In a metal conductor, the electric current is carried by the movement of free electrons. These free electrons are valence electrons that are not bound to any particular atom, and are therefore able to move freely through the metal lattice. When an electric field is applied to the conductor, these free electrons are accelerated in the direction of the field, creating an electric current. The amount of current that flows through the conductor is proportional to the number of free electrons and the strength of the electric field.