  # Potential and Potential Difference

We define the amount of electrical potential energy that a unit charge has as:

The electrical potential energy of a unit charge at a point in a circuit is called the potential at that point.

The bigger the energy change betwen two points in the circuit the bigger the difference in electrical potential. We call this the potential difference between those two points.

The potential difference between two points in a circuit is the work done in moving unit charge (i.e. one coulomb) from one point to the other. The units for potential difference are Joules per coulomb, or volts. (1 volt = 1 Joule/coulomb). Along the connecting wire from the cell to B there is no resistance and so no loss of electrical energy or drop in potential.

In the resistors r and R energy is converted to heat and so the potential drops from B through to E.

From E to the cell there is no loss of electrical energy so the potential at E is the same as that at the negative terminal of the cell – zero.