NCERT Solutions for Class 6 Science Chapter 13 — Fun with Magnets

Key Concepts

Intext Questions (Page-by-Page)

(ii) The Materials which are attracted towards a magnet are called ________.

(iii) Paper is not a ________ material.

(iv) In olden days, sailors used to find direction by suspending a piece of ________.

(v) A magnet always has ________ poles.

(ii) Artificial magnets were discovered in Greece.

(iii) Similar poles of a magnet repel each other.

(iv) Iron is a magnetic material.

(v) A magnet can separate iron pieces from a mixture of iron pieces and sand.

Method 1 — Suspension method: Tie a thread around the middle of the bar magnet and suspend it freely from a stand. Allow the magnet to come to rest. The end of the magnet that points towards the geographic north is the north-seeking pole (N pole), and the end pointing towards the geographic south is the south-seeking pole (S pole).

Method 2 — Using a compass: Place the unmarked bar magnet near a magnetic compass. Observe which end of the bar magnet repels the north-seeking end of the compass needle. The end that repels the north pole of the compass is the north pole of the bar magnet (like poles repel). The other end is the south pole.

• (a) N pole of magnet near N of compass → (iii) Compass needle gets repelled. Like poles repel each other. When the north pole of the bar magnet is brought near the north pole of the compass needle, the needle is pushed away (repelled).

• (b) N pole of magnet near S of compass → (ii) Compass needle gets attracted. Unlike poles attract each other. When the north pole of the bar magnet is brought near the south pole of the compass needle, the needle is pulled towards the magnet (attracted).

• (c) Magnet brought near compass from side → (i) Compass needle deflects and points in different direction. When a magnet is brought near the compass from the side, it disturbs the alignment of the compass needle, causing it to deflect and point in a different direction rather than the usual north-south direction.

Exercise Questions (NCERT Textbook)

(b) A ________ magnet has two poles.

(c) Similar poles of a magnet ________ each other.

(d) A magnet always rests in the ________ direction when suspended freely.

(b) A magnet can attract another magnet.

(c) A magnet can repel a magnetic material.

The items that will definitely be attracted are: iron nail and steel spoon.

1. By heating: When a magnet is heated to a high temperature, the thermal energy causes the orderly arranged magnetic domains to become random and disordered. This destroys the magnetic properties. The temperature at which a magnet loses its magnetism is called the Curie temperature.

2. By hammering or dropping: When a magnet is hammered repeatedly or dropped from a height, the mechanical shock disturbs the alignment of magnetic domains, causing the magnet to lose its magnetism partially or completely.

Other methods include:

• By placing two magnets with unlike poles together for a long time.
• By passing an alternating current through a coil surrounding the magnet (electrical demagnetisation).

1. CDs and hard drives store data using magnetic encoding. A strong external magnet can alter or erase the magnetic data stored on these devices, causing loss of information.

2. Mobile phones contain small magnets for speakers and sensors (like the compass). An external magnet can interfere with these components, causing the compass to give wrong readings and speakers to malfunction.

3. Televisions (especially CRT televisions) use electron beams that are controlled by magnetic fields. Bringing a magnet near the screen can distort the picture by deflecting the electron beams, and can cause permanent damage to the colour display.

4. Credit cards and ATM cards have magnetic strips. A magnet can erase or corrupt the data on these strips.

How it works: The Earth behaves like a giant magnet with its magnetic poles near the geographic poles. The compass needle aligns itself along the Earth's magnetic field, with the north-seeking end pointing towards the geographic north and the south-seeking end pointing towards the geographic south.

Uses: 1. Finding directions — It helps travellers, sailors, and hikers determine the north-south direction. 2. Navigation — Ships and aircraft use compasses for navigation. 3. Map reading — Hikers and surveyors use compasses to orient maps. 4. Military operations — Soldiers use compasses for determining directions in the field.

This property demonstrates that magnetic monopoles do not exist.

Examples of magnetic materials: 1. Iron — used in making electromagnets, motor cores 2. Nickel — used in making coins and plating

Examples of non-magnetic materials: 1. Wood — used in furniture, does not respond to magnets 2. Plastic — used in everyday items, not attracted by magnets

Magnes was tending his flock of sheep on a hillside when he found that the iron nails in his shoes and the iron tip of his shepherd's stick were sticking to a particular type of black rock on the ground. He tried to pull his staff free but found it firmly held by the rock. He was amazed and curious about this strange property of the rock.

This naturally occurring magnetic rock was called lodestone (or magnetite, Fe₃O₄). It was the first known natural magnet. The word "magnet" is believed to have come from the place Magnesia where these lodestones were found.

Later, the Chinese discovered that a piece of lodestone, when suspended freely, always pointed in the north-south direction. This led to the invention of the magnetic compass, which revolutionised navigation.

Multiple Choice Questions (MCQs)

Common Mistakes

1. Confusing attraction with magnetism: Many students think that if an object is attracted by a magnet, it must be a magnet. This is wrong — magnetic materials (iron, nickel, cobalt) are attracted by magnets but are not magnets themselves. Repulsion is the only sure test for a magnet because only a magnet can repel another magnet.

2. Assuming magnets attract all metals: Magnets do NOT attract all metals. They attract only iron, cobalt, and nickel (and alloys containing these like steel). Common metals like aluminium, copper, gold, silver, and brass are NOT attracted by magnets.

3. Thinking a broken magnet has single poles: Some students believe that breaking a magnet in half will give one piece with only a north pole and another with only a south pole. This is incorrect — each broken piece becomes a complete magnet with both north and south poles. Magnetic monopoles do not exist.

4. Confusing magnetic induction with permanent magnetism: When a piece of iron is brought near a magnet, it gets attracted and temporarily behaves like a magnet (magnetic induction). However, once the magnet is removed, the iron piece usually loses its magnetism. Students often confuse this temporary magnetism with permanent magnetism.

5. Ignoring demagnetisation risks: Students sometimes store magnets improperly — placing them near heat sources, dropping them, or storing them without keepers. These actions can weaken or destroy the magnet. Bar magnets should be stored in pairs with unlike poles together and with soft iron pieces (keepers) across the ends.

Exam Checklist

• [ ] I can define a magnet and list magnetic and non-magnetic materials with examples.
• [ ] I can name the two poles of a magnet and explain that poles always exist in pairs.
• [ ] I can state and explain the law of magnetic attraction and repulsion (like poles repel, unlike poles attract).
• [ ] I can describe the suspension method and compass method to identify the poles of an unmarked magnet.
• [ ] I can explain how a magnetic compass works and its uses in navigation.
• [ ] I can list at least three methods of demagnetisation (heating, hammering, dropping) and explain why magnets should be kept away from electronic devices.
• [ ] I can differentiate between magnetic and non-magnetic materials with at least two examples each.
• [ ] I can explain the discovery of magnets and the significance of lodestone.