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Tuesday, 21 August 2012

What is 'electromagnetism"?

(Reviewed and updated on 3/6/2016)

Understanding the term “electromagnetism”:

    • Electromagnetism, as the word suggests, is about two related phenomena, namely:
      • magnetism due to electrons-flow (current) in a conductor (a.k.a. magnetic effect of a current); and,
      • electrons-flow due to magnetism (a.k.a. magnetic induction of electro-motive force (emf) which induces current to flow in a conductor when it is in a complete or closed circuit. If the conductor is not in a complete circuitemf is still induced - but no induced current can flow because the circuit is incomplete or open):

                                                               i.      First Phenomenon - Magnetic Effect of a Current
                                    When current (electrons) flows through a conductor, it creates a magnetic                                           field around the conductor.

                                                                                    This phenomenon was accidentally discovered in 1820 by a Danish physicist, Hans Christian Oersted. This magnetic effect has now been put to good use:

·        To attract (pull) ferromagnetic materials as in:
o       magnetic lifting machine
o       electric bell
o       electromagnetic relay
o       the telephone earpiece; loud speaker, etc.
o       the circuit breaker
  by the use of electromagnets (current-created soft-iron temporary magnetsno current, no magnetism - the soft iron is used merely to concentrate the magnetism when magnetism is there – when there is no current, there is no magnetism in the soft iron. The soft iron, being a soft magnetic material unlike steel, does not turn into a permanent magnet when the current is OFF)

·        To interact with another magnetic field to create:
o       a push (including levitation as in magnetic-levitated (MAG-LEV) train or vehicle),
o       a turning effect as in the motor in a fan, in an electric car, in loudspeakers, moving coil meters, etc.
                                                             ii.      Second Phenomenon (Magnetic Induction of Electro-motive Force (emf) - The Reverse of the 1st Phenomenon): Cutting or changing magnetic lines of force (changing magnetic flux) in a conductor can induce current or electromotive force in the conductor:

                                                                                 i.      In 1831, Michael Faraday succeeded in producing current by moving a conductor in a magnetic field and subsequently in inventing dynamo.

                                                                               ii.      This effect (electromagnetic induction) has now been widely used in:
a.       current-generating device such as dynamo and electric generators - both ac and dc; and,
b.      in step-up and step-down transformers,

to make our modern life possible: Imagine, how our life would be without generators to produce electricity and without transformers to adjust voltages to suit operating voltages (voltage ratings) of various electrical appliances that support our modern lifestyle?!

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