Electro-magnets always have a soft iron core which increases
the strength of the magnet. The core has to be soft - this means
magnetically soft- so that when the current is turned off the
magnetism disappears with it.
There are hundreds of different
kinds of jobs that are done by using electro-magnets. Here are
some other uses:
You can slide the bolts of locks and latches, tap out telegraphic
dots and dashes, open and close switches in distant electric
circuits. The rotors of all electric motors are spun by electro-magnetism.
A relay is a device which uses a low current circuit to switch
high current circuit on/off. A large relay system is used in
cars for switching the starter motor, because it draws a very
When the switch in the low current is closed it turns the electro
magnet on, this attracts the iron rocker. The rocker pivots and
closes the contacts in the high current circuit. When the low
current switch is opened the electro-magnet stops pulling, the
rocker returns and the high current circuit is broken again.
Electro-magnets have been used in hospitals to remove particles
of metal ( those which are magnetic- because not all common metals
are magnetic, e.g. aluminium, copper, brass, gold, silver), which
may have lodged in people's eyes after an accident.
Some large cranes in scrapyards are electromagnetic. The electro-magnet
is made up of a big coil of wire, with many turns and a soft
The crane lifts large pieces of metal when the current is switched
on and drops its load when the current is switched off.
A circuit breaker, also called a resettable fuse is electro-magnetic.
This is placed on the incoming live wire. If the current gets
too high the magnetic field in the coil pulls the iron rocker
which "trips" the switch and breaks the circuit. It
can be reset manually but will always switch itself off if the
current is too high.