Welcome, students! This comprehensive guide provides detailed, text-backed solutions for all the Questions and activities for Chapter 3: Atmosphere and Climate of the Class 9 Social Science (Geography) NCERT textbook. These answers are compiled directly from the lines of the textbook to help you write precise answers and prepare for your school examinations.
Questions and activities
1. What is atmosphere? Explain its composition with the help of a pie diagram.
Answer:
Definition:
According to the textbook: “The Earth’s atmosphere is composed of a mixture of various gases.” It forms a protective layered blanket of gases surrounding the planet.
Composition of the Atmosphere:
The atmosphere consists of the following gases (as illustrated in Figure 3.2 on Page 2):
Nitrogen (78%): The most abundant gas in the atmosphere, essential to life on the Earth.
Oxygen (21%): The second most abundant gas, essential for respiration of living beings.
Argon (0.93%): An inert gas present in the atmosphere in a lesser quantity.
Carbon Dioxide (0.04%): Essential for photosynthesis in plants and plays a key role in trapping heat (greenhouse effect).
Others (0.03%): Includes trace gases such as helium, neon, krypton, xenon, ozone, and hydrogen.
Water Vapour and Dust Particles: “Besides these, the atmosphere also consists of water vapour and tiny dust particles. The amount of water vapour in the atmosphere varies, but it generally ranges from 0.1 per cent to 0.4 per cent. It plays a significant role in cloud formation and precipitation.”
(Student Note for Pie Diagram: You can represent the composition by drawing a circle where a 78% sector represents Nitrogen, a 21% sector represents Oxygen, a 0.93% sector represents Argon, a 0.04% sector represents Carbon Dioxide, and a 0.03% sector represents Others.)
2. Draw a labelled diagram of the structure of atmosphere.
Answer:
According to the textbook (Pages 2–5, Fig. 3.3), the atmosphere has a layered structure. The five major layers extending from the Earth’s surface to outer space are:
Troposphere: “The troposphere is the most important layer of the atmosphere, with an average height of about 12 kilometres. In this layer, temperature decreases with increasing altitude. The air we breathe exists here, along with most of the water vapour and clouds. Nearly all the weather phenomena, such as rainfall, fog, and hail, occur in this layer.” The tropopause separates it from the stratosphere.
Stratosphere: “Above the troposphere lies the stratosphere, extending up to 50 kilometres. This layer is ideal for flying aeroplanes because it is free of clouds and other weather disturbances. A notable feature of the stratosphere is that it contains a layer of ozone gas, which shields us by filtering the Sun’s harmful radiation, including ultraviolet radiation.” The stratopause separates it from the mesosphere.
Mesosphere: “Above the stratosphere lies the third layer of the atmosphere, the mesosphere. It extends up to a height of 80 kilometres. In this layer, temperature decreases with increasing altitude. Most meteorites entering from space burn up in the mesosphere.” The mesopause separates it from the thermosphere.
Thermosphere: “In the thermosphere, temperature rises very rapidly with increasing altitude, as the gas molecules in this layer absorb the X-rays and short-wave ultraviolet radiation of the Sun. The thermosphere extends from 80 to 700 km. It also helps with radio transmission by reflecting radio waves transmitted from the Earth back towards it. Ionosphere is a part of the thermosphere.”
Exosphere: “The uppermost layer of the atmosphere is known as the exosphere, characterised by very thin air. Light gases like helium and hydrogen float into space from this layer due to weak gravity.”
3. Which are the four main seasons of India?
Answer:
The Indian Meteorological Department (IMD) has recognised four distinct seasons in India (Page 9):
Winter: “The winter season generally lasts from December to early April. The coldest months of the year are December and January, when the average temperature in the north-west is around 10–15°C. Temperatures increase towards the equator, reaching around 20–25°C in mainland India’s south-east.”
Summer or pre-monsoon: “The summer or pre-monsoon season spans from April to June, or up to July in north-western India. In western and southern regions, the hottest month is April; in northern regions, it is May. The average temperature across most of inland India ranges from 32–40°C.”
