mission Mausam.

Q5 Climate change is the long-term change in weather caused mainly by human
activities like burning fuels and cutting trees, which leads to global warming and
extreme weather conditions.

What this recap means, expanded. The chapter builds this as a chain of cause and effect, and
it is worth setting out as a chain, because every step of it is also a place to intervene.

Human activities — burning fossil fuels, deforestation, industrial pollution

↓

More greenhouse gases in the atmosphere — carbon dioxide, methane, nitrous oxide, water

vapour

↓
These gases trap heat that would otherwise escape to space

↓

Global temperatures rise

↓

More frequent floods, droughts, melting of glaciers, rising sea levels, loss of biodiversity

The consequences do not stop at the environment. The chapter is explicit that climate
change 'not only threatens ecosystems but also impacts human health, agriculture, and
livelihoods', and that it 'has great impact on almost all sections of the population including
women and children'.

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Class 9 Social Science Chapter 3 Atmosphere and Climate AglaSem · NCERT Solutions

Why trapping heat is not in itself a bad thing — and where it goes wrong: the
very first page of this chapter says the atmosphere 'regulates the Earth's
temperature by trapping some of the Sun's energy and prevents it from escaping
back into space'. That trapping is what makes the Earth warm enough to live on. The
problem is not the greenhouse effect but its increase: adding more of these gases
traps more heat than the system was balanced for, and the balance shifts. Notice too
that carbon dioxide is only 0.04% of the atmosphere — proof that a very small share
of a mixture can have a very large effect.

Connect it to the case study: the Punjab floods of 2025 are the chapter's own
illustration of 'extreme weather conditions' — very heavy monsoon rain, intensified
by western disturbances, falling on rivers already running high.

Q6 We can reduce our carbon footprint by saving energy, using renewable sources,
planting trees, and living in more eco-friendly ways.

What this recap means, expanded. A carbon footprint is the total amount of greenhouse
gases released into the atmosphere as a result of human activities — energy use,
transportation, and the production of goods and services. So reducing it means changing one of
those three.

THE RECAP'S WHAT IT MEANS IN PRACTICE WHY IT REDUCES THE
FOUR ACTIONS FOOTPRINT

Saving energy Switching off lights and fans when not in Most electricity still comes from
use; using water judiciously; walking or burning fossil fuels, so energy saved is
cycling instead of taking a car carbon not released

Using renewable Solar and wind energy instead of coal, oil They generate power without burning
sources and gas anything, so no carbon dioxide is
added

Planting trees Planting and, just as importantly, Growing trees absorb carbon dioxide
protecting existing forests from the air; deforestation releases
what was stored

Living in eco- Reusing and recycling, avoiding single-use Every manufactured object carries the
friendly ways plastics, buying less and repairing more greenhouse gases released in
producing it

Page 36 of 67

Class 9 Social Science Chapter 3 Atmosphere and Climate AglaSem · NCERT Solutions

Why the chapter asks students to score themselves rather than simply telling
them the answer: because a footprint is not a fact about the world, it is a record of
choices — and you cannot change a choice you have not noticed. The four sections
of the LET'S EXPLORE scorecard (transport, electricity, water, waste and plastics) turn
an abstract idea into four things you actually did this week, and the two pledges turn
them into two things you will do next week.

Keep the chapter's own last word: 'Every small step counts, and every human
being plays a vital role in shaping a healthier and greener future.'

Questions and activities — Pages 57–59
End-of-chapter exercise

Q1 What is atmosphere? Explain its composition with the help of a pie diagram.

The atmosphere is the blanket of air surrounding the Earth. It is pulled down around the
Earth by gravity, and is a mixture of gases in various proportions, vital for the survival of
all living beings on the Earth. It shields us from the Sun's harmful radiation, including
ultraviolet; it regulates the Earth's temperature by trapping some of the Sun's energy; and it is
the key component of the Earth's weather and climate systems, influencing temperature,
humidity and air pressure.
Its composition, as a pie diagram:

The last 1%
Carbon dioxide 0.04%

Nitrogen Argon 0.93%
78%

Others 0.03%

The whole bar is only 1% of the pie,
Oxygen 21%
magnified so the trace gases show up.
0.93 + 0.04 + 0.03 = 1.00%

Page 37 of 67

Class 9 Social Science Chapter 3 Atmosphere and Climate AglaSem · NCERT Solutions

Fig. B — A pie diagram of the atmosphere's composition, with the final 1% magnified into a bar so
that argon, carbon dioxide and the other gases can be seen.

