Most modern applications of electricity involve moving electric charges or “current electricity”. Historically, however, the first studies of electricity involved static charges or electrostatics. You certainly feel the effects of electrostatic charges every time you touch a doorknob in the wintertime and get zapped. In this lab, you will be introduced to an instrument called an electroscope, which is used to detect the net electric charge. By the end of this lab, you should understand how the electroscope physically works, you should know how to use it to detect electric charge, and you should be able to use it as a tool to discover some electrical properties of various materials.

THE ELECTROSCOPE: The instrument that you will use in this lab is called an electroscope, shown in Figure 1. The electroscope consists of a metal ball connected by a metal rod (the stem) to a very thin leaf of gold foil. The fragile part of the instrument is enclosed in a protective case. Electrons can flow freely within the ball, stem, and gold leaf. The leaf is very lightweight and floppy so that an electrical repulsive force acting to lift it up can more easily overcome the downward force of gravity.

With the electroscope charged by conduction, bring the charged rod close to, but not touching, the ball. Do the same with the cloth. In each case record and explain clearly (with diagrams) what happens. With the electroscope charged, can you tell the sign of the charge which is close to the ball? If so, how? If not, why not?

ball stem metal case go ld Teaf glass side wall Fig.1. Electroscope