The chapter introduces the concept of magnets through a story about navigation. In ancient times, sailors used the positions of stars to determine directions at night. However, during cloudy weather, they needed another method.

This led to the use of a device called the magnetic compass, which utilizes the property of magnets to indicate direction.

Most people encounter magnets in everyday objects like pencil boxes, purses, refrigerator stickers, and toys, where they are used for holding things together or for attraction.

Magnets were first discovered as naturally occurring stones, known as lodestones. Later, people learned to create magnets from materials like iron. Today, magnets are made from various materials and come in many different shapes and sizes, including bar magnets, U-shaped magnets, ring magnets, and cylindrical magnets.

Magnets found in laboratories and common items are typically artificial magnets.

Magnetic And Non-Magnetic Materials

Not all materials are attracted to a magnet. We can categorize materials based on whether they interact with a magnet.

Identifying Magnetic Materials

When a magnet is brought near different objects, some materials are attracted to the magnet and will stick to it.

Materials that are attracted towards a magnet are called magnetic materials.

The most common magnetic material is iron. Other metals like nickel and cobalt are also magnetic. Certain combinations of these metals with other elements can also be magnetic.

An activity involving collecting objects made of different materials (wood, plastic, glass, iron, etc.) and bringing a magnet near them helps differentiate between magnetic and non-magnetic substances. You would observe that objects made of iron, nickel, or cobalt stick to the magnet.

Identifying Non-Magnetic Materials

Materials that are not attracted towards a magnet are called non-magnetic materials.

Examples include wood, plastic, glass, paper, rubber, and materials like copper or aluminum (though some alloys might have magnetic properties, pure copper/aluminum are non-magnetic).

During the activity, objects made of materials like wood, plastic, or glass would not stick to the magnet.

Poles Of Magnet

Magnets have specific regions where their magnetic strength is concentrated. These regions are called the poles.

Where Iron Filings Stick Most

An activity using iron filings can help visualize where a magnet's strength is strongest.

If you spread iron filings on a sheet of paper and place a bar magnet on top, you'll notice that the iron filings do not stick evenly all over the magnet.

Instead, the maximum number of iron filings accumulate near the ends of the bar magnet. Very few filings stick to the middle part of the magnet.

This observation shows that the attractive force of a magnet is strongest at its ends.

North And South Poles

Every magnet, regardless of its shape, has two poles. These are called the North pole and the South pole.

These poles are located near the ends of a bar magnet or at specific points on other shapes where the magnetic effect is strongest.

Poles Always Exist In Pairs

A fundamental property of magnets is that their poles always come in pairs. Every magnet has both a North pole and a South pole.

It is impossible to isolate a single North pole or a single South pole. If a magnet is broken into smaller pieces, each piece will still have both a North pole and a South pole, no matter how small the piece is.

Finding Directions

One of the most important applications of magnets, historically and currently, is finding direction.

Freely Suspended Magnet Points North-South

When a bar magnet is suspended freely from its center point so that it can rotate horizontally, it will always come to rest in a specific direction.

This direction is approximately the geographic North-South direction.

If you rotate the suspended magnet gently and let it settle, it will consistently point towards the North-South line.

The end of the magnet that points towards the geographic North direction is called the North-seeking pole or simply the North pole (N) of the magnet.

The other end, which points towards the geographic South direction, is called the South-seeking pole or the South pole (S) of the magnet.

This property distinguishes a magnet from other metal pieces. A non-magnetic iron bar, when suspended freely, will not consistently rest in the North-South direction; it can point in any random direction. This provides a simple test to check if a material is a magnet.

Using The Earth's Magnetism

The reason a freely suspended magnet aligns itself in the North-South direction is that our Earth itself behaves like a giant magnet. The Earth has its own magnetic field, and the poles of the suspended magnet are interacting with the Earth's magnetic field, causing them to align.

It's important to note that the Earth's magnetic poles are not exactly at the geographic North and South poles, but they are close enough for navigation purposes using a compass.

The Magnetic Compass

The directional property of magnets led to the development of the magnetic compass, a device used for finding directions.

A typical magnetic compass consists of a small, lightweight magnet, usually in the shape of a needle, which is mounted on a pivot so that it can rotate freely. This needle is enclosed in a small circular box with a transparent cover.

Below the needle, there is a dial marked with directions (N, S, E, W, NE, SE, SW, NW).

When placed on a horizontal surface, the compass needle comes to rest, with one end pointing towards North and the other towards South. The North-pointing end of the needle is often distinguished, for example, by being painted red.

To find directions using a compass, you wait for the needle to settle in the North-South line. Then, you gently rotate the compass box until the 'N' and 'S' markings on the dial align with the North and South poles of the needle, respectively. Once aligned, the dial shows all the directions relative to that location.

