June 2022 – Page 13 – Jharkhand Board Solution

JAC Class 7 Social Science Solutions Geography Chapter 5 Water

June 4, 2022June 1, 2022 by Prasanna

JAC Board Class 7th Social Science Solutions Geography Chapter 5 Water

JAC Class 7th Geography Water InText Questions and Answers

Question 1.
Why water is important for us?
Answer:
Water is the most useful and easily available thing on the earth for the survival. It is useful in many ways. We require water for drinking, cleaning, washing, cooking, bathing, putting out fire, etc.

Question 2.
Suggest some ways in which water can be conserved in your home and in your school.
Answer:
Some ways in which water can be conserved in our home and in our school are:

Use only the amount of water required.
We should not play with water.
We should repair the leakage taps.
We should try to minimise the wastage of water.
We should close the tap after use.
Rainwater harvesting tequniques should be applied.
We should not pollute water.
Water recycling should be done.

JAC Class 7th Geography Wate Textbook Questions and Answers

Question 1.
Answer the following questions.
(i) What is precipitation?
Answer:
Precipitation is the falling of moisture in the form of rainfall, snow, fog, sleet and hailstorm.

(ii) What is water cycle?
Answer:
The process by which water continuously changes its form and circulates between oceans, seas, atmosphere and land is called as water cycle.

(iii) What are the factors affecting the height of the waves?
Answer:
The factors affecting the height of the waves are winds, earthquakes, under water disturbances, volcanic eruptions. The waves become bigger when the winds are stronger.

(iv) Which factors affect the movement of ocean water?
Answer:
The factors which affect the movement of ocean water are winds, temperature, gravitational pull of the sun, the earth and the moon. Apart from these, cold and warm currents also affect the movement of ocean current.

(v) What are tides and how are they caused?
Answer:
In a day, the rhythmic rise and fall of ocean or sea water which occurs twice are called as tides. They are caused by the strong gravitational pull exerted by the sun and moon on the surface of the earth.

(vi) What are ocean currents?
Answer:
The streams of water which flows constantly on the ocean’s surface in definite direction are called the ocean currents.

Question 2.
Give reasons.
(i) Ocean water is salty.
Answer:
Salt in the ocean comes from two sources: runoff from the land and openings in the seafloor. Rocks on land are the major source of salts dissolved in seawater. Rainwater that falls on land is slightly acidic, so it erodes rocks. Ocean water seeps into cracks in the seafloor and is heated by magma from the Earth’s core.

(ii) The quality of water is deteriorating.
Answer:
The quality of water is deteriorating because the portable water which is available is not always of good and pure in terms of quality. This is due to industrial effluents and outflow . and untreated water of factories and . industries get mixed into the rivers and streams. Sewer water also get mixed with them. Hence, it is unfit and poisonous for human and for other living being’s consumption.

Tick (√) the correct answer.

Question 3.

(i) The process by which water continually changes its form • and circulates between oceans, atmosphere and land
(a) Water cycle
(b) Tides
(c) Ocean currents
Answer:
(a) Water cycle

(ii) Generally the warm ocean currents originate near
(a) Poles
(b) Equator
(c) None of these
Answer:
(b) Equator

(iii) The rhythmic rise and fall of ocean water twice in a day is called
(a) Tide
(b) Ocean current
(c) Wave
Answer:
(a) Tide

Question 4.
Match the following.

