We don't really think too much about wires, do we? Resistors and the like may be called "passive" elements but the humble wire is the most passive of them all; it just kind of sits there. As a matter of fact, something extremely important happens with the wire; fundamental and critical to the function of an electric circuit. When a wire connects with a source of positive charge and a source of negative charge, the wire (initially electrically neutral) also becomes charged; the laws of electrostatics determine that this charge rests on the surface of the wire. Of course, a wire in which charge flows is not in electrostatic equilibrium, but the effect is more-or-less to have charges on the wire surface. For a piece of circular wire, the surface charges form a ring, and it can be determined that the net electric field of this ring of charges is straight through the center of the ring, its direction dependent on the ring charges. However, not only is the charge distribution ring-like, but it is also non-uniform. If the wire had uniform (neutral) charge, there would be no net potential difference and thus no current flow. However, the non-uniform distribution ensures a net electric field always moving from positive potential to negative potential, allowing for the proper functioning (indeed, any functioning at all) of the circuit. Not very exciting exposition, but it is an important and often-neglected and under-appreciated mechanism of electric circuits.