Getting to Know: Magnets
Is your refrigerator at home covered with comic strips, photographs, and notes from school?
When you use a magnet to stick a photograph to your refrigerator, you are making use of the magnet’s ability to exert force. A magnet
is an object with a north and south pole that produces a magnetic field and exerts magnetic force. Remember that a force is a push or a pull. Magnetic force can cause objects to attract (move toward one another) or repel (move away from one another). Magnetic force can act over a distance. If you have ever used a strong magnet to pick up paper clips, you may have noticed that a magnet does not actually have to touch an object before it starts to pull on it.
Magnets attract certain metals, including
the iron in these steel paper clips.
Magnets do not attract all materials, but they always attract certain metals, including iron, nickel, and cobalt. Objects made of these materials will always be attracted by magnets, although magnetic force decreases when the distance between a magnet and the other object increases. A magnet can also attract and repel another magnet. However, objects that are attracted to magnets are not necessarily magnets themselves.
Misconception 1: Wait, I thought magnets are only made of iron and can only
attract objects that contain iron.
There are actually several kinds of metals that can be used to make magnets. You
are probably most familiar with iron alloy magnets. Iron is also used to make steel,
which is used in many objects and appliances. Your refrigerator door is made from
steel, for example, and it is the iron in the steel that refrigerator magnets attract.
However, magnets can be made from nickel or cobalt, too. In fact, magnets made from
neodymium cobalt and samarium cobalt are among the strongest magnets. However,
these materials are rare so usually they are only used for industrial purposes.
Concept: Magnets
Getting to Know
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How does a magnetic field exert magnetic force?
Magnets exert magnetic force as a result of their magnetic field—a force field that surrounds
a magnet. This force field extends away from the magnet in all directions and loses strength
with distance from the magnet. A magnet attracts objects within its magnetic field.
The magnetic field has two poles, which we call the north pole and south pole. In a bar magnet, the poles are at opposite ends of the bar. The poles are named for the magnet’s relationship with Earth’s magnetic field. If you hang a bar magnet on a string, the magnet will line up so that its north pole points toward Earth’s north magnetic pole and its south pole points toward Earth’s magnetic south pole. For this reason, a magnet’s poles are sometimes called the north-seeking pole and the south-seeking pole. A compass uses this principle to help people
navigate—a magnetized needle lines up with
its north pole pointing to Earth’s magnetic
north pole.
If you place iron filings around bar
magnets, the filings arrange themselves
along the magnetic field surrounding the
magnets.This can help you visualize the
shape of the magnetic field.
A magnet’s magnetic field is strongest around the
magnet’s poles. Magnetic poles can attract and
repel each other. If you hold two bar magnets with like poles facing each other, they will repel.
If you arrange the magnets so their opposite poles face each other, they will attract.
Misconception 2: I’ve seen a magnetic field in a diagram. A magnetic field is a
pattern of lines around a magnet.
Well that is not exactly true. A magnetic field is actually a force field around a magnet.
The field is stronger in some areas than others. As the above picture shows, if you set a
bar magnet in iron filings, the filings will arrange themselves in lines around the magnet
where the magnetic field is strongest. This can help you see the shape and strength of
the magnetic field, and many diagrams replicate this shape using a series of lines. The
magnetic field is actually three-dimensional—it extends from the magnet on all sides
and in all directions. The lines in the diagram represent variations in this force field.
Where the lines are concentrated, the force is strongest. The force is weaker where the
lines are spread out.
You will learn more about the applications of magnets, magnetic fields, and magnetic force
during our lesson, so let’s get started.
Concept: Magnets
Getting to Know
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© Discovery Education. All rights reserved.
Discovery Education is a subsidiary
of Discovery Communications, LLC.