Class 9 Social Geography Chapter 2 Atmosphere: Structure, Air Pressure and Air Circulation
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Part II: Geography
Atmosphere: Structure, Air Pressure and Air Circulation
Lesson-Based Questions &Answers
Short Answer Type Questions
1. What is meant by atmosphere? Briefly describe its composition with data.
Ans: The gaseous envelope of air surrounding the Earth and extending some distance above the surface is called the “atmosphere.” The atmosphere is composed of various gases, such as nitrogen 78.08% and oxygen 20.94%. Besides these, there are small amounts of argon 0.93%, carbon dioxide 0.036%, and other gases like neon, helium, methane, krypton, hydrogen, ozone, xenon, etc., constituting about 0.014%.
2. Into what main layers can the atmosphere be divided based on chemical composition? Briefly describe their characteristics.
Ans: Based on chemical composition, the atmosphere is mainly divided into two parts: Homosphere and Heterosphere.
Now, a brief discussion of these two layers:
(a) Homosphere: From the Earth’s surface up to about 80 km, the composition of atmospheric gases remains almost uniform; hence this layer is called the homosphere. Based on temperature, this layer is further divided into three parts: Troposphere, Stratosphere, and Mesosphere. The boundary between the homosphere and heterosphere is called the mesopause.
(b) Heterosphere: The layer of the atmosphere above the mesopause is called the heterosphere. As one goes higher from the mesopause, temperature increases rapidly. Due to this, the chemical composition of gases changes. In this layer, gases arrange themselves according to their molecular weight, forming distinct layers such as nitrogen layer, oxygen layer, helium layer, and hydrogen layer. The nitrogen layer extends from about 80 km to 200 km. The oxygen layer extends up to about 1125 km, and the helium layer up to about
3540 km. The hydrogen layer extends up to about 10,000 km.
3. Based on altitude and variation of temperature, into how many layers is the atmosphere divided? Describe with characteristics.
Ans: Based on altitude and temperature variation, the atmosphere is divided into five layers: Troposphere, Stratosphere, Mesosphere, Thermosphere, and Exosphere. Their characteristics are discussed below:
(a) Troposphere: It is the lowest layer of the atmosphere. Its height is not the same everywhere, but the average height is about 12 km. Since it is closest to the Earth’s surface, it contains a large amount of water vapor. Weather phenomena like clouds, rainfall, storms, and winds occur in this layer.
(b) Stratosphere: The layer just above the troposphere is called the stratosphere. The boundary between these two layers is called the tropopause. In the stratosphere, temperature gradually increases. The lower part has a temperature of about –60°C, which gradually increases to about 0°C in the upper part. This layer contains the ozone layer, whose molecules absorb ultraviolet rays from the Sun, causing an increase in temperature. The upper boundary of this layer is called the stratopause.
(c) Mesosphere: The layer above the stratopause is the mesosphere. It extends up to about 80 km. At its upper boundary, called the mesopause, the temperature drops to about –100°C.
(d) Thermosphere: The layer above the mesopause is the thermosphere. It extends from about 80 km to around 400 km. In this layer, temperature canrise up to about 1650°C. The density of air becomes extremely low. Radiowaves are reflected from this layer.
(e) Exosphere: Above the thermosphere, from about 400 km to 1000 km, lies the exosphere. At such high altitudes, the density of air molecules is ex-tremely low. Hydrogen and helium gases predominate here. The temperature may rise up to about 5550°C.
4. Discuss the factors responsible for variation in atmospheric pressure with examples.
Ans: Air is a gaseous substance, yet it has weight and exerts pressure. As altitude increases from the Earth’s surface, air density and pressure decrease. The variation in atmospheric pressure is mainly due to two factors: (a) temperature of air and (b) altitude of the Earth’s surface.
(a) Temperature of air: The distribution of heat on the Earth’s surface depends on latitude. When temperature increases, air pressure decreases. Coldair, being denser and containing less water vapor, exerts higher pressure. Thus, higher temperature leads to lower pressure. Therefore, pressure is lower near the equator and higher towards the poles.
