Name _______ KEY __________________________________ Date _________ Period ______
Electric Motors
1.
What is the purpose of the commutator in a motor?

2.
Why is an electromagnet always used in an electric motor?

3.
An electromagnet is used because it can easily have its magnetic poles switched,
which is necessary to keep the rotor spinning.
Describe the process by which an electric motor spins.

4.
The commutator is used to provide the changing current which flips the
magnetic poles of the electromagnet.
An electric motor spins because an electromagnetic attracts and repels
permanent magnets on a rotating disk. The electromagnet changes polarity to
repel the magnet nearest to it and attract the next magnet.
Look at the diagram below. In which direction will the rotating disk spin? Explain.

In this diagram, the disk will spin
counterclockwise. This is because the north
poles will repel and the south pole will be
attracted to the north pole of the free
magnet. Since the nearest South Pole magnet
is beneath the free magnet, the disk will spin
upwards and counterclockwise.
5.
Draw where you should place the south pole of a magnet to get the disk below to spin in
a clockwise direction.
6.
The rotor in the motor below is spinning clockwise. Is the direction of the current in the
electromagnet from A to B or from B to A? Explain.

The electromagnet has to have a north pole to repel
the permanent magnet and spin clockwise.
Therefore, the current must be flowing from A to B.