Question

Three charges $Q,q,-q$ are placed at the vertices of an equilateral triangle. If the net electric potential energy of the system is $0$, then $Q$ is

• A. $-q$
• B. $q$
• C. $0$
• D. None of the above

Answer 1

The correct option is D None of the above

$U=U_{AB}+U_{AC}+U_{BC}$

$⟹U=\frac{1}{4\pi {ϵ}_o}(\frac{qQ}{l}+\frac{-qQ}{l}+\frac{-q.q}{l})=0$

$⟹q(Q-Q-q)=0$

This gives both $q=Q=0$

And, for any vlaue$Q$, potential energy of this system can't be $0$.