Van de Graaff generator

Some insulating materials when separated from the surface of others, leave those surfaces electrically charged, each with the opposite sign of charge and with a high potential difference. A flexible belt made from an insulating material and running continuously over two rollers can, by the same process, produce a supply of charge where the surfaces separate. The two rollers have to have different surfaces. Charges are sprayed on to and removed from the moving belt by wire brush situated adjacent to the rollers. The lower wire brush is maintained at or close to earth potential and is a drain for negative charge, leaving the belt with positive charges that are carried up to the top brush. The top brush is connected to a collecting can which, will collect and store the charge on its outer surface until discharged either by breakdown of the surrounding air as a spark, or by conduction to an adjacent earthed object.

Voltages of hundreds of thousands of volts can be generated with a home made Van de Graaff generator.