GAS SHARE OF THE AIR ANGLE AT THE CENTRE OF THE PIE

Nitrogen 78% 78 × 3.6° = 280.8°

Oxygen 21% 21 × 3.6° = 75.6°

Argon 0.93% 0.93 × 3.6° = 3.3°

Carbon dioxide 0.04% 0.04 × 3.6° = 0.14°

Other gases 0.03% 0.03 × 3.6° = 0.11°

How to work out each angle for yourself:

A full circle = 360°, and the whole air = 100%

So 1% = 360 ÷ 100 = 3.6°

Check the total: 280.8 + 75.6 + 3.3 + 0.14 + 0.11 ≈ 360°

Two things the pie cannot show, so write them beside it:

Besides these gases the atmosphere also contains water vapour — generally 0.1% to 0.4%
— and tiny dust particles. Water vapour plays a significant role in cloud formation and
precipitation.
The remaining trace gases the chapter names are helium, neon, krypton, xenon, ozone
and hydrogen.

Why the trace gases have to be magnified to be seen: carbon dioxide's slice is
0.14° wide — in a pie of radius 5 cm that is a line about a tenth of a millimetre thick,
thinner than the pencil that draws it. This is exactly why the composition is usually
written as a table of percentages beside the pie, and why a magnified inset like the
one above is worth drawing.

Tip when you draw it in your notebook: draw nitrogen and oxygen accurately with
a protractor, then draw the remaining 1% as a single visible sliver labelled 'other
gases (1%)', and break it up in a separate enlarged bar or a small table. That is
honest, readable, and it is how the chapter's own Fig. 3.2 handles the problem with
leader lines.

Page 38 of 67

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Class 9 Social Science Chapter 3 Atmosphere and Climate
a g l AglaSem · NCERT Solutions

co m
m.
Draw a labelled diagram of the structure of atmosphere.
e
Q2

m l as
.co a g
a
s em
a gl it as a vertical section, with height above sea level on the left-hand axis, the five layers
Draw
stacked in order, the three '-pauses' marked as boundary lines, and the landmark feature of

co m
ag
each layer labelled on the right.

m .
as e
a g l

co m
EXOSPHERE ◂ helium and hydrogen escape air density lowest

m.
100

e
temperature rises

as
◂ auroras; satellites; radio waves

m
THERMOSPHERE

.co a g l
se m
80 Mesopause

g l a
Height above sea level (km)

a MESOSPHERE temperature falls
◂ meteors burn up here

m a s
.co agl
50 Stratopause

se m
g l a
a
STRATOSPHERE temperature rises
◂ OZONE layer filters ultraviolet rays

m
◂ aeroplanes fly here — no clouds

. co
12 Tropopause

e m
temperature falls

as
TROPOSPHERE ◂ weather — clouds, rain, fog, hail

m
air density highest

.co l
Earth's surface — mean sea level = 0

g
0

em a
The scale is broken above 100 km — the thermosphere actually reaches 700 km, and the exosphere fades into outer space.

a s
agl Fig. D — Labelled structure of the atmosphere, with the heights given in the chapter, the three pauses
m
that separate the layers, and the landmark feature of each layer.

a se
.com a g l
m
ase
The labels your diagram must carry, and the values to put on them:

agl

co m
m .
m as e
.co a g l
se m
g l a
a c
m .
m a s e
e m . co agl
g l as
a

co m
m .
m as e
.co


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Class 9 Social Science Chapter 3 Atmosphere and Climate AglaSem · NCERT Solutions

LABEL HEIGHT WHAT TO WRITE BESIDE IT

Troposphere 0 – about 12 km Temperature falls with altitude; the air we breathe; most water
vapour and clouds; nearly all weather — rainfall, fog, hail

Tropopause about 12 km The transition zone separating the troposphere from the
stratosphere

Stratosphere 12 – 50 km Ideal for flying aeroplanes — free of clouds and weather
disturbances; contains the ozone layer, which filters the Sun's
harmful radiation including ultraviolet

Stratopause 50 km Boundary between the stratosphere and the mesosphere

Mesosphere 50 – 80 km Temperature falls with altitude; most meteorites burn up here

Mesopause 80 km Boundary between the mesosphere and the thermosphere

Thermosphere 80 – 700 km Temperature rises very rapidly with altitude; the ionosphere is a
part of it and reflects radio waves back to the Earth; the auroras
occur here

Exosphere above the Uppermost layer; very thin air; helium and hydrogen float into
thermosphere space because gravity is weak

Two things that gain marks in a diagram question: (i) mark the heights on the
axis — 12, 50, 80 and 700 km — because the layers are defined by height; and (ii) add
an arrow on one side showing that air density decreases upward and short notes
on the other showing where temperature falls and where it rises. Those two arrows
are the reason the layers exist, so a diagram that shows them explains as well as
illustrates.

Why the diagram is drawn with a broken scale: the thermosphere alone is 620 km
thick, while the troposphere is only 12 km. Drawn strictly to scale, the layer where all
our weather happens would be a hairline at the bottom of the page. Breaking the
scale above 100 km lets you show the lower layers clearly while still recording the
true height — but always mark the break, so the reader is not misled.