(b) Altitude of the Earth’s surface: As altitude increases above sea level, the amount of atmospheric gases decreases. With decreasing density, the mass of air reduces, resulting in lower pressure. For every 900 feet increase in altitude, air pressure decreases by about 1 inch.
5. Discuss the characteristics of the major pressure belts of the Earth.
Ans: Atmospheric pressure is not uniform over the Earth. Due to variations in pressure, wind movement also varies. The Earth is divided into four main pressure belts: Equatorial low-pressure belt, Subtropical high-pressure belt, Subpolar low-pressure belt, and Polar high-pressure belt.
(a) Equatorial low-pressure belt: This lies between about 10°N and 10°Slatitudes. Due to direct overhead sun rays throughout the year, air becomes warm and less dense, creating low pressure. Moist air rises upward, and winds remain generally calm.
(b) Subtropical high-pressure belt: This lies between about 25°–35° latitudes in both hemispheres. Warm air from the equatorial region movespoleward, cools, and descends near the Tropics, forming high-pressure zones. These are also known as horse latitudes.
(c) Subpolar low-pressure belt: Located between about 60°–70° latitudes in both hemispheres. Due to the movement of air towards subtropical regions,
pressure decreases here, forming low-pressure zones.
(d) Polar high-pressure belt: At the poles, due to extremely low temperatures and lack of water vapor, air remains dense, creating permanent high-pressure zones.
6. Describe the importance of the atmosphere in creating a favourable natural environment on Earth.
Ans: The atmosphere plays a vital role in creating a suitable environment for life on Earth. It supports the existence of living organisms by providing essential gases, water, and climatic conditions. It protects life by absorbing harmful ultraviolet radiation from the Sun. It also helps in rainfall and weather changes, thereby maintaining environmental balance.
7. What is wind? Discuss the causes of wind formation.
Ans: Moving air is called wind. Wind movement is of two types: horizontal and vertical. The main causes of wind are differences in temperature and atmospheric pressure. Wind always flows from high-pressure areas to low-pressure areas. When air becomes warm, it becomes lighter and rises upward. Moist air also rises. To maintain pressure balance, air from surrounding highpressure areas moves in, creating wind.
8. What is the main cause of wind formation? Briefly describe the factors determining its speed and direction.
Ans: The main cause of wind formation is the variation in temperature and atmospheric pressure. The factors determining wind speed and direction are:
(a) Pressure gradient force: This force arises due to differences in atmospheric pressure and causes wind movement. The rate of pressure change between two places is called the pressure gradient.
(b) Gravitational force: Earth’s gravity holds the atmosphere around it and influences air movement. As altitude increases, gravitational pull decreases, leading to reduced pressure.
(c) Centrifugal force (Coriolis force): Due to Earth’s rotation, an outward force is generated, called centrifugal force. This causes deflection in wind direction, known as the Coriolis effect. Winds deflect to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. This is known as Ferrel’s Law.
(d) Frictional force: Friction affects wind movement. Due to uneven surface features like mountains, forests, and buildings, wind speed decreases. Over smooth surfaces like deserts and oceans, wind speed increases.
9. What is meant by Coriolis force? Describe its role in determining wind direction.
Ans: The Coriolis force is the apparent force caused by the Earth’s rotation, which deflects moving air. It plays an important role in determining wind direction. Due to this force, winds in the Northern Hemisphere are deflected to the right, while in the Southern Hemisphere they are deflected to the left. This deflection influences global wind patterns significantly.
10. What is meant by “pressure gradient force”? What is its role in wind movement?
Ans: The force generated due to differences in atmospheric pressure, which causes wind movement, is called the “pressure gradient force.” In other words, the rate of change of atmospheric pressure between two places is called the pressure gradient. This rate depends on the difference in pressure and the distance between the two places. Due to this pressure gradient, the speed and direction of wind in the atmosphere are affected and may change.
