Using 2 aluminum foil circles, about 10-15 cm each,cover the bottom inside and outside of the clear plastic cup. For more information look for Leyden jar . Tape one end of the insulated wire to the foil inside the cup. Tape the other end to the electrostatic generator. Turn the generator on to charge the cup.
Students can experiment with the time.
Disconnect the wire after turning off the generator. Discharge the generator after the wire has been removed. Holding the cup by its top edge only, shake off the aluminum foil liner from the outside and the inside of the cup. Test each piece of foil and the cup for charge by holding them, one at a time, to an electroscope. Note only the cup will be charged.