Answers to Chapter 4: Exploring Magnets
1. Fill in the blanks:
(i) Unlike poles of two magnets attract each other, whereas like poles repel each other.
(ii) The materials that are attracted towards a magnet are called magnetic materials.
(iii) The needle of a magnetic compass rests along the north-south direction.
(iv) A magnet always has two poles.
2. True or False:
(i) A magnet can be broken into pieces to obtain a single pole. (False)
(ii) Similar poles of a magnet repel each other. (True)
(iii) Iron filings mostly stick in the middle of a bar magnet when it is brought near them. (False)
(iv) A freely suspended bar magnet always aligns with the north-south direction. (True)
3. Column Matching:
| Column I | Column II |
|---|---|
| N – N | Repulsion |
| N – S | Attraction |
| S – N | Attraction |
| S – S | Repulsion |
4. Atharv’s Experiment Observations:
Based on the positions in Table 4.3, the correct option is: (ii)
- Position A: 10 U-clips
- Position B: 2 U-clips
- Position C: 10 U-clips
The ends of the magnet attract the most U-clips as the poles have the strongest magnetic force.
5. Identifying magnets and iron bar:
Reshma can identify the two magnets by bringing them close to each other. Magnets repel each other when like poles are brought together, while the iron bar will only be attracted by both poles of the magnets.
6. Finding poles of an unmarked magnet:
Place the unmarked magnet near a marked magnet.
- If the ends attract, they are opposite poles (e.g., North and South).
- If the ends repel, they are like poles (e.g., North and North or South and South).
7. Locating the North pole of a magnet without another magnet:
Suspend the unmarked magnet freely using a thread. The end of the magnet that points towards the Earth’s North is the North pole of the magnet.
8. Poles of Earth’s magnet based on the compass:
The North pole of the compass points towards the Earth’s magnetic South pole (which is geographically the North pole). Hence:
- Earth’s magnetic North pole is near the geographic South pole.
- Earth’s magnetic South pole is near the geographic North pole.
9. Mechanic’s problem with screws falling:
Magnetize the screwdriver by rubbing it with a magnet along its length repeatedly in one direction. The screwdriver will then attract the screws, preventing them from falling.
10. Ring magnets not touching:
The magnets X and Y repel each other because like poles are facing each other. To bring them into contact:
- Flip one of the magnets so that unlike poles face each other.
11. Polarity of magnets (Fig. 4.17):
| End | Polarity |
|---|---|
| 1 | South (S) |
| 2 | North (N) |
| 3 | South (S) |
| 4 | North (N) |
| 5 | North (N) |
| 6 | South (S) |
Further Activities
1. Comparing different magnets’ strength:
- Different magnets may pick up different numbers of pins due to variations in their size, material, and magnetic strength.
2. Making a hopping frog (Fig. 4.18):
- Fix ring magnets with alternating poles on a scale.
- Attach a magnet to a paper frog. The frog will “hop” as the magnets repel.
3. Maglev train model:
- Study how magnetic levitation reduces friction and enables high-speed travel. Create a model using ring magnets with like poles facing to simulate repulsion.
4. Shapes of magnets:
- Magnets come in shapes like bar, cylindrical, disc, and ring to suit different uses, such as in compasses, motors, or speakers.
5. Magnets in medicine:
- MRI Scanners: Use powerful magnets to create detailed body images.
- Magnetic therapy: Uses magnets for pain relief and healing.
Key Takeaways:
- Magnets always have two poles: North and South.
- Magnetic materials like iron and cobalt are attracted to magnets, while non-magnetic materials are not.
- The Earth behaves like a giant magnet, influencing compasses.
- Like poles repel, and unlike poles attract.
Question and Answer Session
1. Fill in the blanks:
- Unlike poles of two magnets attract each other, whereas like poles repel each other.
- The materials that are attracted towards a magnet are called magnetic materials.
- The needle of a magnetic compass rests along the north-south direction.
- A magnet always has two poles.
