William Gilbert invented the first electroscope in 1600. An electroscope is defined as an experimental device that serves us to detect the presence of an electric charge in any object.

The electroscope is responsible for detecting charges through Coulomb’s electrostatic laws. This is solely responsible for detecting the charge and not measuring it.

Construction of Electroscope:

An electroscope consists mainly of a detector knob which is made up of metal. The knob is connected to a tiny pair of metal leaves. These are placed nearly at the bottom part of the connecting rod. When no charge is present the metal leaves are relaxed and they stay there facing downward.

These metal leaves display whether there is any charge or not.

Working of Electroscope

Now let us discuss the working of an electroscope. The idea behind this the working is based on a few basic chemical properties of elements ie. the atomic structure and metallic structure, induced charges, and the basic law of attraction and repulsion.

If you see that the leaves are separated and open:

This means that there is some type of charges in both plates of the leaves. from here it can be concluded that on detecting positive charge, the leaves spread open as the electrons present in the metal of the device are attracted to the same, creating a temporary illusion of positive charge. Hence this condition is when there is a positive charge.

A similar thing happens when there is a negative charge as well.

There is again a similar transform of electrons into the metal of the leaves. This leaves thus again gain a temporary negative charge. As like charges repel the plate of the leaves get separated again.

As soon as the charge source is removed, the leaves no longer remain separated and they move to their initial relaxed position.

From this explanation, it is quite clear that in no way an electroscope can define what kind of charge is acting upon it. It simply determines whether the body placed is charged or uncharged. It does not detect whether it is positive or negative.