http://www.ck12.org Chapter 25. Electromagnetism
FIGURE 25.9
This simple setup shows how electromagnetic induction occurs.The Current Produced by a Magnet
The device in the circuit inFigure25.9 is an ammeter. It measures the current that flows through the wire. The faster
the magnet or coil moves, the greater the amount of current that is produced. If more turns were added to the coil,
this would increase the strength of the magnetic field as well. If the magnet were moved back and forth repeatedly,
the current would keep changing direction. In other words, alternating current would be produced. This is illustrated
inFigure25.10.
FIGURE 25.10
If a magnet is moved back and forth rela-
tive to a coil of wire, alternating current is
produced.Electric Generators and Transformers
Two important devices depend on electromagnetic induction: electric generators and electric transformers. Both
devices play critical roles in producing and regulating the electric current we depend on in our daily lives.
Electric Generators
Anelectric generatoris a device that changes kinetic energy to electrical energy through electromagnetic induction.
A simple diagram of an electric generator is shown inFigure25.11. In a generator, some form of energy is applied
to turn a shaft. This causes a coil of wire to rotate between opposite poles of a magnet. Because the coil is rotating
in a magnetic field, electric current is generated in the wire. If the diagram inFigure25.11 looks familiar to you,
that’s because a generator is an electric motor in reverse. Look back at the electric motor inFigure25.8. If you were
to mechanically turn the shaft of the motor (instead of using electromagnetism to turn it), the motor would generate
electricity just like an electric generator. You can learn how to make a very simple electric generator by watching
the video at the URL below. Making your own generator will help you understand how a generator works.