2. State whether the following statements are True (T) or False (F):
- A magnet can be broken into pieces to obtain a single pole. (F)
- Similar poles of a magnet repel each other. (T)
- Iron filings mostly stick in the middle of a bar magnet when it is brought near them. (F)
- A freely suspended bar magnet always aligns with the north-south direction. (T)
3. Match the columns:
| Column I | Column II |
|---|---|
| N – N | Repulsion |
| N – S | Attraction |
| S – N | Attraction |
| S – S | Repulsion |
4. Observations in Atharv’s Experiment:
- Observation:
Option (iii) is most likely: 10 pins at A, 2 pins at B, and 10 pins at C. - Reason: Most iron filings are attracted to the poles of the magnet.
5. Identifying Magnets from Metal Bars:
- Bring one metal bar near another.
- If there is repulsion, both bars are magnets. If there is only attraction, one is a magnet and the other is a piece of iron.
6. Identifying Poles of an Unmarked Magnet Using a Marked Magnet:
- Bring one pole of the marked magnet near the unmarked magnet.
- If the two ends repel, the poles are similar (e.g., North-North).
- If the two ends attract, the poles are opposite (e.g., North-South).
7. Identifying North Pole Without Another Magnet:
- Suspend the unmarked magnet freely using a thread.
- Let it settle in the north-south direction.
- The end pointing towards the Earth’s geographic North is the magnet’s North pole.
8. Earth’s Magnetic Poles and Compass Directions:
- The Earth’s geographic North corresponds to its magnetic South pole, and its geographic South corresponds to its magnetic North pole.
9. Suggestion for the Mechanic:
- Solution: Magnetize the screwdriver by rubbing a strong magnet along its length multiple times in one direction. This will attract the screws to the screwdriver.
10. Reason for Magnet X Not Moving Down:
- Reason: Magnet X is repelled by Magnet Y because their like poles face each other.
- Solution: Reverse the polarity of Magnet X by flipping it.
11. Polarity of Magnets in Fig. 4.17:
| End | Polarity |
|---|---|
| 1 | South |
| 2 | North |
| 3 | South |
| 4 | North |
| 5 | North |
| 6 | South |
12. Magnet Through Non-Magnetic Materials (Table 4.2):
| Material Placed Between Magnet and Compass | Observations |
|---|---|
| Wood | Needle still deflects |
| Cardboard | Needle still deflects |
| Plastic | Needle still deflects |
| Glass | Needle still deflects |
Conclusion: Magnetic effects can pass through non-magnetic materials.
13. Making a Simple Magnetic Compass:
- Rub a needle with one pole of a magnet repeatedly in one direction.
- Place the needle through a cork.
- Float the cork in a bowl of water.
- The needle will align itself along the north-south direction.
14. Difference Between Magnetic and Non-Magnetic Materials:
- Magnetic materials: Attracted by a magnet (e.g., iron, cobalt, nickel).
- Non-magnetic materials: Not attracted by a magnet (e.g., wood, plastic, glass).
15. Uses of Magnets in Everyday Life:
- Magnetic compasses for navigation.
- Magnets in refrigerators, toys, and pencil boxes.
- Magnets in MRI machines for medical imaging.
- Magnets in electric motors and speakers.
16. What Happens When Magnets Are Brought Close to Each Other?
- Like poles (North-North or South-South): Repel.
- Unlike poles (North-South): Attract.
17. Making Magnets of Different Shapes and Sizes:
- Bar magnets: General use in labs.
- Ring magnets: Used in speakers and motors.
- U-shaped magnets: Ideal for lifting heavy materials.
- Disc magnets: Compact applications like gadgets.
18. Why Should We Store Magnets Properly?
Improper storage can lead to magnets losing their magnetic properties.
- Store them in pairs with opposite poles facing each other, separated by a wooden piece.
19. Fun Activities with Magnets:
- Magnetic Garland: Arrange pins or beads using a magnet.
- Maze Game: Use a magnet below a maze to guide a metal ball.
- Fishing Game: Pick metal clips from water without wetting the magnet.
These questions and answers summarize the key learnings from Chapter 4: Exploring Magnets while ensuring clarity and engagement.
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