Topic outline

    • Some Natural Phenomena

      Q43. Suppose you are outside your home and an earthquake strikes. What precaution would you take to protect yourself?

      Ans. If we are outside our home and an earthquake strikes, then

                              i.        We should try to find a clear spot, away from buildings, trees and overhead power lines. Drop to the ground.

                             ii.        If we are in a car or a bus, we should not come out. We should ask the driver to drive slowly to a clear spot. We should not come out till the tremors stop.


      Q44. Name the scale on which the destructive energy of an earthquake is measured. An earthquake measures 3 on this scale. Would it be recorded by a seismograph? Is it likely to cause much damage?

      Ans. The destructive energy of an earthquake is measured by Richter scale. An earthquake of 3 Richter can be recorded by a seismograph. An earthquake of magnitude 3 on Richter scale is often felt but not likely to cause much damage. Really destructive earthquakes have magnitudes higher than 7 on the Richter scale.

      Q45. What precautions would you take to protect yourself during an earthquake if you are at home?

      Ans. In order to protect ourselves during an earthquake we must take following precautions:

                               i.        We should take shelter under a table and stay there till shaking stops.

                              ii.        We should stay away from tall and heavy objects that may fall on us.

                             iii.        If we are in bed then we should not get up and should protect our head with a pillow.


      Q46. Suggest three measures to protect ourselves from lightning.

      Ans. Measures to protect ourselves from lightning

                             i.        A house or a building is a safe place. If we are travelling by car or by bus, we are safe inside with windows and doors of the vehicle shut.

                            ii.        Lightning can strike telephone cords, electrical wires and metal pipes.      During a thunderstorm when lightning is taking place, contact with these should be avoided.

                            iii.        Carrying umbrella is not a good idea at all during lighting because lightning may strike the top end of the metal rod of umbrella and harm us.

      Q47. What causes an earthquake?

      Ans. Causes of an earthquake

                              i.        The outermost layer of the earth is not in one piece. It is fragmented. Each fragment is called a plate. These plates are in continual motion. When they brush past one another, or a plate goes under another due to collision, they cause disturbance in the earth’s crust. It is this disturbance that shows up as an earthquake on the surface of the earth.

                             ii.        Tremors on the earth can also be caused when a volcano erupts, or a meteor hits the earth, or an underground nuclear explosion is carried out.


      Q48. What causes lightning in the sky?

      Ans. During the development of a thunderstorm, the air currents move upward while the water droplets move downward. These vigorous movements cause separation of charges. The positive charges collect near the upper edges of the clouds and the negative charges accumulate near the lower edges. There is accumulation of positive charges near the ground also. When the magnitude of the accumulated charges becomes very large, the air which is normally a poor conductor of electricity is no longer able to resist their flow. Negative and positive charges meet, producing streaks of bright light and sound. We see streaks as lightning. The process is called an electric discharge.

      Q49. State some precautions that people should take to protect themselves against earthquakes if they live in seismic zones of the country.

      Ans. People living in seismic zones should take the following measures for protection against earthquakes:

                              i.        All the buildings in these zones should be designed so that they can withstand major tremors. Modern building technology can make it possible.

                             ii.        In highly seismic areas, the use of mud or timber is better than the heavy construction material. Keep roofs as light as possible. In case the structure falls, the damage will not be heavy.

                            iii.        It is better if the cupboards and shelves are fixed to the walls, so that they do not fall easily.

                            iv.        Wall clocks, photo-frames, water heaters etc., should be mounted securely on the walls, so that in the event of an earthquake, they do not fall on people.

                             v.        Since some buildings may catch fire due to an earthquake, it is necessary that all buildings, especially tall buildings, have fire fighting equipment in working order.


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