These DAV Class 7 SST Book Solutions Pdf and DAV Class 7 SST Chapter 4 Question Answer – Air Around Us are thoughtfully prepared by experienced teachers.
DAV Class 7 SST Ch 4 Question Answer – Air Around Us
DAV Class 7 SST Ch 4 Solutions – Air Around Us
Something To Know
A. Tick (✓) the correct option.
Question 1.
In normal lapse rate, temperature decreases at the rate of 1°C with every
(a) 165 m ascend
(fa) 175m ascend
(c) 185 m ascend
(d) 195 m ascend
Answer:
(a) 165 m ascend
Question 2.
Which layer is safe for flying aircraft?
(a) troposphere
(b) stratosphere
(c) mesosphere
(d) thermosphere
Answer:
(b) stratosphere
Question 3.
The role of ion particles in the ionosphere is to
(a) absorb ultraviolet rays
(b) enable wireless communication
(c) burn meteors
(d) enable rainfall
Answer:
(b) enable wireless communication
Question 4.
Which one of the following is the main cause of global warming?
(a) air pollution
(b) water pollution
(c) soil pollution
(d) land degradation
Answer:
(a) air pollution
Question 5.
Smog causes
(a) breathing problems
(b) purification of air
(c) heavy rainfall
(d) reduction in temperature
Answer:
(a) breathing problems
B. Fill in the blanks.
1. Atmosphere is mainly composed of three major gases—nitrogen, …………….., ………….. and …………
2. Gases like argon, helium, methane, etc. are present in ……………. amounts in the air.
3. All weather phenomena occur in the ……………..
4. Atmospheric conditions over a long period of time and on a larger area are called …………..
5. The normal air pressure at sea level is …………..
Answer:
1. oxygen, carbon dioxide; helium,
2. small
3. smoke
4. climate,
5. 1,013 millibars.
C. Match the following:
| A | B |
| Mono-oxide gas | (a) Weight or pressure exerted by the air. |
| Weather | (b) Most harmful gas present in the atmosphere. |
| Barometer | (c) The falling of water drops on the Earth’s surface. |
| Atmospheric pressure. | (d) An instrument to measure atmos-pheric pressure. |
| Rainfall | (e) Atmospheric conditions for a specific place covering a short period of time. |
Answer:
| A | B |
| Mono-oxide gas | (b) Most harmful gas present in the atmosphere. |
| Weather | (e) Atmospheric conditions for a specific place covering a short period of time. |
| Barometer | (d) An instrument to measure atmos-pheric pressure. |
| Atmospheric pressure. | (a) Weight or pressure exerted by the air. |
| Rainfall | (c) The falling of water drops on the Earth’s surface. |
D. Answer the following questions in brief.
Question 1.
Name the layers of the atmosphere.
Answer:
Troposphere, Stratosphere, Mesosphere, Ionosphere and Thermosphere.
Question 2.
How do plants absorb nitrogen?
Answer:
Plants absorb nitrogen through the soil.
Question 3.
What is the importance of water vapours in the atmosphere?
Answer:
Water vapours are important because they form clouds that bring rainfall on Earth.
Question 4.
Name the different variables of the atmosphere.
Answer:
Our atmosphere is made up of three major gases—nitrogen (78%), oxygen (21%) and carbon dioxide (0.03%). Apart from these major gases, the atmosphere has also argon, helium, methane, hydrogen, etc. in small amounts. The water vapours and dust particles are other important components present in the atmosphere.
Question 5.
What type of climate does India have?
Answer:
India has the monsoonal type of climate.
E. Answer the following questions
Question 1.
What is the importance of carbon dioxide and oxygen for living beings?
Answer:
Carbon dioxide is an important gas in the atmosphere. It absorbs heat of the Sun and warms up the lower atmosphere of the earth’s surface. Human beings and animals release carbon dioxide during the process of respiration. The green plants use this carbon dioxide to make their food and release oxygen.
It is the oxygen that all the living beings on the earth inhale. In this way, a balance is maintained in the atmosphere. If we cut trees, this balance gets disturbed. We must keep it in mind that the atmosphere is continuously replenished of oxygen by green plants through the process of photosynthesis. A healthy balance of oxygen in the air is, thus, maintained.
