Exploring Magnets — NCERT Solutions, AI Tutor & Practice

Understand: A magnet does not attract every material around it. Based on their behaviour with a magnet, materials are grouped into two types.

Magnetic materials: Materials that are attracted by a magnet.

• Examples: iron, nickel, cobalt (and steel).

Non-magnetic materials: Materials that are not attracted by a magnet.

• Examples: plastic, wood, rubber, glass, paper, aluminium.

Conclude: Iron and steel objects (like pins, nails) stick to a magnet, while wooden or plastic objects do not.

Understand: Every magnet has two ends called poles.

The two poles are:

1. North pole (N)
2. South pole (S)

Strength of a magnet:

• The pulling (attracting) power of a magnet is strongest at its two poles.
• It is weakest in the middle of the magnet.

Activity evidence: If you dip a bar magnet in iron filings, most filings stick at the two ends (poles) and very few in the middle.

Conclude: A magnet's magnetic force is concentrated at its poles.

Understand: When two magnets are brought close, their poles either pull toward or push away from each other.

Law of magnetic poles:

• Like poles repel each other (N–N or S–S push apart).
• Unlike poles attract each other (N–S pull together).

Example:

• If the north pole of one magnet is brought near the north pole of another → they repel.
• If the north pole is brought near the south pole → they attract.

Conclude: Same poles push away; opposite poles pull together.

Understand: If a bar magnet is hung freely by a thread so it can rotate, it does not stop randomly.

Observation:

• The magnet always comes to rest pointing in the North–South direction.
• The end pointing towards geographic north is called the North-seeking pole (North pole), and the other end points south (South pole).

This property is called: the directive property of a magnet.

Conclude: Because of this property, magnets are used to find directions — this is the working principle of a magnetic compass.

Understand: A magnetic compass is a small device used to find geographical directions.

Construction:

• It has a small, freely rotating magnetised needle placed inside a round box.
• The needle has a coloured (usually red) end marking the north.

Working:

• Because of the directive property of magnets, the needle always aligns itself in the North–South direction.
• The red (north) end points toward geographic north.

Use: Travellers, sailors and hikers align the compass so the needle matches the marked North; then they can read all other directions (East, West, South).

Conclude: A compass helped ancient travellers and sailors navigate long before modern GPS.

Understand: An ordinary iron object can be turned into a magnet by a method called magnetisation by stroking.

Materials needed: an iron nail, a bar magnet, some iron pins.

Steps:

1. Place the iron nail on a table.
2. Take one pole of the bar magnet and stroke it along the nail from one end to the other.
3. Lift the magnet at the end, bring it back to the starting point, and stroke again in the same direction.
4. Repeat this 30–40 times in the same direction.

Test: Bring the nail near iron pins — the pins now stick to it.

Conclude: The nail has become a temporary magnet. If you stroke in random directions, it will not become magnetised.

Understand: It seems like breaking a magnet might separate the North pole from the South pole.

Analyse:

• When a bar magnet is broken into two pieces, each piece becomes a complete magnet.
• Each new piece has both a North pole and a South pole.
• No matter how many times you break it, you can never get a magnet with only one pole.

Conclude: A single, isolated magnetic pole cannot exist — every magnet always has two poles.

Understand: Magnets do not stay magnetic forever if they are handled carelessly.

Ways a magnet loses its magnetism:

1. Heating the magnet strongly (in a flame).
2. Hammering or dropping it hard repeatedly.
3. Storing it carelessly without keepers, or keeping like poles of magnets together.

How to protect magnets:

• Store bar magnets in pairs with unlike poles together, separated by wooden pieces, and place soft iron bars (keepers) across the ends.

Conclude: Heat and rough handling weaken or destroy a magnet's magnetism, so magnets must be stored properly.

Understand: Both bars are made of iron and look the same, so we must use a magnetic property to tell them apart.

Method (using only the two bars):

1. Hold one bar and bring its end to the middle of the other bar.
2. If there is attraction → the bar you are holding is the magnet (a magnet's pole attracts the middle of the iron bar).
3. Now do the reverse: bring the end of the second bar to the middle of the first. If the middle does not attract → that middle belongs to the plain iron bar.

Key idea: A magnet attracts iron at its middle, but the middle of a magnet is a weak/neutral region and shows little attraction. Only the magnet's poles attract strongly.

Conclude: The bar whose end attracts the middle of the other bar is the magnet; the ordinary iron bar has no such strong-weak pattern.

Understand: Magnets are used in many objects we use daily, often without us noticing.

Everyday uses of magnets:

1. In the door of refrigerators to keep them closed tightly.
2. In magnetic pencil boxes, stickers and toys.
3. In a magnetic compass to find directions.
4. In speakers, headphones and electric bells.
5. To pick up and separate iron objects (e.g., in scrapyards).

Conclude: Magnets are useful for holding, attracting, sorting iron things, and for navigation.

Understand: A healthy compass needle should always swing and settle in the North–South direction because of the directive property.

Analyse the problem:

• If the needle stays stuck at one wrong position, it may be:
  1. Physically jammed on its pivot (friction/dust), or
  2. Placed near a magnet or iron object that pulls it, or
  3. The needle has lost its magnetism.

How to check:

1. Move the compass away from any magnets, iron objects, or mobile phones.
2. Gently tap it — a free needle should swing and return to North–South.
3. If it still does not align, the needle may be demagnetised and needs to be re-magnetised or replaced.

Conclude: A properly working compass, free from nearby magnetic disturbance, always realigns North–South.

Understand: Magnets were first discovered from a naturally occurring stone.

The story:

• Long ago, a shepherd named Magnes was walking on a hill (in a place called Magnesia).
• The iron nails of his shoes and the iron tip of his stick got stuck to certain black rocks on the ground.
• These rocks were natural magnets, later called magnetite or lodestone.

Connection:

• This natural stone that attracts iron is called a natural magnet.
• The word 'magnet' is believed to come from the name Magnes (or the place Magnesia).

Conclude: The accidental discovery of the naturally magnetic stone lodestone led to our knowledge of magnets.