Monsoon or rainy (Advancing monsoon): “The monsoon season generally spans from June to September. This season is dominated by the humid south-west summer monsoon, which slowly sweeps across the country in late May or early June. Monsoon rain begins to recede from north India at the beginning of October, and South India typically receives more rainfall during this time.”
Post-monsoon (Retreating monsoon): “The post-monsoon season lasts from October to December. In north-western India, October and November are usually cloudless.”
4. Why do you not feel the pressure of the atmosphere?
Answer:
According to the textbook (Page 5, “DON’T MISS OUT”):
“The air above us exerts a significant force on our bodies, and yet we do not feel it. This is because air presses on us from all sides, and our bodies exert a counter-pressure in response. The pressure inside our bodies is also equal to the atmospheric pressure and cancels the pressure from outside.”
5. In which layer of the atmosphere do aeroplanes fly and why?
Answer:
According to the textbook (Page 4):
Layer: Stratosphere.
Reason: “Above the troposphere lies the stratosphere, extending up to 50 kilometres. This layer is ideal for flying aeroplanes because it is free of clouds and other weather disturbances.”
6. Distinguish between the following:
a. The troposphere and stratosphere
Answer:
| Feature | Troposphere | Stratosphere |
|---|---|---|
| Altitude | Average height of about 12 kilometres. | Extends up to 50 kilometres. |
| Weather | Nearly all weather phenomena, such as rainfall, fog, and hail, occur in this layer. | Free of clouds and other weather disturbances, making it ideal for flying aeroplanes. |
| Temperature | Temperature decreases with increasing altitude. | Contains the ozone gas layer, which absorbs the Sun’s harmful radiation. Temperature increases with height in upper parts. |
b. The south-west monsoon and north-east monsoon
Answer:
| Feature | South-West Monsoon | North-East Monsoon |
|---|---|---|
| Wind Flow Direction | Winds blow from sea to land (across the Indian Ocean, Arabian Sea, and Bay of Bengal). | Winds blow from land to sea (cold and dry winds). |
| Season Span | Active from June to September. | Occurs in India from October to February. |
| Mechanism | Land heats up faster than oceans, creating low pressure over the subcontinent. Winds move from high-pressure ocean to low-pressure land. | Land cools faster than oceans, creating high pressure over the land and low pressure over the seas. |
| Rainfall Distribution | Accounts for most of the rainfall in the country throughout the year. | Generally dry, but causes rainfall on the eastern coast (especially Tamil Nadu, Andhra Pradesh, and parts of Karnataka) after picking up moisture over the Bay of Bengal. |
7. Do it yourself: Table 3.3 shows the average monthly temperatures and rainfall amounts for 10 representative stations. Study these figures on your own and convert them into ‘temperature and rainfall’ graphs. The visual representations will help you grasp their similarities and differences at a glance. One such graph (Fig. 3.14) is already prepared for you. See if you can arrive at some broad generalisations about our diverse climatic conditions.
