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When current travels
through a wire, a
magnetic field, made of
lines of force, is
formed around the wire.
If the wire is coiled,
the lines of force link
with each other.
The result is a magnetic
field with the same
shape as the field
surrounding
a bar magnet.
The strength of the
field is determined by
the number of turns and
the
current through the
coil.
The field can be
concentrated by placing
a steel or iron CORE in
the centre of the coil.
This is called an
ELECTROMAGNET or
SOLENOID.
If a soft
iron
core is used, it becomes
only temporarily
magnetised when the
current is switched on,
losing its magnetism
when switched off.
This effect is used in
bells and buzzers, and
in scrapyards for
shifting metal scrap
around.
The field has a North
and a South pole.
It obeys the same
rules as a bar magnet.
Like poles repel each
other, unlikes attract.
Electromagnets can react
with bar magnets.
This effect is used in
loudspeakers, moving
coil meters etc.
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