(i) Caspian Sea	(a) Largest lake
(ii) Tide	(b) Periodic rise and fall of water
(iii) Tsunami	(c) Strong seismic waves Streams of water
(iv) Ocean currents	(d) moving along definite paths
	(e) Water cycle

Answer:

(i) Caspian Sea	(a) Largest lake Periodic rise
(ii) Tide	(b) and fall of water
(iii) Tsunami	(c) Strong seismic waves
(iv) Ocean currents	(d) Streams of water moving in along definite paths

Question 5.
(For Fun) Be a Detective
(i) The name of one river is hidden in each of the sentences below. Spot it. Example: Mandira, Vijayalakshmi and Surinder are my best friends
Answer:
Ravi
(a) The snake charmer’s bustee, stables where horses are housed, and the piles of wood, all caught fire accidentally. (Hint: Another name for River Brahmaputra)

(b) The conference manager put pad, material for reading and a pencil for each participant. (Hint: A distributary on the Ganga-Brahmaputra delta)

(d) Bhavani germinated the seeds in a pot (Hint: Look for her in West Africa)

(e) “I am a zonal champion now” declared the excited atheletic. (Hint: The river that has he biggest basin in the world)

(f) The tiffin box rolled down and all the food fell in dusty potholes. (Hint: Rises in India and journeys through Pakistan)

(g) Malini leaned against the pole when she felt that she was going to faint. (Hint: Her delta in Egypt is famous)

(h) Samantha mesmerised everybody with her magic tricks. (Hint: London is situated on her estuary)

(i) “In this neighbourhood, please don’t yell! Owners of these houses like to . have peace”. Warned my father when . we moved into our new flat”. (Hint: colour!)

(j) ‘Write the following words, Marc!’ “On”, “go”, “in” said the teacher to the little boy in KG Class. (Hint: Rhymes with ‘bongo’). Now make some more on your own and ask your classmates to spot the hidden name. You can do this with any name: that of a lake, mountains, trees, fruits, school items, etc.
Answer:
(a) Teesta
(b) Padma
(c) Orange
(d) Niger
(e) Amazon
(f) Indus
(g) Nile
(h) Thames
(i) Yellow
(j) Congo

Carry on Detective
(ii) With the help of an atlas, draw each river which you discoverd in For fun (i), on an outline map of the world. Answer: Student need to do it on their own.

JAC Class 7th Geography Water Important Questions and Answers

Multiple Choice Questions

Question 1.
The word Tsunami derived from a Japanese word which means
(a) Ocean waves
(b) Harbour waves
(c) Ocean wind
(d) None of these
Answer:
(b) Harbour waves

Question 2.
World Water Day is celebrated on
(a) 22nd March
(b) 22nd May
(c) 24th March
(d) 28th July
Answer:
(a) 22nd March

Question 3.
The earth surface is …….covered by water.
(a) one-fourth
(b) one-third
(c) three-fourth
(d) half
Answer:
(c) three-fourth

Question 4.
The sources of fresh water are
(a) river, spring, salt lakes
(b) pond, river, glacier
(c) ocean, sea, river
(d) glacier, sea, river
Answer:
(b) pond, river, glacier

Question 5.
…….. has a saline water body.
(a) Glenwood Springs
(b) The Sambar lake
(c) The Amazon river
(d) None of these
Answer:
(b) The Sambar lake

Question 6.
The percentage of freshwater foundin rivers are
(a) 0.01%
(b) 0.00001%
(c) 0.001%
(d) 0.0001%
Answer:
(d) 0.0001%

Question 7.
A huge tidal wave is also called
(a) a Tsunami
(b) a tide
(c) a super wave
(d) all of these
Answer:
(a) a Tsunami

Question 8.
When the water covers much of the shore by rising to its highest level then the tide is called as
(a) Spring tide
(b) Neap tide
(c) Low tide
(d) igh tide
Answer:
(d) igh tide

Question 9.
The following is not a result of high tides
(a) generation of electricity
(b) growth of bananas
(c) better fishing
(d) better navigation
Answer:
(b) growth of bananas

Question 10.
The current which originates near the equator and moves towards the poles are
(a) warm ocean currents
(b) frozen ocean current
(c) cold ocean currents
(d) tidal ocean currents
Answer:
(a) warm ocean currents

Very Short Answer Type Questions

Question 1.
Which condition causes evaporation of water from earth’s surface?
Answer:
The condition which causes evaporation of water from earth’s surface is the sun’s heat.

