Magnets and magnetism
Magnets are all around you: on the fridge door, inside your computer,
in the monitor, in audio speakers, in your telephone, and even as you
work you are in Earth's magnetic field. Magnetism is used to read and
write information to your computer discs and magnetic tapes. The magnetic
force is an important and very useful force.
The magnetic force is a force that can be experienced at a distance.
You can observe this force by holding any kind of magnet above a few metal
paper clips on your desk and observing what happens.
Magnets in history
Magnetic force has been known for a very long time. The Ancient Greeks
knew that certain rocks, called lodestones (or leading stones, as they
were used for finding direction) attracted some metals, and that they
could be used to find direction on the oceans. It wasn't until 1269, when
a Frenchman named Petrus Peregrinus investigated lodestone scientifically,
that the two ends, or poles, of the magnet were found to be different.
Magnetic Island, off the coast of Queensland, was so called because
Captain Cook's compass behaved oddly when approaching the island. He thought
that there must have been magnetic material in the island, hence the name.
What is happening inside a magnet?
Common bar magnets are largely made of iron. Inside the iron bar
are tiny magnetic regions called domains. When a strong magnet is present,
these domains line up with most of the north seeking ends in the same
direction. This is what causes the poles to be different. One end of a
magnet is called the south-seeking pole and the other north-seeking. This
description is used because the Earth is described as though it has a
great magnet inside it, and the Antarctic region has been called the South
Pole - these are used as reference points. A bar magnet placed in Earth's
magnetic field will align itself so that its south seeking pole points
to Earth's South magnetic pole and the north seeking pole points to Earth's
North magnetic pole.
Attraction and repulsion
If you hold two bar magnets, and bring one close to the other, you will
observe one of two things. Either the magnets will resist being pushed
together, or they will snap together. Here is a perfect example of force
as a push or a pull. When two opposite magnetic poles are close, they
attract each other. When like poles are pushed together, there is a force
of repulsion. The rule for magnets is that like poles repel and unlike
Magnetic force in action
One of the most common everyday uses for magnets is in a simple compass.
The compass needle is a small magnet resting on a fine point so that it
can rotate freely. Provided there are no other magnets or large steel
objects near by, the compass needle will align itself with Earth's magnetic
field. At our southern latitudes the "south" end of the needle
will then be directed toward the South Magnetic Pole. This information
will enable you to orient a map accurately wherever you are.
A simple game can be made by using magnets, at the same time using the
fact that magnetic fields can pass through cardboard or paper. Draw a
squiggly circuit on a piece of card and place several paper clips on top.
Using a magnet under the cardboard, see how expertly you can manoeuvre
the clips around the circuit.