Properties of magnetic lines of flux
Magnetic lines of fux always flow from the north pole of amagnet to the
south pole.
Magnetic lines of flux always form closed loops.
" They behave like stretched elastic bands, always trying to shorten themselves.
They never intersect each other.
Magnetic linesof flux that are parallel and flowing in the same direction will
always repel cach other.
Types of magnets
Natural magnets
Natural magnets, referred to as lodestone (or loadstone), are pieces of
magnetite or other magnetised minerals,found buried near the surface
of the Earth.
Permanent magnets
Figure 1.2: Lodestone Permanent magnets can be made from /ron, nickel and cobalt by exposing
or magnetite them to an external magnetic field. When the external magnetic fheld
is removed, the metal retains its magnetism permanently; a property
referred to as ferromagnetism.
Electromagnets or temporary magnets
Unlike apermanent magnet, an electromagnet is temporary in the sense
that a magnetic field is produced by an electric current and disappears as
Figure 1.3: A permanent soon as the current is turned off.
magnet
The magnet is made up of a coil of closely-spaced conductive wire, such as copper,
lodestone (or
wrapped around a ferromagnetic core. When the electricity is switched on,
loadstone):
current flows through the wire, also known as a solenoid, creating a magnetic
a naturally
field and magnetising the core as if it were a permanent magnet.
magnetised Electromagnets are used as components in many electrical devices incuding
mineral that can motors, generators and transformers, as well as in industry where lifting and
be used as a
moving heavy metallic objectssuch as cars or scrap metal is required. Figure l4
magnet
shows a simple electromagnet.
ferromag
netism: the
mechanism by -magnetiC
lines of flux
which certain
metals, such -coil (solenoid)
as iron, nickel
and cobalt, are ferromagnetic
magnetised bar
by an external
magnetic field
and retaintheir
magnetism after
this field has
been removed
solenoid: a coil
of wire that acts
like a magnet
when carrying
electromagnet
Current Fiqure 1.4: Asimple
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