Question 2.
Which place was the epicentre of the earthquake of 26th December, 2004?
Answer:
Sumatra was the epicentre of the earthquake of 26th December, 2004.

Question 3.
What was the magnitude of 26th December, 2004 earthquake?
Answer:
The magnitude of 26th December, 2004 earthquake was 9.0 on the Richter scale.

Question 4.
What happens in the areas where warm and cold current meet?
Answer:
The areas where warm and cold current meet, there they experience a foggy and misty weather which makes navigation very difficult.

Question 5.
Which place/s are the best fishing grounds in the world?
Answer:
The best fishing grounds in the world are the seas around eastern coast of North America and Japan.

Question 6.
What are the major sources of fresh water?
Answer:
The major sources of fresh water are river, lakes, springs, glaciers and ponds.

Question 7.
Is it possible to float in the Dead Sea? Why?
Answer:
Yes, it is possible to float in the Dead Sea because it becomes very dense by the increased salt contents.

Question 8.
From where cold currents originates?
Answer:
Cold current originates from the poles.

Question 9.
What do you mean by waves?
Answer:
The water of the ocean surface rises and falls alternatively, they are known as waves.

Question 10
Which is the southernmost point ofIndia? What happened in 2004?
Answer:
Indira point is the southernmost point of India. It submerged due to Tsunami in 2004.

Short Answer Type Questions

Question 1.
What happens during high tide and low tide?
Answer:
When high tide occurs waves rise very high and water covers much of the sea shore. When low tide occurs water falls to its lowest level and go back and recedes from the shore.

Question 2.
Define salinity? What is the salinity of seas and oceans?
Answer:
Salinity is the amount of salt in grams present in 1000 grams of water. The average salinity of the oceans is 35 parts per thousand.

Question 3.
Name the different types in which the movements of ocean w ater can be categorized.
Answer:
The movements of ocean water can be categorized as

waves
currents
tides

Question 4.
What is the initial sign or indication of a tsunami?
Answer:
The initial sign or indication of a tsunami is that there is a rapid withdrawal and pull-out of water from the coastal region followed by destructive and disastrous wave.

Question 5.
What do you mean by spring tide and neap tide?
Answer:
Spring tides occurs during the full moon and new moon days, when the sun, the earth and the moon are in the same line and the tides are at its highest level.Neap tide occurs when the moon is in its first and last quarter, then the ocean water get drawn in diagonally opposite directions by the gravitational pull of sun and earth which results in low tides.

Question 6.
In which way waterbodies are distributed on the surface of the earth?
Answer:
The following table gives the distribution of water in percentage

Saline water	Oceans	97.3
Fresh water	Ground water	0.68
	Ice caps	2.0
	Fresh water lakes and Inland seas	0.009
	Salt lakes	0.009
	Atmosphere	0.0019
	Rivers	0.0001
	Total	100.00

Question 7.
Differentiate between warm ocean current and cold ocean current.
Answer:
Difference between:

Warm ocean currents	Cold ocean currents
• These originates near the equator and move towards the poles.	• These carry water , from the polar or higher latitudes to tropical or lower latitudes.
• Such as – The Gulf Stream	• Such as – The Labrador Ocean Current.
• It brings warm temperature over the surface of the land.	• It bring the cold temperature over surface of the land.

Question 8.
Differentiate between waves and tides.

Waves	Tides
• Waves happens all day long means 24 hours a day.	• Tides happens twice a day; once early morning and late at night.
• Due to the different actions of the wind, there are up and down movements of ocean water are called as waves.	• Due to the gravitational pull of the sun and the moon, there are up and down movement of ocean water are called as tides.
• The waves are not so useful’. As a matter of fact, they can be destructive and devastating.	• Tides are very useful.

