Flow of Current through a Conductor

A current does not require negatively charged carriers specifically -- it can, in general, be generated by the motion of positively charged particles, negatively charged particles, or both together. In an ELECTROLYTE (an ionic solution), both positive ions and negative ions move and both contribute to the conduction. In a METAL, however, the positive ions are fixed in the crystal lattice and only the free (conduction) electrons are mobile, so conduction in a metal is entirely due to electron flow.

These free electrons flow and generate a net current only under the action of an applied electric field; as long as a steady field is maintained across the conductor, the electrons continue to flow as a steady current. Such a steady field is what a cell or battery is built to supply and sustain across an external circuit. …