Q.Name the apparatus used to detect electric charge on a body.

Gold-Leaf Electroscope

A gold-leaf electroscope is a simple, historic instrument for detecting electric charge. It consists of a metal rod ending in two very thin gold leaves, all enclosed in a glass case (to shield them from air currents) with a metal disc or knob on top.

How it works

Touch or bring a charged body to the top knob and charge spreads down the conducting rod to the two leaves. Both leaves receive like charge, and since like charges repel, the leaves diverge — they fly apart. The instrument reports charge by that visible splaying of the leaves.

What it can tell you

• Presence of charge: if the leaves diverge, the body carried charge.
• Rough magnitude: a larger charge produces a wider divergence.
• Sign of charge: first give the electroscope a known charge so the leaves stand apart. Now bring the test body near. If the divergence increases, the test charge has the same sign; if it decreases, the test charge is opposite. (Merely observing divergence alone cannot fix the sign, because both charging and induction can cause it.)

Charging by induction …