Materials
- Battery (D or C cell)
- Insulated wire, about 18-24 gauge
- Small Magnet
- 2 Large Uncoated Paper Clips
- Masking tape
- Wire Cutters
- Sand paper
Procedure
- Have students cut about one meter of insulated wire off the spool
- Wrap the wire around the circle part of the battery at least ten times
- Leave about 5 cm of wire on both ends of the coil
- Take one five centimeter end of the wire and stick it through the center of all ten loops, then bring the end around to the outside and wrap all the loops with the end.
- Do the same with the other end of the wire
- Lay the coil flat on a table surface
- Sand the insulation off of the half of wire facing you on the 5 cm ends that are sticking out
- Tape a paper clip on each end of a battery and bend the top of the paper clip out so it can be bent into a holder for the metal coil
- Place the magnet on the battery between the two paper clips that are sticking out
- Place the coil on top of the two paper clips and give a little spin, if it doesn’t start rotating on it’s own, try spinning it the other way
- Johnson motors need a little fine tuning, try adjusting the paper clips, sanding off the contact leads or making the coils around the motor more uniform
- Be sure not to sand away too much insulation or your Johnson Motor won’t work.
Explanation
When the coil of wire is placed on the paper clips so that the uninsulated part of the wire is touching the metal of the paper clips, a complete circuit is formed. As the current through the wire changes it induces a magnetic field. This magnetic field repels the magnetic field of the permanent magnet attached to the battery. Therefore the coil turns to align itself properly with the magnetic field. The coil gets halfway through its rotation and then the insulated part of the coil is not in contact with the paper clips. Since there is no current, there is no magnetic field, so the coil’s inertia carries the coil the rest of the way through the rotation until the coil rotates enough so that there is current going through the coil again. The current causes a magnetic field that repels the permanent magnet and the process continues causing the coil to rotate very quickly.
Reinforcement Activities
The Ring Thrower is an excellent way to demonstrate that a changing electric field produces a changing magnetic field and vise versa. This device will throw a metal ring up to 12 feet in the air using principles of electromagnetism. It can also be used to demonstrate that current is indeed being produced around the ring launcher. Students can light a light bulb around the launcher without using a battery.
Don’t want to hunt down all the supplies needed for this kit yourself? The World’s Simplest Motor Kit comes with everything you need to make the motor described above except for a D cell battery.
Make many different types of electromagnetic motors, several different kits are listed below to suit your varying needs.