Extra Information: Long before modern compasses, similar devices were used. For instance, the 'matsya-yantra' used in ancient India was a magnetised fish-shaped iron piece floated in a vessel of oil to find direction at sea.

Making Your Own Magnetic Compass

You can create a simple magnetic compass using a few basic items:

Steps:

1. Magnetise a needle: Take an iron sewing needle and stroke it repeatedly (at least 30-40 times) in the same direction with one pole of a strong magnet. Always lift the magnet away from the needle after each stroke and return to the starting point to repeat. This process aligns the magnetic domains within the needle, making it a magnet. You can test its magnetism by seeing if it attracts iron filings or small steel pins.
2. Mount the needle: Pass the magnetised needle horizontally through a small piece of cork.
3. Float it: Place the cork with the needle floating in a bowl of water. Ensure the needle stays above the water surface.

When the cork and needle come to rest, the needle will point approximately towards the North-South direction, acting as a compass.

Attraction And Repulsion Between Magnets

When two magnets are brought near each other, they exert forces on each other, either pulling together or pushing apart. These interactions depend on which poles are facing each other.

Like Poles Repel

If you bring the North pole of one magnet near the North pole of another magnet, you will feel a force pushing them apart. Similarly, if you bring the South pole of one magnet near the South pole of another magnet, they will also push each other away.

Poles of the same type (North-North or South-South) are called like poles. Like poles repel each other.

Unlike Poles Attract

If you bring the North pole of one magnet near the South pole of another magnet, they will pull towards each other. This force will make them stick together.

Poles of different types (North-South or South-North) are called unlike poles. Unlike poles attract each other.

Repulsion As A Test For Magnetism

While magnets attract magnetic materials (like iron) and also attract unlike poles of other magnets, the most definitive test to determine if a piece of metal is truly a magnet is repulsion.

A magnet will attract an iron object using either of its poles. However, a magnet will *only* repel another magnet when their like poles are brought close. If a piece of metal is attracted by both poles of a known magnet, it is likely an ordinary magnetic material (like iron) and not a magnet itself.

Interaction With A Compass Needle

Since a compass needle is a small magnet, its interaction with another magnet follows the rules of attraction and repulsion. Bringing the North pole of a bar magnet near the North pole of the compass needle will cause the compass needle to deflect away (repel).

Bringing the South pole of a bar magnet near the North pole of the compass needle will cause the compass needle to deflect towards it (attract).

Magnetic Effect Through Non-Magnetic Materials

Magnets can exert their influence even through materials that are not magnetic. If you place a non-magnetic material like a piece of wood, cardboard, plastic, or glass between a magnet and a compass needle, the compass needle will still be affected by the magnet and deflect.

This shows that the magnetic force can pass through non-magnetic substances.

Fun With Magnets

Magnets offer many possibilities for interesting activities that demonstrate their properties.

• Making a Magnetic Garland: You can link steel paperclips together by touching them to a magnet. The paperclips become temporarily magnetized and attract each other, forming a chain or "garland".
• Moving Steel Balls in a Maze: Steel balls placed in a maze on a non-magnetic surface (like cardboard) can be guided through the maze by moving a magnet underneath the surface. The magnetic force attracts the balls, moving them without direct contact.
• Picking Up Objects In Water: A steel paperclip or pin that has fallen into water can be retrieved using a magnet without getting the magnet or your fingers wet. You can simply bring the magnet near the object in the water, and it will attract and lift it out.
• Magnetic Cars: Attaching magnets to toy cars allows for exploring attraction and repulsion. If two cars have magnets attached with like poles facing each other, they will repel and push away. If unlike poles face each other, they will attract and move towards each other.

These activities highlight that magnets can interact with magnetic objects and other magnets even without physical contact, demonstrating the presence of a magnetic field.

Caring For Magnets

Magnets need to be handled and stored carefully to maintain their strength (magnetism).

Things that can weaken or demagnetize a magnet:

• Heating a magnet.
• Dropping a magnet forcefully.
• Hammering a magnet.
• Keeping magnets near certain electronic devices like mobile phones or remote controls (strong magnets can sometimes interfere with these devices).

Proper storage helps magnets retain their magnetism:

• For bar magnets, they should be stored in pairs with their unlike poles facing the same direction. A piece of non-magnetic material (like wood) should be placed between the two magnets. Two pieces of soft iron, called keepers, should be placed across the ends of the pair.
• For other shapes like ring magnets, storing them with poles alternately arranged in a stack can help.

Following these precautions ensures that your magnets remain strong and useful for a longer time.

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