Exploring Magnets

(i) Given/Concept: When two magnets are brought close, unlike poles attract and like poles repel.
Answer: Unlike poles of two magnets attract each other, whereas like poles repel each other.

(ii) Given/Concept: Materials classified on the basis of their behaviour near a magnet.
Answer: The materials that are attracted towards a magnet are called magnetic materials.

(iii) Given/Concept: A freely suspended magnet always aligns along a fixed geographical direction.
Answer: The needle of a magnetic compass rests along the north-south direction.

(iv) Given/Concept: Poles of a magnet always exist in pairs; a single pole cannot exist.
Answer: A magnet always has two (North and South) poles.

(i) Statement: A magnet can be broken into pieces to obtain a single pole.
Answer: False (F)
Reason: When a magnet is broken into pieces, each piece has both a North pole and a South pole. A single pole (monopole) cannot be obtained.

(ii) Statement: Similar poles of a magnet repel each other.
Answer: True (T)
Reason: Like poles (N–N or S–S) always repel each other.

(iii) Statement: Iron filings mostly stick in the middle of a bar magnet when it is brought near them.
Answer: False (F)
Reason: Iron filings mostly stick near the ends (poles) of a bar magnet, where the magnetic force is strongest. Very few filings stick in the middle.

(iv) Statement: A freely suspended bar magnet always aligns with the north-south direction.
Answer: True (T)
Reason: Due to the Earth's magnetic field, a freely suspended bar magnet always comes to rest along the geographic north-south direction.

Concept used: Like poles repel each other; unlike poles attract each other.

Working:
- N – N → Both poles are the same (like poles) → Repulsion
- N – ? → For attraction, the other pole must be unlike → S (i.e., N – S → Attraction)
- S – N → The poles are unlike → Attraction
- ? – S → For repulsion, the other pole must be like → S (i.e., S – S → Repulsion)

Completed Table:

| Column I | Column II |
|---|---|
| N – N | Repulsion |
| N – S | Attraction |
| S – N | Attraction |
| S – S | Repulsion |

Given: A bar magnet is rolled over a heap of steel U-clips. Position A and Position C are the two ends (poles) of the bar magnet, and Position B is the middle portion.

Concept used: The magnetic force is strongest at the poles (ends) of a magnet and weakest at the middle. Therefore, maximum iron clips/filings are attracted at the poles and very few at the middle.

Working:
- Position A (one pole/end) → Maximum clips attracted → 10
- Position B (middle of magnet) → Minimum clips attracted → 2
- Position C (other pole/end) → Maximum clips attracted → 10

Answer: Option (i) — Position A: 10, Position B: 2, Position C: 10 — is the correct observation.

Given: Three identical-looking metal bars — two are magnets and one is a plain iron bar. No other material is available.

Concept used: A magnet attracts an iron bar from both its poles as well as its middle. However, a magnet can only repel another magnet (like poles repel). An iron bar is always attracted to a magnet — it is never repelled.

Method (Step-by-step):

Step 1: Label the three bars as Bar 1, Bar 2, and Bar 3.

Step 2: Bring one end of Bar 1 close to one end of Bar 2.
- If they repel → both Bar 1 and Bar 2 are magnets (since only a magnet can repel another magnet).
- If they attract → one of them could be the iron bar; proceed to Step 3.

Step 3 (if attraction is observed): Now bring the middle portion of Bar 1 close to one end of Bar 2.
- If Bar 2 is attracted to the middle of Bar 1 → Bar 2 is the plain iron bar (iron is attracted everywhere, including the middle, where a magnet has no magnetic force).
- If Bar 2 is NOT attracted to the middle of Bar 1 → Bar 1 is the plain iron bar.

Key Rule: The middle of a magnet has negligible magnetic force. So if a bar is attracted to the middle of another bar, the attracted bar is the iron piece (not a magnet).

Conclusion: The two bars that repel each other (at their ends) are the two magnets. The bar that is attracted to the middle of another bar is the plain iron bar.

Given: One magnet with poles marked (known magnet) and one magnet with poles unmarked (unknown magnet).

Concept used: Like poles repel each other and unlike poles attract each other.

Steps:

Step 1: Hold the known magnet in one hand. Bring its North pole close to one end of the unknown magnet.

Step 2: Observe the interaction:
- If the end of the unknown magnet is repelled → that end is also the North pole (like poles repel).
- If the end of the unknown magnet is attracted → that end is the South pole (unlike poles attract).

Step 3: Once one pole of the unknown magnet is identified, the other end is automatically the opposite pole.

