ABSTRACT
As we have seen, rubbing a glass or an amber rod with a piece of cloth produces an electric charge on the rod (Figure 13.1a). If the rod is made of metal, no charge develops (Figure 13.1b). However, touching a metal rod with a charged object will cause the metal to become charged (Figure 13.1c). The reason for this behavior is that the atoms in a metal have some electrons that are not tightly bound to their nuclei and are free to move about. Any excess charge readily moves in conductors. In metals, then, electric charges move or ow through the material. We say that metals are good conductors of electricity. In glass, amber or other materials like them, on the other hand, electrons are not free to move; they are bound to individual molecules or atoms. Any excess charge placed on them remains (unless they are touched by some other object). These materials are called insulators.
