Download Using Electricity to Produce Magnetism

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Using Electricity to Produce
Magnetism
7.2
TRY THIS: EXPERIMENT WITH MAGNETS
Skills Focus: observing, inferring, communicating
A magnet has two distinct poles: a north pole and a south pole.
Experiment with two bar magnets. Bring the opposite poles together.
Observe what happens. Turn around one of the magnets so that the same
poles face each other. Bring the poles together. Observe what happens.
Put a sheet of paper over one of the magnets. Sprinkle some iron filings
on top. Observe what happens.
1. How were you holding the magnets when they attracted each other?
2. How were you holding the magnets when they repelled each other?
3. How is this attracting and repelling similar to what you saw when you
charged the balloon in the Try This activity in section 5.1?
Magnets exert a force. The area of force around a magnet is called
the magnetic field. The magnetic field is strongest at the poles of
the magnet. As you saw in the activity, unlike poles attract each
other and like poles repel each other. In this way, magnets are just
like electric charges.
About 2500 years ago, people noticed that some rocks, called
lodestones, attracted small pieces of iron (Figure 1). We now call
the property of attracting or repelling iron magnetism.
Scientists have found that electric currents produce magnetic
fields the same way that magnets do. In other words, electricity
produces magnetism. We call the magnetic forces produced by
electricity electromagnetism.
LEARNING TIP
Magnetite was first
discovered near Magnesia,
Greece. This is where the
word “magnetism” comes
from.
Figure 1
A piece of magnetite that is magnetic
is called a lodestone, or “leading
stone,” because it points north and
can be used to lead the way home.
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TRY THIS: MAKE AN ELECTROMAGNET
Skills Focus: creating models, observing
Use sandpaper to remove the insulation
from the ends of an insulated wire. Wrap
the wire in tight, even coils, as many times
as you can around a long iron nail. Leave
about 10 cm of wire at both ends of the
nail to attach to a battery. Attach the ends
of the wire to the battery. Hold the nail
above a pile of paper clips. Observe what
happens. Disconnect one of the wires from
the battery. Hold the nail above the paper
clips again. Observe what happens.
1. What does this activity show you
about electricity and magnetism?
Do not leave the
electromagnet connected
for too long. It will become
very hot.
Magnets that are created using electricity are called electromagnets
(Figure 2). An electromagnet has a source of electricity, such as a
battery, and a wire coiled around an iron object, called a core. An
electromagnet works as long as the circuit is closed and the electric
current is flowing. When the circuit is open, there is no attraction.
This means that an electromagnet can be turned on and off.
Figure 2
Huge electromagnets are attached
to cranes and used to separate
iron and steel scrap in recycling
plants. These electromagnets are
even strong enough to pick up
an entire car!
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Unit B
Electricity
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Did you know that there are many electromagnets in your home?
Doorbells, telephones, and electric motors all contain electromagnets.
Electromagnets are also being used to develop high-speed trains,
called magnetic levitation, or maglev, trains (Figure 3). These trains do
not run on tracks, but use electromagnetism to float above the track.
Figure 3
A maglev train travels at speeds up to 500 km/h along a test track in Japan.
Electricity and magnetism are related. Electricity moving through
a wire produces a magnet. Similarly, a magnet moving inside a coil
of wire produces an electric current in the wire. Electrical generators
use the principle of electromagnetism to produce electricity. In
Chapter 8, you will learn more about how electricity is generated.
CHECK YOUR UNDERSTANDING
1. How can you use electric currents to produce magnetism?
2. What is the difference between a permanent magnet and an
electromagnet? What is the advantage of using an electromagnet
over using a permanent magnet?
3. How would your day be different without electromagnetism?
Draw two pictures that show what your life would be like with and
without electromagnetism.
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