11. Briefly write the role of Earth’s gravitational force in wind movement.
Ans: The gravitational force of the Earth acts as a driving force in wind movement. It holds the entire atmosphere surrounding the Earth. As altitude increases from the Earth’s surface and sea level, the gravitational pull decreases, resulting in a gradual decrease in air pressure or weight.
12. What is meant by naming of winds? How are winds named in a place?
Ans: Winds that blow over the Earth’s surface at different times of the year, from different directions and with varying speeds, are given specific names. Generally, winds are named according to the direction from which they blow. For example, a wind blowing from the south is called a southerly wind, and a wind blowing from the west is called a westerly wind. Sometimes, winds are also named after the region or place from which they originate. For example, winds blowing over or coming from the sea are called ‘seawinds,’ and winds blowing across deserts are called ‘desert winds.’
13. How is wind speed measured? What are its units?
Ans: Wind speed is measured with an instrument called an anemometer. Another instrument called an anemograph is used to automatically record both wind direction and speed.
The unit of wind speed is ‘knot.’ One knot means one nautical mile per hour. One nautical mile equals 1.854 kilometers.
14. How are winds classified? Briefly discuss with examples.
Ans: Based on their extent, winds are classified into three categories: primary winds, secondary winds, and local winds.
15. What is meant by primary winds? Show their distribution with adiagram and mention their main characteristics.
Ans: The regular movement of air over the Earth associated with permanent pressure belts is called “primary” or “planetary winds.” These are also known as permanent or prevailing winds. These winds continuously blow from the subtropical and polar high-pressure belts towards the equatorial and subpolar low-pressure belts in both hemispheres. The three main types of primary winds are trade winds, westerlies, and polar winds.
16. What is meant by secondary winds? Describe their role in determining the climate of a place with examples.
Ans: The air movements that are generated in different regions of the Earth due to variations in relief features, differences in extent, and regional and seasonal pressure variations are called “secondary winds.” These include cyclonic winds, anticyclonic winds, air masses, fronts, monsoon winds, etc. Secondary winds play an important role in determining the climate of aplace, as they bring about changes in weather conditions.
17. What are local winds? How do they influence the weather of a place? Briefly discuss with examples.
Ans: The air movements that occur over a limited area due to variations in landforms and differences in altitude are called “local winds.” They are also known as temporary or irregular winds. Some examples of local winds are seabreeze, land breeze, valley breeze, loo, chinook, and foehn.
Local winds are caused by differences in local relief and temperature. They bring changes in the weather of a specific region.
18. What is meant by “cyclonic wind”? How many types are there and what are they? Briefly mention their effects on weather or climate.
Ans: When strong winds from surrounding high-pressure areas rush towards a low-pressure center in tropical regions and collide, creating a circular motion, it is called a “cyclonic wind.” Cyclones are of two types: tropical cyclones and extratropical (temperate latitude) cyclones.
Cyclonic winds significantly affect the weather and climate of a place. They often cause dense cloud formation and heavy rainfall. If the upper air becomes extremely cold, hailstorms and thunderstorms with lightning may occur. Afterward, the sky clears, strong winds continue to blow, and the weather becomes cooler.
19. What is an “air mass”? How is it classified? What is its role in determining the climate of a place?
Ans: A large body of air having uniform characteristics of temperature and humidity is called an “air mass.” When air remains stationary for a long time, it gets influenced by the underlying surface and acquires its temperature and moisture characteristics. Based on the source region and characteristics, air masses are classified into four types:
(a) Continental tropical air mass
(b) Maritime tropical air mass
(c) Continental polar air mass
(d) Maritime polar air mass
Air masses have a significant influence on the climate of a place. As an airmass moves over a region, it acquires the characteristics of that region. Air masses originating from oceans carry a large amount of moisture, making the weather humid. On the other hand, air masses moving over tropical deserts are dry and hot.
