Wednesday, 8 February 2012

Magnetism . Electromagnetism . Magnetic Flield

     The principles of magnetism are of great importance in the field of electiricity as generators , transformers and motors depend on magnets and magnetism in their operation.
     A magnet can be either permanent or temporary . If a piece of  iron or is magnetized and retains its magnetism , it is a permanent magnet . Permanent magnets are the basis for some of the simpler devices . The compass needle responds to the magnetic field of the Earth which is itself a permanent magnet . Other examples of permanent magnets are a horseshoe magnet , a bar magnet , etc. Each of these magnets has a north and a south magnetic poles .
     Permanent magnets are used for producing the magnetic field necessary for operation of small , inexpensive electrical motors.
     When current flows through a coil , a magnetic field with a north and south poles is set up like that of a permanent magnet . However , when the current flow stops , the magnetic field disappears as well . This type of temporary magnetism is called electromagnetism .When electricity flows through a wire or conductor , magnetic lines of force (magnetic flux) are created around that wire . When a piece of wire is passed through a magnetic field , electricity is in that wire .
      Electromagnetic method of  producing electricity is based on operation generators in which the electricity is by conductors moving through a magnetic field . This method is used for generators of various sizes .









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