Q3 Which are the four main seasons of India?

The Indian Meteorological Department (IMD) recognises four distinct seasons in India:

Page 40 of 67

Class 9 Social Science Chapter 3 Atmosphere and Climate AglaSem · NCERT Solutions

# SEASON MONTHS ITS CHARACTER

1 Winter December to early Coldest months December and January; average
April about 10–15°C in the north-west, 20–25°C in
mainland India's south-east

2 Summer or pre- April to June (up to Hottest month is April in the west and south, May
monsoon July in north-western in the north; average 32–40°C across most of
India) inland India

3 Monsoon or rainy June to September Dominated by the humid south-west summer
(advancing monsoon, which sweeps across the country in
monsoon) late May or early June

4 Post-monsoon October to December Monsoon rain recedes from north India from the
(retreating beginning of October; in north-western India
monsoon) October and November are usually cloudless

Add the exception: the Himalayan states, being more temperate, experience two additional
seasons — autumn and spring.

Why India's seasons are named after the monsoon rather than after
temperature: in temperate countries the year is divided by how warm it is — spring,
summer, autumn, winter. Here two of the four names, 'monsoon' and 'post-
monsoon', refer to the rain-bearing wind, and a third, 'pre-monsoon', is defined by
waiting for it. That is what a tropical monsoon climate means: the wind reversal,
not the thermometer, is what organises the year.

Did you know? Traditionally India recognises six seasons of about two months each
— Vasanta, Grīṣhma, Varṣhā, Śharad, Hemanta and Śhiśhira — based on the
astronomical division of the twelve months into six parts, and still reflected in the
traditional Indian calendar (Table 3.2).

Q4 Why do you not feel the pressure of the atmosphere?

Because the pressure is balanced on both sides of you. The chapter gives both halves of the
reason: air presses on us from all sides, and our bodies exert a counter-pressure in
response — the pressure inside our bodies is equal to the atmospheric pressure and cancels
the pressure from outside.

Page 41 of 67

Class 9 Social Science Chapter 3 Atmosphere and Climate AglaSem · NCERT Solutions

Push from the air on the outside = push from inside the body

Net force on you = outside − inside = zero

No net force → nothing to feel

Two separate ideas are doing the work here, and a full answer needs both:

The air pushes from every direction, not just downward. If it pressed only from above you
would feel it as a weight on your shoulders. Because it presses equally on your back, your
front and your sides, the pushes cancel out.
Your body pushes back. The fluids and gases inside you are at the same pressure as the air
outside, so the walls of your body are not squeezed inward.

Why you do notice it when the balance breaks: your ears pop when a bus climbs a
ghat or a plane takes off. The chapter's own rule explains it — as we go higher in
the atmosphere, pressure falls rapidly — so the outside pressure drops while the
air trapped behind your eardrum is still at the pressure of the valley below. For a
moment inside and outside no longer match, and you feel exactly the pressure you
never notice at rest. When the ear 'pops', the two have equalised again.

Check it yourself: a sealed empty plastic bottle carried down from a hill station
arrives crumpled. Nothing pressed harder on it at the bottom than presses on you
right now — the difference is only that the air sealed inside the bottle was still at the
thin, high-altitude pressure and could not push back.

Q5 In which layer of the atmosphere do aeroplanes fly and why?

Aeroplanes fly in the stratosphere — the layer above the troposphere, extending up to 50
kilometres. The chapter's reason is short and exact: this layer is ideal for flying aeroplanes
because it is free of clouds and other weather disturbances.

Page 42 of 67

Class 9 Social Science Chapter 3 Atmosphere and Climate AglaSem · NCERT Solutions

TROPOSPHERE (BELOW) STRATOSPHERE (WHERE
PLANES FLY)

Clouds and water Most of the atmosphere's water vapour and Free of clouds
vapour clouds are here

Weather Nearly all weather phenomena — rainfall, No weather disturbances
fog, hail

Effect on a flight Turbulence, storms, poor visibility, icing A smooth, steady, predictable flight

Why the stratosphere is calm, when the troposphere is not: it comes back to the
temperature profile. In the troposphere temperature falls with height, so warm air
near the ground is lighter than the cold air above it and keeps rising — that
overturning is what builds clouds, storms and turbulence. In the stratosphere
temperature rises with height, because ozone absorbs ultraviolet and warms the
upper part of the layer. Warm air lying on top of cooler air has no reason to rise, so
the layer stays stable and still. The absence of weather in the stratosphere is not a
coincidence; it is a direct consequence of its inverted temperature profile.

Note the second benefit: flying above the weather also means flying in thinner air,
where there is less resistance, so the aircraft uses less fuel for the same speed. And
the ozone layer that makes the stratosphere calm is the same layer that shields the
Earth from ultraviolet radiation.