Question 2.
Name three major sources of pollutants in the air. Also state the ill-effects of these air pollutants.
Answer:
Carbon mono-oxide, sulphur dioxide and lead particles. These pollutants when released by automobiles cause air pollution which in turn is a cause of several diseases. The smoke particles when combined with fog form smog, causing serious health problems like irritation in eyes, skin diseases, respiratory diseases, etc. Volcanic eruptions, in some countries, also add the gaseous substances in large quantity to the atmosphere. Sometimes forest fires add pollutants and cause further damage to the atmosphere.
Question 3.
What is the importance of ozone gas? Why is global warming a threat to life on the earth?
Answer:
Ozone is a special form of oxygen found in the upper stratosphere and lower mesosphere. This ozone layer is very important as it acts as a filter and absorbs harmful ultraviolet sunrays from reaching the earth’s surface. a result of the sea level would rise, causing floods in the coastal areas. There may be drastic changes in the climate of a place leading to extinction of some plants and animals on Earth. Global warming can be prevented by minimising the use of CO2, CFCs, methane, etc.
Question 4.
How is rainfall caused? Explain it with the help of a diagram.
Answer:
When the hot air rises, it reaches high in the atmosphere where it cools down due to low temperature there. Thus, the water present in the form of water vapours condenses into tiny droplets of water or crystals of ice. In due course of time, these tiny droplets of water join together and form clouds. Due to further cooling, these tiny condensed droplets join and form larger droplets. When these droplets of water become too heavy to float into the air, they fall down on Earth as rainfall or snowfall.
Question 5.
Write the difference between weather and climate.
Answer:
Weather. It refers to the state of the atmosphere that includes its temperature, pressure and humidity for a specific place and for a short period of time. It is hour-to-hour, day-to-day condition of the atmosphere. Thus, it keeps on changing. Climate. It refers to the state of atmospheric condition that includes temperature, rainfall, and pressure over a long period of time and covers a larger area.
Value-Based Question
‘Global warming is threatening the life support system of the earth.’
- How can we relate our life with it? Give examples in support of your answer.
- Explain any two measures to combat this problem.
Answer:
Do yourself with the help of the Internet and other sources.
Something To Do
Question 1.
Collect the weather report of the last week from the newspapers and write it in the following tabular form.
| Day | Monday | Tuesday | Wednesday | Thursday | Friday | Saturday | Sunday |
| Date | |||||||
| Weather | |||||||
| report |
Answer:
Students are suggested to do this activity themselves.
Question 2.
Make a PowerPoint presentation on the following topics and present it is the class,
(a) Global warming
(b) Air pollution
Answer:
Do yourself.
DAV Class 7 Social Science Chapter 4 Question Answer – Air Around Us
A. Tick (✓) the correct option.
Question 1.
The uppermost layer of the atmosphere is
(a) troposphere
(b) stratosphere
(c) mesosphere
(d) thermosphere
Answer:
(d) thermosphere
Question 2.
The temperature is almost constant in the lower part of the
(a) troposphere
(b) stratosphere
(c) mesosphere
(d) thermosphere
Answer:
(b) stratosphere
Question 3.
The ultraviolet rays of the Sun can cause
(a) tuberculosis
(b) skin cancer
(c) allergies
(d) Both (b) and (c)
Answer:
(d) Both (b) and (c)
Question 4.
The most plentiful gas in the air is
(a) hydrogen
(b) oxygen
(c) nitrogen
(d) carbon dioxide
Answer:
(c) nitrogen
Question 5.
Thermosphere lies above
(a) mesosphere
(b) troposphere
(c) stratosphere
(d) None of them
Answer:
(a) mesosphere
Question 6.
Global warming can be prevented by minimising the use of
(a) C02
(b) CFCs
(c) methane
(d) All of them
Answer:
(d) All of them
Question 7.
One of the following which is not a gaseous pollutant is
(a) mono oxide
(b) sulphur dioxide
(c) lead particles
(d) nitrogen
Answer:
(d) nitrogen
Question 8.
