NCERT Solutions Class 9 Social Science (Understanding Society: India and Beyond, Part I) Chapter 3 – Atmosphere and Climate
Circle of Learning • New NCERT textbook (2026-27) • In-text questions, activities and end-of-chapter questions – complete answers
The Big Questions
Answer
What is the composition of the atmosphere?
The atmosphere is a mixture of gases. Nitrogen (78%) and oxygen (21%) are the most abundant, followed by argon (0.93%), carbon dioxide (0.04%) and others (0.03%) such as helium, neon, krypton, xenon, ozone and hydrogen. It also contains water vapour (generally 0.1 to 0.4 per cent) and tiny dust particles.
How do the different layers of the atmosphere affect the planet Earth?
Answer
The troposphere holds the air we breathe and nearly all weather. The stratosphere has the ozone layer that filters harmful ultraviolet radiation. Meteorites burn up in the mesosphere. The thermosphere reflects radio waves back to Earth and is where auroras occur, and light gases escape to space from the exosphere. Together they protect life and control weather and climate.
Answer
What is the mechanism of monsoon?
The monsoon is the seasonal reversal of wind direction caused by unequal heating of land and sea. In summer, land heats faster, creating low pressure over India, so moist winds blow from the high-pressure ocean to the land and bring rain (south-west monsoon). In winter, land cools faster, so high pressure develops over land and cold, dry winds blow from land to sea (north-east monsoon).
Answer
How can we reduce our carbon footprint?
We can walk, cycle or use public transport, switch off appliances when not in use, save water, reuse and recycle, avoid single-use plastics, use renewable energy, plant and protect trees, and adopt sustainable lifestyles.
Think About It (Page 39)
Can you imagine what would happen if there were no atmosphere? Discuss your thoughts with your friends and teachers.
Answer
Without the atmosphere there would be no oxygen to breathe or carbon dioxide for plants, so life could not exist. Harmful ultraviolet radiation from the Sun would reach the surface directly. Without heat being trapped, days would be extremely hot and nights extremely cold. There would be no clouds, rain, wind or weather, no sound (which needs air to travel), and meteors would strike the Earth instead of burning up.
Let's Recall
Answer
How is nitrogen useful for plants?
Plants need nitrogen to make proteins and grow, but they cannot use nitrogen gas directly from the air. Nitrogen-fixing bacteria, such as Rhizobium living in the root nodules of leguminous plants (pulses), and some bacteria in the soil convert atmospheric nitrogen into compounds that plants can absorb. This enriches the soil naturally.
Think About It (Page 45)
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?
Answer
Sample answer: Strong winds have blown dust into our eyes and homes during a dust storm, turned umbrellas inside out during rain, broken tree branches that blocked roads, knocked down electric wires causing power cuts, blown away clothes from the drying line, and made cycling to school very difficult. During cyclones, strong winds can also damage roofs and boats.
Let's Explore (Page 46)
Find out other categories of wind based on speed and their common effects, and share your findings in class.
Answer
Wind | Speed (km/hr) | Common effects |
|---|---|---|
Light air | 1–5 | Smoke drifts and shows wind direction, but wind vanes do not move. |
Gentle breeze | 12–19 | Leaves and small twigs move constantly; light flags extend. |
Moderate breeze | 20–28 | Dust and loose paper are raised; small branches move. |
Fresh breeze | 29–38 | Small trees in leaf begin to sway. |
Near gale | 50–61 | Whole trees move; walking against the wind is difficult. |
Gale | 62–74 | Twigs break off trees; walking is very difficult. |
Strong gale | 75–88 | Slight damage to buildings, such as roof tiles blown off. |
Whole gale | 89–102 | Trees uprooted; considerable damage to buildings. |
Hurricane / Cyclone | 118 and above | Very severe and widespread destruction. |
(These categories are based on the Beaufort wind scale; the book's table already shows calm, light breeze, strong breeze and storm.)
Let's Analyse
Note down the weather report from a local newspaper for two weeks and observe the changes occurring in the weather.
Answer
Guidance and sample: Make a table with columns for date, maximum temperature, minimum temperature, humidity, rainfall, wind and sky condition (sunny/cloudy). After two weeks, observe patterns. For example: "In the first week of September, maximum temperatures stayed around 33°C with high humidity and rain on four days. In the second week, rain stopped, skies cleared, humidity fell and night temperatures dropped slightly." This shows that weather changes from day to day, while the overall pattern reflects the season.
