Chapter Exercises

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Q1. 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.

Q2. State whether True or False

(i) A magnet can be broken into pieces to obtain a single pole. Answer: False. (Poles always exist in pairs).

(ii) Similar poles of a magnet repel each other. Answer: True. (North repels North).

(iii) Iron filings mostly stick in the middle of a bar magnet when it is brought near them. Answer: False. (They stick mostly at the ends/poles).

(iv) A freely suspended bar magnet always aligns with the north-south direction. Answer: True.

Q3. Matching Magnetic Interactions

Q4. Atharv’s Experiment (Pins on a Magnet)

Atharv rolled a bar magnet over a heap of steel U-clips. The table shows the number of pins attracted at positions A (End), B (Middle), and C (End).

Analysis:

• A and C are the poles (Ends), so attraction should be maximum.
• B is the center, so attraction should be minimum.

Correct Option: (iv) 10, 10, 10 is incorrect (uniform attraction). (iii) 2, 10, 10 is incorrect (weak at one pole). (i) 10, 2, 10 matches the theory (Strong at poles A and C, weak at center B).

Answer: (i) Position A: 10, Position B: 2, Position C: 10.

Q5. Identifying the Iron Bar

Problem: Reshma has 3 metal bars. Two are magnets, one is iron. How to identify them without extra material?

Solution:

1. Take two bars at a time (Bar 1 and Bar 2).
2. Bring one end of Bar 1 close to both ends of Bar 2.
3. If there is attraction at one end and repulsion at the other, both are magnets.
4. If there is attraction at both ends, then one of them is a magnet and the other is the iron bar.
5. To confirm, take the known magnet (from step 3) and test the third bar. If it attracts at both ends, the third bar is the iron piece.

Reasoning: Repulsion is the sure test for magnetism.

Q6. Finding Unknown Poles

Problem: You have a magnet with no markings. You have another magnet with marked poles.

Solution:

1. Bring the North Pole of the marked magnet near one end of the unknown magnet.
2. If they repel, the unknown end is also a North Pole.
3. If they attract, the unknown end is a South Pole.
4. Once one pole is identified, the opposite end is the other pole.

Q7. Finding North Pole without another Magnet

Problem: How to find the North pole of a bar magnet without using another magnet?

Solution:

1. Suspend the bar magnet freely using a thread tied to its center.
2. Allow it to come to rest.
3. The magnet will align itself in the North-South direction due to Earth’s magnetism.
4. The end pointing towards the Geographic North is the North Pole of the magnet.

Q8. Earth’s Magnetic Poles

Question: If Earth is a magnet, guess the poles based on a compass.

Answer:

• The North Pole of a compass points roughly to the Geographic North.
• Since unlike poles attract, the Earth’s magnetic pole located near the Geographic North must actually be a Magnetic South Pole.
• Similarly, the Earth’s magnetic pole near the Geographic South is a Magnetic North Pole.

Q9. The Mechanic’s Problem

Problem: Screws keep falling off the screwdriver.

Suggestion: The mechanic should magnetize the screwdriver.

1. Take a permanent bar magnet.
2. Rub it along the length of the screwdriver’s metal shaft in one direction repeatedly (30-40 times).
3. The screwdriver will become a temporary magnet and hold the steel screws effectively.

Q10. Levitating Ring Magnets

Observation: Ring magnet X floats above Ring magnet Y.

Reason: This happens due to Magnetic Repulsion. The face of magnet X facing down and the face of magnet Y facing up must be Like Poles (e.g., North facing North).

How to bring them in contact? To bring X in contact with Y without pushing, simply flip magnet X upside down. Now, unlike poles will face each other, and they will attract and snap together.

Q11. Polarity of Three Magnets

Problem: Determine the polarity of ends 1, 2, 3, 4, 6 given that end 5 is North (N).

Logic: The magnets are arranged in a chain (likely attracted to each other at the corners).

1. Given: End 5 is N.
2. Therefore, End 6 (other end of same magnet) is S.
3. End 6 (S) is touching End 4. For attraction, End 4 must be N.
4. If End 4 is N, then End 3 (other end of same magnet) is S.
5. End 3 (S) is touching End 2. For attraction, End 2 must be N.
6. If End 2 is N, then End 1 (other end of same magnet) is S.

Result:

• 1 = S
• 2 = N
• 3 = S
• 4 = N
• 6 = S