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DAV Class 7 SST Chapter 4 Question Answer Air Around Us
DAV class 7 sst question answer chapter 4 Air Around Us is given below. Here DAV class 7 Social Science Question Answer is provided with great explanation.
A. Tick the correct option.
1. In normal lapse rate, temperature decreases at the rate of 1°C with every
Answer: 165 m ascend
2. Which layer is safe for flying aircrafts?
3. The role of ion-particles in the ionosphere is to
Answer: enable wireless communication
4. Which one of the following is the main cause of global warming?
Answer: air pollution
5. Smog causes
Answer: 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 is called ___________.
5. The normal air pressure at sea level is ___________.
Answer: (1) oxygen, carbon dioxide (2) small (3) troposphere (4) climate (5) 1,013 millibar
C. Match the following:
Answer: (1) b, (2) e, (3) d, (4) a, (5) c
D. Answer the following questions in brief.
1. Name the layers of the atmosphere.
Answer: The layers of atmosphere are troposphere, stratosphere, mesosphere and thermosphere.
2. How do plants absorb nitrogen?
Answer: Plants absorb the nitrogen through the soil.
3. What is the importance of water vapours in the atmosphere?
Answer: Water vapours are important because they form clouds that bring rainfall on the earth.
4. Name the different variables of atmosphere.
Answer: The different variables of atmosphere are water vapor, dust particles and ozone.
5. What type of climate does India have?
Answer: India has monsoonal type of climate.
E. Answer the following questions.
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, carbon dioxide and oxygen are important for living beings.
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 are major sources of pollutants in the air. 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 and 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.
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 protects the Earth from harmful ultraviolet (UV) rays from the Sun. This layer, thus, acts as a shield over the earth’s surface. Without the Ozone layer in the atmosphere, life on Earth would be very difficult.
Global warming is a threat to life on the earth as it causes the snow in coldest parts of the world to melt. As 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.
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. 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 snow fall, depending upon the atmospheric temperature of the region.
5. Write the difference between weather and climate.
Answer: Weather – It refers to the state of 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, pressure over a long period of time and covers a larger area.