Magnetism and Matter
Magnetism and Matter :- There is an island in the Greek country named Magnesia [now this place is a part of western Turkey and now its name is Manisa], where deposits of magnetic ores were found in 600 BC. When the shepherds used to go to this island to graze sheep, they found that their sticks with iron caps in their hands and their wooden shoes (which had iron nails stuck in them) used to stick to the rocks located there. The word ‘magnet’ is derived from the name of this Greek island, Magnesia.
The ore found on these rocks was named Magnetite, whose chemical formula is Fe3O4. Magnetite is called a natural magnet. Magnetite has the property of attracting iron, nickel, cobalt etc. towards itself, which is called magnetism.
The credit for discovering the physical properties of magnets goes to the Chinese. They found that when a natural magnet is kept freely in the horizontal plane (by tying a thread at the center of gravity or placing it on a cork and floating it in still water) then it always remains in the north-south direction. Due to its directional property, magnetite came to be called lodestone, which means leading stone.
The shape and size of a natural magnet is uncertain, hence it is not suitable to be used for experimental and scientific works. Besides, the magnetism of a natural magnet is also very weak. For this reason, artificial magnets (man-made magnets) made of iron, steel and nickel are made whose magnetism is very strong. There are two types of artificial magnets :-
- Permanent Magnet :- Permanent magnets are made from hardened steel or alloys like Alnico(Al+NI+Co), cobalt, steel, tungsten etc. which are not easily demagnetized. The main drawback of permanent magnets is that their magnetism cannot be controlled, that is, its poles cannot be changed and its strength cannot be increased or decreased.
- Temporary Magnet :- These are made from soft iron or steel. Their magnetism can be controlled. As long as the magnetizing force is present, they remain magnetized and as soon as the magnetizing force is removed, they become demagnetized. Their polarity and strength can also be changed.