This article treats about a classical standard approach on potential difference.
Consider the following basic circuit
In which we will admit the following polarities and direction of current, thus like the electricals nets I and II, and junctions A, A', A'', B, B' and B''.
We will attack the problem considering the Kirchhoff´s Law about "voltages" and currents.
In the Net I:
In the Net II:
In the A' junction(Point):
In the Same Way:
It can be this values any potential. Including . Verify!!!
Take a look that,
These ones are dependents of e .