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Electricity and Energy – Build Your Own “Perpetual Motion” Machine
Lesson Overview:
In this lesson, students will learn that they can convert different types of energy from one
to another; in this case electrical energy into kinetic energy. They will then explore the
properties of magnetism and electricity by constructing the simplest possible electric
motor. The homopolar motor consists of a wire and a standard battery. Students can
experiment with different kinds of wire and batteries. By measuring the motor RPM,
students can evaluate quantitatively to determine which configuration provides the best
performance. More advanced students can consider how kinetic energy is produced from
conversion of electrical energy. The motor will operate until the battery power runs
down, which may be several days.
Unit Questions:
 What is the simplest kind of electric motor?
 How does a homopolar motor work?
 Who invented the first homopolar motor?
 How is the performance of the homopolar motor measured?
 In what ways is the homopolar motor similar and different from conventional
electric motors?
 Why is the homopolar motor unsuitable for most commercial applications?
Learning objectives:
 Identify the function of a typical electric motor.
 Understand that a force is induced when an electric current passes through a
magnetic field (Lorentz’s Law).
 Use the equations that describe how force is induced when electric current passes
through a magnetic field
 Construct a homopolar electric motor using everyday materials and evaluate its
performance.
 Describe how electrical energy can be transformed into kinetic energy.
Academic Standards:
Next Generation Science Standards
HS-PS4-3.
 Evaluate the claims, evidence, and reasoning behind the idea that
electromagnetic radiation can be described either by a wave model or a
particle model, and that for some situations one model is more useful than
the other.
PS4.B: Electromagnetic Radiation
 Electromagnetic radiation (e.g., radio, microwaves, light) can be modeled
as a wave of changing electric and magnetic fields or as particles called
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informational purposes only; Discovery Education and 3M assume no liability or your use of the information. Published by Discovery
Education. © 2013. All rights reserved.
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photons. The wave model is useful for explaining many features of
electromagnetic radiation, and the particle model explains other features.
(HS-PS4-3) Cross-cutting Concepts: Systems and System Models
 Models (e.g., physical, mathematical, computer models) can be used to
simulate systems and interactions— including energy, matter, and
information flows—within and between systems at different scales. (HSPS4-3)
Common Core State Standards Connections
ELA/Literacy
 RST.11-12.1: Cite specific textual evidence to support analysis of science
and technical texts, attending to important distinctions the author makes
and to any gaps or inconsistencies in the account. (HS-PS4-3)
 RST.9-10.8: Assess the extent to which the reasoning and evidence in a text
support the author’s claim or a recommendation for solving a scientific or
technical problem. (HS-PS4-3)
 RST.11-12.8: Evaluate the hypotheses, data, analysis, and conclusions in a
science or technical text, verifying the data when possible and
corroborating or challenging conclusions with other sources of
information. (HS-PS4-3)
Mathematics
 MP.2: Reason abstractly and quantitatively. (HS-PS4-3)
 HSA-SSE.A.1: Interpret expressions that represent a quantity in terms of its
context.
 HSA-SSE.B.3: Choose and produce an equivalent form of an expression to
reveal and explain properties of the quantity represented by the expression.
 HSA.CED.A.4: Rearrange formulas to highlight a quantity of interest, using
the same reasoning as in solving equations.
Background Information for the Teacher:
This lesson is a hands-on approach to learning about electricity and magnetism.
Typically, students learn about electric motors from diagrams. In this lesson, they build a
homopolar motor – the simplest possible electric motor. First built by Michael Faraday in
1821, this was the first electric motor with rotational motion, which laid the foundation
for modern electric motors. The homopolar motor is surprisingly easy to construct yet
provides insights into electricity, magnetism, and transformation of energy. Once set up,
the motor will run seemingly without stopping, giving the impression of a perpetual
motion machine. However, the homopolar motor works by converting electrical energy to
mechanical energy. The magnetic field in the magnet interacts with the electric current
flowing through the wire from the battery to induce a force due to Lorentz’s Law. This
force causes the wire to rotate. Once the source of electrical energy runs down, the motor
ceases to operate.
Materials for the Teacher:
 A used, partially dismantled electric motor, such as an old fan from a thrift store
or a windshield wiper motor from a car junkyard (optional)
A good scientist is a safe scientist. Do not conduct any experiment without adult supervision. This content is provided for
informational purposes only; Discovery Education and 3M assume no liability or your use of the information. Published by Discovery
Education. © 2013. All rights reserved.
