Chapter 4 Notes: Exploring Magnets

A magnet is an object that attracts certain materials like iron, nickel, and cobalt. Magnets can be natural (lodestones) or artificial (made in labs, used in pencil boxes, toys, etc.). They come in different shapes such as bar magnets, U-shaped magnets, and ring magnets.

Materials that are attracted towards a magnet are called magnetic materials (e.g., iron, nickel, cobalt). Materials that are not attracted are called non-magnetic materials (e.g., wood, plastic, glass, rubber). A magnet can attract magnetic materials even through non-magnetic materials like wood or cardboard.

A magnet has two ends called poles—the North pole (N) and the South pole (S). The magnetic force is strongest at the poles. Iron filings stick most at the two ends of a bar magnet and least in the middle. Poles always exist in pairs—even if a magnet is broken into pieces, each piece will have both a North and a South pole.

A freely suspended magnet always comes to rest in the North-South direction because the Earth itself behaves like a giant magnet. The end pointing North is the North pole and the end pointing South is the South pole. This property is used in a magnetic compass to find directions. An iron bar (non-magnet) does NOT always settle in the North-South direction.

When two magnets are brought close to each other:

• Unlike poles (N–S) attract each other.
• Like poles (N–N or S–S) repel each other.

Repulsion is the sure test to identify a magnet, because a magnet repels only another magnet—it always attracts iron or other magnetic materials.

You can make a simple compass by stroking a magnet along an iron needle 30–40 times in the same direction to magnetise it. Place the needle through a cork and float it in water—it will align in the North-South direction. This is similar to the ancient Indian matsya-yantra used for sea navigation.

Magnets can lose their magnetic properties if mishandled. To keep magnets safe: store in pairs with unlike poles facing the same side with a piece of wood in between; place soft iron pieces across the ends. Do not heat, drop, hammer, or keep near mobile phones or remote controls.