Making magnets
Magnets are commonly pieces of iron that have a magnetic pole at
each end, and have a magnetic field around them. Magnets can be made
by a process called induction. There are three basic methods:
- using an existing magnet
- using Earth's magnetic field
- inducing magnetism by an electric current
Metals that can be permanently magnetised are called magnetically hard
because they can only be magnetised using a strong magnetic field. They
are often made of steel with the addition of small amounts of nickel
and cobalt. Inside the steel are tiny areas called domains, each with
a North and South pole.
To make the metal magnetic these domains must be lined up so that most
of the North poles are facing in one direction and the South poles in
the opposite direction. The combined magnetic fields produce a magnet
with North and South poles
Using the magnetic
field of an existing magnet
One way of aligning the poles is by a process called stroking. An existing
permanent magnet is stroked from one end of the bar of metal to be magnetised
to the other end, then raised well out of the way before repeating the
process in the same direction.
Using Earth's magnetic field
A second method of magnetising a piece of steel is by hammering it into
the Earth's magnetic field. By lining the piece of steel to be magnetised
along the North/South axis, the weak magnetic field of the Earth is
able to influence the magnetic domains of the steel. If the piece of
steel is now hammered several times the domains are disturbed and tend
to line up in the Earth's magnetic field. This only makes a weak magnet,
but a new magnet has been produced.
Inducing magnetism by an electric
current
A magnetic field is generated when an electric current flows in a coil
of wire. This magnetic field can be used to magnetise a piece of steel
by placing it inside the coil then completing the circuit so that an
electric current flows. The magnetic field generated lines up the domains
and produces a permanent magnet.
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