20. What is meant by ‘front’? How is it formed? Briefly discuss the relationship between climate and fronts.
Ans: When two air masses with opposite characteristics of temperature, humidity, pressure, and density meet but do not mix immediately, a boundary surface or line is formed between them; this is called a “front.” Fronts are formed under two conditions:
(a) One air mass must be colder and heavier than the other.
(b) The air flow must be convergent so that the two air masses move towards each other from opposite directions, with the warm lighter air lying above the cold heavier air in a state of equilibrium.
Based on characteristics and nature, fronts are classified into four types: cold front, warm front, stationary front, and occluded front.
There is a close relationship between fronts and climate. In frontal zones, due to opposing pressure gradients, air convergence occurs. As the front advances, changes in temperature and humidity lead to cloud formation, making the climate of that region humid.
21. What is meant by “monsoon wind”? How is it formed? In which regions of the Earth is its effect clearly seen?
Ans: Seasonal winds that blow depending on the change of seasons arecalled “monsoon winds.” These are regional winds of tropical and subtropical
regions.
During summer, the southwest and southeast monsoon winds blow from the Arabian Sea and the Bay of Bengal. In winter, dry northeast monsoon winds absorb moisture from the Bay of Bengal and then move towards South India.
During summer, monsoon winds bring heavy rainfall to the southern part of Meghalaya, the foothills of Assam, and the western slopes of the Western Ghats.
22. Answer the following with reasons:
(a) Why do most weather phenomena occur in the troposphere?
Ans: The troposphere is the lowest layer of the atmosphere, with an average height of about 12 km. Being closest to the Earth’s surface, it contains a large amount of water vapor. Hence, clouds, rainfall, storms, and other weather activities occur mainly in this layer.
(b) What will be the effect if the amount of carbon dioxide increases in the atmosphere?
Ans: An increase in carbon dioxide in the atmosphere will cause breathing difficulties for living organisms and may lead to serious problems. It will also result in climatic changes and an increase in the Earth’s surface temperature.
(c) Why is the pressure of dry air higher than that of moist air?
Ans: Moist air contains water vapor, which makes it lighter and reduces its pressure. In contrast, dry air has less water vapor and is denser, resulting inhigher pressure. In general, an increase in temperature reduces air pressure.
(d) How does the ozone layer benefit living beings?
Ans: Ozone molecules absorb harmful ultraviolet rays coming from the Sun. In this way, the ozone layer protects living organisms on Earth.
(e) Why is air pressure highest at sea level?
Ans: Air is compressible, so the lower layers become more compressed. As compression increases, density increases, which leads to higher pressure. Since sea level is the lowest part of the atmosphere, air pressure is highest there.
(f) Why does the vertical extent of the troposphere differ between the equatorial and polar regions?
Ans: In the equatorial region, the Sun’s rays fall vertically, resulting in maximum heating. Towards the poles, the rays are slanting, so the temperature is lower.
(g) Why is horizontal wind movement generally not felt in the equatorial low-pressure belt?
Ans: In the equatorial region, pressure remains low due to high moisture content. The heated air rises vertically, so horizontal wind movement is generally not experienced.
23. Answer the following briefly:
(a) Up to what height does the atmosphere extend?
Ans: The atmosphere extends up to about 10,000 km above the Earth’s surface.
(b) Up to what height does the chemical composition of atmospheric gases remain nearly uniform?
Ans: The chemical composition remains nearly uniform up to about 80km above the Earth’s surface.
(c) What is the boundary between the homosphere and heterosphere called?
Ans: The boundary is called the ‘mesopause.’
(d) What is Ferrel’s Law?
Ans: Due to the Earth’s rotation, winds are deflected to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. This is calledFerrel’s Law.
(e) What is the Beaufort scale? Briefly write its usefulness with example.
Ans: The Beaufort scale, developed by British scientist Francis Beaufort, is a scale from 0 to 12 used to estimate wind speed and its effects. It helps in understanding the nature and impact of wind based on its speed.
