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.
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