Question 9.
What do you understand by vertical circulation of ocean water.
Answer:
When the water surface gets heated by sun, water evaporates and increases the concentration of salts. Surface water becomes more dense and sinks and eventually sub-surface water rises up. Hence, the salinity of ocean water causes vertical circulation.

Question 10.
In which way Tsunami cause?
Answer:
A volcanic eruption, under water landslide, an earthquake shifts large amount of ocean water. Hence, huge and large waves are formed which are known as Tsunami.

Long Answer Type Questions

Question 1.
What are the important and major movements of ocean water?
Answer:
The important movements that occur in oceans can be classified as waves, tides and currents.

Waves occurs when the water on the surface of the ocean rises and falls alternatively. Waves are formed when winds scrape and push across the ocean surface. The bigger the wave becomes when the stronger the wind blows.
Tides are the rhythmic rise and fall of ocean water twice in a day. High tide occurs when water covers much of the shore by rising to its highest level. Low tide occurs, when water falls to its lowest level and recedes and move back from the shore. The strong gravitational pull exerted by the sun and the moon on the earth’s surface causes the tides.
Ocean Currents are the streams of water flowing constantly on the ocean surface in definite directions. The ocean currents may be warm or cold. Normally, the warm ocean currents originate near the equator and move towards the poles. The cold currents carry water from polar or higher latitudes to tropical or lower latitudes. The Labrador Ocean current is cold current while the Gulf Stream is a warm current.

Question 2.
Explain in brief about Tsunami.
Answer:
Tsunami:

Tsunami is a Japanese word which means ‘Harbour waves’ as the harbours get destroyed whenever there is tsunami.
A volcanic eruption, an earthquake or underwater landslides can shift large amounts of ocean water.
Hence, a huge tidal wave known as tsunami which may be as high as 15 m is formed. The largest tsunami ever measured was 150 m high. These waves travel at a speed of more than 700 km per hour.
The tsunami of 2004 caused devastating and disastrous damage in the coastal areas of India. The Indira point in the Andaman and Nicobar islands got submerged after the tsunami.
On 22nd December, 2018, huge, monstrous and gigantic waves crashed into the coastal areas of Java and Sumatra in Indonesia. The volcano named Anak Karakatau erupted again on the following day causing huge damage which took many lives.
These damage caused to life and property are due to the lack of monitoring the early warning systems and knowledge among the coast dwellers.

JAC Class 7 Social Science Solutions

JAC Class 7 Social Science Solutions Geography Chapter 4 Air

June 4, 2022June 1, 2022 by Prasanna

JAC Board Class 7th Social Science Solutions Geography Chapter 4 Air

JAC Class 7th Geography Air InText Questions and Answers

Page 21

Question 1.
Is global warming a serious issue in today’s world?
Answer:
Concern about climate change is much less pervasive in the United States, China and Russia than among other leading nations. Just 44% in the U.S. and Russia, and even fewer in China (30%), consider global warming to be a very serious problem.

Page 23

Question 2.
For ten days note down weather report from a local newspaper and observe the changes occurring in the weather.
Answer:
Students need to do it by their own.

JAC Class 7th Geography Air Textbook Questions and Answers

Question 1.
Answer the following questions.
(i) What is atmosphere?
Answer:
Atmosphere is a huge layer of air that surrounds the earth. It shields and guard us from the harmful rays of the sun. rays of the sun. rays of the sun.

(ii) Which two gases make the bulk of the atmosphere?
Answer:
The two gases which make the bulk of the atmosphere are nitrogen (78% ) and oxygen (21%).

(iii)
Which gas creates greenhouse effect in the atmosphere?
Answer:
The gas which creates greenhouse effect in the atmosphere is carbon dioxide.

(iv) What is weather?
Answer:
An hour to hour, day to day condition of the atmosphere is called as the weather. It is the total atmospheric conditions of a particular place at a particular time regarding temperature, air pressure, clouds, wind, humidity, etc.

