Electroscope

Electroscope, a device for measuring the amount of electric charge an object has. Electroscopes have been made obsolete by more accurate electronic devices; today they are used for demonstration purposes only.

In simplified form the electroscope consists of two lightweight conductors suspended in a container of glass or other insulating material. The two conductors are electrically connected to a third conductor that is outside the container. When the outside conductor is touched to a charged body, the two conductors inside the container become charged with similar charges and repel each other. By measuring how far the conductors are forced apart, the amount of the charge can be calculated.