Electromagnetism Electromagnetism

Magnetic Force and Electric Current
At the beginning of this section you learned that an electric
current can cause a compass needle to move. The needle, a
small magnet, moves because the electric current in a wire creates
a magnetic field that exerts a force on the needle. If a
current-carrying wire causes a magnet to move, can a magnet
cause a current-carrying wire to move? Figure 16 shows that
the answer is yes.
Figure 16 A magnet exerts a force on a current-carrying wire.
a When a current-carrying wire is
placed between two poles of a
magnet, the wire will jump up.
b
Applications of Electromagnetism
Electromagnetism is useful in your everyday life. You already
know that electromagnets can be used to lift heavy objects
containing iron. But did you know that you use a solenoid
whenever you ring a doorbell or that there are electromagnets
in motors? Keep reading to learn how electromagnetism makes
these devices work.
Doorbells Many doorbells contain
a solenoid with an iron rod inserted
part way in it. The electric current in
the solenoid is controlled by the doorbell
button. When you press the button,
a switch in the solenoid circuit
closes, creating an electric current in
the solenoid. What happens next is
shown in Figure 17.
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If the direction of the electric current
in the wire is reversed, the wire is
pushed down instead of up.
Figure 17 An electric current in the
solenoid of a doorbell produces a
magnetic field. This field pulls
the iron rod through the
solenoid, and the rod
strikes the bell.
Electromagnetism 465