Conclusion: By using repulsion (the sure test for identifying poles), we can correctly identify both poles of the unmarked magnet.

Given: A bar magnet with no pole markings. No other magnet is available.

Concept used: A freely suspended magnet always aligns itself in the north-south direction, with its North pole pointing towards geographic North.

Steps:

Step 1: Tie a thread to the middle of the bar magnet so that it is balanced horizontally.

Step 2: Suspend the magnet freely (hang it from a support) and allow it to come to rest on its own.

Step 3: The magnet will align itself along the north-south direction.

Step 4: Identify the geographic North direction (using the position of the Sun — the Sun rises in the East, so North is to the left when you face East).

Step 5: The end of the magnet that points towards geographic North is the North pole of the magnet.

Conclusion: The end of the freely suspended bar magnet that points towards geographic North is its North pole.

Given: The Earth behaves like a giant magnet. A magnetic compass needle points towards geographic North.

Concept used: Unlike poles attract each other. The North pole of a compass needle points towards geographic North.

Reasoning:
- The North pole of the compass needle is attracted towards the geographic North of the Earth.
- Since unlike poles attract, the pole of the Earth's magnet located near the geographic North must actually be a South magnetic pole of the Earth's magnet.
- Similarly, the pole of the Earth's magnet located near the geographic South must be a North magnetic pole of the Earth's magnet.

Conclusion: Yes, we can guess the poles of the Earth's magnet. The Earth's geographic North Pole corresponds to the South magnetic pole of the Earth's magnet, and the Earth's geographic South Pole corresponds to the North magnetic pole of the Earth's magnet.

Given: A mechanic is using a screwdriver and steel screws keep falling down.

Concept used: Steel is a magnetic material and is attracted to magnets. A magnetised screwdriver will attract and hold steel screws.

Suggestion:
The mechanic should magnetise the tip of the screwdriver by rubbing it with one pole of a permanent magnet in one direction (the same way as described in Activity 4.4 — stroking method) at least 30–40 times.

How it helps: Once the tip of the screwdriver becomes a magnet, it will attract and hold the steel screws firmly. The screws will stick to the magnetised tip and will not fall down, making the mechanic's work easier.

Conclusion: Magnetising the screwdriver tip is a simple and effective solution to prevent the screws from falling.

Given: Two ring magnets X and Y are arranged on a vertical rod/stick. Magnet X is above magnet Y and does not move down further (it appears to float).

Reason (Concept used — Like poles repel):
Magnet X does not move down because the like poles of the two ring magnets are facing each other (e.g., South pole of X faces South pole of Y, or North pole of X faces North pole of Y). Since like poles repel, the repulsive force between them balances the weight of magnet X, causing it to float/hover above magnet Y.

Way to bring X in contact with Y (without pushing either magnet):
To bring magnet X in contact with magnet Y, flip (turn over/invert) one of the magnets so that the unlike poles face each other (North pole of one faces South pole of the other). Unlike poles attract each other, so magnet X will move down and come in contact with magnet Y.

Note: Since we cannot push either magnet, we simply reverse the orientation of one magnet on the rod so that attraction replaces repulsion.

Given: Three bar magnets are arranged in a shape (as in Fig. 4.17). End 5 is given as North (N).

Concept used:
- Each magnet has two poles — one end is North and the other end is South.
- Where two magnets are joined/touching, the poles at the junction must be unlike poles (North meets South) for attraction to hold them together.
- The two ends of the same magnet are always opposite poles.

Working (step-by-step):

Based on the typical arrangement shown in Fig. 4.17 (a U-shape or triangular arrangement of three bar magnets where ends are labelled 1 through 6, with end 5 = N):

- End 5 = N (given)
- End 5 and End 6 are the two ends of the same magnet → End 6 = S
- End 6 (S) is joined to End 1 at the junction → for attraction, End 1 = N
- End 1 and End 2 are the two ends of the same magnet → End 2 = S
- End 2 (S) is joined to End 3 at the junction → for attraction, End 3 = N
- End 3 and End 4 are the two ends of the same magnet → End 4 = S
- End 4 (S) is joined to End 5 (N) → unlike poles meet ✓ (consistent)

Final Answer:
$$\text{End 1} = N, \quad \text{End 2} = S, \quad \text{End 3} = N, \quad \text{End 4} = S, \quad \text{End 5} = N \text{ (given)}, \quad \text{End 6} = S$$

Note: If the figure shows a different arrangement, the same logic applies — opposite ends of the same magnet have opposite poles, and at every junction where two magnets meet, unlike poles face each other.