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The Electrophorus: A Simple Electrostatic Generator

- William J. Beaty

An electrophorus is a simple, high-voltage electrostatic generator that can be used to demonstrate the power of an electrostatic charge, or to power the Soda Bottle Electrostatic Motor.


  • cardboard at least 8" square
  • aluminum foil
  • insulating material for handle: plastic or Styrofoam cup, or small Styrofoam block
  • easily charged object: balloon, thick plastic sheet, plastic cutting board, Styrofoam packing block, etc.
  • charging item: artificial fur, wool sweater, wig, hair on your head (if clean), etc.

NOTE: You need a low-humidity day to operate the electrophorus successfully.

To test humidity:

  • Rub your "easily charged object" with the "charging item."
  • Determine whether the object has become charged by holding the charging item close to the charged area on the charged object.
  • If this makes the fibers of the charging item stand on end, then the humidity is sufficiently low for your electrophorus to operate successfully.
  • If the charged object does not raise the fibers, the humidity is too high. Wait for a drier day, or go into an air-conditioned building and try again.


  • Cut a disk from the cardboard about 8" to 12" in diameter.
  • Cover one side of the disk with aluminum foil.
  • Fold the foil up over the other side of the disk so it partially covers it.
  • With the disk positioned foil-side down, make a "handle" by taping or gluing your chosen insulating material to the center of the remaining cardboard area on the non-foil side.

                | | Handle
                | |
        =================== Foil-covered cardboard


Note: When holding the disk by its handle, your fingers on the handle should be some distance away from the foil wrapped up over the edges.

  • Place your "easily charged object" on a table and rub its surface with the "charging item" to charge it well.
  • Holding the cardboard/foil disk by the handle, place it upon the charged surface of the object, foil side down.
  • With the disk still on the charged surface, touch the foil to allow it to steal charge from your body. You'll feel a tiny spark.

           \\          _
            \\        | | Handle
             \\       | |          
  >TOUCH!<    =================== Foil-covered cardboard
                         Charged item

  • Now, while holding the disk only by the insulating handle, lift it from the charged surface.
  • The disk is now charged!

  • Even though it has been used to charge the foil, the charged object still remains fully charged. It need not be rubbed for a while and can be used to charge the foil plate again and again.
  • This is possible since the charging of the foil DID NOT remove any charge from the charged object. How? The charged object in this generator acts more like a magnet than like a source of energy, and it does not lose its strength when it attracts charge into the foil.
  • From where does the electrical energy come? It comes from the work your arm did in pulling the foil disk away from the charged surface.

What to Do with Your Charged Electrophorus

Each time you charge your electrophorus, you can use it to demonstrate the electrostatic charge:

  • Blink a small NE-2 neon bulb.
  • Create small sparks.
  • Pick up lint.
  • Deflect the leaf of an electroscope.
  • Charge a Leyden Jar capacitor.

You can even use your charged electrophorus to power the Soda Bottle Electrostatic Motor.

Used with permission of William J. Beaty.

Be sure to check out our Science Fair Project Books and Kits too. You'll find plenty of exciting projects and ideas for budding young scientists!
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