Topic outline

    • Air

      Q43. Why is the greenhouse effect important?

      Ans. Carbon dioxide released in the atmosphere creates a greenhouse effect by trapping the heat radiated from the earth. It is therefore called a greenhouse gas and without it the earth would have been too cold to live in.


      Q44. Why amount of insolation decreases from equator towards poles?

      Ans. Sun rays falls almost vertically on the equator and covers less space whereas sun rays falls at slanting angle on the poles and covers more space. Thus, the amount of insolation decreases from the equator towards the poles.


      Q45. How air circulation takes place?

      Ans. When air is heated, it expands, becomes lighter and goes up. Cold air is denser and heavy. That is why it tends to sink down. When hot air rises, cold air from surrounding area rushes there to fill in the gap. That is how air circulation takes place.

      Q46. Air above us presses us with a great force on our bodies. However, we don’t even feel it. Why?

      Ans. Air above us presses us with a great force on our bodies. However, we don’t even feel it. This is because the air presses us from all directions and our body exerts a counter pressure.


      Q47. Why do astronauts wear space suits on the moon?

      Ans. Astronauts have to wear special protective space suits filled with air when they go to the moon. If they did not wear these space suits, the counter pressure exerted by the body of the astronauts would make the blood vessels burst. The astronauts would bleed.


      Q48. Why temperature in cities much higher than that of villages?

      Ans. Temperature in cities is much higher than that of villages because

                              i.        The concrete and metals in buildings and the asaphalt of roads get heated up during the day. This heat is released during the night.

                             ii.        Also, the crowded high rise buildings of the cities trap the warm air and thus raise the temperature of the cities.


      Q49. Why is the atmosphere essential for life?

      Ans. All living beings on this earth depend on the atmosphere for their survival. It provides us the air we breathe and protects us from the harmful effects of the sun’s rays. Without this blanket of protection, we would be baked alive by the heat of the sun during day and get frozen during night. So it is this mass of air that has made the temperature on the earth liveable.

      Q50. What are the harmful effects arising from the greenhouse effect?

      Ans. When its level in the atmosphere increases due to factory smoke or car fumes, the heat retained increases the temperature of the earth. This is called global warming. This rise in temperature causes the snow in coldest parts of the world to melt. As a result the sea level rises, 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 in the long run.


      Q51. Discuss the importance of stratosphere?

      Ans. Importance of stratosphere

                              i.        Above the troposphere lies the stratosphere. It extends up to a height of 50 km. This layer is almost free from clouds and associated weather phenomenon, making conditions most ideal for flying aeroplanes.

                             ii.        One important feature of stratosphere is that it contains a layer of ozone gas which protects us from the harmful effect of the sun rays.


      Q52. What is the composition of the atmosphere?

      Ans. The air we take in while breathing is actually a mixture of many gases. Nitrogen (78%) and oxygen (21%) are two gases which make up the bulk of the atmosphere. Carbon dioxide (O.3%), helium, ozone, argon (0.93%) and hydrogen are found in lesser quantities. Apart from these gases, tiny dust particles are also present in the air. The pie chart gives you the percentage of different constituents of air.

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