Response to the following problem:
Plot the force of attraction (in newtons) versus separation (in meters) for two charges of 2 mC and -4 µC. Set r to 0.5 m and 1 m, followed by 1-m intervals to 10 m. Comment on the shape of the curve. Is it linear or nonlinear?
What does it tell you about the force of attraction between charges as they are separated?
What does it tell you about any function plotted against a squared term in the denominator?