Potential difference:
When charges move from one point to another, it is not the actual values of potential at those points which are Important, but the potential different (pd) through which the charge has travelled. Just as lifting weight in the gymnasium, the height above sea level is not important, but the distance between the gym floor and the height of one's body. In cases where an actual level of potential is required, the zero of potential is taken as Earth and whenever the potential at a point is given, it means the difference in potential between the point and the earth's surface.
If one coulomb of electricity requires one joule of work to move it between two points, then there is a potential difference of 1 volt between them. It is sometimes helpful to think of potential difference as a difference of â€˜electrical pressure' forcing a current through a load.
If a current flows round a circuit, then a potential difference must exist between any two points in that circuit and each point in the circuit must be at a different potential. However because there is very little opposition to current flow in conducting wires, very little potential difference is required to push the current along the wires and it is normally assumed to be zero. Whenever the opposition to current flow is not negligible, then a potential different exists across that component to push the electrons through the device
The converse is also true, if no current is flowing, then no potential difference exists. The larger the potential difference the larger the current.