Topic outline

    • Some Natural Phenomena

      Q50. Draw a labelled diagram of a seismograph. Explain its working.

      Ans. The tremors produce waves on the surface of the earth. These are called seismic waves. The waves are recorded by an instrument called the seismograph. The instrument is simply a vibrating rod, or a pendulum, which starts vibrating when tremors occur. A pen is attached to the vibrating system. The pen records the seismic waves on a paper which moves under it. By studying these waves, scientists can construct a complete map of the earthquake. They can also estimate its power to cause destruction.

       Image from NCERT

      Q51. Describe with the help of a diagram an instrument which can be used to detect a charged body.

      Ans. An electroscope may be used to detect whether a body is charged or not.

       Image from NCERT

      Construction of a simple electroscope

                              i.        Take an empty jam bottle.

                             ii.        Take a piece of cardboard slightly bigger in size than the mouth of the bottle.

                            iii.        Pierce a hole in it so that a metal paper clip could be inserted.

                            iv.        Open out paper clip as shown in Figure.

                            v.        Cut two strips of aluminium foil about 4 cm × 1 cm each. Hang them on the paper clip as shown.

                           vi.        Insert the paper clip in the cardboard lid so that it is perpendicular to it. Charge a refill and touch it with the end of the paper clip.


                              i.        The aluminium foil strips receive the same charge from the charged refill through the paper clip. The strips carrying similar charges repel each other and they become wide open.

                             ii.        Touch the end of the paper clip gently with hand and you will find a change in the foil strips. They come back to their original state. The reason is that the foil strips lose charge to the earth through your body.

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