Description:A charged rod (black rubber in the photograph is negative) is held near the top plate of the electroscope, causing the electroscope to deflect. While the rod is in this position, the plate is touched by a grounded banana wire, and the electroscope returns to the uncharged position. When the charged rod is pulled away, the electroscope is charged positive, and deflects. This experiment can also be done using a positive glass rod to charge the electroscope negative by induction.
The sign of the charge on the electroscope can be checked as follows: a rod with the same charge as the electroscope will cause further deflection of the electroscope when held close to the top plate, but a rod with charge opposite that of the electroscope will cause less deflection of the electroscope when brought close to the plate.