Materials Included In Kit

Additional Materials Required

Prelab Preparation

Cut the copper wire into 1-ft lengths, enough for each group to have one piece for the Introductory Activity. Enough wire is provided for each group to have an additional 3 feet for the design challenge.

Safety Precautions

While 1.5-volt batteries are not harmful, small shocks are possible. Do not allow the wire to spin on the battery for longer than 15 seconds. Since there is very little resistance in the wire, the battery and wire can become very hot if connected for a long duration. Care should be taken when shaping the wire. The pointed ends of the wire may be sharp. Use caution when handling the neodymium magnet. These magnets are very strong and may quickly snap to a metal object and pinch skin. The magnets are also fragile and may shatter if dropped or if they hit another object too hard. Keep the magnets away from computers and other electronics. Wear safety glasses.

Disposal

All materials may be saved for future use. Used wire may be disposed of in the regular trash.

Lab Hints

• Enough materials are provided in this kit for 30 students working in groups of three or for 10 groups of students. Both parts of this laboratory activity can reasonably be completed in one or two 50-minute class periods. The prelaboratory assignment may be completed before coming to lab, and the post-lab questions may be completed the day after the lab.
• Bending the copper wire into the desired shape with the proper contacts is the most challenging part of the activity. Coiling the wire around a thick marking pen or highlighter will help make smooth turns. Pliers may also be used to bend the ends of the wire for good contact with the magnets and battery.
• Additional materials may be used for the design challenge (e.g., tape, string, cardboard or cardstock, craft beads).
• Two neodymium magnets may work better than one for some wire designs. Additional magnets are available from Flinn Scientific, Catalog No. AP5666.

Teacher Tips

• Knowledge of magnetic fields is helpful in understanding how a motor works.
• If time allows, let students experiment with the homopolar motor. Variables to test may include adding another magnet, flipping the magnet over to reverse the poles, flipping the battery over to reverse the current or using a different metal wire.
• Insulated wire may also be used to create colorful motor designs. Flinn Scientific has insulated copper wire in red, black and white (Catalog Nos. AP4715, AP4716, and AP4717, respectively). If using insulated wire, the insulation must be stripped from each end and any portion of the wire that touches the positive terminal of the battery.
• To make a different type of motor, try the DC Motor Made Simple—Super Value Kit (Flinn Catalog No. AP6263).
• A video of this activity, “Build a Simple Motor,” is available on the Flinn Scientific website.

Answers to Prelab Questions

1. What is the function of a motor?

   A motor converts electrical energy to mechanical energy.

2. Why is it important to not allow the wire to spin on the battery for more than 15 seconds?

   The battery and wire may get hot if they are connected for very long.

Answers to Questions

1. Consider the first homopolar motor you created.
   1. What difficulties, if any, did you encounter in getting the wire to spin?

      Getting the wire to just touch the magnet without creating too much drag was a challenge. Creating a shape that balanced without rotating off the battery was also a challenge.

   2. What changes did you make to overcome any difficulties?

      Pliers were used to bend the wire into the correct position to complete the circuit with the wire just brushing against the battery. Washers were taped to the positive end of the battery to keep the wire from rotating off the battery.

2. Draw your creative design in the space.
3. Would the homopolar motor work if a nonmetallic ceramic magnet were used instead of the neodymium magnet?

   No, since ceramic is nonmetallic, it does not conduct electricity; therefore, a complete circuit cannot be made.

Introduction

Motors are a fundamental driving force of the modern world. It is a very rare occasion when you do not see or use the action of a motor during your daily life. Make a very simple model of a motor out of just three items: a battery, a strong magnet and a wire.

Concepts

• Electricity
• Energy conversion
• Lorentz force
• Magnetism

Background

Hans Christian Oersted (1777–1851), a Danish physicist, was performing an experiment in 1820 when he noticed that whenever an electric current from a battery was switched on or off, a nearby magnetic compass needle was deflected. Through additional experiments, Oersted was able to demonstrate the link between electricity and magnetism. The following year, English scientist Michael Faraday (1791–1867) created a device that produced “electromagnetic rotation.” This device is known as a homopolar motor since the current always flows in one direction—the electrical polarity never changes, unlike other types of motors that reverse polarity every half turn.

A motor converts electrical energy to mechanical energy. For a simple homopolar motor, direct electric current (DC) from a battery travels through and over the surface of a permanent magnet (made from conductive metal) when a wire touching one end of the battery makes contact with the side of the magnet attached to the other end (see Figure 1). The homopolar motor changes the electrical energy output provided by the battery to mechanical energy as the copper wire is set into rotational motion. Any current-carrying wire produces an associated magnetic field. The electrons in the wire are subjected to a magnetic field and experience a force—referred to as the Lorentz force—that is perpendicular to the direction of the current and the magnetic field. The force on the current-carrying wire is tangential and induces a torque on the copper wire. This torque causes the copper wire to spin.

Experiment Overview

The purpose of this activity is to build a simple motor with a battery, copper wire and magnet. Then a second wire will be used to make a creative shape that will spin while balanced on the battery.

Materials

Prelab Questions

1. What is the function of a motor?
2. Why is it important to not allow the wire to spin on the battery for more than 15 seconds?

Safety Precautions

While 1.5-volt batteries are not harmful, small shocks are possible. Do not allow the wire to spin on the battery for longer than 15 seconds. Since there is very little resistance in the wire, the battery and wire can become very hot if connected for a long duration. Care should be taken when shaping the wire. The pointed ends of the wire may be sharp. Use caution when handling the neodymium magnet. These magnets are very strong and may quickly snap to a metal object and pinch skin. The magnets are also fragile and may shatter if dropped or if they hit another object too hard. Keep the magnets away from computers and other electronics. Wear safety glasses. Wash hands thoroughly with soap and water before leaving the laboratory. Please follow all laboratory safety guidelines.

Procedure

Part A. Introductory Activity

1. Attach the magnet to the negative terminal of the AA battery.
2. Set the battery-magnet apparatus vertically on a level surface with the magnet on the bottom and the battery centered over the magnet (see Figure 2).
   {12617_Procedure_Figure_2}
3. Bend the copper wire into one of the two shapes shown in Figure 3. For shape b, try coiling the wire around a thick marking pen or highlighter to make smooth turns.
   {12617_Procedure_Figure_3}
4. Carefully lower the shaped copper wire onto the battery-magnet so the wire is balanced and makes contact with the positive terminal at the top and the magnet at the bottom. Note: Pliers may be needed to bend the ends of the wire for good contact with the magnet and battery. The lower end of the wire should just barely touch the magnet.
5. When the wire is shaped correctly and the system is balanced, the wire should start to spin. If it doesn’t, check the contacts and then gently nudge one side of the wire to begin the rotation. If it still doesn’t spin, go on to step 6.
6. Reshape the wire as needed so a complete circuit is made from the positive terminal of the batter to the magnet at the other end. Caution: Do not leave the wire on the battery-magnet for more than a few seconds as the wire may get hot. Remove the wire each time adjustments are made.
7. If the wire spins off the battery, either reshape for a better balance or tape one or two washers to the positive end of the magnet. Make sure the terminal is not covered with tape (see Figure 4).
   {12617_Procedure_Figure_4}

1. Sketch your design first and determine what length of wire you will need.
2. Other materials may be used upon approval by your instructor.
3. Your motor should spin smoothly for 15 seconds.

Student Worksheet PDF

12617_Student1.pdf