Topic outline

    • Air Around us

      Q23. Why mountaineers carry oxygen cylinders with them, while climbing high mountains?

      Ans. Mountaineers carry oxygen cylinders with them, while climbing high mountains because as we go up higher and higher, level of oxygen decreases.


      Q24. Why do you feel suffocated in a closed space after sometime if a material is burning?

      Ans. Burning of some material releases smoke and soot which is harmful, thus we feel suffocated in a closed space, where some material is burning.


      Q25. Why does the transparent glass of windows appear hazy if not wiped off for long time?

      Ans. Air contains water vapors and dust particles which stick to transparent glass of windows. Thus glass of windows appears hazy.


      Q26. Why is it not advisable to breathe through our mouth?

      Ans. It is not advisable to breathe through our mouth because if we do that, harmful dust particles may enter our body.

      Q27. Dia took an open mouth bottle and dips it upside down into the water. Will the water move inside the bottle? Give a reason to support your answer.

      Ans. No, water will not move inside the bottle because it was filled completely with air and there was no space for air to escape.


      Q28. When an open mouth bottle is tilted and dipped into water, bubbles coming out of the bottle was observed. Explain the reason.

      Ans. When the bottle was tilted, the air was able to come out in the form of bubbles, and water filled up the empty space that the air has occupied.


      Q29. How carbon dioxide enters the atmosphere?

      Ans. Carbon dioxide enters the atmosphere in the following way:

                                i.        Respiration by plants and animals

                               ii.        Burning of fuel

      Q30. List two uses of wind energy.

      Ans. Two uses of wind energy

                                 i.        It is used to pump the ground water.

                                ii.        It is used to generate electricity with the help of windmills.

      Q31. How does weathercock (Wind vane) work?

      Ans. It shows the direction in which the air is moving at that place. Thus, if the wind is blowing from the north, the arrow will point towards the northern direction.

      Q32. Is it possible to light up a candle on the moon? Give reason.

      Ans. No, it is not possible to light up a candle on the moon because there is no oxygen on the moon. Oxygen is one of the basic requirements for burning.


      Q33. Earthworms come out of the soil during heavy rains. Why?

      Ans. When it rains heavily, water fills up all the spaces occupied by the air in the soil. In this situation, animals living in the soil such as earthworms have to come out for respiration.


      Q34. Why does the candle go off after some time when we cover it with a glass tumbler?

      Ans. The amount of oxygen component inside the glass is limited. When most of this oxygen is used up by the burning candle, it can no longer burn and blows out.

      Q35. What happens when air comes in contact with a cool surface?

      Ans. When air comes in contact with a cool surface, air gets cooled and it can no longer hold as much water vapor. Thus water vapor in the air condenses and drops of water appear on cool surface.

      Q36. Why long chimneys are preferred in factories?

      Ans. The burning of fuel produces smoke. Smoke contains a few gases and fine dust particles and is often harmful. Long chimneys in factories take the harmful smoke and gases away from us.


      Q37. What is the role of fine hair and mucus inside the nose?

      Ans. We inhale air when we breathe through our nostrils. Fine hair and mucus are present inside the nose to prevent dust particles from getting into the respiratory system.


      Q38. Why do policemen regulating traffic at a crowded crossing wear a mask to cover his face?

      Ans. Policemen regulating traffic at a crowded crossing wear a mask to cover his face to protect himself from the polluted air that emits from the vehicles which may enters his nose and cause him serious problem.


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