We know that, like charges repel and unlike charges attract, therefore to create an excess or deficit of electrons at a point, some work is to be done in moving the charges (or electrons) against the forces between them. The force between the two charges is zero when they are at infinite separation.
Hence, quantitatively, potential at a point is measured in terms of work done in bringing a charge q from infinity to that point. If work W‘ is done in bringing a charge q from infinity to a point, then potential at that point is:
V = W’ / q
Hence, the potential difference between two conductors is measured in terms of work done in transferring the charge from one conductor to the other, through a metallic wire.
Potential difference is a scalar quantity.