Reference Table (Table 3.3 data from the textbook):
| Station | Metric | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | Annual Rain |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Bengaluru (12°58’N, 909m) | Temp (°C) | 20.5 | 22.7 | 25.2 | 27.1 | 26.7 | 24.2 | 23.0 | 23.0 | 23.1 | 22.9 | 18.9 | 20.2 | 88.9 cm |
| Rain (cm) | 0.7 | 0.9 | 1.1 | 4.5 | 10.7 | 7.1 | 11.1 | 13.7 | 16.4 | 15.3 | 6.1 | 1.3 | ||
| Mumbai (19°N, 11m) | Temp (°C) | 24.4 | 24.4 | 26.7 | 28.3 | 30.0 | 28.9 | 27.2 | 27.2 | 27.2 | 27.8 | 27.2 | 25.0 | 183.4 cm |
| Rain (cm) | 0.2 | 0.2 | – | – | 1.8 | 50.6 | 61.0 | 36.9 | 26.9 | 4.8 | 1.0 | – | ||
| Kolkata (22°34’N, 6m) | Temp (°C) | 19.6 | 22.0 | 27.1 | 30.1 | 30.4 | 29.9 | 28.9 | 28.7 | 28.9 | 27.6 | 23.4 | 19.7 | 162.5 cm |
| Rain (cm) | 1.2 | 2.8 | 3.4 | 5.1 | 13.4 | 29.0 | 33.1 | 33.4 | 25.3 | 12.7 | 2.7 | 0.4 | ||
| Delhi (29°N, 219m) | Temp (°C) | 14.4 | 16.7 | 23.3 | 30.0 | 33.3 | 33.3 | 30.0 | 29.4 | 28.9 | 25.6 | 19.4 | 15.6 | 67.0 cm |
| Rain (cm) | 2.5 | 1.5 | 1.3 | 1.0 | 1.8 | 7.4 | 19.3 | 17.8 | 11.9 | 1.3 | 0.2 | 1.0 | ||
| Jodhpur (26°18’N, 224m) | Temp (°C) | 16.8 | 19.2 | 26.6 | 29.8 | 33.3 | 33.9 | 31.3 | 29.0 | 20.1 | 27.0 | 20.1 | 14.9 | 36.6 cm |
| Rain (cm) | 0.5 | 0.6 | 0.3 | 0.3 | 1.0 | 3.1 | 10.8 | 13.1 | 5.7 | 0.8 | 0.2 | 0.2 | ||
| Chennai (13°4’N, 7m) | Temp (°C) | 24.5 | 25.7 | 27.7 | 30.4 | 33.0 | 32.5 | 31.0 | 30.2 | 29.8 | 28.0 | 25.9 | 24.7 | 128.6 cm |
| Rain (cm) | 4.6 | 1.3 | 1.3 | 1.8 | 3.8 | 4.5 | 8.7 | 11.3 | 11.9 | 30.6 | 35.0 | 13.9 | ||
| Nagpur (21°9’N, 312m) | Temp (°C) | 21.5 | 23.9 | 28.3 | 32.7 | 35.5 | 32.0 | 27.7 | 27.3 | 27.9 | 26.7 | 23.1 | 20.7 | 124.2 cm |
| Rain (cm) | 1.1 | 2.3 | 1.7 | 1.6 | 2.1 | 22.2 | 37.6 | 28.6 | 18.5 | 5.5 | 2.0 | 1.0 | ||
| Shillong (24°34’N, 1461m) | Temp (°C) | 9.8 | 11.3 | 15.9 | 18.5 | 19.2 | 20.5 | 21.1 | 20.9 | 20.0 | 17.2 | 13.3 | 10.4 | 225.3 cm |
| Rain (cm) | 1.4 | 2.9 | 5.6 | 14.6 | 29.5 | 47.6 | 35.9 | 34.3 | 30.2 | 18.8 | 3.8 | 0.6 | ||
| Thiruvananthapuram (8°29’N, 61m) | Temp (°C) | 26.7 | 27.3 | 28.3 | 28.7 | 28.6 | 26.6 | 26.2 | 26.2 | 26.5 | 26.7 | 26.6 | 26.5 | 181.2 cm |
| Rain (cm) | 2.3 | 2.1 | 3.7 | 10.6 | 20.8 | 35.6 | 22.3 | 14.6 | 14.6 | 27.3 | 20.6 | 7.5 | ||
| Leh (34°N, 3506m) | Temp (°C) | -8.5 | -7.2 | -0.6 | 6.1 | 10.0 | 14.4 | 17.2 | 16.1 | 12.2 | 6.1 | 0.0 | -5.6 | 8.5 cm |
| Rain (cm) | 1.0 | 0.8 | 0.8 | 0.5 | 0.5 | 0.5 | 1.3 | 1.3 | 0.8 | 0.5 | – | 0.5 |
7.1. Now look at Table 3.3 again. Re-arrange the 10 stations according to their distance from the equator.
Answer:
Arranged from nearest to the equator (lowest latitude) to farthest from the equator (highest latitude):
Thiruvananthapuram: Latitude 8°29’N
Bengaluru: Latitude 12°58’N
Chennai: Latitude 13°4’N
Mumbai: Latitude 19°N
Nagpur: Latitude 21°9’N
Kolkata: Latitude 22°34’N
Shillong: Latitude 24°34’N
Jodhpur: Latitude 26°18’N
Delhi: Latitude 29°N
Leh: Latitude 34°N
7.2 Find out:
a. Two stations with the most extreme climate.