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Materials for a group of students (or individual student):
 AA alkaline battery
 Neodymium magnet, 0.5 inch diameter (disk shaped)
 Length of copper wire (18 gauge thickness)
 Narrow nose pliers with wire cutter edges
 3M electrical tape (double-sided)
 3M safety goggles
Additional materials (optional)
 D battery
 0.5 inch hex nut
 Various types of wire
 1 inch steel screw
Teacher Preparation:
 Partially dismantle an old electric motor to demonstrate its main components.
 Review the items in Resources for demonstrations of how to build the motor, and
possible variations.
Classroom Activities:
Note: For this activity, students can work individually or in small groups.
In this session, students review the basic functioning of an electric motor and build a
simple homopolar motor.
Engage
1. Ask the class if they like to wear clean clothes or drink smoothies.
2. Explain that a washing machine, a dryer and a blender are examples of how
electric motors are applied for practical use.
3. Have the class brainstorm other examples of electric motors. Students can create a
list of everyday uses of electric motors such as household appliances, toys, and
motor vehicles.
Explore
1. Ask students if they know anything about how an electric motor works. If
necessary, review the function of these commonplace motors. If available, use an old
electric motor to point out the main components. A normal electric motor works when
a current is applied to the “armature” which comprises a wire coil surrounded by a
magnet. The electric current creates a magnetic field that causes rotation of the
armature. In this way, mechanical energy is derived from electrical energy.
4. Have students work in small groups to discuss the key principles behind a
functioning electric motor. The most basic concept they need to understand is that
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informational purposes only; Discovery Education and 3M assume no liability or your use of the information. Published by Discovery
Education. © 2013. All rights reserved.
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electric current (comprised of moving charges) is subject to a force when it moves
through a magnetic field. This force is the Lorentz force.
5. Explain to students that they will now build an electric motor!
6. Ask students if they think it is possible to build a motor using just a magnet,
battery and wire. They will likely be skeptical.
7. Review the procedure for building the motor with students using the Student
Worksheet.
8. Have students experiment with different ways to configure the motor using the
various materials. (You can see various examples online.) Encourage students to
develop methods to measure the performance of the motor. For example, they can
measure how fast the wire spins (revolutions per minute).
9. Have students in small groups work to determine the best configuration for speed
or creativity.
10. Lead a discussion about the role of the magnetic field in the homopolar motor.
Guide students to the conclusion that the electric current in the battery flows
through the wire, interacting with the magnetic field in the magnet. This
interaction causes the wire to turn.
Explain
1. Have students discuss the function of the homopolar motor. They can research
online for design variations. Guide the discussion by asking questions such as:
i.
Why does the wire turn? (Review Lorentz’s Law)
ii. Can you use the right hand rule to predict which way the wire will rotate?
iii. What configurations of wire shape work best?
iv.
What other ways can a homopolar motor be constructed?
v.
Are there practical applications for the homopolar motor?
2. Have student groups draw a diagram showing the fields of magnetic force in the
homopolar motor.
3. Have the groups create a presentation featuring their configuration for the
homopolar motor and its performance and creativity.
Extend
1. Introduce students to Lorentz’s Law, which describes the magnitude of the forces:
Fe = qE
Where Fe = electric force, q = charge and E = electric field.
A good scientist is a safe scientist. Do not conduct any experiment without adult supervision. This content is provided for
informational purposes only; Discovery Education and 3M assume no liability or your use of the information. Published by Discovery
Education. © 2013. All rights reserved.
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2. Introduce students to the right hand rule. This describes the direction of the
electric current and magnetic field. It shows that the direction of the electric
current is perpendicular to the direction of the magnetic field.
3. Introduce students to the second equation of Lorentz’s Law, which describes the
magnetic force:
Fm = qv×B
Where Fm = magnetic force, qv = charge velocity of particle (electrons) and B =
magnetic field.
4. The combined equation is the basis of electromagnetism: F = qE + (qv×B)
5. The importance of this equation is to show how force is induced when an electric
current moves through a magnetic field.
6. Advanced students can use the equations and the right hand rule to test
predictions of the system, such as what direction the wire will turn, or the
estimated amount of force generated by the turning wire.
7. Students can use information from their homopolar motor to learn about energy
conversion. Have students consider the types of energy in the homopolar motor.
Lead them to conclude that (as with a conventional motor) it converts electrical
energy into kinetic (or mechanical) energy.
