Answer
See image:
Work Step by Step
The level curves (equipotential curves) have the form:
$k=\displaystyle \frac{c}{\sqrt{r^{2}-x^{2}-y^{2}}}$
$x^{2}+y^{2}=r^{2}-(\displaystyle \frac{c}{k})^{2} $, a family of circles
(Graphed with geogebra, taking r=5, c=5)