(f) What is lapse rate?
Ans: The decrease in air temperature by about 6.5°C for every 1 km increase in altitude is called the “lapse rate.”
24. Write short notes:
(a) Homosphere
Ans: The layer of the atmosphere up to about 80 km, where the composition of gases remains nearly uniform, is called the homosphere. It is divided into three parts: troposphere, stratosphere, and mesosphere. The boundary between the homosphere and the heterosphere is called the mesopause.
(b) Heterosphere
Ans: The layer above the mesopause is called the heterosphere. As altitude increases, temperature rises rapidly, causing changes in chemical composition. Gases arrange themselves according to molecular weight into layers, such as nitrogen, oxygen, helium, and hydrogen layers.
(c) Relationship between air temperature, altitude, and air pressure
Ans: As air temperature increases, air expands and its density decreases. With increase in altitude, atmospheric pressure decreases.
(d) Polar high-pressure belt
Ans: The polar regions are extremely cold and covered with ice, with almost no water vapor. Hence, permanent high pressure exists in these regions, known as the polar high-pressure belt.
(e) Wind system
Ans: Wind system refers to the continuous movement of air that helps in transferring heat, moisture, and physical properties of the atmosphere from one place to another.
(f) Pressure gradient
Ans: The force generated due to differences in atmospheric pressure that causes wind movement is called the pressure gradient.
(g) Trade winds
Ans: Winds blowing from the subtropical high-pressure belts (around 30°Nand 30°S) towards the equatorial low-pressure belt are called trade winds.
(h) Horse latitudes
Ans: The regions between about 30° and 35° latitudes in both hemispheres are called horse latitudes.
(i) Roaring forties
Ans: The region between 40° and 60° latitudes in the Southern Hemisphere, dominated by strong westerly winds over oceans, is called the “Roaring Forties.”
(j) Anticyclone
Ans: When high-pressure conditions prevail over a large area and air flows outward in a circular manner from the center, it is called an anticyclone.
(k) Jet stream
Ans: A fast-flowing narrow air current in the upper atmosphere, generally from west to east, is called a jet stream.
(l) Isobar
Ans: Lines joining places of equal atmospheric pressure on a map are called isobars.
(m) Tropical cyclone
Ans: A cyclonic system formed around a low-pressure center in tropical regions with strong circular winds is called a tropical cyclone.
25. Write the differences:
(a) Horizontal flow and vertical flow
Ans: Air moving parallel to the Earth’s surface is called horizontal flow, whereas air moving upward is called vertical flow.
(b) Wind and air mass
Ans: Moving air is called wind, whereas a large body of air with uniform characteristics is called an air mass.
(c) Tropical cyclone and extratropical cyclone
Ans: A cyclone formed in tropical regions around a low-pressure center is called a tropical cyclone, whereas cyclones formed in temperate and high latitude regions are called extratropical cyclones.
(d) Sea breeze and land breeze
Ans: Wind blowing from sea to land during the day is called sea breeze, while wind blowing from land to sea at night is called land breeze.
(e) Mountain wind and valley wind
Ans: Cold air flowing down from mountains at night is called mountain wind, whereas warm air moving upward from valleys during the day is called valley wind.
(f) Cyclone and anticyclone
Ans: A cyclone is a system where winds move in a circular motion around a low-pressure center, whereas an anticyclone is a system where winds moveoutward from a high-pressure center.
(g) Cold front and warm front
Ans: A cold front is formed when cold air replaces warm air, whereas a warm front is formed when warm air rises over cold air and replaces it.
(h) Troposphere and stratosphere
Ans: The troposphere is the lowest layer of the atmosphere where weather phenomena occur. The stratosphere lies above it, where temperature increases with altitude and the ozone layer is present.
26. Choose the correct answer:
( a ) Where is the ozone layer located?
Ans: In the stratosphere.
(b) What is the percentage of oxygen in the atmosphere?
