chapter that electric force is also as pervasive and is in fact stronger than the gravitational force by several orders of magnitude (refer to Chapter of Class XI Physics Textbook). A simple apparatus to detect charge on a body is the gold-leaf electroscope [Fig. . (a)].
It consists of a vertical metal rod housed in a box, with two thin gold leaves attached to its bottom end. When a charged object touches the metal knob at the top of the rod, charge flows on to the leaves and they diverge. The degree of divergance is an indicator of the amount of charge. Students can make a simple electroscope as follows [Fig.
. (b)]: Take a thin aluminium curtain rod with ball ends fitted for hanging the curtain. Cut out a piece of length about cm with the ball at one end and flatten the cut end. Take a large bottle that can hold this rod and a cork which will fit in the opening of the bottle.
Make a hole in the cork sufficient to hold the curtain rod snugly. Slide the rod through the hole in the cork with the cut end on the lower side and ball end projecting above the cork. Fold a small, thin aluminium foil (about cm in length) in the middle and attach it to the flattened end of the rod by cellulose tape. This forms the leaves of your electroscope.
Fit the cork in the bottle with about cm of the ball end projecting above the cork. A paper scale may be put inside the bottle in advance to measure the separation of leaves. The separation is a rough measure of the amount of charge on the electroscope. To understand how the electroscope works, use the white paper strips we used for seeing the attraction of charged bodies.
Fold the strips into half so that you make a mark of fold. Open the strip and iron it lightly with the mountain fold up, as shown in Fig. . .
Hold the strip by pinching it at the fold. You would notice that