Homopolar Motor Motion | Dig Into Mining

Homopolar Motor Motion

Objective

In this activity, students will discover how the Lorentz force can be used to create a homopolar motor out of just

a few magnets, a battery, and copper wire. The Lorentz force is generated when electricity moves through a

magnetic ﬁeld. The copper wire conducts electricity from one end of the battery to the other, creating a force that

causes it to spin! Once students understand how this process works, they will be able to get creative using their

hands or pliers to bend the copper wire to create spinning shapes, spirals, or even a dancing ﬁgure on the top of

their motor!

Materials (per student)

• 1 14-gauge piece of copper wire (various lengths depending on the desired shape)

• 1 (or more) neodymium magnet

• 1 AA battery

• Pliers or wire cutters

• Various other craft supplies to add to copper wire designs (glue guns and sticks,

fabric, mini pipe cleaners, etc.)

Before You Start

For a simple design, you can shape the copper wire into a shepherd’s crook, with the tip of the crook touching

the positive terminal of the battery and the bottom of the wire coiling tightly around (but not touching) the magnet

to which the bottom of the battery is attracted. For another simple and successful shape, bend long piece of

copper wire to make a small “v” in the middle of it. Then, bend the sides out a half-inch and down to create

two arms running vertically down the battery. Finally, create a coil with the ends of the arms to wrap around the

battery (without making direct contact). The tip of the “v” will touch the positive terminal of the battery. You may

have to adjust the copper wire by moving it around or shifting it to the side lip of the positive terminal to get it to

start spinning. Remember—practice makes perfect!

How-to

1. Demonstrate the action of the simple homopolar motor to the students and asking a series of questions

(you can add in your own if you’d like!):

a. How do motors work?

b. What do you think is causing the copper wire to spin?

c. What direction is electricity is ﬂowing through this homopolar motor?

2. Explain that the movement in a homopolar motor relies on something called the Lorentz force. There are

a few physics terms to know to understand how the Lorentz force works.

a. Provide a quick deﬁnition for each:

i. A conductor is a material or device that transmits heat, electricity, or sound.

ii. Electricity is the transfer of energy resulting from the ﬂow of charged particles

(such as electrons).

iii. Electrons are negatively charged subatomic particles found in all atoms. They act as the

primary carrier of electricity in solids.

iv. A magnet is an object or a device that gives o an external magnetic ﬁeld.

v. An electromagnetic ﬁeld is a magnetic ﬁeld produced by moving electrically

charged objects.

3. While other types of motors are much more complex, the electric homopolar motor was one of the

earliest motors ever built. Ours uses simple materials to create a direct current that powers rotational

movement. Let’s look at how we can use the energy of a battery, a magnetic ﬁeld, the conductivity of

copper, and the Lorentz force to create a simple spinning motor!

a. The battery is passing its stored electricity through the copper wire. Copper is an excellent

conductor of electricity, passing the energy of electrons from one copper atom to another, all the

way to the negative terminal of the battery.

b. The electrical current ﬂows from the positive terminal of the battery through the copper wire to

the negative battery terminal and into the magnet. This current then ﬂows from the magnet to

the edge where the copper wire connects and travels up the copper wire back to the positive

terminal of the battery to complete the circuit.

c. The magic happens when the copper wire comes in contact with the magnets, creating an

electromagnetic ﬁeld and setting the stage for the Lorentz force to go to work!

d. As the negatively-charged electrons move through the copper wire, they create their own magnetic

ﬁeld. The magnetic ﬁeld of the electrons interacts with the magnetic ﬁeld created by the magnet,

creating the Lorentz force and resulting in the rotation of the copper wire you see in the motor.

4. Now, it’s time to get hands-on!

a. Provide each student with the materials they need to construct their own homopolar motor.

(Students may also work as partners on one motor design if they struggle.)

b. Explain to students that the copper wire can be bent into various shapes, such as a spinning

heart, a spiral, a twirling dancer, or a unique design of their own!

c. Before building, be sure to give students these important guidelines to building their homopolar

motor shape with the copper wire:

i. The copper wire must be touching the positive terminal.

ii. The shape of your copper wire MUST be as balanced as possible to stay on the positive

terminal of the battery.

iii. The copper wire must make contact with the battery—looping it around is the best way.

iv. Use caution! The wire and battery can become very hot if left spinning for a period of time.

d. Provide students with 10–15 minutes to bend their copper wire into the shape they would like to

use for their homopolar motor.

e. As students work, walk around the classroom to assist as needed and call out any especially

creative designs you see! There is deﬁnitely a learning curve to this, so encourage students to keep

trying and to continue to modify their design if they are struggling to get the copper wire to spin.

5. When students are ﬁnished with their homopolar motor construction, it’s time to test their designs:

a. Instruct students to get with a partner, form a small group, or form one large group.

b. Give students time to explain their design. They may discuss why they thought their design

would be successful, or if it represents a personal interest of theirs, etc. They will then setup and

test their homopolar motor.

6. When the tests are complete, hold a group discussion and ask students to reﬂect on the designs they

have seen in a group discussion:

a. Which motors were the most successful? What made them successful?

b. Which copper designs were the fastest or slowest and which stayed centered best? Which

designs were most creative or fun to look at as they spun?

c. What would happen if you used a wire with a material other than copper? Why is it so important

to use copper for this?

d. How would you change or reﬁne the design of your homopolar motor to make it more

successful?