MEASUREMENT OF CHARGE

We can measure electric charge on a charged body with the help of a simple apparatus called electroscope. There are two types of electroscope and they can be used to measure charges and find their nature.

(a)           PITH- BALL ELECTROSCOPE

(b)          GOLD LEAF ELECTROSCOPE

(a)           PITH- BALL ELECTROSCO                                 A pith- ball electroscope consists of a pith- ball        suspended from a support by a single silk fiber) fig 32.6). Pith is a light and spongy materials extracted from the stream of some plants. If it is gilded (overlaid with thin covering of gold) it works better. To test whether the body has got charge it is brought near an uncharged pith- ball. The pith ball will be attracted towards it. If it touches the pith ball, they will be repelled. The repulsion is due to same kinds of charges shared after touching the body, To find the type of charge on it, the pith- ball is charged by known type. Suppose the pith ball is charged positively. The body whose nature of charge is to be determined is brought near. It will be repelled if it is positively charged and will be attracted if it has negatively charges on it.

(b)          THE GOLD- LEAF ELECTROSCOPE (GLE)

This is a sensitive instrument. It can be used to detect charge and its nature. It can also give us a roughly the amount of charges on the body. That is why it is commonly used for demonstration. A typically gold leaf electroscope is shown in the figure32.7.

It consists a vertical metal rod, with a metal disk on top, going inside through an insulated hole on the top lid of a glass box. The lower end of the rod has two thin gold leaves attached to it (Aluminums foils can also be used). The sensitivity of this instrument can be increased by passing two strips of tin foil on the inner side of the glass panes facing the leaves. The tin- foils cover the level of gold leaves and pass down to the base of the instrument so that the electroscope can be grounded. The utility of these foils is to cancel any influence due to outside charges.