Simon Fraser University
Engaging the World

Department of Physics

Demonstrations

5K40.10 World's Simplest Motor

Concepts

Torque on a current loop, basic operation of a DC motor

Overview

This is a small motor made from simple household supplies. A battery pushes current through a coil of copper wire under the influence of a permanent magnet. The coil spins freely when operating.

Details

Equipment

  • [1] D-cell battery
  • [1] Copper coil
  • [1] Rubber band
  • [2] Copper contact
  • [1] Permanent magnet
  • [1] Piece of Scotch-Brite
  • [1] Document camera or overhead projector

Classroom Assembly

  1. Remove oxides on the bare copper surfaces with Scotch-Brite, careful not to remove any insulation.
  2. Stretch the rubber band around the battery lengthwise.
  3. Insert the copper contacts into the rubber band so they touch the electrodes of the battery.
  4. Put the magnet on top of the battery so that it is centred between the two contacts.
  5. Insert the copper wire loop into the circular loops of the contacts.
  6. Spin the copper wire loop and it will begin to rotate freely, but only in one direction.

Important Notes

  • Disconnect the motor when done.

Script

  1. Introduce this motley-looking thing as the world's simplest motor! Tada!
  2. Put coil on contacts.
  3. Give coil a starting spin if required.
  4. Remove coil.

 

Additional Resources

References

  • PIRA 5H50.45, 5K40.10

Disclaimer

  • Don't attempt this at home!

Last revised

  • 2022

Technicals

  • Original construction: the battery is a D-cell and the magnet is a rubber fridge magnet, magnetized perpendicular to the magnet. The paper clips were straightened and wound around a pencil to from a 1-turn circular loop with two arms of equal length. Any stiff uninsulated wire can be used in place of the paper clips. The insulated copper wire consists of about 6 turns of 24 gauge (or similar) wire wound into a square loop with two arms. In this setup, the wire was wound around a 9 V battery to make an even and consistent square loop. Once the square loop was formed, the insulation was removed from the top half of the arms of the loop. If all the insulation is removed, the motor should not work in theory. However, in practice, it can rotate in either direction as vibrations in the system will cause it to 'jump' to the next step in the motor rotation.
  • When making more coils, a razor blade is quite handy for scratching off the insulation. Be sure to only take off about half, on a 180 degree arc around the diameter of the wire.
  • #64 rubber bands are pretty good for this. They tend to decay when exposed to air for a long time, so check them before the demo.

Related AV

Related demos

  • Lorentz force on a current-carrying wire

 

If you have any questions about the demos or notes you would like to add to this page, contact Ricky Chu at ricky_chu AT sfu DOT ca.