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Electricity and Magnetism
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Printed: December 23, 2012
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C ONCEPT
Concept 1. Electricity and Magnetism
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Electricity and Magnetism
Lesson Objectives
• Outline how electromagnetism was discovered.
• Describe the magnetic field created by an electric current.
Lesson Vocabulary
• electromagnetism
Introduction
The crane magnet in the opening photo is an electromagnet. Like all electromagnets, its magnetism is produced by
electric current. This type of magnetism is called electromagnetism.
Discovery of Electromagnetism
In 1820, a physicist in Denmark, named Hans Christian Oersted, discovered how electric currents and magnetic
fields are related. However, it was just a lucky accident. Oersted, who is pictured in Figure 1.1, was presenting a
demonstration to his students. Ironically, he was trying to show that electricity and magnetism are not related. He
placed a wire with electric current flowing through it next to a magnet, and nothing happened. After class, a student
held the wire near the magnet again, but in a different direction. To Oersted’s surprise, the pointer of the magnet
swung toward the wire so it was no longer pointing to Earth’s magnetic north pole. Oersted was intrigued. He turned
off the current in the wire to see what would happen to the magnet. The pointer swung back to its original position,
pointing north again. Oersted had discovered that an electric current creates a magnetic field. The magnetic field
created by the current was strong enough to attract the pointer of the nearby compass.
FIGURE 1.1
Hans Christian Oersted was the scientist who discovered electromagnetism.
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Oersted wanted to learn more about the magnetic field created by a current, so he placed a magnet at different
locations around a wire with current flowing through it. You can see some of his results in Figure 1.2. They show
that the magnetic field created by a current has field lines that circle around the wire. You can learn more about
Oersted’s investigations of current and magnetism at the URL below.
http://www.youtube.com/watch?v=BM4m2GId3F8 (2:00)
MEDIA
Click image to the left for more content.
FIGURE 1.2
In Oersted’s investigation, the pointer of the magnet moved continuously
as it circled the wire.
Electric Currents and Magnetic Fields
The magnetic field created by a current flowing through a wire actually surrounds the wire in concentric circles.
This magnetic field is stronger if more current is flowing through the wire. The direction of the magnetic field also
depends on the direction that the current is flowing through the wire. A simple rule, called the right hand rule,
makes it easy to find the direction of the magnetic field if the direction of the current is known. The right hand rule
is illustrated in Figure 1.3. When the thumb of the right hand is pointing in the same direction as the current, the
fingers of the right hand curl around the wire in the direction of the magnetic field. You can see the right hand rule
in action at this URL: http://www.youtube.com/watch?v=eK1Ar5WPJj8&feature=related.
FIGURE 1.3
The right hand rule shows the direction of the magnetic field around a wire
that is carrying electric current.
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Concept 1. Electricity and Magnetism
Lesson Summary
• Electromagnetism is magnetism produced by an electric current. Electromagnetism was discovered by Oersted
in 1820.
• The magnetic field produced by a current in a wire moves around the wire in concentric circles. More current
creates a stronger magnetic field, and the direction of the current determines the direction of the magnetic
field.
Lesson Review Questions
Recall
1. Define electromagnetism.
2. Describe how Oersted discovered electromagnetism.
3. What is the right hand rule?
Apply Concepts
4. The drawing below shows part of a wire that has current flowing through it. The arrow shows the direction of
the current. Apply the right hand rule, and sketch the magnetic field lines around the wire.
Think Critically
5. Relate the properties of an electric current to its magnetic field.
Points to Consider
The magnetic field created by a single wire with current flowing through it is too weak to be very useful. However,
technologies have been developed to make stronger electromagnetic fields. You can learn what they are in the next
lesson on "Using Electromagnetism."
• What might make an electromagnetic field stronger?
• How might the wire that carries the current be arranged to increase the strength of the magnetic field?
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