25.1. Electricity and Magnetism http://www.ck12.org
25.1 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 calledelectromagnetism.
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 inFigure25.1, 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.
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 inFigure25.2. 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 use the URL below.
URL: http://www.ck12.org/flx/render/embeddedobject/5062