Think About It (Page 48)
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.
Answer
Season (Ṛtu) | Rāgas commonly associated |
|---|---|
Vasanta (spring) | Rāga Basant, Rāga Bahār, Rāga Hindol |
Grīṣhma (summer) | Rāga Dīpak (associated with heat and fire), Rāga Sāraṅg |
Varṣhā (monsoon) | Rāga Megh, Rāga Miyān kī Malhār and other Malhār rāgas |
Śharad (early autumn) | Rāga Bhairav, Rāga Mālaśhrī |
Hemanta (late autumn) | Rāga Mālkauns |
Śhiśhira (winter) | Rāga Śhrī |
Note: Different musical traditions and texts link rāgas to seasons slightly differently; the Malhār–monsoon and Basant–spring links are the most widely accepted.
Let's Explore (Page 52)
Describe in your own words how monsoon affects the lives of the people around you.
Answer
Sample answer: Around us, farmers wait for the monsoon to sow paddy and other kharif crops, so a good monsoon brings good harvests and income, while a delayed or weak monsoon causes worry and higher vegetable prices. The rains fill wells, ponds and reservoirs, ending summer water shortages, and bring relief from heat. However, heavy rain also causes waterlogged roads, traffic jams, school closures, power cuts and diseases like dengue and malaria. Festivals such as Teej and Onam and many local fairs are linked to the monsoon.
Let's Explore (Page 53) – My Carbon Footprint
Tick your daily habits (transport, electricity use, water use, waste and plastics), score yourself (low = 1, medium = 2, high = 3, very high = 4), add up your total score and write two changes for your Climate Action Pledge.
Answer
Sample response:
(i) Transport: I use public transport/carpool – 2 points
(ii) Electricity: I sometimes forget to switch off appliances – 2 points
(iii) Water: I use water judiciously – 1 point
(iv) Waste and plastics: I sometimes use disposable plastics – 2 points
Total score: 7 points (the lowest possible score is 4, the highest 13).
My Climate Action Pledge
1. I will switch off lights and fans every time I leave a room.
2. I will carry a cloth bag and a refillable water bottle instead of using plastic bags and bottles.
Punjab Floods 2025: Classroom Discussion
To what extent did natural factors cause these floods compared to human activities?
Answer
Natural factors triggered the floods: very heavy monsoon rain, intensified by western disturbances, fell in Punjab, Himachal Pradesh and Jammu & Kashmir, while the Satluj, Beas, Ravi and Ghaggar were already flowing high. However, human activities made the damage much worse: weak and old embankments (dhūsī bāndh), houses and farms built too close to rivers, silt reducing river and dam capacity, and late or unclear warnings. So nature caused the flood, but human factors largely decided how destructive it was.
Do you think better planning could have reduced the damage? How?
Answer
Yes. Strengthening and regularly maintaining embankments, stopping construction on floodplains, desilting rivers and reservoirs, releasing dam water in a planned way, and issuing early, clear warnings through mobile phones, radio and local leaders would have reduced losses. Ready relief camps, evacuation plans and safe storage of fodder and grain would also have protected people and animals.
What are the guidelines for the management of floods according to the National Disaster Management Authority (NDMA)?
Answer
Key points of the NDMA flood management guidelines:
(i) Flood forecasting and early warning systems, with timely communication to people.
(ii) Floodplain zoning – regulating construction and land use in flood-prone areas.
(iii) Structural measures: building and maintaining embankments, reservoirs, drainage channels and desilting rivers.
(iv) Flood-proofing of buildings and raised platforms for people and animals.
(v) Watershed management and afforestation in catchment areas.
(vi) Community preparedness, evacuation plans, mock drills, and relief and rehabilitation arrangements.
What role can students/youth play in helping with disaster preparedness?
Answer
Students can spread awareness about warnings and safety rules, take part in school mock drills, learn first aid, and help prepare family emergency kits and evacuation plans. During and after disasters, youth can volunteer with NCC, NSS, Scouts and Guides or local bodies to distribute relief, help the elderly, and share only verified information to stop rumours.
Questions and activities
What is atmosphere? Explain its composition with the help of a pie diagram.
Answer
The atmosphere is the blanket of air surrounding the Earth, held by gravity. It is a mixture of gases vital for life; it shields us from harmful radiation and regulates the Earth's temperature.
