These are great for demonstrating basic electrostatics. The nub sticking out the top is connected to the stuff in the middle. The stuff in the middle comprises of the continuation of the solid conducting rod and a strip of foil. Normally, they sit in contact, but if they are given a charge they will repel.
The electroscope is an early scientific instrument used to detect the presence of electric charge on a body. It detects charge by the movement of a test object due to the Coulomb electrostatic force on it. The amount of charge on an object is proportional to its voltage. The accumulation of enough charge to detect with an electroscope requires hundreds or thousands of volts, so electroscopes are used with high voltage sources such as static electricity and electrostatic machines. An electroscope can only give a rough indication of the quantity of charge; an instrument that measures electric charge quantitatively is called an electrometer.
Figure 1. This power adapter uses metal wires and connectors to conduct electricity from the wall socket to a laptop computer. The conducting wires allow electrons to move freely through the cables, which are shielded by rubber and plastic. Some substances, such as metals and salty water, allow charges to move through them with relative ease. Some of the electrons in metals and similar conductors are not bound to individual atoms or sites in the material.
The previous section of Lesson 2 discussed the process of charging an object by friction or rubbing. Friction charging is a very common method of charging an object. However, it is not the only process by which objects become charged.