Using an electroscope, you can determine whether an object is charged or the polarity of the charge.
When the (+) charged body is close to the metal plate, the metal foil’s free electrons are attracted to the metal plate, and a positive charge is induced in the metal foil. The electric force unfolds metal foil.
In addition, when the (-) charged body is brought close to the metal plate, free electrons of the metal plate are pushed out, and negative charges are induced in the metal foil. As before, the metal foil is unfolded by the electric force.
In other words, when the electroscope is electrically neutral, the metal foil will unfold when a positive or negative electric charge comes close to it.
Check the polarity of the charged body using an electroscope
Using an electroscope, you can check the polarity of an electric charge. For example, let’s assume an electroscope in which a metal foil is opened with a negative charge.
If you bring the (+) charged body close to this electroscope, the metal foil will shrink.
On the other hand, if you get closer to the (-) charged body, the metal foil will unfold more.