Coulomb's Law with multiple discrete charges

Like Unequal charges   Unlike Unequal charges

Description : Two fixed charges are shown in black. They might be "Equal/Unequal" (in terms of magnitude) or "Like/Unlike" (in terms of their sign .. positive or negative). Drag the small green test charge around the screen and observe the relationship between the force vector and its proximity to the charges. Can you find a "force-free" point in each of the two cases?

Credits : Initial Physlet concept for this problem authored by Scott Bonham and modified by Wolfgang Christian. Greatly modified further by Scott Schneider.