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Wee-Kiat Kong (wkkong@senet.com.au) wrote:
: I'm doing as assignment for Physics about induced EMF and I have to describe 
: how a transformer works.

: My problem is that I don't quite understand what the iron core in 
: transformers actually do. Does an alternating current get induced in the core 
: due to the magnetic field caused by the primary coil's alternating current? 
: Does it (the iron core) therefore create another stronger magnetic flux which 
: induces an EMF in the secondary coils?

If you thrust a magnet into a coil, a voltage appears  at the coil's
terminals, right?  And if the terminals are connected to a resistor, there
will be an electric current.

On the other hand, if you have a piece of iron in a coil, and then you
create an electric current in the coil, the iron will become a magnet.

Transformers harness both of the above effects.  The primary coil causes
the core to magnetize.  When the core magnetizes, it's as if a magnet has
been thrust into the coil, and so a voltage appears on the secondary.

Also, it turns out that iron rings can develop fierce levels of magnetism,
far larger than iron rods.  So, a transformer should take the form of two
coils wound around a thick iron donut.

Without the iron, the transformer has "loose coupling".  If an iron-core
transformer is like one gear turning another, then an air-core transformer
is like one propeller blade blowing wind upon another propellor and making
it turn.  


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