A pith ball electroscope is shown in Fig. It consists of a small pith ball suspended with the help of a dry silk thread from an insulating stand.
The working of the electroscope:
To find out whether the body is charged or uncharged : The body is brought near the pith ball (without touching it). If the pith ball shows a movement towards the body, the body is charged, but if the pith ball remains static the body is uncharged.
To find out whether the body has a positive charge or a negative charge : First of all, a pith ball electroscope is charged positively by conduction. Now the charged body is brought near the electroscope. If the pith ball moves away the body has a positive charge, but if the body moves towards the body, it is negatively charged.