Sunday, June 24, 2012
The atoms form metallic bond with each other to give a closely packed stable structure to the metal. During the formation of these metallic bonds, the valence electrons present in the outermost orbit are completely detached from the parent atom and move freely in the space that lies within the lattice structure of the metal. These free electrons are spread over the entire solid. This large number of free electrons gives metals their values of electrical conductivity. These electrons move freely randomly even without any electric field. Because of the random movement, there is zero net current when there is no electric field. However when a metal wire is connected across two terminals of a voltage source with positive and negative terminals, the source places an electric field across the metal wire. Free electrons are forced to move toward the positive terminal under the influence of this field. This movement of electrons is called current. The free electrons are available in metallic conductors because in conductors the valance band and conduction band overlap and electrons from valance band can go to the conduction band. In the case of insulators the gap between the valance band and conduction band is quite large and hence electrons cannot jump from valance band to conduction band and hence there are no free electrons. Because of the free electrons in conductors, electric current passes through conductors.