Mapping the electric potential for two positive charges in the x-y plane produces two hills. As the charges move closer together, a saddle develops between the hills. Unlike for the magnitude of the electric field, there is no hole in the saddle.
Remember that the electric field is related to the slope of the potential. At the saddle point, both the x and the y slopes are zero, so the electric field is zero at this point. We will see that saddles and "wells", places where there is a depression in the potential which can trap a particle, form important structures.
Textbooks refer to equipotential lines which are lines of constant potential. In the surface maps of the potential, these lines are "constant" height lines. In your journal, sketch the equipotential lines for the potential shown above.The next video clip showns how to visualize these lines.
Next go to Exercise 1