1. In this activity, students working in small groups use the superposition principle to write the electrostatic potential due, either to two positive charges or to a dipole, separated by a distance D.
2. The groups are then asked to expand this potential in a series, either on the axis or the plane of symmetry, and either close to the center of the charge distribution or far away.
3. A follow-up class discussion highlights the role of symmetry in this calculation.

Reasons to spend class time on this activity:

To be successful in this activity, students need to learn to understand the physical and geometric meaning of one over (r minus r’). This activity can be thought of as a warm-up for a series of activities that focus on unpacking successively more complicated superposition integrals.

Although our students have some experience with power series from mathematics courses, they have never before had the chance of employing the common physics strategy substituting into known series by rewriting an expression in terms of dimensionless parameters. (same link as “expand this potential”)

Authors: Corinne A. Manogue, Len Cerny