Here present the article about the what is magnetism and nature of magnetism
Megnetism
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| What is magnetism |
About twenty centuries before it was discovered that certain lead coloured stones possess a peculiar property of attracting fillings of small pieces of steel. Since this mineral was found in Magnesia(a province in Asia)in plenty,it was given a name of Magnetite. Magnetite(Fe3O4)is a magnetic oxide of iron and is found in large quantity in Sweden and North America.
Later on it was discovered that if an elongated piece of this mineral is suspended and made free to rotate in a horizontal plane, it would come to rest pointing north and south.The north seeking end of bar magnet is called its north(N-)pole, and the south seeking end its south(S-) pole.This mineral is also called the lode stone meaning leading stone.
What is magnetism?
An Any body which possesses the power of attracting pieces of iron is known as a magnet and the property of a body by virtue of which this attraction takes place is known as magnetism.
Since lode stone possesses magnetism when it is taken out from the earth,it is called a natural magnet.Natural magnets are rugged and clumsy and also comparatively weak,therefore, have no practical utility.Commercial magnets are made artificially from iron and steel or alloy materials and are called artificial magnets.
Artificial magnets can be made either by rubbing a piece of iron or steel with the lode stone or by passing a heavy direct current through a coil wound over the piece of iron or steel.In the former method an iron or steel piece is magnetised by repeatedly rubbing a magnet over its entire length in the same direction. The piece converted into a magnet has its first terminal the same polarity and the last terminal has the opposite polarity to that of the end of the magnet used for rubbing.In the second method, which is more, common convenient, suitable and effective. direct current is passed in an insulated Copper coil wound round a piece of soft iron. Magnets prepared in this way are called electro- magnets.
Magnets employed in electrical machines and equipment aie of artificial type and generally horse shoe or U-shaped Because they can retain their magnetism for a very long time.
Magnets may be classified as being permanent or temporary,depending on their ability to retain magnetism.
Hardened steel and certain alloys of nickel and cobalt, when magnetised, retain their magnetism unaltered for long time after removal of magnetising force.Such substances are said to have high retentivity power and after being magnetized are termed as permanent magnets. Alnico is a widely used alloy (aluminium,nickel,cobalt,iron) for making permanent magnets. Permanent magnets are used extensively in telephone receivers,door latches,small DC motors, electrical measuring instruments, speedo-meters,and a great variety of gadgets.
Other substances,like soft iron are easily and strongly magnetized but lose most of their strength when the magnetizing force is removed.Such substances are said to have low retentivity power and termed as temporary magnet materials.These materials are of more importance than permanent magnet materials,both in total amount in use and in variety of applications.In electric generators and motors where it is desirable to control the amount of magnetism present in the magnet, soft iron temporary magnets are employed.
NATURE OF MAGNETISM
A Magnets have two opposite kinds of magnetism or magnetic poles,which attract or repel each other.One of the magnetic poles is known as north pole and other as south pole. From experiments it has been observed that
(i) the Similar poles repel each other and opposite poles attract each other.
(ii)an Attractive or repulsive force between the two magnetic poles is directly proportional to the product of their pole strengths and inversely proportional to the square of the distance between them.
(iii) Molecules of all magnetic materials are complete magnets in themselves,each having north and south poles.If a bar magnet is broken into two parts. each part would be complete magnet in itself i.e.two new poles would appear at the breakage point. a new south pole on the piece which has the original north pole and a new north pole on the piece which has the original south pole. The subdivision of the bar magnet may be continued infinitely, but always with the same result,as illustrated . No process of division can produce an isolated single pole.If it were physically possible to break a magnet into so many pieces that each piece is a molecule,it would be logical to assume that each of these molecules would be a magnet.
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