Composition (draw a pie diagram with these sectors)
Gas | Percentage | Angle in pie diagram (approx.) |
|---|---|---|
Nitrogen | 78% | 281° |
Oxygen | 21% | 76° |
Argon | 0.93% | 3° |
Carbon dioxide | 0.04% | less than 1° (thin line) |
Others (helium, neon, krypton, xenon, ozone, hydrogen) | 0.03% | less than 1° (thin line) |
The atmosphere also contains water vapour (0.1 to 0.4 per cent, which helps form clouds and rain) and dust particles.
Draw a labelled diagram of the structure of atmosphere.
Answer
Guidance (follow Fig. 3.3): Draw a vertical bar with height in km on the side and mark these layers from bottom to top:
(i) Troposphere – 0 to about 12 km (weather, clouds); boundary: tropopause.
(ii) Stratosphere – up to 50 km; mark the ozone layer and an aeroplane; boundary: stratopause.
(iii) Mesosphere – up to 80 km; mark meteors; boundary: mesopause.
(iv) Thermosphere – 80 to 700 km; mark the ionosphere, aurora and satellites.
(v) Exosphere – uppermost layer with very thin air.
Answer
Which are the four main seasons of India?
According to the Indian Meteorological Department (IMD), the four seasons are: (i) Winter – December to early April; (ii) Summer or pre-monsoon – April to June (up to July in north-western India); (iii) Monsoon or rainy season (advancing monsoon) – June to September; and (iv) Post-monsoon (retreating monsoon) – October to December.
Answer
Why do you not feel the pressure of the atmosphere?
Air presses on our bodies from all sides with great force, but we do not feel it because our bodies exert an equal counter-pressure from inside. The pressure inside our bodies is equal to the atmospheric pressure and cancels the pressure from outside.
Answer
In which layer of the atmosphere do aeroplanes fly and why?
Aeroplanes fly in the stratosphere (just above the troposphere). This layer is ideal for flying because it is free of clouds and other weather disturbances such as rain, storms and turbulence, giving a smooth and safe flight.
Answer
Distinguish between the following
a. The troposphere and stratosphere
b. The south-west monsoon and north-east monsoon
a.
Troposphere | Stratosphere |
|---|---|
Lowest layer, average height about 12 km. | Lies above the troposphere, extending up to 50 km. |
Temperature decreases with increasing altitude. | Temperature does not decrease with altitude (it decreases only in the troposphere and mesosphere). |
Contains the air we breathe, most water vapour and clouds; nearly all weather occurs here. | Free of clouds and weather disturbances; ideal for flying aeroplanes. |
Separated from the layer above by the tropopause. | Contains the ozone layer, which filters ultraviolet radiation; bounded above by the stratopause. |
b.
South-west monsoon | North-east monsoon |
|---|---|
Also called the summer monsoon; June to September. | Also called the winter monsoon; October to February. |
Land heats faster than the sea, creating low pressure over land. | Land cools faster than the sea, creating high pressure over land. |
Moist winds blow from sea to land. | Cold, dry winds blow from land to sea. |
Brings most of India's annual rainfall. | Generally dry, but brings rain to the east coast (Tamil Nadu, Andhra Pradesh, parts of Karnataka) after picking up moisture over the Bay of Bengal. |
Do it yourself: Study Table 3.3 (average monthly temperatures and rainfall for 10 stations) and convert the figures into 'temperature and rainfall' graphs like Fig. 3.14. See if you can arrive at some broad generalisations about our diverse climatic conditions.
Answer
How to draw: For each station, mark the months (Jan–Dec) on the horizontal axis. Use the left vertical axis for temperature (°C) and draw a line graph; use the right vertical axis for rainfall (cm) and draw bars for each month.
Broad generalisations
(i) Most stations receive the bulk of their rainfall between June and September (south-west monsoon).
(ii) Winters are generally dry over most of India.
(iii) Coastal and southern stations (Mumbai, Chennai, Thiruvananthapuram) have small temperature ranges, while interior northern stations (Delhi, Jodhpur) and Leh have large ranges.
(iv) Rainfall decreases from east to west across northern India (Shillong, Kolkata, Delhi, Jodhpur) and is highest on windward slopes and hills.
(v) Temperature generally falls with altitude, as seen at Shillong and Leh.
Question 7.1
Re-arrange the 10 stations according to their distance from the equator.