(v) Name three types of rainfall?
Answer:
Three types of rainfall are:

Convectional rainfall
Orographic rainfall
Cyclonic rainfall

(vi) What is air pressure?
Answer:
Air pressure is the pressure which is exerted by the weight of air on the earth’s surface.

Tick (√) the correct answer.

Question 2.
(i) Which of the following gases protects us from harmful sun rays?
(a) Carbon dioxide
(b) Nitrogen
(c) Ozone
Answer:
(c) Ozone

(ii) The most important layer of the atmosphere is
(a) Troposphere
(b) Thermosphere
(c) Mesosphere
Answer:
(a) Troposphere

(iii) Which of the following layers of the atmosphere is free from clouds?
(a) Troposphere
(b) Stratosphere
(c) Mesosphere
Answer:
(b) Stratosphere

(iv) As we go up the layers of the atmosphere, the pressure
(a) Increases
(b) Decreases
(c) Remains the same
Answer:
(b) Decreases

(v) When precipitation comes down to the earth in the liquid form, it is called
(a) Cloud
(b) Rain
(c) Snow
Answer:
(b) Rain

Question 3.
Match the following.

(i) Trade winds	(a) Incoming solar energy
(ii) Loo	(b) Seasonal wind
(iii) Monsoon	(c) Horizontal movement of Air
(iv)Wind	(d) Layer of ozone gas
	(e) Permanent wind
	(f) Local wind

Answer:

(i) Trade winds	(e) Permanent wind
(ii) Loo	(f) Local wind
(iii) Monsoon	(b) Seasonal wind
(iv) Wind	(c) Horizontal movement of air

Question 4.
Give reasons.

Wet clothes take longer time to dry on a humid day?
Amount of insolation decreases from equator towards poles?

Answer:
1. The air is full of water vapour on a humid day. So, the evaporation is very slow due to low temperature. That’s why, wet clothes take longer time to dry on a humid day.

2. On equator, insolation comes through on vertical rays. So, it covers up less amount of space but more heat is felt when it goes up from equator towards poles and the sun rays become slanting. Though slanting rays heat up more amount of space, the level of hotness is felt less. That’s why, amount of insolation decrease from equator towards poles.

Question 5.
(For Fun)

(i) Solve this crossword puzzle with the help of given clues:

Across:
6. An Indian tree having extraordinary quality of providing oxygen round the clock
8. Gas present in atmosphere occupying only 0.03% by volume
11. Outermost layer of atmosphere
12. Mixture of many gases
14. Life giving gas
15. Air in motion
16. An indian tree valued highly for medicinal properties
18. Gas protecting us from harmful sun rays
19. Low pressure area

Down
1. Amount of water vapour in air
2. Condensation of water vapours around dust particles in atmosphere
3. Example of local wind blowing in summer in northern india
4. Short term changes in atmosphere
5. Precipitation in liquid form
7. Blanket of air around the earth
9. Instrument to measure pressure
10. Incoming solar radiation
13. Reduces visibility in winters
17. It is time when sun is overhead
Answer:

Across:
6. Peepal
11. Exosphere
14. Oxygen
16. Neem
19. Cyclone

Down:
1. Humidity
3. Loo
5. Rain
9. Barometre
10. Insolation
17. Noon
8. Carbon dioxide
12. Air
15. Wind
18. Ozone

(ii) Make a weather calendar for one week. Use pictures or symbols to show different types of weather. You can use more than one symbol in a day, if the weather changes. For example, the sun comes out when rain stops. An example is given below:

Answer:
Hint: Students can do it in this manner.

