Transcript Magnets and Magnetism

Magnets and Magnetism
• Did you know? More than 2000 years
ago, the Greeks discovered a mineral
that attracted objects containing iron.
Because this mineral was found in a
part of Turkey called Magnesia, the
Greeks called it Magnetite. Today any
material that attracts iron is called a
magnet.
Magnets and Magnetism
• The magnetic effects of a
magnet are NOT evenly
distributed through the magnet.
• The parts of a magnet where the
magnetic effects are strongest
are called the poles.
Magnets and Magnetism
• If you attach a magnet to a
string so that the magnet is free
to rotate, you will see that one
end of the magnet always ends
up pointing north and the other
end will point to the south.
• Magnetic poles always occur in
pairs, you will never find a
magnet with only a north pole or
only a south pole.
Magnets and Magnetism
• The force of
attraction or
repulsion between
the poles of
magnets is called
the magnetic force.
• The magnetic force
depends on how
the poles of the
magnets line up.
Magnets and Magnetism
• A magnetic field
exists in the
region around a
magnet in which
magnetic forces
can act.
Magnets and Magnetism
• Magnetic field lines are close
together where the magnetic force is
strongest, and
farther away
where the
force is weaker.
Magnets and Magnetism
• Some materials are magnetic,
and some are not. What causes
the difference?
• Whether a material is magnetic
depends on the atoms in the
material.
Magnets and Magnetism
• All matter is composed of atoms that
include protons, electrons and
neutrons. Moving electrons produce
magnetic fields that can give an
atom a north and a south pole.
• In most materials, the magnetic
fields of individual atoms cancel
each other out.
Magnets and Magnetism
• But in some
materials, the
atoms in a
magnetic domain
are arranged so
that the north
and south poles
of all the atoms
line up and
create a strong
magnetic field.
Magnets and Magnetism
Types of magnets:
Ferromagnets – magnets made with
metals
Electromagnets – produced by an electric
current.
Temporary magnets – made from
materials that are easy to magnetize,
but they lose their magnetization easily
too.
Permanent magnets – difficult to
magnetize, but retain their magnetic
properties better.
Magnets and Magnetism
Did you know?
In 1600, English
physician
William Gilbert
suggested that
magnets point to
the north
because Earth
itself is one
GIANT magnet.
Magnets and Magnetism
• Although you can think of Earth
as have a giant bar magnet in
the center, there really isn’t a
magnet there.
• The temperature of Earth’s core
is so high that atoms in it move
too violently to remain in
domains.
Magnets and Magnetism
• Earth’s magnetic
field is produced
by the
movement of
charges in the
Earth’s core.
Magnets and Magnetism
• One of the most spectacular
effects caused by the Earth’s
magnetic field is a curtain of
light called an aurora.
Magnets and Magnetism
• An aurora is formed when charged
particles from the sun interact with
atoms in Earth’s atmosphere. We
see the interactions at Earth’s
magnetic field.