My PBL Project

Introduction

The homopolar motor was the first electrical motor to ever be built. Michael Faraday first demonstrated the homopolar motor at the Royal Institution in 1821. The homopolar motor consists of a neodymium magnet attached at the negative terminal of a double A battery with a copper wire bent into a shape touching the positive terminal of the battery and going down to the magnets. The magnetic field from the magnets causes the electric current from the battery to spin in a circle causing the copper wire to spin.

Materials

• At least one neodymium magnet

• 1 AA battery

• Copper wire

• Scissors

Procedure

1. Cut the wire into three sections.

2. Bend the wires into three shapes large enough to touch the positive terminal of the batter and to reach the magnets.

3. Place the magnet(s) under the negative terminal of the battery.

4. Place one of the wires over the battery with one end touching the positive terminal of the battery.

5. Adjust the wire so that it will spin by itself.

Safety

• Be careful when handling sharp objects

• Be careful when using strong magnets. Keep magnets away from the objects that can be damaged by them. Don't let the magnets snap together forcefully enough to shatter.

• Open circuits before they become too hot.

Pictures and Action Video

Essential Understanding

A homopolar motor works because of the Lorentz force. The electric current is flowing from the positive terminal from the battery to its negative terminal and into the magnet. The current then flows from the middle of the battery and into the edge of the wire. The current then flows up the wire back to the positive terminal and completes the circuit. The wire spins because the electrical flow is perpendicular to the magnetic field. The Lorentz force is applied on the wire which is perpendicular to the direction of the current and the magnetic field and that generates the motion.

Real Life Connections

The homopolar motor can't be used for anything other than demonstrations. They can't produce enough energy to power any appliances but they are fun to make and can be used to demonstrate how electric motors work. The battery loses it's life quickly due to the high currents that flow through the wire. Also, the battery get's really hot when used for a long time which adds to why homopolar motors can't be applied to real life. Maybe we could find ways to improve the homopolar motor such as finding ways for the battery not to heat up, die quickly, or to produce more energy. Unfortunately the homopolar motor doesn't have that many real life applications but there hopefully, there can be more in the future.

Investigation Questions

1. Would this demonstration work with any kind of magnet, such as a ceramic refrigerator magnet, or must it be a rare earth (neodymium) magnet?

2. ~The demonstration will work with any magnet that has a permanent magnetic field.

3. What applications does the homopolar motor have in industry or daily life? Are there any drawbacks to this type of motor? If so, describe them.

4. ~The homopolar motor is a representation of the electric motor. It can be applied to electric appliances such as a DVD player or a fan. The homopolar motor produces can't produce enough energy to power objects for extended periods of times and it will also heat up if you used for too long.

5. What variables, if any, affect the rate of spin of the homopolar motor? How would you modify your design to make it spin faster?

6. ~The shape of the wire and how tight the wire is affect the rate of spin of the homopolar motor. I would shape the wire into a shape where it only touche the magnets and the positive terminal of the battery. I would also shape a wire to where it will go with the current more easily.

7. Would a spiral coil of wire work with the homopolar motor? If so, would this change the forces exerted on or by the magnetic field(s)?

8. ~I spiral coil of wire will work with the homopolar motor. It won't change the forces exerted on or by the magnetic field(s).

9. Suppose the homopolar motor was spinning in the clockwise direction. What would happen if you used your finger to force it to spin in the anticlockwise direction?

10. ~The homopolar motor would stop spinning if I were to touch it and if I forced it to, the homopolar motor would spin in the opposite direction.

11. How is the torque produced that causes the homopolar motor to turn?

12. ~The torque is produced by the Lorentz force. The force from the magnetic field is being exerted on the moving electric charge in the wire.

13. Why do the components of the homopolar motor become hot after operating for a short time?

14. ~The components of the homopolar become hot due to the energy given off by the electron moving through the circuit that is created by the copper wire.