(Figure 3.41) shows the lines of constant potential in region in which an electric field is present. The values of potentials are written in brackets. At which points A, B or C, the electric field is greatest.
.

Explanation

E is larger where equipotential surfaces are closer. ELOF is perpendicular to equipotential surfaces. In the figure, we can see that point B they are closer so E at point B is maximum.