Introduction to Magnets

You may have encountered magnets in everyday items like refrigerator stickers, pin holders, or pencil boxes. These objects have the fascinating ability to stick to certain surfaces, like iron almirahs, without any glue. This property is due to a force called magnetism. Large, powerful magnets are even used in cranes to lift heavy iron junk from scrapyards.

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How Magnets Were Discovered

The discovery of magnets is linked to an ancient story. It is said that there was a shepherd named Magnes in ancient Greece. He had a wooden stick with a small iron tip. One day, while grazing his sheep, he was surprised to find that the iron tip of his stick got stuck to a large black rock. He had to pull hard to free it.

This rock was a natural magnet, and it was attracting the iron on his stick. Such rocks were later given the name magnetite, possibly after the shepherd Magnes or the region of Magnesia where it was first discovered. Magnetite is a naturally occurring rock that contains iron and has the property of attracting iron.

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Natural vs. Artificial Magnets

Based on their origin, magnets can be classified into two types:

• Natural Magnets: These are magnets that occur naturally, like the rock magnetite. They have irregular shapes and often have weaker magnetic force.
• Artificial Magnets: These are man-made magnets, created by magnetizing pieces of iron or other specific materials. They are much more common today and can be made much stronger than natural magnets. Artificial magnets are prepared in various convenient shapes.

Common Shapes of Artificial Magnets:

• Bar magnet (rectangular)
• Horseshoe magnet (U-shaped)
• Cylindrical magnet
• Ball-ended magnet

Magnetic and Non-Magnetic Materials

A key property of a magnet is its ability to attract certain materials. However, a magnet does not attract everything. Based on this property, we can classify materials into two groups.

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Magnetic Materials

The materials which get attracted towards a magnet are called magnetic materials. These are materials that a magnet can pull towards itself.

Examples: Iron, Nickel, and Cobalt. Objects made from these materials, like an iron ball, a steel needle, or a key, will stick to a magnet.

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Non-Magnetic Materials

The materials which are not attracted towards a magnet are called non-magnetic materials. A magnet will have no effect on these materials.

Examples: Plastic, wood, rubber, glass, leather, cloth, aluminium, copper, and soil.

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Identifying Magnetic and Non-Magnetic Objects

We can use a magnet (or a "Magnes stick") to test various objects and identify the materials they are made from.

Name of the object	Material which the object is made of	Attracted by magnet? (Yes/No)	Type of Material
Iron ball	Iron	Yes	Magnetic
Plastic scale	Plastic	No	Non-Magnetic
Shoe	Leather	No	Non-Magnetic
Sewing needle	Steel (an alloy of iron)	Yes	Magnetic
Wooden block	Wood	No	Non-Magnetic
Glass tumbler	Glass	No	Non-Magnetic

Poles of a Magnet

When a magnet attracts magnetic materials like iron filings, the attraction is not uniform all over the magnet's surface. The magnetic force seems to be concentrated in specific regions.

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Location of Magnetic Poles

If you spread some iron filings on a sheet of paper and place a bar magnet on it, you will observe that the iron filings are attracted more towards the regions close to the two ends of the magnet. Very few filings stick to the middle portion.

These ends, where the magnetic attraction is the strongest, are called the poles of the magnet.

Every magnet, regardless of its shape, has two poles. For a bar magnet, the poles are located at its ends. For a horseshoe magnet, the poles are at its two free ends.

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A Puzzle: Identifying a Magnet

Puzzle: You are given two identical iron bars. One is a magnet, and the other is a simple iron bar. How will you find out which one is the magnet?

Solution: The key is knowing that a magnet's attraction is strongest at its poles and weakest at its centre.

1. Take one bar (let's call it Bar A) and bring its end to the middle of the other bar (Bar B).
2. If there is a strong attraction, then Bar A is the magnet.
3. If there is no attraction, then Bar B is the magnet.

This works because the middle of a magnet has almost no magnetic force, while the end of a magnet (its pole) has a strong force. The simple iron bar will be attracted to any part of the magnet.

Finding Directions with Magnets

One of the most useful properties of a magnet is its ability to indicate direction. This property has been used by travellers for centuries.

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The Directive Property of a Magnet

If a bar magnet is suspended freely (for example, by tying a thread at its middle) so that it can rotate without any friction, it will always come to rest pointing in a particular direction. This direction is the geographic North-South direction.

This property is called the directive property of a magnet.

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The North and South Poles

The two poles of a magnet are named based on this directive property:

• North Pole (N): The end of a freely suspended magnet that points towards the geographic North is called its North-seeking end, or the North pole.
• South Pole (S): The end that points towards the geographic South is called its South-seeking end, or the South pole.

All magnets have two poles, and they are usually marked with 'N' and 'S' for identification.

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The Magnetic Compass

A device developed based on the directive property of magnets is the compass. It is an instrument used for finding directions.

A compass is usually a small box with a glass cover. Inside it, a small, magnetised needle is pivoted at the centre, allowing it to rotate freely. The needle always aligns itself with the North-South direction when at rest. A dial with directions (N, S, E, W) marked on it is placed below the needle. To identify the North pole, the tip of the needle pointing North is often painted a different colour (usually red).

Attraction, Repulsion, and Magnet Care

Magnets interact with each other in predictable ways. This interaction can be either an attraction (pulling together) or a repulsion (pushing apart). We can also create our own magnets and must know how to care for them properly.

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Make Your Own Magnet

It is possible to turn a piece of iron, like an iron bar or a needle, into a magnet. This process is called magnetisation.

The Single-Touch Method

1. Take a rectangular piece of iron and place it on a table.
2. Take a bar magnet and place one of its poles (e.g., the North pole) on one edge of the iron bar.
3. Without lifting, stroke the magnet along the entire length of the iron bar until you reach the other end.
4. Lift the magnet and bring the same pole back to the starting point.
5. Repeat this stroking process in the same direction about 30-40 times.

After this process, the iron bar will become a magnet. You can check this by bringing some iron pins near it.

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Attraction and Repulsion between Magnets

When two magnets are brought near each other, they exert a force on one another. This force can be either attraction or repulsion, and it follows a fundamental law:

Like poles repel each other, and unlike (opposite) poles attract each other.

• Repulsion: If you bring the North pole of one magnet near the North pole of another, they will push each other away. The same happens with two South poles. (N-N repel, S-S repel).
• Attraction: If you bring the North pole of one magnet near the South pole of another, they will pull towards each other. (N-S attract).

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A Few Cautions: How to Care for Magnets

Magnets can lose their magnetic properties (demagnetize) if they are not handled or stored properly.

Things to Avoid:

• Heating: Do not heat a magnet.
• Hammering: Do not hammer or hit a magnet.
• Dropping: Avoid dropping magnets from a height.

Proper Storage:

Magnets become weak if not stored correctly. To keep them safe:

• Bar Magnets: Should be stored in pairs with their unlike poles on the same side. A piece of wood should be kept between them, and two pieces of soft iron, called keepers, should be placed across their ends.
• Horseshoe Magnet: A single piece of soft iron should be kept across its poles.

Additionally, magnets should be kept away from electronic devices like cassettes, mobiles, televisions, music systems, computers, and CDs, as their magnetic fields can damage these items.

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