Part 1 Chapter 4: Fun with Magnets - Exercise
1. Fill in the blanks.
(a) Materials that are attracted by a magnet are called magnetic materials.
(b) Magnets made artificially for various purposes are called artificial magnets.
(c) Rubber is a non-magnetic substance.
(d) If we break a bar magnet into two pieces, we will get two independent magnets.
(e) Similar poles of two magnets repel each other.
(f) Magnets always have two poles.
2. State whether the following are True ($\checkmark$) or False ($\times$).
(a) Magnets attract all kinds of objects. — $\times$
(b) There is attraction between the opposite poles of two magnets. — $\checkmark$
(c) Cobalt is a magnetic substance. — $\checkmark$
(d) A bar magnet always aligns in the North-South direction when suspended freely. — $\checkmark$
(e) Magnets lose their magnetic properties when heated strongly. — $\checkmark$
3. Match Column A with Column B.
| Column A | Column B |
| (i) Compass | (d) At rest, it remains in the North-South direction. |
| (ii) Iron nails | (c) Is attracted by a magnet. |
| (iii) Magnetite | (a) A naturally occurring magnet. |
| (iv) Permanent magnet | (b) Retains magnetic properties for a long time. |
4. Interaction between Poles.
Complete the table showing the action between magnetic poles:
| Pole 1 | Pole 2 | Action |
| North | North | Repulsion |
| North | South | Attraction |
| South | North | Attraction |
| South | South | Repulsion |
5. Multiple Choice Questions.
(i) Which of the following is a magnetic substance?
(a) Iron Pin (Alpin)
(b) Rubber
(c) Plastic bangle
(d) Wooden scale
Ans: (a) Iron Pin
(ii) Which of the following is a non-magnetic substance?
(a) Iron nail
(b) Rubber band
(c) Steel safety pin
(d) Iron paper clip
Ans: (b) Rubber band
(iii) How many poles does a single magnet have?
(a) Two
(b) One
(c) Three
(d) Four
Ans: (a) Two
Short Answer Questions
6. If a bar magnet is brought near iron filings, in which part will the filings stick the least?
Ans: Iron filings will stick the least at the center (equator) of the bar magnet. This is because the magnetic strength is concentrated at the poles and is weakest at the midpoint.
7. The poles of a bar magnet are not marked. How do you find its North pole?
Ans: Suspend the magnet freely from a wooden stand using a thread. Once it comes to rest, the end pointing toward the Earth's geographic North is the North pole of the magnet.
8. Is it possible to have a magnet with a single pole (monopole)?
Ans: No. Magnetic poles always exist in pairs. Even if you break a magnet into smaller pieces, each piece will develop its own North and South poles.
9. State two fundamental properties of a magnet.
Ans:
Directive Property: A freely suspended magnet always points in the North-South direction.
Attractive Property: A magnet attracts magnetic substances (like iron, nickel, and cobalt) most strongly at its poles.
10. How can you convert an iron nail into a temporary magnet?
Ans: Using the Single Touch Method: Place the iron nail on a table. Rub one pole of a bar magnet along the length of the nail from one end to the other. Lift the magnet and repeat the process in the same direction several times. The nail will become magnetized.
11. Why does a freely suspended bar magnet always point North-South?
Ans: The Earth behaves like a giant bar magnet with its own magnetic field. A suspended magnet aligns itself with the Earth’s magnetic field lines, causing it to point in the North-South direction.
12. How is a compass used to find directions?
Ans: A compass has a magnetized needle that rotates freely. Its North-seeking pole (usually colored red) always points North. Once North is identified, the other directions (South, East, and West) can easily be determined.
13. How would you identify the poles of a horseshoe magnet?
Ans: You can identify the poles by bringing a marked bar magnet or a compass near the ends of the horseshoe magnet. The end that repels the North pole of the bar magnet is the North pole of the horseshoe magnet.
