Topic outline

    • Fun with Magnets

      Q30. Draw the diagram of
      (a) Bar Magnet          (b) Horse-shoe Magnet



      Q31. Draw a diagram of a magnetic compass.


      Q32. A boy has two rods. How can he identify which one is a magnet?

      Ans. Through the following activity he can identify which rod is a magnet.

      Take both rod and suspend freely with the help of thread. Now, bring one end of a bar magnet close to both the ends of the suspended rods one by one. If it shows attraction at both the ends then it is an iron rod. If it shows attraction at one end and repulsion at the other end, then it is a bar magnet.


      Q33. Write properties of a magnet.

      Ans. Properties of a magnet are:

             1.   Magnet attracts materials like iron, nickel, cobalt.

             2.   The force of attraction of magnet is greater at the poles than at the centre.

             3.   Like poles repel each other and unlike poles attract each other.

             4.   Magnetic poles always exist in pairs.

             5.   If a bar magnet is suspended by a thread and if it is free to        rotate, its South Pole will move towards the North Pole of the earth and vice versa.


      Q34. How can we safely store magnets?

      Ans. To keep them safe, bar magnets should be kept in pairs with their unlike poles on the same side. They must be separated by a piece of wood while two pieces of soft iron should be placed across their ends. For horse-shoe magnet, one should keep a piece of iron across the poles. Keep magnets away from cassettes, mobiles, television, music system, compact disks (CDs) and the computer.

      Q35. Prove with the help of an experiment that a freely suspended magnet comes to rest in the north-south direction.

      Ans. Take a bar magnet. Put a mark on one of its ends for identification. Now, tie a thread at the middle of the magnet and suspend it freely from a wooden stand. The magnet comes to rest in the north-south direction after some time. Rotate the magnet in other directions and note the final direction in which it comes to rest. We will find that the magnet always comes to rest in the north-south direction.


      Q36. Show with help of an activity that the magnet has two poles.

      Ans. The two ends of a magnet where the magnetic force is the strongest are called the poles of the magnet. A magnet has two poles.

      Spread some iron filings on a sheet of paper. Now, place a bar magnet on this sheet. Pick up the magnet and observe how the iron fillings are distributed all over the magnet. We find that most of the iron filings are attracted towards the two ends of a bar magnet. These ends are the poles of the magnet.


      Q37. How Magnets Were Discovered?

      Ans. It is said that, there was a shepherd named Magnes, who lived in ancient Greece. He used to take his herd to the mountains for grazing. He would take a stick with him to control his herd. The stick had a small piece of iron attached at one end. One day he was surprised to find that he had to pull hard to free his stick from a rock on the mountain side. It seemed as if the stick was being attracted by the rock. The rock was a natural magnet and it attracted the iron tip of the shepherd's stick. It is said that this is how natural magnets was discovered.


      Q38. How can you make a magnet?

      Ans. Take a rectangular piece of iron. Place it on the table. Now take a bar magnet and place one of its poles near one edge of the bar of iron. Without lifting the bar magnet, move it along the length of the iron bar till you reach the other end. Now, lift the magnet and bring the pole (the same pole you started with) to the same point of the iron bar from which you began. Move the magnet again along the iron bar in the same direction as you did before. Repeat this process about 30-40 times. Bring a pin or some iron filings near the iron bar to check whether it has become a magnet. If not, continue the process for some more time. Remember that the pole of the magnet and the direction of its movement should not change.


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