1. Introduction to Magnets

Magnets are objects that exert a force that pulls on other magnetic materials and attracts or repels other magnets. The study of magnets began with the discovery of natural magnets, but today we predominantly use man-made versions.

Discovery and History

• Lodestones: These are naturally occurring magnets discovered in ancient times. They were used by early travellers to find directions.
• Artificial Magnets: In modern times, magnets are prepared from pieces of iron, steel, or other alloys. They are stronger and more durable than natural magnets.

Common Shapes of Magnets

Magnets are manufactured in various shapes depending on their specific application:

• Bar Magnet: A simple rectangular block used in laboratories.
• U-shaped or Horse-shoe Magnet: Bent in a 'U' shape to bring both poles closer, increasing the magnetic strength.
• Ring Magnet: Circular magnets commonly found in electronic speakers and motors.
• Cylindrical Magnet: Shaped like a rod or tube.
• Needle Magnet: Very thin magnets used in magnetic compasses.

Ancient Indian Navigation: Matsya-yantra

India has a rich history of maritime trade. Long before modern compasses became standard, Indian sailors used the Matsya-yantra (also known as machchh-yantra):

• It consisted of a magnetized iron piece, often shaped like a fish.
• It was placed in a vessel filled with oil.
• Because it floated freely, it aligned itself with the Earth's magnetic field, helping sailors navigate the vast oceans.

2. Magnetic and Non-magnetic Materials

Every material in our daily life responds differently to a magnet. Based on this attraction, we classify materials into two distinct groups.

Classification of Materials

• Magnetic Materials:
  • Materials that are strongly attracted towards a magnet.
  • Examples: Iron, Nickel, and Cobalt.
  • Steel is also magnetic because it contains a large percentage of iron.
• Non-magnetic Materials:
  • Materials that are not attracted towards a magnet.
  • Examples: Plastic, Wood, Rubber, Glass, and Paper.
  • Common metals like Aluminium, Copper, and Gold are also non-magnetic.

Material Identification Table

Object Name	Primary Material	Attracted by Magnet?
Sewing Needle	Steel/Iron	Yes
Pencil	Wood	No
Glass Tumbler	Glass	No
Iron Nail	Iron	Yes
Eraser	Rubber	No
Conclusion	Iron based	Strongly Attracted

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3. Poles of a Magnet

When we interact with magnets and iron filings (tiny pieces of iron), we observe that the magnetic strength is not the same throughout the body of the magnet.

Observation of Magnetic Strength

• When a bar magnet is dipped in iron filings, the filings stick more at the two ends.
• Very few iron filings stick to the middle part of the magnet.
• This indicates that the force of attraction is maximum at the ends of a magnet.

Defining the Poles

The two ends of a magnet, where the magnetic strength is concentrated, are called Poles:

1. North Pole (N): The pole that points towards the North when freely suspended.
2. South Pole (S): The pole that points towards the South when freely suspended.

Properties of Magnetic Poles

• Existence in Pairs: Magnetic poles always exist in pairs. It is impossible to have a magnet with only one pole (monopole).
• Breaking a Magnet: If you break a bar magnet into two pieces:
  • Each broken piece will automatically become a complete magnet.
  • New North and South poles will be formed at the broken ends.
  • Even the smallest particle of a magnet will still have both poles.

4. Finding Directions and the Magnetic Compass

The most useful property of a magnet is its directive property. Since ancient times, travelers have used magnets to find their way across vast oceans and deserts.

The Property of Direction

A freely suspended bar magnet always aligns itself in a North-South direction. This behavior is due to the following reasons:

• The Earth behaves like a giant magnet with its magnetic poles located near the geographic North and South poles.
• The North-seeking pole (North pole) of a magnet points towards the geographic North.
• The South-seeking pole (South pole) of a magnet points towards the geographic South.

The Magnetic Compass

A magnetic compass is a specialized device used to identify directions at any given location. Its construction includes:

• Compass Box: A small box, usually made of aluminum or plastic, with a transparent glass or plastic cover.
• Magnetic Needle: A tiny, lightweight magnet shaped like a needle that is pivoted at the center to rotate freely.
• Marked Dial: A dial placed below the needle with directions like North, South, East, and West marked on it.
• Identification: To avoid confusion, the North end of the needle is traditionally painted red.

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Indian Historical Context: Matsya-yantra

Long before the modern compass, Indian sailors used a indigenous device for navigation at sea:

• It was called the Matsya-yantra or Machchh-yantra.
• It consisted of a magnetized fish-shaped iron piece.
• The iron fish was kept floating in a vessel of oil, allowing it to move freely and point North-South.

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5. Attraction and Repulsion between Magnets

Magnets exert forces on each other even without touching. This interaction follows the fundamental Laws of Magnetism.

Laws of Attraction and Repulsion

The behavior of two magnets brought close to each other depends on the poles facing each other:

• Like Poles: When two North poles ($N-N$) or two South poles ($S-S$) are brought together, they Repel (push away from) each other.
• Unlike Poles: When a North pole and a South pole ($N-S$) are brought together, they Attract (pull towards) each other.

Pole of Magnet A	Pole of Magnet B	Resulting Action
North ($N$)	North ($N$)	Repulsion
South ($S$)	South ($S$)	Repulsion
North ($N$)	South ($S$)	Attraction
South ($S$)	North ($N$)	Attraction

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Repulsion: The Sure Test for Magnetism

How can you distinguish between a magnet and a simple iron bar? We use the test of repulsion:

1. Bring a known magnet's North pole near one end of the unknown object. If it attracts, the object could be iron or a magnet (with South pole facing).
2. Bring the same North pole to the other end of the unknown object.
3. If that end is repelled, the object is definitely a magnet.
4. If both ends are attracted, the object is just a magnetic material (like iron) and not a magnet itself.

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Magnetic Force through Non-magnetic Barriers

Magnetic force can pass through several non-magnetic materials without significantly losing its strength. Experiments show that magnets can attract pins through:

• Wood (like a table top).
• Glass (like a bowl of water).
• Cardboard or Plastic sheets.

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6. Proper Care and Maintenance of Magnets

Magnets are not permanent in the absolute sense; they can lose their magnetic strength (a process called demagnetization) if handled improperly.

Causes of Demagnetization

Magnets lose their properties if they are subjected to extreme conditions. To avoid this:

• Do not Heat: High temperatures disturb the internal alignment of magnetic particles.
• Do not Hammer: Strong mechanical shocks can destroy the magnetism.
• Do not Drop: Dropping a magnet repeatedly on a hard floor weakens its field.
• Electronic Interference: Keep magnets away from mobile phones, televisions, remote controls, and computers.

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How to Store Magnets Safely

To prevent magnets from becoming weak over time (self-demagnetization), follow these storage steps:

1. In Pairs: Bar magnets should be stored in pairs with unlike poles on the same side.
2. Wooden Spacer: Always place a piece of wood between the two magnets to keep them separated.
3. Magnetic Keepers: Place two pieces of soft iron (called keepers) across the ends of the magnets.
4. U-shaped Magnets: For a horse-shoe magnet, place a single iron keeper across its two poles.

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Conclusion: Fun with Magnets

Magnets are used in many daily items in Indian households, such as:

• Pencil boxes and purses with magnetic clasps.
• Refrigerator stickers and gaskets.
• Magnetic maze games and toys.

Always remember the caution: "Treat magnets with care to keep their magic alive!"

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