From nearest to farthest: Thiruvananthapuram (8°29'N), Bengaluru (12°58'N), Chennai (13°4'N), Mumbai (19°N), Nagpur (21°9'N), Kolkata (22°34'N), Shillong (24°34'N), Jodhpur (26°18'N), Delhi (29°N), Leh (34°N).
Question 7.2
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. Leh (from –8.5°C in January to 17.2°C in July, a range of 25.7°C) and Jodhpur (14.9°C in December to 33.9°C in June, a range of 19.0°C). Delhi is almost as extreme (14.4°C to 33.3°C, a range of 18.9°C).
b. Chennai (30.6 cm in October and 35.0 cm in November, its wettest months) and Thiruvananthapuram (27.3 cm in October and 20.6 cm in November).
c. (i) February: Thiruvananthapuram (27.3°C) and Chennai (25.7°C).
(ii) June: Jodhpur (33.9°C) and Delhi (33.3°C).
Question 7.3
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) lies at 1461 m on the Meghalaya plateau. Moisture-laden winds of the Bay of Bengal branch of the monsoon are forced to rise up the hills, cool and pour heavy rain on the windward slopes. Kolkata (162.5 cm) lies on the flat plains at only 6 m, where the winds are not forced to rise so sharply.
b. Delhi (67.0 cm) receives rain from the Bay of Bengal branch of the monsoon, which moves up the Ganga plains from east to west. By the time the winds reach Jodhpur (36.6 cm), in the Thar desert farther west, they have lost most of their moisture. Also, the Arabian Sea branch passes parallel to the Aravallis without being forced to rise, so Jodhpur gets little rain.
Question 7.4
Now think why
a. Thiruvananthapuram has an equable climate?
b. Chennai has more rainfall only after the fury of the monsoon is over in most parts of the country?
Answer
c. Leh has moderate precipitation almost throughout the year?
Answer
a. Thiruvananthapuram is close to the equator (8°29'N), so it gets high insolation all year, and it lies on the coast, where the sea and land and sea breezes moderate temperature. Its temperature stays between 26.2°C and 28.7°C, a range of only 2.5°C.
b. Chennai is on the east (Coromandel) coast, which lies in the rain shadow of the Western Ghats during the south-west monsoon, so it gets little rain from June to September. In October–November, the north-east (winter) monsoon winds pick up moisture over the Bay of Bengal and bring heavy rain to Tamil Nadu, so Chennai's wettest months are October and November.
c. Leh is a high-altitude cold desert (3506 m) beyond the Great Himalaya, in the rain shadow of the monsoon. It receives only small amounts of precipitation (8.5 cm a year), spread over most months, mainly as snowfall from western disturbances in winter and a little rain in summer, so it has no single rainy season.
Question 7.5
Despite these differences across regions, can you observe any substantial evidence to conclude that the monsoons provide a very strong framework, lending overall climatic unity to the whole country?
Answer
Yes. (i) At almost every station, rainfall is concentrated in a few months and winters are dry – a seasonal rhythm set by the monsoon. (ii) Mumbai, Kolkata, Delhi, Jodhpur, Nagpur and Shillong all get most of their rain from June to September from the south-west monsoon. (iii) Chennai and Thiruvananthapuram receive their rain from the advancing and retreating monsoon. (iv) At many stations, temperatures fall slightly in July–August after the rains arrive. (v) The whole country follows the same cycle of winter, summer, rainy and retreating monsoon seasons. Thus the monsoon binds India's diverse climates into one unified pattern, and agriculture and life across the country depend on it.
Collect pictures of houses and clothing of people from different regions of India. Examine whether they reflect any relationship with the climatic conditions or the relief of those regions.
Answer
Region | Houses | Clothing | Link with climate/relief |
|---|---|---|---|
Rajasthan (hot desert) | Thick mud or stone walls, small windows, flat roofs | Loose, light cotton clothes; turbans and ghunghat cover the head | Keeps out heat and sand; protects from the sun |
Ladakh/Himachal (cold mountains) | Thick stone and wood walls, small windows; sloping roofs in snowy areas | Thick woollen clothes, caps, long robes (goncha) | Retain heat; slopes let snow slide off |
Kerala/Konkan (heavy rain) | Steep sloping tiled roofs, raised floors | Light cotton mundu or lungi | Rain drains quickly; cotton suits the humid heat |
Assam/North-East (heavy rain, floods) | Bamboo houses on stilts | Light cotton clothes such as the mekhela chador | Stilts protect from floods and dampness; bamboo is locally available |
Conclusion: Houses and clothing clearly reflect the climate and relief of each region.
