Introduction to SAT II Physics - FreeExamPapers

Permanent Magnets
Like all other materials, permanent magnets are made up of atoms that have electrons
orbiting a nucleus of protons and neutrons. In moving around the nucleus, these
electrons create miniscule magnetic fields. In most materials, these tiny fields all point in
different random directions, so the bulk material does not have a magnetic field. But in
permanent magnets, the fields are all lined up together, and so the material is
magnetized. Materials, like iron, that can be magnetized, are called ferromagnetic.
There are two other types of magnetic materials: If a nonferromagnetic material is
attracted by a magnet, it is called paramagnetic. The atoms in an paramagnet line up in
the direction of an external field. If a nonferromagnetic material is repelled by a magnet,
it is called diamagnetic. The atoms in a diamagnet line up against an external field.
Magnetic Field Lines
Permanent magnets—and electromagnets—have positive and negative poles, often called
“north” and “south,” respectively. Like electric field lines, magnetic field lines go from the
positive, or north, pole, toward the negative, or south, pole. For example, the magnetic
field of a bar magnet looks like this:
A horseshoe-shaped magnet creates a magnetic field like this:
It is possible to do a nifty experiment to see these magnetic field lines by scattering iron
fillings around a permanent magnet—the filings will move to trace the lines.
The Earth’s Magnetic Field
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