8.2.P11

Dipoles play a critical role in the electric responses of ionic fluids. In the figure at the right is shown a molecular dipole approximated by two point charges separated by a rigid bar. Some equipotential lines are drawn showing what the potential is at various points (using an arbitrary scale). On the figure are drawn two lines labeled I and II. Below are shown a set of 5 possible graphs.   A. Which graph of the electrostatic potential would a Cl- ion measure as it moved along line I?   B. Across line II?

(The arrows on the lines I and II indicate the positive directions and the crossing line indicates the origin on that line to match with the + directions on the graphs below.)

C. How would your answers change if the electrostatic potential were being probed by a Na⁺ ion instead of by a Cl^- ion?

1. The graphs would remain the same.
2. The graphs would flip left to right (reflect around the vertical axis)
3. The graphs would flip up to down (reflect around the horizontal axis).

Joe Redish and Bill Dorland 5/18/18