Reference: EM35
Category: Electromagnetism
Purpose: Illustrates the basic principle of many electrostatic machines.
Description: A “cake” of Perspex rests on a circular, earthed, brass plate. It is given a charge by flicking with a piece if silk. It is then covered by another brass plate with an insulating handle. Briefly touch the top surface of the top plate, thus earthing it. Lift up the top plate by means of the handle. A sufficient potential difference develops for an audible spark to pass when this plate is brought near to the rim of a Bunsen burner, which will ignite the gas emerging from the burner. Turn off the gas supply momentarily, and replace the plate on the Perspex cake. The process can be repeated many times without recharging the Perspex. The energy required is provided by the mechanical work done pulling the plate away from the Perspex.