8. Have students consider how they can show how energy is not lost in the system,
but transformed. Students should conclude that electrical energy from the battery
is transformed into kinetic energy.
Evaluate
1. Have students complete the worksheet assessment questions.
2. Have groups share their presentations with the class on the performance and
creativity of their homopolar motors.
Resources
 http://www.animations.physics.unsw.edu.au/jw/homopolar.htm
 http://vimeo.com/60505745
 http://vimeo.com/16316492
 http://vimeo.com/62455651
 http://isaac.exploratorium.edu/~pauld/activities/electric/homopolarmotor.htm
 http://electronics.howstuffworks.com/motor.htm
 http://evankontras.com/Maximum_Theoretical_Efficiency_of_a_Homopolar_Dev
ice.pdf
 http://physicsed.buffalostate.edu/SeatExpts/resource/rhr/rhr.htm
A good scientist is a safe scientist. Do not conduct any experiment without adult supervision. This content is provided for
informational purposes only; Discovery Education and 3M assume no liability or your use of the information. Published by Discovery
Education. © 2013. All rights reserved.
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Build Your Own “Perpetual Motion” Machine student activity sheet
Overview
In this lesson, you will learn that different types of energy can be converted from one to
another; in this case electrical energy into kinetic energy. You will then explore the
properties of magnetism and electricity by constructing the simplest possible electric
motor. The homopolar motor consists of a wire and a standard battery. You can
experiment with different kinds of wire and batteries, and use different configurations for
creative variations. By measuring the motor rotations per minute (RPM), you can
evaluate quantitatively to determine which configuration provides the best performance.
Materials
 AA alkaline battery
 Neodymium magnet, 0.5 inch diameter (disk shaped)
 Length of copper wire (18 gauge thickness)
 Narrow nose pliers with wire cutter edges
 Timing device
 3M electrical tape (double-sided)
 3M safety goggles
Additional materials (optional)
 D battery
 0.5 inch hex nut
 Various types of wire
 1 inch steel screw
Your teacher will review the basic functioning of an electric motor and you will build a
simple homopolar motor.
Procedure to build the motor
1. Wear 3M safety goggles since the ends of cut wire are sharp.
2. Place a short length of tape on a flat surface.
3. Place the neodymium magnet on the tape, so it firmly adheres.
4. Place the negative terminal of the battery (flat end) on the magnet, so it stands
vertically.
5. Shape the wire as shown in the diagram. (Note: if the wire is plastic coated, strip
the plastic off first.)
6. Place the shaped wire over the battery, and the wire will start to spin.
7. If the wire does not spin, refer to Resources for hints on how to shape the wire
better.
A good scientist is a safe scientist. Do not conduct any experiment without adult supervision. This content is provided for
informational purposes only; Discovery Education and 3M assume no liability or your use of the information. Published by Discovery
Education. © 2013. All rights reserved.
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8. To help the wire spin, you can place a hex nut over the positive end of the
battery to locate the wire over the center of the terminal.
9. Experiment with the shape of the wire and use the additional materials to
discover how different configurations affect the operation of the motor.
10. Use a stopwatch to time the number of rotations in a given unit time. Since the
motor may spin fast, you can have one person count the rotations and another
to observe the time.
Diagram of the magnetic field
Based on your group discussion, draw a diagram showing the magnetic field of the
homopolar motor.
A good scientist is a safe scientist. Do not conduct any experiment without adult supervision. This content is provided for
informational purposes only; Discovery Education and 3M assume no liability or your use of the information. Published by Discovery
Education. © 2013. All rights reserved.
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Questions
Why does the wire turn in the homopolar motor?
How did you estimate the performance of your motor?
What is the importance of Lorentz’s Law equations?
What energy conversion is involved in the homopolar motor?
Resources
 http://www.animations.physics.unsw.edu.au/jw/homopolar.htm
 http://isaac.exploratorium.edu/~pauld/activities/electric/homopolarmotor.htm
 http://electronics.howstuffworks.com/motor.htm
 http://evankontras.com/Maximum_Theoretical_Efficiency_of_a_Homopolar_Dev
ice.pdf
 http://physicsed.buffalostate.edu/SeatExpts/resource/rhr/rhr.htm
A good scientist is a safe scientist. Do not conduct any experiment without adult supervision. This content is provided for
informational purposes only; Discovery Education and 3M assume no liability or your use of the information. Published by Discovery
Education. © 2013. All rights reserved.