Chapter 4: Exploring Magnets
4.1 Magnetic and Non-magnetic Materials
Types of Magnets
- Lodestones: Naturally occurring magnets discovered in ancient times.
- Artificial Magnets: Man-made magnets of various shapes (e.g., bar, U-shaped, ring, disc, cylindrical, spherical magnets).
Classification of Materials
- Magnetic Materials: Materials attracted towards a magnet. Examples include iron, nickel, and cobalt.
- Non-magnetic Materials: Materials that are not attracted towards a magnet. Examples include wood, plastic, glass, paper, and rubber.
4.2 Poles of a Magnet
Magnetic Poles
- Poles: The regions near the ends of a magnet where the magnetic attraction is strongest.
- Every magnet has two poles: the North pole (N) and the South pole (S).
- Pair Existence: Magnetic poles always exist in pairs. It is impossible to isolate a single north or south pole; if a magnet is broken, each piece will still have both poles.
4.3 Finding Directions
Directive Property of Magnets
- A freely suspended bar magnet always comes to rest pointing in the North-South direction.
- The end pointing towards the geographic north is the North-seeking pole (North pole), and the end pointing south is the South-seeking pole (South pole).
- This alignment happens because the Earth itself behaves like a giant magnet.
The Magnetic Compass
- Magnetic Compass: A device developed for finding directions, containing a magnetized needle that can rotate freely on a pivot.
- The north-seeking end of the compass needle is typically painted red.
- Matsya-yantra: An ancient Indian navigation device consisting of a magnetized, fish-shaped iron piece kept in a vessel of oil, used for sea navigation.
4.4 Attraction and Repulsion between Magnets
Laws of Magnetic Poles
- Attraction: Unlike poles (North and South) attract each other.
- Repulsion: Like poles (North-North or South-South) repel each other.
- Sure Test of Magnetism: Repulsion is the only sure test to determine if an object is a magnet, as an unmagnetized magnetic material (like iron) will be attracted to both poles of a magnet.
- Magnetic Penetration: Magnetic forces can act through non-magnetic barriers (such as wood, plastic, cardboard, and glass).
4.5 Care and Safety of Magnets
How to Keep Magnets Safe
- Store bar magnets in pairs with unlike poles on the same side, separated by a piece of wood, with soft iron pieces (keepers) placed across their ends.
- Do not heat, drop, or hammer magnets, as they can lose their magnetic properties (demagnetize).
- Keep magnets away from electronic devices such as mobile phones, computers, television screens, and remote controls.