Extra Important Questions
Multiple Choice Questions
1. The ozone layer is found in the
(a) Troposphere (b) Stratosphere (c) Mesosphere (d) Exosphere
Answer: (b) Stratosphere
2. Most meteorites entering from space burn up in the
(a) Troposphere (b) Stratosphere (c) Mesosphere (d) Thermosphere
Answer: (c) Mesosphere
The word 'monsoon' is derived from the Arabic word 'mausim', which means:
Answer
(a) Rain (b) Wind (c) Season (d) Cloud
Answer: (c) Season
4. Climate is the average of weather conditions usually over
(a) One year (b) Ten years (c) Thirty years or more (d) One season
Answer: (c) Thirty years or more
5. In the traditional Indian calendar, Varṣhā ṛtu corresponds to
(a) March–April (b) May–June (c) July–August (d) November–December
Answer: (c) July–August
Which work written around the 5th century CE mentions the date of onset of the monsoon over central India?
Answer
(a) Arthaśhāstra (b) Bṛihatsaṁhitā (c) Meghadūtam (d) Kṛiṣhiparāśhara
Answer: (c) Meghadūtam by Kālidāsa
Short Answer Questions
Distinguish between weather and climate.
Answer
Weather refers to the hour-to-hour and day-to-day conditions of the atmosphere and can change significantly from day to day. Climate is the sum total of weather conditions and variations over a large area for an extended period, usually thirty years or more.
Explain the difference between a sea breeze and a land breeze.
Answer
A sea breeze blows from sea to land during the day, especially in the afternoon, because land becomes warmer than the sea, forming low pressure over land. A land breeze blows from land to sea at night because land cools faster than the sea; as the temperature and pressure difference is small, its speed is low. Both moderate the climate of coastal areas.
Why does temperature decrease from the equator towards the poles?
Answer
Temperature depends largely on insolation, the incoming solar energy intercepted by the Earth. Near the equator, the Sun's rays strike most directly, so insolation is high. Towards the poles, rays strike at a low angle and spread over a larger area, so insolation and temperature decrease.
Answer
What is the importance of the thermosphere?
In the thermosphere (80 to 700 km), temperature rises rapidly as gas molecules absorb X-rays and short-wave ultraviolet radiation. It helps radio transmission by reflecting radio waves back to Earth, contains the ionosphere, and is where the auroras (northern and southern lights) occur.
Long Answer Questions
Explain the mechanism of the south-west and north-east monsoons and their importance for India.
Answer
(i) Monsoon means the seasonal reversal of wind direction during a year, caused by unequal heating of land and sea.
(ii) South-west monsoon (June–September): In summer the Indian landmass heats faster than the oceans, forming low pressure over land while the Indian Ocean has high pressure. Moist winds blow from the Indian Ocean, Arabian Sea and Bay of Bengal towards land and bring most of India's annual rainfall.
(iii) North-east monsoon (October–February): In winter land cools faster, forming high pressure over land and low pressure over seas. Cold, dry winds blow from land to sea, but after crossing the Bay of Bengal they bring rain to Tamil Nadu, Andhra Pradesh and parts of Karnataka.
(iv) Importance: Most agriculture depends on monsoon rain; it fills rivers, reservoirs and wells; it affects transport, festivals and rural employment. Excess rain causes floods, while weak monsoons cause droughts, so the monsoon shapes India's economy and livelihoods.
What is climate change? Explain its causes, effects and the steps needed to tackle it.
Answer
(i) Meaning: Climate change refers to long-term changes in weather patterns such as temperature, rainfall and wind.
(ii) Causes: Mainly human activities – burning fossil fuels, deforestation and industrial pollution – which increase greenhouse gases like carbon dioxide, methane, nitrous oxide and water vapour that trap heat and raise global temperatures.
(iii) Effects: More frequent floods and droughts, melting glaciers, rising sea levels and loss of biodiversity; harm to human health, agriculture and livelihoods, with great impact on women and children.
(iv) Steps: Reduce carbon footprints, use renewable energy, protect forests and adopt sustainable lifestyles. Programmes such as the National Monsoon Mission and Mission Mausam improve forecasting so India becomes 'Weather Ready' and 'Climate Smart'. Every individual's small steps count.