JAC Class 7th Geography Air Important Question and Answers

Multiple Choice Questions

Question 1.
In the atmosphere, the most abundant gas is
(a) Oxygen
(b) Carbon dioxide
(c) Nitrogen
(d) Helium
Answer:
(c) Nitrogen

Question 2.
The winds which below constantly throughout the year in a particular direction is known as
(a) Local winds
(b) Seasonal winds
(c) Permanent winds
(d) None of the these
Answer:
(a) Local winds

Question 3.
An hour to hour, day to day condition of the atmosphere is known as
(a) temperature
(b) weather
(c) climate
(d) degree
Answer:
(b) weather

Question 4.
Exosphere is the layer of the atmosphere.
(a) uppermost
(b) middle
(c) lower most
(d) none of these
Answer:
(a) uppermost

Question 5.
The thermosphere extends between
(a) 90 – 370 km
(b) 100 – 350 km
(c) 50 – 300 km
(d) 80 – 400 km
Answer:
(d) 80 – 400 km

Question 6.
The balance of and gets disturbed, if we cut down trees and forests.
(a) oxygen, helium
(b) nitrogen, heiium
(c) oxygen, carbon dioxide
(d) oxygen, nitrogen
Answer:
(c) oxygen, carbon dioxide

Question 7.
The air which we inhale and exhale means breathe exists in the
(a) mesosphere
(b) stratosphere
(c) troposphere
(d) exosphere
Answer:
(c) troposphere

Question 8.
The instrument which measures the temperature is
(a) Barometer
(b) Thermometer
(c) Wind vane
(d) None of these
Answer:
(b) Thermometer

Question 9.
In the atmosphere, the ozone layer exists in the
(a) Stratosphere
(b) Exosphere
(c) Mesosphere
(d) Troposphere
Answer:
(a) Stratosphere

Question 10.
The other name of greenhouse gas is
(a) oxygen
(b) nitrogen
(c) argon
(d) carbon dioxide
Answer:
(b) nitrogen

Very Short Answer Type Questions

Question 1.
What do you mean by smog?
Answer:
Smog is the combination of smoke and fog. It generally occurs during winter season.

Question 2.
What will happen if there is very less rainfall?
Answer:
Water scarcity and drought occurs if there is very less rainfall.

Question 3.
What are the various forms of precipitation?
Answer:
Various forms of precipitation are rain,snow, sleet and hail.

Question 4.
Give a word/term for the hot and dry wind of northern plains of India.
Answer: Loo.

Question 5. Air pressure is highest at which area?
Answer:
Air pressure is highest at the sea level

Question 6.
What are the three types of winds?
Answer:
The three types of winds are:

Permanent winds
Seasonal winds
Local winds.

Question 7.
When air is heated, what occurs?
Answer:
Air expands and becomes lighter and goes up when the air is heated.

Question 8.
Ozone layer is important for us. Why?
Answer:
Ozone layer is important for us because it protects and shields us from harmful reactions and effects of the sun rays.

Question 9.
Green plants use carbon dioxide. Why?
Answer:
Green plants use carbon dioxide because it helps them to prepare their food and release oxygen.

Question 10.
What is the consequence and importance of greenhouse gas?
Answer:
The consequence and importance of greenhouse gas is that the earth would have been too cold to live in.

Short Answer Type Questions

Question 1.
What are the instruments called for the measurement of air pressure and the measurement of amount of rainfall?
Answer:
The instruments are called as barometer for the measurement of air pressure and rain gauge for the measurement of amount of rainfall.

Question 2.
What do you mean by a climate of a place or area?
Answer:
The average weather condition of a place or area for a longer period of time constitutes the climate of a place.

Question 3.
What are permanent winds?
Answer:
Winds which blow constantly throughout the year in a particular direction is called as the permanent winds. The trade wind, westerlies and easterlies are the permanent winds.

Question 4.
What is the role of water vapour?
Answer:
One of the major component of the atmosphere is water vapour and it plays a very important role in climatic changes and results in precipitation.

Question 5.
How many types of pollutants are found in the atmosphere?
Answer:
There are mainly two types of pollutants found in the atmosphere

Gaseous – carbon dioxide and smog
Solid – dust and bacteria

Question 6.
Which ty pe of pressure are exerted by cold and hot air?
Answer:
The air expands when heated up hence becomes lighter and goes up. Cold air is heavy and dense so it tends to go down and sinks. When hot air goes up and rises, from surrounding areas, cold air rushes to fill the gap.

