13. Fun with Magnets

Introduction: Paheli and Boojho saw a crane picking up iron junk from a heap. It had a large magnet attached to it. Magnets are very common – in refrigerator doors, pin holders, and pencil boxes.

Discovery of Magnets

It is said that a shepherd named Magnes in ancient Greece discovered natural magnets. The iron tip of his stick got stuck to a rock. The rock was a natural magnet, now known as Magnetite. It contains iron.

Magnetic vs Non-Magnetic Materials:

Magnetic: Materials that get attracted towards a magnet. (e.g., Iron, Nickel, Cobalt).
Non-Magnetic: Materials that are not attracted towards a magnet. (e.g., Plastic, Wood, Rubber, Cloth).

ACTIVITY 2: Finding Iron

Observation: If you rub a magnet in sand or soil, some particles stick to it. These are small pieces of iron filings present in the soil.

Poles of Magnet

If you observe iron filings sticking to a bar magnet, they stick mostly at the two ends. These ends are called the Poles of the magnet.

North Pole (N)
South Pole (S)

Finding Directions

A freely suspended magnet always comes to rest in the North-South direction. The end pointing towards North is called North seeking end (North Pole). The other is South seeking end (South Pole).

Compass: A device used to find directions based on this property. It has a small magnetic needle that can rotate freely.

Review: Make your own Magnet

Method: Take an iron bar. stroke it with one pole of a bar magnet along its entire length. Lift the magnet and bring the same pole back to the starting point. Repeat 30-40 times. The iron bar becomes a magnet!

Attraction and Repulsion

When two magnets are brought close to each other:

Like Poles Repel: North-North or South-South push each other away.
Unlike Poles Attract: North-South pull each other closer.

Caution!

Magnets lose their properties if they are heated, hammered or dropped from some height. Also keep them away from mobiles, TV, computers and music systems.

Chapter Summary

Magnetite is a natural magnet.
Magnet attracts materials like iron, nickel, cobalt. These are called magnetic materials.
Materials that are not attracted towards magnet are called non-magnetic.
Each magnet has two magnetic poles—North and South.
A freely suspended magnet always aligns in N-S direction.
Opposite poles of two magnets attract each other whereas similar poles repel one another.

Exercise Q1: Fill in the blanks

Artificial magnets are made in different shapes such as Bar magnet, Horse-shoe magnet and Cylindrical magnet.
The materials which are attracted towards a magnet are called Magnetic materials.
Paper is not a Magnetic material.
In olden days, sailors used to find direction by suspending a piece of Bar magnet / Magnetite.
A magnet always has Two poles.

Exercise Q2: True or False

A cylindrical magnet has only one pole. (False)
Artificial magnets were discovered in Greece. (False)
Similar poles of a magnet repel each other. (True)
Maximum iron filings stick in the middle of a bar magnet when it is brought near them. (False)
Bar magnets always point towards North-South direction. (True)
A compass can be used to find East-West direction at any place. (True)
Rubber is a magnetic material. (False)

Exercise Q3

Q: It was observed that a pencil sharpener gets attracted by both the poles of a magnet although its body is made of plastic. Name a material that might have been used to make some part of it.

Ans: The blade of the sharpener is made of Iron/Steel, which is a magnetic material. That is why it gets attracted to the magnet.

Exercise Q5

Q: Write any two properties of a magnet.

Ans:

A magnet attracts magnetic materials like iron, nickel and cobalt.
A freely suspended magnet always aligns itself in the North-South direction.

Exercise Q6

Q: Where are poles of a bar magnet located?

Ans: The poles are located at the two ends of the bar magnet.

Exercise Q7

Q: A bar magnet has no markings to indicate its poles. How would you find out near which end is its north pole located?

Ans: Suspend the magnet freely using a thread. Wait for it to come to rest. The end that points towards the North direction is the North pole of the magnet.

Exercise Q8

Q: You are given an iron strip. How will you make it into a magnet?

Ans: By 'Single Touch Method':

Place the iron strip on a table.
Take a bar magnet and place one of its poles near one edge of the iron strip.
Move the magnet along the length of the strip till you reach the other end.
Lift the magnet and bring the same pole to same starting point.
Repeat this process 30-40 times. The strip will become a magnet.

Exercise Q9

Q: How is a compass used to find directions?

Ans: A compass has a magnetic needle which can rotate freely. When kept at a place, the needle aligns in North-South direction. The red-painted end usually indicates North. By knowing North, we can find other directions (East, West, South).

Key Facts and Definitions

1. Important Definitions

Magnet: A material that attracts iron, nickel and cobalt.
Magnetite: Natural magnet (Iron ore).
Compass: Device used to find specific direction (North-South).
Pole: The ends of the magnet where magnetic force is strongest.

2. Cautions for Magnets

Magnets lose their properties if:

Heated.
Hammered.
Dropped from a height.

Keep magnets away from mobiles, TV, music systems, and computers.

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