Ans: 20.94%
(c) The main cause of wind movement is:
Ans: Difference in pressure.
(d) The instrument used to measure wind speed is:
Ans: Anemometer
(e) The unit of wind speed is:
Ans: Knot
(f) Monsoon winds belong to which category?
Ans: Secondary winds
(g) What is the name of cyclones in the western Pacific region?
Ans: Typhoon
Additional Questions and Answers
1. In what works can we use argon gas?
Ans: It is used in the preparation of electric bulbs, welding work, and similar applications.
2. What is the cause of the recent increase in Earth’s temperature?
Ans: In recent times, the number of vehicles has increased worldwide, and the use of coal and fossil fuels has also increased. As a result, the amount of carbon dioxide in the atmosphere has risen, leading to an increase in the Earth’s temperature.
3. What is meant by a pressure cell?
Ans: Due to differences in temperature between land and water surfaces, variations in air pressure occur. In such cases, smaller pressure cells are formed within larger pressure systems.
4. What is meant by the radio wave layer?
Ans: The ionosphere, which contains electrically charged particles (ions), is called the radio wave layer because radio waves are reflected from this layer.
5. What is a wind vane?
Ans: A wind vane is an instrument used to determine the direction of the wind accurately.
6. What is a valley breeze?
Ans: Air over highlands is less dense and absorbs less heat, while the denser air in valleys heats up quickly. As a result, air flows upward along mountain slopes, which is called a “valley breeze.”
7. Where are deltas formed?
Ans: Deltas are formed at the mouth of rivers.
Multiple Choice Questions (MCQs)
1. What is the atmosphere?
(a) A solid layer of Earth
(b) A liquid layer surrounding Earth
(c) A gaseous envelope surrounding Earth
(d) A rocky outer crust
Ans: (c)
2. Which gas is found in the highest proportion in the atmosphere?
(a) Oxygen
(b) Nitrogen
(c) Carbon dioxide
(d) Argon
Ans: (b) 3. What is the approximate percentage of oxygen in the atmosphere?
(a) 78%
(b) 20.94%
(c) 0.93%
(d) 0.036%
Ans: (b)
4. Up to what height does the homosphere extend?
(a) 50 km
(b) 80 km
(c) 100 km
(d) 200 km
Ans: (b)
5. The boundary between homosphere and heterosphere is called:
(a) Tropopause
(b) Stratopause
(c) Mesopause
(d) Ionosphere
Ans: (c)
6. Which is the lowest layer of the atmosphere?
(a) Stratosphere
(b) Mesosphere
(c) Troposphere
(d) Thermosphere
Ans: (c)
7. In which layer do most weather phenomena occur?
(a) Thermosphere
(b) Troposphere
(c) Exosphere
(d) Mesosphere
Ans: (b)
8. What is the average height of the troposphere?
(a) 5 km
(b) 8 km
(c) 12 km
(d) 20 km
Ans: (c)
9. Which layer contains the ozone layer?
(a) Troposphere
(b) Stratosphere
(c) Mesosphere
(d) Exosphere
Ans: (b)
10. What is the main function of the ozone layer?
(a) Reflect radio waves
(b) Absorb ultraviolet rays
(c) Produce oxygen
(d) Increase pressure
Ans: (b)
11. Which layer has the lowest temperature?
(a) Mesosphere
(b) Troposphere
(c) Stratosphere
(d) Thermosphere
Ans: (a)
12. What happens to air pressure with increase in altitude?
(a) Increases
(b) Remains constant
(c) Decreases
(d) Fluctuates
Ans: (c)
13. Wind always flows from:
(a) Low pressure to high pressure
(b) High pressure to low pressure
(c) Equator to poles
(d) Land to sea
Ans: (b)
14. What is the unit of wind speed?
(a) Meter
(b) Knot
(c) Pascal
(d) Joule
Ans: (b)
15. Which instrument measures wind speed?
(a) Barometer
(b) Thermometer
(c) Anemometer
(d) Hygrometer
Ans: (c)