Q6 Distinguish between the following: a. The troposphere and stratosphere b. The
south-west monsoon and north-east monsoon

a. The troposphere and the stratosphere

Page 43 of 67

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Class 9 Social Science Chapter 3 Atmosphere and Climate
a g l AglaSem · NCERT Solutions

co m
m.
BASIS TROPOSPHERE STRATOSPHERE

mThe lowest layer, resting on the Earth's as e
Position
.co surface a g l
Lies immediately above the troposphere

se m
g l a
aExtent Average height about 12 km Extends up to 50 km — so about 38 km thick

m
.co ag
Temperature Decreases as you go up Increases as you go up

sem
with altitude

a
Water vapour
and clouds clouds
agl
Holds most of the water vapour and Free of clouds

co m
m.
Nearly all weather phenomena —
e
Weather Free of weather disturbances

m l as
.co
rainfall, fog, hail — occur here

a g
se m
l a
Special feature Contains the air we breathe; it is Contains the ozone layer, which filters the

a g called the most important layer of the
atmosphere
Sun's harmful radiation including ultraviolet;
aeroplanes fly here

m a s
.co agl
Upper boundary The tropopause The stratopause

a s em
aglthe north-east monsoon
b. The south-west monsoon and

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m .
m as e
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se m
g l a
a
se m
com g l a
m . a
ase
agl

co m
m .
m as e
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se m
g l a
a c
m .
m a s e
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g l as
a

co m
m .
m as e
.co


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Class 9 Social Science Chapter 3 Atmosphere and Climate AglaSem · NCERT Solutions

BASIS SOUTH-WEST MONSOON NORTH-EAST MONSOON

Also called The summer monsoon The winter monsoon

Season June to September October to February

Direction of From sea to land — across the From land to sea
the wind Indian Ocean, the Arabian Sea and
the Bay of Bengal

Pressure Land heats faster → low pressure Land cools faster → high pressure over the land, low
pattern over the subcontinent, high pressure over the seas
pressure over the cooler Indian
Ocean

Nature of Moist and humid Cold and dry
the winds

Rainfall Brings most of the rainfall in the Generally brings no rainfall to most parts of India —
country throughout the year but after crossing the Bay of Bengal it picks up
moisture and rains on the eastern coast: Tamil Nadu,
Andhra Pradesh and parts of Karnataka

Region it Almost the whole country The south-eastern regions of India
matters most
to

The one idea behind both halves of this question: in each case the difference
comes from where the heat is and where it is not. The troposphere is heated from
below by the ground and the stratosphere from within by ozone — that single
difference explains their opposite temperature profiles, and everything else follows
from it. In the same way, whether the land or the sea is the warmer of the two is
what decides which way the monsoon blows. Learn the cause and you do not have
to memorise the table.

Page 45 of 67

Class 9 Social Science Chapter 3 Atmosphere and Climate AglaSem · NCERT Solutions

Q7 Do it yourself: Table 3.3 shows the average monthly temperatures and rainfall amounts
them into 'temperature and rainfall' graphs. The visual representations will help you gr
already prepared for you. See if you can arrive at some broad generalisations about ou
Table 3.3. Average monthly temperatures and rainfall for 10 representative stations (te

Page 46 of 67

Class 9 Social Science Chapter 3 Atmosphere and Climate AglaSem · NCERT Solutions

STATION LATITUDE ALTITUDE JAN. FEB. MAR. AP
(M)

Bengaluru 12°58'N 909 Temperature 20.5 22.7 25.2 27
(°C)

Rainfall 0.7 0.9 1.1 4.5
(cm)

Mumbai 19°N 11 Temperature 24.4 24.4 26.7 28
(°C)

Rainfall 0.2 0.2 – –
(cm)

Kolkata 22°34'N 6 Temperature 19.6 22.0 27.1 30
(°C)

Rainfall 1.2 2.8 3.4 5.1
(cm)

Delhi 29°N 219 Temperature 14.4 16.7 23.3 30
(°C)

Rainfall 2.5 1.5 1.3 1.0
(cm)

Jodhpur 26°18'N 224 Temperature 16.8 19.2 26.6 29
(°C)

Rainfall 0.5 0.6 0.3 0.3
(cm)

Chennai 13°4'N 7 Temperature 24.5 25.7 27.7 30
(°C)

Rainfall 4.6 1.3 1.3 1.8
(cm)

Nagpur 21°9'N 312 Temperature 21.5 23.9 28.3 32
(°C)

Rainfall 1.1 2.3 1.7 1.6
(cm)

Shillong 24°34'N 1461 Temperature 9.8 11.3 15.9 18
(°C)

Rainfall 1.4 2.9 5.6 14
(cm)