14. You are given a bar magnet, a plastic scale, a piece of wood, and an iron nail. Which of these can be magnetized?
Ans: Only the iron nail can be magnetized because it is a ferromagnetic material. Plastic and wood are non-magnetic and cannot be magnetized. You can verify the nail has become a magnet if it can pick up small steel pins or paper clips.
15. You are given a bar magnet and some iron pins. How do you determine the poles?
Ans: Dip the magnet into a pile of pins. The areas where the maximum number of pins cling are the poles. To distinguish which is North or South, you would need a known reference (like a compass or a marked magnet).
16. How will you mark the poles of an unmarked magnet using a compass?
Ans: Place the compass near one end of the magnet. If the South-pointing end of the compass needle is attracted to the magnet, that end of the magnet is the North pole (since opposite poles attract).
17. A steel needle falls into a narrow crack on the floor where your fingers cannot reach. How can you retrieve it?
Ans: You can use a strong magnet. By bringing the magnet close to the crack, the magnetic force will attract the steel needle, allowing you to lift it out easily.
18. If you are lost in an unfamiliar place with a compass, how will it help you?
Ans: By holding the compass flat, the needle will show you where North is. If you know your destination is to the East, you simply turn 90° to the right of the direction the needle is pointing.
Additional Exercises: Fun with Magnets
7. Practical Application Questions
(i) Imagine you have a mixture of iron nails and brass screws. How can you separate them quickly? Ans: Use a bar magnet. The iron nails are magnetic and will cling to the magnet, while the brass screws (non-magnetic) will remain behind.
(ii) Why are magnets often used in refrigerator doors? Ans: Refrigerator doors have magnetic strips around the edges to ensure an airtight seal. This prevents cold air from escaping and keeps the food fresh.
(iii) Why is it advised to keep magnets away from mobile phones, computers, and credit cards? Ans: These devices use magnetic storage or sensitive electronic components. A strong magnet can interfere with their data or damage the internal circuitry.
8. Magnet Safety & Maintenance
Fill in the blanks regarding magnet care: (a) Magnets lose their power if they are heated, hammered, or dropped from a height. (b) To store bar magnets safely, they should be kept in pairs with opposite poles on the same side. (c) A piece of soft iron (called a "keeper") should be placed across the poles of a horseshoe magnet during storage.
9. Critical Thinking (High Order Thinking Skills)
Q: If you break a bar magnet into four equal pieces, how many North poles will you have in total? Ans: You will have four North poles. Every piece of a broken magnet becomes a complete magnet with its own North and South pole.
Q: Repulsion is the "surest test" for magnetism. Why not attraction? Ans: Because a magnet can attract both another magnet (opposite pole) and a non-magnetized magnetic material (like an iron nail). However, a magnet will only repel another magnet. Therefore, if two objects repel, you can be 100% sure both are magnets.
10. "Did You Know?" (Website Side-Bar Content)
The First Magnet: Natural magnets were first discovered in ancient Greece (Magnesia) and were called Lodestones (Magnetite).
Earth as a Magnet: The Earth behaves like a giant bar magnet. Interestingly, the Earth’s Magnetic South Pole is actually located near the Geographic North Pole!
Maglev Trains: Some of the fastest trains in the world, like the Maglev in Japan, use powerful magnets to "float" above the tracks to reduce friction.
11. Fun DIY Activity for Students
Make Your Own Compass:
Magnetize a sewing needle using the single-touch method.
Pass the needle through a small piece of cork or foam.
Place the cork in a bowl of water so it floats freely.
The needle will rotate and settle in the North-South direction.
12. Quick Quiz (Multiple Choice)
1. Which of the following is a natural magnet? (a) Bar magnet (b) Horseshoe magnet (c) Lodestone (d) Electromagnet Ans: (c) Lodestone
2. Where is the magnetic strength maximum in a bar magnet? (a) At the center (b) At the poles (c) Along the sides (d) It is uniform everywhere Ans: (b) At the poles
3. Which metal is NOT attracted to a magnet? (a) Iron (b) Nickel (c) Cobalt (d) Aluminum Ans: (d) Aluminum
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