03 Feb What is magnetism?
We are back with another exciting story for your physics tuition. Your physics tuition will always come up with interesting facts about physics. About 800 B.C., a black stone was discovered in Magnesia, a province of Asia Minor. It was observed to be having a strong attraction for iron. Since it was found in Magnesia, it came to be known as a magnet. This stone was in fact an ore and is nowadays called magnetite.
In experiment, it was found that if this piece of loadstone was dipped in iron fillings and then lifted out, the fillings mainly adhered to its certain parts, the other parts remaining bare. These regions of greatest attraction were called the poles and the place where there was little attraction was called a neutral region.
It was also discovered that if a piece of loadstone was suspended by a thread or floated on a piece of wood, it came to rest in a definite direction-pointing towards north and south. The pole pointing towards the north was known as the North Pole and that pointing towards the south was the South Pole. This property was used by the Chinese in 13th century to make use of the magnets as compasses for finding the direction in the sea voyages.
The experiment in this field further revealed that if two loadstones were brought together, the north and the south poles attracted, while north-north and south-south poles repelled each other. This established the fact that dissimilar poles attracted each other and similar poles repelled each other.
If a bar of iron or steel is rubbed from end to end with a piece of loadstone, it also acquires magnetic properties and becomes a magnet. Such a magnet is known as an artificial magnet. This method was used for a long time for making artificial magnets.
Gradually the scientists working in this field also discovered that a magnet could also be made by winding an insulated wire round a piece of iron and passing an electric current through it. This is called an electromagnet. Such magnets are used in electric motors.
The next important discovery in the field of magnetism came in 1600. The English scientist, Sir William Gilbert, suggested that the earth was a giant magnet. This explained the fact why a freely suspended magnet points to the north and south of the earth
During the next few hundred years, more discoveries were made in this regard. However, the ‘phenomenon magnetism’ was not properly understood until the 19th century.
Now the scientists know that magnetism is caused by moving electrons. All matter is made up of atoms and atoms have a central core called the nucleus around which electrons revolve in different orbits. These electrons carry a negative charge. Whenever an electric charge moves, it produces a magnetic effect. The moving electrons make a substance magnet. Sometimes the magnetism of the different electrons in each atom gets neutralized, that is why some materials are non-magnetic in nature.
Magnetism occurs most strongly in three metals: iron, cobalt and nickel. These metals can be used to make strong magnets. Iron is almost always used because it is the cheapest of the three metals. Usually magnets are made of steel, an alloy of iron.
Magnets are very useful in our daily life. They are used in making the Mariner’s compass to guide the ships. They are also used in radio sets, television sets, telephones, microphones, and in many other electronic instruments. They are also used in electric generators and motors.