Page 47 of 67

Class 9 Social Science Chapter 3 Atmosphere and Climate AglaSem · NCERT Solutions

Thiruvananthapuram 8°29'N 61 Temperature 26.7 27.3 28.3 28
(°C)

Rainfall 2.3 2.1 3.7 10
(cm)

Leh 34°N 3506 Temperature -8.5 -7.2 -0.6 6.1
(°C)

Rainfall 1.0 0.8 0.8 0.5
(cm)

Page 48 of 67

as e
Class 9 Social Science Chapter 3 Atmosphere and Climate
a g l AglaSem · NCERT Solutions

co m
e m.
m l as
m .co a g
l a se Delhi — 29°N, 219 m Annual rainfa
a g
35
co m
e m . ag
30
g l as
a
Temperature (°Celsius)

25
co m
em.
m l as
m .co 20 a g
l a se
a g 15
m a s
m .co agl
se
10
g l a
a
5
co m
m .
m 0
l a se
m .co Jan ag May Jun
Feb Mar Apr Jul
ase
agl monthly rainfall (bars, right-hand scale)
se m
o m g l a
Hot from
m .c April to June, wet from July to Sept
a
l a
falls se in the four monsoon months, and the te
ag

co m
m .
o m l a se
g from Delhi's row in Table 3.3. (Th
.c Fig. 3.14, page 59 — temperature and rainfall of Delhi,adrawn
se m
g l a table's figure is u

a c
m .
m a s e
m . co agl
se

l a
g 3.3 turned into a picture:
How to draw a temperature-and-rainfall graph (a climograph). Copy the method of Fig. 3.14,
which is the Delhi row ofaTable

com
m .
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Class 9 Social Science Chapter 3 Atmosphere and Climate AglaSem · NCERT Solutions

1. Put the twelve months along the horizontal axis, January to December.
2. Put temperature in °C on the left-hand vertical axis and rainfall in cm on the right-hand
vertical axis. Use the same two scales for every station you draw, or you will not be able to
compare them.
3. Draw the rainfall as bars from the base line.
4. Plot the temperature as a dot for each month and join the dots into a line.
5. Title the graph with the station's name, latitude and altitude — those three explain most of
what the graph shows.

Two worked examples, drawn from Table 3.3, that show the two great families of Indian
climate:

Mumbai — 19°N, 11 m
Annual rainfall 183.4 cm
40 65

52
30
Temperature (°C)

Rainfall (cm)
39
20
26

10
13

0 0
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Rain arrives in one block, Jun–Sep: 175.4 cm = 95.6% of the year's 183.4 cm.
The temperature line dips while it rains — a west-coast, SW-monsoon station.

Fig. F — Climate graph of Mumbai, drawn from its row in Table 3.3, in the style of Fig. 3.14.

Page 50 of 67

Class 9 Social Science Chapter 3 Atmosphere and Climate AglaSem · NCERT Solutions

Chennai — 13°4'N, 7 m
Annual rainfall 128.6 cm
40 65

52
30
Temperature (°C)

Rainfall (cm)
39
20
26

10
13

0 0
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

The rain peak is Oct–Nov, not Jun–Sep: 79.5 cm in Oct–Dec = 61.8% of the year.
An east-coast station watered by the retreating, north-east monsoon.

Fig. G — Climate graph of Chennai, drawn from its row in Table 3.3. Compare its November peak with
Mumbai's July peak.

The broad generalisations you should arrive at. Every figure below is worked out from Table
3.3 itself:

Page 51 of 67

Class 9 Social Science Chapter 3 Atmosphere and Climate AglaSem · NCERT Solutions

# GENERALISATION THE EVIDENCE IN TABLE 3.3

1 Temperature falls as you move away Mean of the twelve months: Thiruvananthapuram
from the equator. (8°29'N) 27.1°C; Chennai (13°4'N) 28.6°C; Delhi (29°N)
25.0°C; Leh (34°N) 5.0°C

2 Altitude cools a place even at the same Bengaluru (909 m) averages 23.1°C, Chennai (7 m)
latitude. 28.6°C — and they are only 6 minutes of latitude apart.
That is 5.5°C over 902 m, about 0.61°C for every 100 m
of climb

3 The sea makes a climate equable; Annual range (warmest month − coldest month):
distance from it makes the climate Thiruvananthapuram 2.5°C, Mumbai 5.6°C — both on
extreme. the coast; Jodhpur 19.0°C, Leh 25.7°C — both far inland

4 Rainfall is concentrated in the four Nine of the ten stations have their wettest month between
monsoon months almost everywhere. June and September. Mumbai takes 95.6% of its rain in
those four months, Nagpur 86.1%, Delhi 84.2%

5 Rainfall totals vary enormously from Shillong 225.3 cm against Leh 8.5 cm — 225.3 ÷ 8.5 ≈ 26
place to place. times as much

