Electroscope is the instrument used to detect the presence of electric charges is called gold leaf electroscope. It consists of an insulated brass rod with two pieces of thin gold foil at one end and a brass cap at the other end. The main functions of electroscope includes;-
1. Testing for the sign of the charge on the body; To test for a positive sign， the initia charge on the electroscope must be negative， when the materials placed near the cap of the electroscope， a collapse of the leaf indicates that the materials is positive charged.
To test for a negative sign， the initial charge on the electroscope must be positive， if the materials placed ner the cap causes a collapse of the leaves then this is a clear indicating of the presence of a negative charge on the materials. For example， if a glass rod is rubbed with silk and brought near the brass cap， there is a decrease in leaf divergence.
2. Identifying the insulating properties of materials; An electroscope that is positively charged can be used to test for insulating properties of materials.
3. Detecting the presence of charge on a body; When a charge is induced on the gold leaf and the btass plate of an electroscope，repulsion occurs between them. When the charged body is removed the leaf collapse indicating that the induced charge on an electroscope is temporary.