Download Magnetism

Magnetism
Notes
Magnetism gets its name from Magnesia in Turkey
where, over 2000 years ago, the ancient Greeks came
across pieces of rock, which possessed mysterious
powers. (This rock was called lodestone!)
A magnet is the name for a substance (usually a metal
such as iron or steel) that has been ‘magnetized’ so that
it will behave like a magnet.
Another characteristic of a magnet is that if it is left to
float on the water, or suspended in air from a thread
tied around its middle, it will always end up pointing in a
north-south direction.
The two ends of a magnet are described as northseeking and south-seeking poles. Magnetic objects
entering the field area around a magnet are affected
by the magnet’s forces of attraction and repulsion.
This area is called a magnetic field.
The larger the magnet the stronger the field. If you
divide a magnet in half, it produces 2 whole fields.
Although the field itself is invisible, there are ways of
finding out what it looks like.
Metal objects that are attracted by magnets become
magnets too, although this effect dies away once the
object has been moved from the magnetic field. You
can create a magnet yourself by magnetizing
something metal (such as a needle or a paper clip.)
Rub it with a strong magnet in the same direction 30
or 40 times. Some metals are magnetized easily and
some metals take longer.
Electromagnets
7. An electric current flowing through a wire gives rise
to a magnetic field whose direction depends upon the
direction of the current.
8. Electricity through a wire creates a magnetic field.
9. Electromagnetism is the relationship b/t electricity &
magnetism.
10. Electromagnets are temporary magnets made by
wrapping a coil of wire around a soft iron core and
passing an electric current through the wire.
11. Two ways to increase the strength of an
electromagnet:
a. more coils
b. increase current or voltage
12. The advantage of electromagnets is that they can be
turned on and off.
13. An electric motor converts electric energy into
mechanical energy. It consists of an electromagnet
free to rotate. It also has a permanent magnet in a
fixed position
14. The current is reversed in the coil of wire in the
electromagnet causing it to spin inside the permanent
magnet. The spinning allows the motor to do work. A
galvanometer uses magnetism to detect electric current.
Uses for electromagnets:
Earth’s magnetic field lines