The gas having the property of absorbing heat is
(a) Carbon dioxide
(b) oxygen
(c) nitrogen
(d) hydrogen
Answer:
(a) Carbon dioxide
Question 9.
Clouds do not form in the
(a) troposphere
(b) stratosphere
(c) mesosphere
(d) thermosphere
Answer:
(b) stratosphere
Question 10.
A life-supporting gas is
(a) oxygen
(b) nitrogen
(c) hydrogen
(d) carbon dioxide
Answer:
(a) oxygen
B. Very Short Answer Type Questions
Question 1.
What would happen on the earth in the absence of air?
Answer:
The earth would turn into a frozen lifeless planet in the space like any other planet.
Question 2.
Which is the densest layer of the atmosphere?
Answer:
Troposphere is the densest layer of the atmosphere.
Question 3.
Why is the temperature very low in high mountains?
Answer;
In the troposphere, on average, the temperature decreases at a rate of 1°C with every 165 m ascend. That is why, the temperature is very low in high mountains.
Question 4.
What prevents the formation of clouds in the layer of stratosphere?
Answer:
There is total absence of water vapours and dust particles in the layer of stratosphere. This prevents the formation of clouds in that layer.
Question 5.
Which layer of the atmosphere acts as a shield over the earth’s surface?
Answer;
The layer of mesosphere acts as a shield over the earth’s surface.
Question 6.
How is nitrogen beneficial to plants?
Answer:
Nitrogen supports the growth and development of plants.
Question 7.
What is the main cause of global warming?
Answer:
The increase of carbon dioxide in the atmosphere is the ultimate cause of global warming.
Question 8.
What is measured by the use of barometer?
Answer:
The pressure or weight of air is measured by the use of a barometer.
Question 9.
Atmospheric temperature and pressure are opposite to each other on the earth’s surface. What does it mean?
Answer:
Higher the temperature, lower is the pressure.
Question 10.
What type of wind is the monsoon? The monsoon is a seasonal wind. What happens in the absence of rain?
Answer:
The absence of rain causes drought which is a natural calamity. It brings poverty.
Question 11.
What is rain gauge?
Answer:
A rain gauge is an instrument to measure the quantity of rainfall.
C. Short Answer Type Questions
Question 1.
Give three features of troposphere.
Answer:
Troposphere is the most important layer of the atmosphere. Its three features are given below:
- The air we breath in exists in this layer
- Almost all the weather phenomena such as rainfall, fog and hailstorm occur here.
- In this layer, on average, the temperature decreases at the rate of 1°C with every 165 m ascend.
Question 2.
Mention three features of the stratosphere.
Answer:
The stratosphere lies above the troposphere. Three features of this layer are:
- This layer is free from clouds and associated with weather phenomena.
- It provides visibility at its finest.
- This layer provides ideal conditions for flying aeroplanes.
Question 3.
One of the worst calamities of recent times is the super cyclone having a speed of 250 km/h that hit Odisha coast in 1999. It caused the deaths of over 10.000 people Cyclones are classified into the following categories as per their wind speeds.
| Description | Wind Speeds in KNOTS/KMPH |
| (a) Cyclonic storm | 34-47/63-88 |
| (b) Severe cyclonic | 48-63/89-117 |
| (c) Very severe cyclonic | 64-119/118-221 |
| (d) Super cyclonic storm | 120 and above/222 and above. |
Find out some such cyclones and the places affected by them.
Answer:
| Cyclone Type | Year | Place |
| (i) Phailin-a very severe cyclonic storm | Oct, 2013 | Odisha and North-East Andhra coast |
| (ii) Helen-a cyclonic storm | Nov, 2013 | Andhra Pradesh |
Question 4.
State three important uses of weather reports.
Answer:
Three important uses of weather reports are –
- It gives us information regarding daily temperature and pressure conditions of the place where we live on.
- We prepare ourselves for a particular weather condition of a distant place when we set forth for it.
