Concepts

Electrostatic induction, dielectric breakdown, capacitors

Overview

This electrostatic machine will spark from the round discharge electrodes when the crank is turned steadily.

The crank rotates Plexiglas wheels that have small metal discs on them. Redistribution of charge on the metal discs is the key to the demo. If you assume a slight charge inequality between two flat collector electrodes, this induces charge on the discs. Each wheel has a conducting rod above it that redistributes charge on the metal discs such that one collector always sees positive discs and the other sees negative discs. Charges jump to the collectors and connected Leiden jars. Eventually, enough charge builds up to make a spark.

Details

Equipment

• [1] Wimshurst machine
  

Classroom Assembly

1. Adjust the discharge electrodes to about 1 cm apart.
   
2. Test the Wimshurst machine.

Important Notes

• The copper wire brushes that touch the discs should only make very light contact with the discs, or else they may drag the attached conducting rods with them.
• The crank only turns one way.
• The machine tends not to arc between the discharge electrodes when they are about 5 cm apart.
  

Script

1. Turn the crank until the machine sparks.
2. Adjust the discharge electrodes to a different position and turn the crank again.
   

Additional Resources