Question

The instrument which can be used to detect a charged body is :

• A. Electroplate
• B. Leaf electroscope
• C. Capacitor
• D. Galvanometer

Answer 1

The correct option is B Leaf electroscope

The leaf electroscope is an instrument used to detect the presence of electric charge on a body. It contains a vertical metal rod, with a round metal ball or knob on top, housed in a box. The metal rod and the box are insulated with each other by hard rubber or amber. Two very thin leaves of gold (or aluminium) are attached to bottom end of the rod.

Detection of presence of charge on a body using electroscope :

When the electroscope is uncharged, the two leaves hang parallel and vertically downwards due to its own weight [see fig. (a)]. Suppose a negatively charged rod touches the knob. Because the metal is a good conductor, electrons travel down the rod into the leaves. Both leaves become negatively charged as they gain electrons [see fig.(b)]. Because the leaves have similar charges, they repel each other. When the positively charged glass rod is brought into contact with the metal knob of an uncharged electroscope, electrons flow out of the metal leaves and onto the rod. The leaves repel each other because each leaf becomes positively charged [see fig.(c)].