- The weather reports give us also information regarding atmospheric conditions like forecast of temperature, humidity, rainfall, wind velocity, sunrise and sunset. These pieces of information are useful for us in a variety of ways. Hence, we should make it a habit to read the weather report on daily basis.
Question 5.
What is wind? Which type of wind is monsoon? How is it beneficial for us?
Answer:
The air when gets heated due to high temperature of the area rises upward. This causes fall in air pressure and the area, thus, becomes a low pressure area. The space vacated by hot air is replaced by cold, denser air of the surrounding high pressure area. This flow or movement of air is called wind.
Here, it becomes clear that wind always flows from a high pressure area to a low pressure area. Monsoon is a seasonal wind that brings rain on the earth. Our country receives monsoon rains which are essential for agricultural activities. If there is enough rain, farmers harvest good crops, if it comes late or if there is poor rainfall, farmers get disheartened. They fall victim to poverty.
D. Long Answer Type Questions
Question 1.
Describe the composition of air with the help of a diagram.
Answer:
The air that we breathe in is a mixture of many gases. Nitrogen (78%) and oxygen (21%) are the two gases which make up the bulk of atmosphere. Carbon dioxide, helium, ozone, argon and hydrogen are found in small amounts. Apart from these gases, the air also contains some amount of dust particles and water vapours.
Question 2.
Describe how are the various constituents of air important for us.
Answer:
The various constituents of air are-nitrogen, oxygen, carbon dioxide, ozone, helium, argon and hydrogen. Apart from these gases, the air also contains some amounts of dust particles and water vapours. All the constituents of air are important in some way or the other.
(i) Nitrogen – It occupies 78% of the total volume in the air. It is, thus, the most plentiful gas. But it has little importance to living organisms. When we inhale air, a major amount of nitrogen does not utilise inside our body system. But plants need nitrogen for their survival. They absorb it through the soil. In this way, we can say that this gas is indirectly useful for us.
(ii) Oxygen – It is the second major gas in volume which makes up about 21% of the air. It is essential for all living organisms. Therefore, it is said to be a life supporting gas. The atmosphere is continuously replenished of oxygen by green plants through the process of photosynthesis and this keeps a healthy balance of oxygen in the air. Cutting of trees would disturb this balance.
(iii) Carbon Dioxide – It constitutes a very small percentage, i.e. 0.03% of the air, yet it is an important gas in maintaining the life cycle of plants, over the earth. This gas absorbs heat of the sun and warms up the lower atmosphere of the earth’s surface. Human beings and animals release carbon dioxide which is taken in by the green plants.
Here it is worth mentioning that the amount of carbon dioxide released by humans or animals should be equal to the amount used by the plants because only then there would be a perfect balance. However, the balance is upset resulting in causes many environmental problems. The water vapours and dust particles also play an important role in the atmosphere. The dust particles act as hydroscopic nucleus around which water vapours get condensed to form clouds.
Question 3.
Discuss the structure of the atmosphere with the help of a diagram.
Answer:
The atmosphere is divided into four different layers. Starting from the earth’s surface, the four layers are – Troposphere, Stratosphere, Mesosphere and Thermosphere.
(a) Troposphere: It is the densest layer of the atmosphere. We live in this portion. It is this layer of atmosphere where all weather phenomena like rainfall, fog and hailstorm take place. In the troposphere, on an average, the temperature decreases at a rate of 1°C with every 165 m ascend.
(b) Stratosphere: This layer lies above the layer of troposphere. Here the air is calm and clear. The total absence of water vapours and dust particles in this layer prevents the formation of clouds. Thus, it provides visibility at its finest. Aircrafts fly often through the lower layer of the stratosphere because it facilitates visibility.
(c) Mesosphere: It lies above the stratosphere. A special form of oxygen, called ozone is found in the upper stratosphere and lower mesosphere. This ozone gas protects us from the harmful effect of the sunrays.
(d) Thermosphere: It lies above the mesosphere. Here the air is very thin. In the lower layer of thermosphere, ion-particles are present in concentration. These ion-particles are electrically charged and play an important role in our wireless communication. Radio waves can be sent to different places through these ion- particles.