Take an empty jam bottle. Take a piece of cardboard slightly bigger in size than the mouth of the bottle. Pierce a hole in it so that a metal paper clip can be inserted. Open out the paper clip as shown in Fig. Cut two strips of aluminium foil about 4 cm × 1 cm each. Hang them on the paper clip as shown. Insert the paper clip in the cardboard lid so that it is perpendicular to it (Fig.). Charge a refill and touch it with the end of the paper clip. Observe what happens. Is there any effect on the foil strips? Do they repel each other or attract each other? Now, touch other charged bodies with the end of the paper clip. Do foil strips behave in the same way in all cases? Can this apparatus be used to detect whether a body is charged or not? Can you explain why the foil strips repel each other?
We observed that aluminium foil strips received the same charge from the charged refill through the metal paper clip as it is good conductor of electricity. The strips carrying similar charges repelled each other and they became wide open. Such a device which can be used to test the charge on an object is called electroscope. When we touch the metal paper clip with other charged bodies, the foil strips behave in the same way in all cases. Thus, we find that electrical charges can be transferred from a charged object to another through a metal conductor.