Answer:
1. Leh: Has extreme cold climate, with temperature dropping to -8.5°C in January and rising to 17.2°C in July.
2. Jodhpur (or Delhi): Jodhpur has extreme hot and dry desert climate, with temperature rising to 33.9°C in June and dropping to 14.9°C in December.
b. Two stations influenced by retreating monsoons.
Answer:
1. Chennai: Receives major rainfall in October (30.6 cm) and November (35.0 cm).
2. Thiruvananthapuram: Receives high rainfall in October (27.3 cm) and November (20.6 cm).
c. The two hottest stations in the months of:
(i) February
Answer: Thiruvananthapuram (27.3°C) and Chennai (25.7°C).
(ii) June
Answer: Jodhpur (33.9°C) and Delhi (33.3°C).
7.3. Now find out:
a. Why does Shillong experience more rainfall than Kolkata?
Answer: Shillong is situated in the Khasi Hills at a high altitude of 1,461 metres. The relief features act as a physical barrier that traps moisture-laden winds of the Bay of Bengal branch, forcing them to rise and causing high orographic rainfall (225.3 cm). Kolkata, being in the plains, lacks high mountain barriers, receiving lower rainfall (162.5 cm).
b. Why does Delhi receive more rainfall than Jodhpur?
Answer: Delhi is located further east and gets rainfall from both branches of the Southwest monsoon. Jodhpur lies further west in Rajasthan, where the Aravalli hills run parallel to the Arabian Sea winds (causing no barrier to intercept winds), and the Bay of Bengal winds have already lost most of their moisture by the time they reach Rajasthan.
7.4. Now think why
a. Thiruvananthapuram has an equable climate?
Answer: Thiruvananthapuram is close to the Equator (8°29’N) and is located along the coast. The maritime influence (moderating land and sea breezes) regulates the climate, preventing extreme temperature ranges throughout the year.
b. Chennai has more rainfall only after the fury of the monsoon is over in most parts of the country?
Answer: During the advancing southwest monsoon (June–September), Chennai lies in the rain-shadow of the Western Ghats. However, during the retreating monsoon season (October–November), northeast winds blow over the Bay of Bengal, pick up moisture, and hit the Coromandel coast directly, bringing heavy rain to Chennai.
c. Leh has moderate precipitation almost throughout the year?
Answer: Leh is located at a very high altitude (3,506 metres) in the trans-Himalayan region. The high Himalayan mountain ranges block the entry of moisture-laden monsoon winds, placing Leh in a rain-shadow zone with very low precipitation (8.5 cm annually) mostly as snow.
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, the monsoon provides a unifying framework because:
1. The seasonal reversal of the wind system affects the entire country, defining the agricultural calendar and seasons.
2. Farmers across almost all states rely directly on monsoon rainfall for sowing and growing crops.
3. The cultural life, daily routines, and traditional festivals of India are deeply linked with the monsoon season, tying the diverse regions together.
8. 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:
Relationship with Clothing:
Hot and Humid Regions (e.g., Kerala, Tamil Nadu): People wear light-colored, loose cotton clothes (like lungis and cotton sarees) to stay cool.
Cold Mountain Regions (e.g., Ladakh, Kashmir):** People wear thick woolens, long coats (pherans), and wool caps to protect themselves from sub-zero temperatures.
Relationship with Housing:
- Heavy Rainfall Areas (e.g., Assam, Western Ghats): Houses have sloped roofs so rainwater runs off easily. In flood-prone regions, houses are built on stilts.
- Hot and Dry Regions (e.g., Rajasthan): Traditional houses have thick mud walls and flat roofs to keep the interior cool.
- High-Altitude Cold Deserts (e.g., Leh): Houses are made of sun-dried bricks with thick walls and double-glazed windows to conserve heat.