2-1-A: Electroscope

The tool to test whether an object is charged or not is an electroscope; an example is shown in the following figure.
In an electroscope, a pair of light metal foils are hung down from an electrode in a container of an insulator like a glass bottle as shown in the figure.
If we touch a charged object to the electrode of the electroscope, then the metal foils charge and they open the angle between the foils due to the repulsive force. The angle may roughly indicate the amount of the charge.
Since an electronic device with high accuracy is used today, this type of electroscope is no longer used except for educational purpose.