6 Temperature falls when the rains arrive Nagpur cools from 35.5°C in May to 27.7°C in July, a
— exactly as the chapter says rain 'lowers drop of 7.8°C, while July rainfall jumps to 37.6 cm.
the temperature of a place'. Bengaluru falls from 27.1°C (April) to 23.0°C (July)

Two of those figures, worked out in full:

Bengaluru mean = 277.5 ÷ 12 = 23.1°C · Chennai mean = 343.4 ÷ 12 = 28.6°C

Difference = 28.6 − 23.1 = 5.5°C for an altitude difference of 909 − 7 = 902 m

Rate = 5.5 ÷ 9.02 = 0.61°C per 100 m

Shillong mean = 198.1 ÷ 12 = 16.5°C · Kolkata mean = 316.3 ÷ 12 = 26.4°C

Difference = 9.9°C for 1461 − 6 = 1455 m → 0.68°C per 100 m — very nearly the same

rate

Page 52 of 67

Class 9 Social Science Chapter 3 Atmosphere and Climate AglaSem · NCERT Solutions

Why three things — latitude, altitude and distance from the sea — explain
almost the whole table: latitude fixes how much insolation a place receives, and
insolation decreases from the equator towards the poles. Altitude works within the
troposphere, where temperature falls as you go up. And the sea moderates: water
heats and cools slowly, so a coastal station never gets very hot or very cold, while an
inland one swings widely. Read any row of Table 3.3 with those three in mind and
you can predict most of it before you look.

Two things worth noticing in the printed table. (i) Fig. 3.14 is drawn from Delhi's
row, but two of its plotted points differ slightly from the table — the graph shows
about 17.7°C for February and about 30.5°C for June where Table 3.3 prints 16.7°C
and 33.3°C. Plot from the table, since that is what the question gives you. (iii) Two of
the printed annual totals are a rounding out: adding Chennai's twelve monthly
figures gives 128.7 cm against the 128.6 printed, and Shillong's gives 225.2 cm
against 225.3 — differences of 0.1 cm, which change nothing. (ii) Jodhpur's row
prints 20.1°C for September and 27.0°C for October, which would make October
hotter than September — an unlikely order for the season, and probably a misprint.
It does not affect any of the answers below.

Q7.1 Now look at Table 3.3 again. Re-arrange the 10 stations according to their distance
from the equator.

Distance from the equator is simply latitude, so arrange the stations by the latitude column,
nearest the equator first.

Page 53 of 67

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Class 9 Social Science Chapter 3 Atmosphere and Climate
a g l AglaSem · NCERT Solutions

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# STATION LATITUDE MEAN ANNUAL TEMPERATURE (COMPUTED)

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Thiruvananthapuram 8°29'N 27.1°C
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Bengaluru 23.1°C
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3 Chennai 13°4'N 28.6°C

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4 Mumbai 19°N
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6 Kolkata 22°34'N 26.4°C
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7 Shillong 24°34'N 16.5°C

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8 Jodhpur 26°18'N 25.2°C

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10 Leh 34°N

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Bengaluru 12°58'N and Chennai 13°4'N

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13°4' = 12°64', and 12°64' − 12°58' = 6 minutes of latitude
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interesting. If latitude alone

cooler than Chennai (3rd), and Shillong (7th) is 8.7°C cooler than Jodhpur (8th),
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a g l Page 54 of 67

Class 9 Social Science Chapter 3 Atmosphere and Climate AglaSem · NCERT Solutions

Q7.2 Find out: a. Two stations with the most extreme climate. b. Two stations
influenced by retreating monsoons. c. The two hottest stations in the months of (i)
February (ii) June

a. The two stations with the most extreme climate: Leh and Jodhpur.
'Extreme' means the temperature swings widely through the year, so the measure to use is the
annual range — the warmest monthly average minus the coldest.

Annual temperature range = warmest monthly mean − coldest monthly mean (Table 3.3)
-14° -6° 2° 10° 18° 26° 34°

Leh -8.5 17.2 25.7°C
34°N, 3506 m
Jodhpur 14.9 33.9 19.0°C
26°18'N, 224 m
Delhi 14.4 33.3 18.9°C
29°N, 219 m
Nagpur 20.7 35.5 14.8°C
21°9'N, 312 m
Shillong 9.8 21.1 11.3°C
24°34'N, 1461 m
Kolkata 19.6 30.4 10.8°C
22°34'N, 6 m
Chennai 24.5 33.0 8.5°C
13°4'N, 7 m
Bengaluru 18.9 27.1 8.2°C
12°58'N, 909 m
Mumbai 24.4 30.0 5.6°C
19°N, 11 m
Thiruvananthapuram 26.2 28.7 2.5°C
8°29'N, 61 m

Widest range = the most extreme climate (Leh, then Jodhpur). Narrowest = the most equable (Thiruvananthapuram).

