Question

Two point charges 2q and 8q are placed at a distance r apart. Where should a third charge -q be placed between them so that the electrical potential energy of the system is a minimum.

• A. At a distance of r/3 from 2q.
• B. At a distance of 2r/3 from 2q.
• C. At a distance of r/16 from 2q.
• D. There is no such position.

Answer 1

Answer: (D)

There is no such position.

The potential energy can be as negative as we want by placing the negative charge infinitesimally close to one of the positive charges.