CHAPTER- 4 EXPLORING MAGNETS
NOTES
1. In ancient times, the magnets used by sailors were naturally occurring magnets. These were known as magnetite stones, and their discovery dates back to ancient times.2. Magnetic materials- Substances ubstances that are attracted to a magnet. Examples include iron, nickel, cobalt, etc.
3. Non-magnetic materials- Substances that are not attracted to a magnet.
4. Poles of a magnet- A magnet has two ends (poles), which are called the north pole and the south pole.
- No matter how many small pieces a magnet is broken into, even the smallest piece always contains both a north pole and a south pole.
5. The end of a magnet that points towards the north is called the north-seeking pole or the north pole of the magnet.
- The other end, which points towards the south, is called the south-seeking pole or the south pole of the magnet.
- A magnet always comes to rest only in the north–south direction. This property is used to determine directions. On this basis, in ancient times a small instrument called the magnetic compass was developed to find directions.
6. Compass- It contains a needle-shaped magnet that can rotate freely. The needle of the magnetic compass indicates the north–south direction.
- The compass is placed at the location where we want to find the directions.
7. When two magnets are brought close to each other, like poles (north–north or south–south) repel each other, while unlike poles (north–south) attract each other.
LET US ENHANCE OUR LEARNING
Question- 1. Fill in the blanks
1) Unlike poles of two magnets ________ each other, whereas like poles _______ each other.
2) The materials that are attracted towards a magnet are called _____.
3) The needle of a magnetic compass resta along the ________ direction.
4) A magnet always has _______ poles.
Answer- 1) Attracted, repelled; 2) Magnetic; 3) North–South; 4) Two.
Question- 2. State whether the following statements are True (T) or False (F).
1) A magnet can be broken into pieces to obtain a single pole. ( )
2) Similar poles of a magnet repel each other. ( )
3) Iron filings mostly stick in the middle of a bar magnet when it is brought near them. ( )
3) Iron filings mostly stick in the middle of a bar magnet when it is brought near them. ( )
4) A freely suspended bar magnet always aligns with the north-south direction. ( )
Answer- (1)- (×), (2)- (✓), (3)- (×), (4)- (✓).
Question- 3. Column 1 shows different positions in which one pole of a magnet is placed near that of the other. Column 2 indicates the resulting interaction between them for different situations. Fill in the blanks.
Answer- 
Question- 4. Atharv performed an experiment in which he took a bar magnet and rolled it over a heap of steel U-Clips (Fig 4.15).
According to you, which of the options given in Table 4.3 is likely to be his observation?
Table 4.3 : Number of pins attracted by the magnet at its various positions
Answer- In this experiment, the attraction is greatest at both poles of the magnet, while the attraction is weaker in the middle part. Therefore, the number of pins will be maximum at position ‘A’ and position ‘C’, and fewer at position ‘B’.
Question- 5. Reshma bought three identical metal bars from the market. Out of these bars two were magnets and one was just a piece pf iron. How will she identify which two amongst the three could be magnets (without using any other material)?
Answer- Reshma will bring all three rods close to each other and change their ends one by one. The two rods that repel each other will be magnets. The rod that does not show any repulsion with any of the others will be made of iron.
Question- 6. You are given a magnet which does not have the poles marked. How can you find its poles with the help of another magnet which has its poles marked?
Answer- Bring the north pole of the magnet with marked poles close to the given magnet. If the two magnets attract each other, then this pole of the given magnet will be the south pole. If this does not happen, that is, if they repel each other, then the pole of the magnet will be the north pole.
Question- 7. A bar magnet has no markings to indicate its poles. How would you find out near which end its North pole is located without using another magnet?
Answer- Tie the magnet at its center with a thread and suspend it. When it comes to rest, its north end will point towards the north direction, which will be the north pole of the magnet.
Question- 8. If the earth is itself a magnet, can you guess the poles of earth's magnet by looking at the direction of the magnetic compass?
Answer- Yes, the Earth’s magnetic poles can be estimated by observing direction with a magnetic compass. The needle of the compass can rotate freely. When the compass is placed on a stable surface, its needle settles in the north–south direction due to the Earth’s magnetic field. By observing the direction with a magnetic compass, the Earth’s magnetic poles can be accurately estimated.
Question- 9. While a mechanic was repairing a gadget using a screw driver, the steel screws kept falling down. Suggest a way to solve the problem of the mechanic on the basis of what you have learnt in this chapter.
Answer- The mechanic should first rub the screwdriver with a magnet, which will make it magnetized. This will cause the steel screws to stick to the screwdriver, and they will not fall down.
Question- 10. Two ring magnets X and Y are arranged as shown in fig. 4.16. It is observed that the magnet X does not move down further. What could be the possible reason? Suggest a way to bring the magnet X in contact with magnet Y, without pushing either of the magnets.
Answer- In this situation, magnets ‘X’ and ‘Y’ have like poles facing each other, so they are repelling each other. This is the reason why magnet ‘X’ is not moving downward.
To bring magnet ‘X’ into contact with magnet ‘Y’ without pushing it, one of the magnets should be rotated to change its orientation. This will cause their opposite poles to face each other. As a result, they will attract each other, and magnet ‘X’ will slide and come into contact with magnet ‘B’.
Question- 11. Three magnets are arranged on a table in the form of the shape shown in fig 4.17. What is the polarity, N or S, at the ends 1, 2, 3, 4 and 6 of the magnets? Polarity of one end (5) is given for you.
Answer- According to the figure, the polarity of the ends of the magnets can be as follows:
End 1: S (It is near End 2, and opposite poles of magnets attract each other.)
End 2: N (It is connected to End 1, and the pole of End 1 is S.)
End 3: S (Since the pole of End 2 is N, its opposite end will be S.)
End 4: S (It is s near End 5, and the pole of End 5 is N.)
End 6: N (The pole of End 4 is S.)
Thus, the polarity of the ends will be:
End 1: S, End 2: N, End 3: S, End 4: S, End 6: N.