Fig. H — The annual temperature range of all ten stations of Table 3.3, computed and ranked. The
longer the bar, the more extreme the climate.

Leh: 17.2 (July) − (−8.5) (January) = 25.7°C — the widest range in the table

Jodhpur: 33.9 (June) − 14.9 (December) = 19.0°C

Delhi: 33.3 (May and June) − 14.4 (January) = 18.9°C — only 0.1°C behind Jodhpur

So the answer is Leh and Jodhpur, with Delhi so close behind Jodhpur that it is worth naming.
Leh's climate is extreme in an additional sense too: it is the only station in the table with
temperatures below 0°C — in January (−8.5), February (−7.2), March (−0.6) and December
(−5.6).
b. Two stations influenced by the retreating monsoon: Chennai and Thiruvananthapuram.
The retreating (post-monsoon) season runs from October to December, so add each station's
October, November and December rainfall and see whose share is largest.

Page 55 of 67

Class 9 Social Science Chapter 3 Atmosphere and Climate AglaSem · NCERT Solutions

Chennai: 30.6 + 35.0 + 13.9 = 79.5 cm out of 128.6 cm = 61.8% of the year's rain

Thiruvananthapuram: 27.3 + 20.6 + 7.5 = 55.4 cm out of 181.2 cm = 30.6%

Bengaluru: 15.3 + 6.1 + 1.3 = 22.7 cm out of 88.9 cm = 25.5%
(For comparison, Mumbai gets just 4.8 + 1.0 + 0 = 5.8 cm = 3.2%)

Chennai's November alone (35.0 cm) is its wettest month of the whole year — the clearest
possible sign of the retreating monsoon. Bengaluru is a reasonable third answer, being on the
same side of the peninsula.
c. The two hottest stations in (i) February and (ii) June

HOTTEST SECOND HOTTEST NEXT

(i) February Thiruvananthapuram — 27.3°C Chennai — 25.7°C Mumbai 24.4°C

(ii) June Jodhpur — 33.9°C Delhi — 33.3°C Chennai 32.5°C

Why the answer changes completely between February and June — and this is
the real point of part (c): in February it is the middle of winter, and the only thing
that keeps a place warm is being near the equator. So the two hottest are the two
southernmost coastal stations, Thiruvananthapuram (8°29'N) and Chennai (13°4'N).
By June the Sun is overhead in the northern half of India, and the far north-west has
had months of clear, dry, cloudless heating with no sea nearby to moderate it — so
Jodhpur (26°18'N) and Delhi (29°N) take the lead, even though they are the coldest
places in the table in January. The stations that are hottest in June are not the ones
nearest the equator; they are the ones with a continental position. Compare
Thiruvananthapuram, which barely moves at all: 27.3°C in February, 26.6°C in June.

Q7.3 Now find out: a. Why does Shillong experience more rainfall than Kolkata? b. Why
does Delhi receive more rainfall than Jodhpur?

a. Shillong (225.3 cm) against Kolkata (162.5 cm) — the difference is 62.8 cm, and the cause
is relief.
The chapter names three factors that affect precipitation: prevailing winds, mountains, and
seasons. Here the first two act together.

Page 56 of 67

Class 9 Social Science Chapter 3 Atmosphere and Climate AglaSem · NCERT Solutions

SHILLONG KOLKATA

Altitude 1461 m — on the Meghalaya hills 6 m — on the flat delta plain

Annual rainfall 225.3 cm 162.5 cm

Wettest month June — 47.6 cm August — 33.4 cm

June rainfall 47.6 cm 29.0 cm

Both places are fed by the same moist south-west monsoon winds coming off the Bay of
Bengal. Over Kolkata those winds travel across a flat plain only 6 m above sea level, so nothing
forces them upward and only part of their moisture falls. When the same winds reach the hills
on which Shillong stands, they must climb more than 1400 m. Rising air cools, its capacity to
hold water vapour drops — the chapter's own rule is that 'as the air gets warmer, its capacity to
hold water vapour increases', so cooling reverses it — the vapour condenses, and it rains
heavily. That is why the hill station gets 1.4 times the rain of the plain.
b. Delhi (67.0 cm) against Jodhpur (36.6 cm) — Delhi gets 30.4 cm more, nearly twice as
much.

67.0 ÷ 36.6 = 1.83 — Delhi receives about 1.8 times Jodhpur's rain

In the two wettest months: Delhi 19.3 + 17.8 = 37.1 cm; Jodhpur 10.8 + 13.1 = 23.9 cm

Notice first what does not explain it. The two stations are almost twins in the table: Delhi is
219 m above sea level and Jodhpur 224 m, so altitude is out; and Jodhpur at 26°18'N is actually
nearer the equator than Delhi at 29°N, so latitude cannot be the reason either. The answer has
to lie in where each one sits along the monsoon's path, and the chapter's two maps show it.

