http://www.ck12.org Chapter 5. Energy
FIGURE 5.187
Easy On and Off
Besides their strength, another pro of electromagnets is the ability to control them by controlling the electric current.
Turning the current on or off turns the magnetic field on or off. The amount of current flowing through the coil can
also be changed to control the strength of the electromagnet.
Q:Why might it be useful to be able to turn an electromagnet on and off?
A:Look back at the electromagnet hanging from the crane in the opening photo. It is useful to turn on its magnetic
field so it can pick up the metal car parts. It is also useful to turn off its magnetic field so it can drop the parts into
the train car.
Summary
- An electromagnet is a solenoid wrapped around a bar of iron or other ferromagnetic material. The magnetic
field of the solenoid magnetizes the iron bar. - The combined magnetic force of the magnetized wire coil and iron bar makes an electromagnet very strong.
- Electromagnets can be turned on or off and their strength can be changed by controlling the electric current.
Vocabulary
- electromagnet: Magnet created by electric current flowing through a coil of wire that is wrapped around a
bar of iron or other ferromagnetic material.
Explore More
Experiment with the electromagnet simulation at the following URL. Then fill in the blanks in the sentences below.
http://phet.colorado.edu/en/simulation/magnets-and-electromagnets
- Increasing the number of loops in the wire coil __ the strength of the magnetic field.
- Decreasing the voltage of the direct current __ the strength of the magnetic field.
- Each time the alternating current changes direction, the magnetic field __.