Two equal charges, each Q, are separated by some distance. What third charge would need to be placed half way between the two charges so that the net force on each charge would be zero?

Question

Quizplus · Accepted Answer

To make the net force on each charge zero, the third charge must exert an equal and opposite force to the force between the two charges. By placing a charge of -Q/4 halfway, it balances the forces due to the symmetry and equal magnitude of the charges.

Two Equal Charges, Each Q, Are Separated by Some Distance