Page 57 of 67

Class 9 Social Science Chapter 3 Atmosphere and Climate AglaSem · NCERT Solutions

40°N 40°N
68°E 72°E 76°E 80°E 84°E 88°E 92°E 96°E 68°E 72°E 76°E 80°E 84°E 88°E 92°E 96°E
30 June 20 June 20 Sep 25 Sep 5 Oct
25 June 15 June 17 Sep 30 Sep 10 Oct
8 July
5 July
32°N 32°N

10 June
5 June

8 July
24°N 5 July 24°N 17 Sep
30 June 1 June 20 Sep
25 June 25 Sep
20 June 26 May 30 Sep 15 Oct
15 June 22 May 5 Oct
16°N 10 June 16°N 10 Oct

5 June 15 Oct

N N

8°N 8°N

1 June 26 May 22 May

Fig. 3.10 Fig. 3.11
Normal dates of advancing of the south-west monsoon Normal dates of the retreating monsoon

Each red line joins the places the monsoon normally reaches on that date. In June–July the rain
spreads north-west across India; from mid-September it withdraws in the same direction, north-west first.

Figs. 3.10 and 3.11, pages 50–51 — the normal dates on which the south-west monsoon advances
across India and on which it retreats. Each red line is an isochrone: it joins the places the monsoon
normally reaches on that date.

Fig. 3.10 (advancing monsoon): Delhi is crossed in the last week of June, while the desert
corner in which Jodhpur lies is reached only by the 5 July and 8 July lines — the very last part
of India the monsoon arrives in.
Fig. 3.11 (retreating monsoon): withdrawal begins in that same north-western corner, on
17 September, and only then moves east and south.

So Jodhpur has the shortest rainy season of the two — the monsoon arrives there last and
leaves there first. On top of that, by the time the winds have travelled that far inland over dry,
hot land they have already given up most of their moisture, and Jodhpur lies in the desert
region of western Rajasthan where there is no relief barrier to force the air upward.

The rule behind both answers: rain falls where moist air is made to rise and cool.
Shillong gets more than Kolkata because the hills lift the air; Delhi gets more than
Jodhpur because the moist air still reaches it, and for longer. Wherever either of
those two conditions fails — no lifting, or no moisture left — the rainfall total
collapses, which is why Jodhpur (36.6 cm) and Leh (8.5 cm) sit at the bottom of the
table.

Page 58 of 67

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Class 9 Social Science Chapter 3 Atmosphere and Climate
a g l AglaSem · NCERT Solutions

co m
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Now think why a. Thiruvananthapuram has an equable climate? b. Chennai has
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Q7.4

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country? a
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a. Thiruvananthapuram has an equable climate because it is coastal and very near the
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Warmest month: April 28.7°C · coldest month: July and August 26.2°C

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Annual range = 28.7 − 26.2 = 2.5°C — the smallest of all ten stations

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Compare Leh: 25.7°C · Jodhpur: 19.0°C · Delhi: 18.9°C
a g
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Two reasons, both visible in its own row of the table:

Latitude 8°29'N — the nearest station to the equator. Insolation there is high and, more
m a s
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importantly, it barely changes through the year, so there is no cold season to fall into.
.
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Altitude 61 m, on the coast — the sea

a g lasea breezes described on page 46 carry that steadiness
slowly than land, so the land and
ashore. As the chapter says, land and sea breezes 'are essential in creating moderate climatic

m
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Notice the sign of the sea's work: the hottest month is April, before the monsoon, and the
m
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temperature then falls through the rainy season instead of rising. Every month lies between
m a
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26.2°C

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Chennai in June–September: 4.5 + 8.7 + 11.3 + 11.9 = 36.4 cm = 28.3% of the year
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Chennai in October–December: 30.6 + 35.0 + 13.9 = 79.5 cm = 61.8% of the year

Wettest month = November, 35.0 cm

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(Mumbai, on the other coast, gets 95.6% of its rain in June–September)

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During

a se the moist winds from the Arabian Sea have already crossed the land, so they arrive with much
agl less to give. Then in October the wind reverses. The north-east monsoon blows from land to
c
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sea, and the chapter says these winds are cold and dry and bring no rain to most of India — but
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when they pass over the Bay of Bengal they pick up moisture and cause rainfall on the
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eastern coast of India, especially m in Tamil Nadu, Andhra Pradesh and parts of Karnataka.
Chennai is on that coast. Sola
a g its rainy season begins where everyone else's is ending, which is
precisely why the chapter calls the winter monsoon 'important for the rainfall of the south-

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Page 59 of 67