In other
materials, notably metals, some of the electrons are practically free to move
within the bulk material These materials, generally called conductors,
develop electric currents in them when an electric field is applied If we consider solid conductors, then of course the atoms are tightly
bound to each other so that the current is carried by the negatively
charged electrons There are, however, other types of conductors like
electrolytic solutions where positive and negative charges both can move