Electrophorus

An early device for generating charge by induction, attributed to and named in 1775 by Volta. Comprises a nonconductive plate or “cake” which can be charged by rubbing, and an isolated metal plate which can be placed on the charged cake. After contact is made, a charge is induced on the metal plate; if the top of the metal plate is grounded momentarily, the “like” charge induced by the cake is conducted to ground while an equal and opposite charge remains on the metal plate. After the plate is lifted from the cake, it retains the opposite charge. The process may be repeated indefinitely to produce charge on metal plates without recharging the cake. Charge transfers are typically of the order 1 mC. GLOSSARY 265