The electroscope is used to detect and test of small quantities of an electric charge. It is constructed from a metal disc connected to two thin leaves of gold foil suspended from an electrode, and enclosed in a glass envelope to protect them from draughts, and the envelope may be evacuated to minimize charge leakage as shown in Figure 1.

Figure 1: Uncharged electroscope

When the electrode is charged by induction or by contact, the leaves acquire similar electric charges and repel each other due to the Coulomb force. Their separation is a direct indication of the net charge stored on them, as shown in Figure 2. Therefore, the electroscope is an instrument for detecting the presence of static electricity (charges).

Figure 2: Charged electroscope