Question 7.
Explain the temperature in cities are much higher than that of the villages.
Answer:
In the cities, we find many high rise buildings. The fnetals and concretes in these buildings and the asaphalt of roads get heated up during the day and this heat is released in the night.The other important cause is that in the cities the crowded buildings trap the warm air and hence raise the temperature of the cities. Therefore, the temperature in cities are much higher than that of the villages.

Question 8.
Poles are covered with snow always. Why?
Answer:
From the equator towards the poles the amount of insolation decreases. Hence, the temperature decreases in the same manner. This is the reason why poles are covered with snow always..

Question 9.
What do you mean by global warming?
Answer:
Global warming happens when the level of carbon dioxide increases in the atmosphere due to factory smoke or car fumes and the heat retained increases the temperature of the earth.

Question 10.
Rainfall is important for us when there is excess rain, what happens?
Answer:
For the survival of animals and plants,rainfall is very important. It actually brings fresh water to the surface of the earth. There is water scarcity and drought like situation when there is less rainfall. And, if there is excess rainfall then floods take place which makes the life very difficult to sustain. Many things get damaged such as crops, houses, etc.

Question 11.
In which manner bacteria help plants use nitrogen?
Answer:
For the plant’s survival, nitrogen is very crucial and important. But plants cannot take nitrogen directly from the atmosphere. Hence, bacteria that lives in the soil and roots of some plants take nitrogen from air and changes its form so that the plant can use it.

Long Answer Type Questions

Question 1.
Discuss the different layers of the atmosphere.
Answer:
The atmosphere has five different layers. They are:

Troposphere
Stratosphere
Mesosphere
Thermosphere
Exosphere
Troposphere:
All the weather characteristics occurs here such as fog, rainfall, hailstorm. This is the thickest and the most important layer of the atmosphere. It has the average height of 13 km. We also find the air which we breathe.
Stratosphere:
It lies just above the troposphere and presents the ideal conditions for flying aeroplanes. Stratosphere extends upto a height of 50 km. It also contains the ozone gas layer which protects us from harmful ultraviolet rays of the sun.
Mesosphere:
It lies above the stratosphere. It extends upto the height of 80 kms. In this layer, meteorites bum up on entering from the space.
Thermosphere:
It lies just above the mesosphere. It extends between 80 400 km. Temperature rises very fast with the increase in height in this layer. In thermosphere, radio waves are transmitted from the earth are reflected back to the earth.
Exosphere:
This is the last and the uppermost layer with very thin air. Light gases such as helium and hydrogen float -into the space from exosphere.

Question 2.
What are the different constituents of air? How they are important to us?
Answer:
The different constituents of air are oxygen, nitrogen, carbon dioxide, ozone, helium, argon and hydrogen. Besides these gases, the air also contains some amount of water vapour and dust particles. They are important to us in many ways:

Oxygen:
It is one of the major gas and second most in volume which makes up about 21% of the air. It is also called as life supporting gas. The atmosphere is continuously recharged and restored of oxygen by green plants through the photosynthesis process and thus keeps a healthy and efficient balance of oxygen in the air. Nitrogen: The total volume of nitrogen is about 78% in the air. The major amount of nitrogen is not utilized in our body system when we inhale. But, plants need nitrogen for the well being and survival.

They absorb it through soil and plant roots. Carbon Dioxide: Carbon dioxide is composed of very small percentage around 0.03% of the air. Then also, it is one of the important gas in maintaining the life cycle of plants on the earth. Carbon dioxide absorbs heat of the sun and warms up the lower atmosphere of the surface of the earth. It is taken by the green plants when human beings and animals release it.

JAC Class 7 Social Science Solutions