A SIMPLE ELECTROSTATIC GENERATOR
The Electrophorus
1996 Bill Beaty

Cut out a disk of cardboard about 8" to 12" in diameter. Cover one side with aluminum foil, and fold the foil up over the other side so it partially covers it. Attach some sort of insulating handle to the center of the remaining cardboard area (tape a plastic or styrofoam cup to the cardboard, or glue a small block of styrofoam) When holding the disk by its handle, the far side of the disk should be entirely covered with foil, and your fingers on the handle should be some distance away from the foil.

           _  Insulating
          | | handle
          | |
  =================== Foil-covered 
                       cardboard

You need a low-humidity day to operate the Electrophorus successfully. To test humidity, rub your plastic object with the fur or sweater and see if it becomes charged and makes the fur stand on end when it's held close to the charged area on the plastic. If you can't get the plastic object to raise the fur, wait for a less moist day. Or go into an airconditioned building and try again. (Or sometimes a warm sweater fresh from the clothes-dryer will work. But don't use anti-static fabric softener!)

To operate the electrophorus, place your plastic object on a table and rub its surface with fur or wool to charge it well. Or if your hair is clean and without grease, try rubbing the object on your head to charge it up.) Place the cardboard/foil disk upon the charged surface, foil side down. With the disk still on the plastic, touch the foil to allow it to steal charge from your body. You'll feel a tiny spark.

\  \ finger
  \_ \
  _\ \ \            _
  \\\\_\\\         | | Handle
          \\       | |       Foil-covered
>TOUCH!<    =================== cardboard
              |_____________|
                      Styrofoam block

Now, while holding the disk only by the insulating handle, lift it from the charged surface. The disk is now charged, and it can be used to blink a small NE-2 neon bulb, or to create small sparks, to deflect an electroscope leaf, pick up lint, charge a Leyden Jar capacitor, etc.

The plastic object remains fully charged, even though it has been used to charge the aluminum foil. It need not be rubbed for a while and can be used again and again to charge the foil plate, since the charging of the foil DID NOT remove any charge from the plastic surface. This seems really weird, or even impossible? The charged plastic 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. But from where does the electrical energy come? It comes from the work your arm did in pulling the foildisk away from the plastic surface.

The electrophorus WILL run the Soda Bottle motor very slowly. (If humidity is high it will not work.) Connect the foil of one of the motor's bottles to ground. (water faucets connect to ground, or connect to the screw on a wall switch cover plate.) Charge the electrophorus disk and touch it to the OTHER, non-grounded bottle foil of the motor. Do this over and over fairly fast, and the motor will slowly turn.

• PBS Kids: electroscope (PDF)
• Simple electroscope
• Electroscope problem