Diagram (a) shows that 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 and so the potential at E is the same as that at the negative terminal of the cell –
zero.
Diagrams (b) and (c) show that when no current flows in a circuit there is no
change of potential and therefore no potential difference between two parts of that circuit that are
connected while (d) shows an equal potential drop across parallel resistors.
(Assume that the energy
lost in the connecting wires is negligible and ignore it.)