16. Which instrument measures wind direction?
(a) Wind vane
(b) Barometer
(c) Thermometer
(d) Altimeter
Ans: (a)
17. What is the equatorial pressure belt?
(a) High pressure belt
(b) Low pressure belt
(c) Neutral belt
(d) Variable belt
Ans: (b)
18. The subtropical regions are known for:
(a) Low pressure
(b) High pressure
(c) No pressure
(d) Variable pressure
Ans: (b)
19. The pressure belt near 60° latitude is:
(a) Equatorial low
(b) Subtropical high
(c) Subpolar low
(d) Polar high
Ans: (c)
20. Polar regions have:
(a) Low pressure
(b) High pressure
(c) Medium pressure
(d) No pressure
Ans: (b)
21. What is Coriolis force?
(a) Force due to gravity
(b) Force due to rotation of Earth
(c) Force due to pressure
(d) Force due to friction
Ans: (b)
22. In Northern Hemisphere, wind deflects to:
(a) Left
(b) Right
(c) Upward
(d) Downward
Ans: (b)
23. What are trade winds?
(a) Local winds
(b) Seasonal winds
(c) Permanent winds
(d) Temporary winds
Ans: (c)
24. Monsoon winds are:
(a) Permanent winds
(b) Local winds
(c) Seasonal winds
(d) Polar winds
Ans: (c)
25. What is a cyclone?
(a) High pressure system
(b) Low pressure system with circular winds
(c) Straight wind flow
(d) Calm air
Ans: (b)
26. Anticyclones are associated with:
(a) Low pressure
(b) High pressure
(c) No pressure
(d) Equal pressure
Ans: (b)
27. What is an air mass?
(a) Small air pocket
(b) Large body of air with uniform properties
(c) Wind current
(d) Storm
Ans: (b)
28. What is a front?
(a) Wind direction
(b) Boundary between two air masses
(c) Pressure line
(d) Temperature zone
Ans: (b)
29. What is lapse rate?
(a) Increase in temperature with height
(b) Decrease in temperature with height
(c) Pressure increase
(d) Wind speed change
Ans: (b)
30. What is sea breeze?
(a) Wind from land to sea
(b) Wind from sea to land
(c) Wind from pole to equator
(d) Wind from equator to pole
Ans: (b)
31. Which layer reflects radio waves?
(a) Troposphere
(b) Stratosphere
(c) Ionosphere
(d) Mesosphere
Ans: (c)
32. Which factor primarily controls wind speed?
(a) Temperature
(b) Pressure gradient
(c) Humidity
(d) Altitude
Ans: (b)
33. What is the main cause of formation of pressure belts?
(a) Earth’s rotation only
(b) Uneven heating of Earth
(c) Ocean currents
(d) Rainfall
Ans: (b)
34. Which type of front forms when cold air replaces warm air?
(a) Warm front
(b) Cold front
(c) Stationary front
(d) Occluded front
Ans: (b)
35. Which air mass is dry and hot?
(a) Maritime polar
(b) Continental tropical
(c) Maritime tropical
(d) Continental polar
Ans: (b)
36. What happens in horse latitudes?
(a) Strong winds
(b) Calm conditions
(c) Heavy rainfall
(d) Storms
Ans: (b)
37. Which wind is known as “Roaring Forties”?
(a) Trade winds
(b) Polar winds
(c) Westerlies
(d) Monsoon winds
Ans: (c)
38. Which force balances pressure gradient force in upper atmosphere?
(a) Gravity
(b) Friction
(c) Coriolis force
(d) Heat energy
Ans: (c)
39. Which region receives heavy rainfall due to monsoon winds?
(a) Sahara Desert
(b) Western Ghats
(c) Antarctica
(d) Greenland
Ans: (b)
40. Which type of wind blows over a small area and for a short time?
(a) Primary wind
(b) Secondary wind
(c) Local wind
(d) Planetary wind
Ans: (c)
