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Electromagnetic Coil.
The magnetic
field around a straight wire is not very strong.
A strong field can be made by
coiling the wire
around a piece of soft iron.
This electromagnet is sometimes called
a solenoid.
The shape of the magnetic field is the same as a bar magnet.
The soft iron inside the
coil makes the magnetic field stronger
because it becomes a magnet itself
when the current is flowing.
Soft iron is used because it loses its magnetism
as soon as the current stops
flowing.
Soft iron
is said to form a temporary
magnet.
In this way, the electromagnet can be
switched on and off
by turning the electricity on and
off.
Steel forms a permanent
magnet.
If steel was used inside the
coil,
it would continue as a magnet after the electricity was switched
off.
It would not be useful as an electromagnet.
Permanent magnets are needed for
electric
motors, generators, loudspeakers and
microphones.
The strength of the magnetic
field around the coil can be
increased by
1. Using a soft iron core (core means middle bit).
2. Using more turns of
wire on the coil.
3. Using a bigger
current.
Reversing the direction of the current
will reverse the magnetic field direction.
An electromagnet is used in the electric bell, relay,
circuit
breaker, loudspeaker and microphone.
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Copyright © 2008 Dr. Colin France. All Rights Reserved.