Effect of Material
Substances, which allow electric current to flow through them, are called conductors. Those, which do not, are called insulators. Metals behave as conductors because of their structure. In a metal structure the metal atoms release their outermost electrons to form an “electron cloud” throughout the whole structure. In other words the atoms in a metal exist as ions surrounded by an electron cloud. If a potential difference is applied to the metal the electrons in this cloud are able to move.