Students work in groups of three to use Coulomb's Law
\[\vec{E}(\vec{r}) =\frac{1}{4\pi\epsilon_0}\int\frac{\rho(\vec{r}^{\,\prime})\left(\vec{r}-\vec{r}^{\,\prime}\right)}{\vert \vec{r}-\vec{r}^{\,\prime}\vert^3} \, d\tau^{\prime}\]
to find an integral expression for the electric field, \(\vec{E}(\vec{r})\), everywhere in space, due to a ring of charge.

In an optional extension, students find a series expansion for \(\vec{E}(\vec{r})\) either on the axis or in the plane of the ring, for either small or large values of the relevant geometric variable. Add an extra half hour or more to the time estimate for the optional extension.

Find the electric field around an infinite, uniformly charged,
straight wire, starting from the following expression for the electrostatic
potential:
\begin{equation}
V(\vec r)=\frac{2\lambda}{4\pi\epsilon_0}\, \ln\left( \frac{ s_0}{s} \right)
\end{equation}

Find the electric field around a finite, uniformly charged, straight
rod, at a point a distance \(s\) straight out from the midpoint,
starting from Coulomb's Law.

Find the electric field around an infinite, uniformly charged,
straight rod, starting from the result for a finite rod.

Students work in small groups to use the superposition principle
\[V(\vec{r}) = \frac{1}{4\pi\epsilon_0}\sum_i \frac{q_i}{\vert\vec{r}-\vec{r}_i\vert}\]
to find the electrostatic potential \(V\) everywhere in space due to a pair of charges (either identical charges or a dipole).
Different groups are assigned different arrangements of charges and different regions of space to consider: either on the axis of the charges or in the plane equidistant from the two charges, for either small or large values of the relevant geometric variable.
Each group is asked to find a power series expansion for the electrostatic potential, valid in their group's assigned region of space.
The whole class wrap-up discussion then compares and contrasts the results and discuss the symmetries of the two cases.