Q 12-02-024NEETJEE MainMedium
Three charges $q$, $q$ and $-q$ are at the corners of an equilateral triangle of side $a$. The electrostatic potential energy of the system is
Answer: (A) $-\dfrac{kq^2}{a}$
Concept. System PE is the sum over pairs.
Step 1. Pairs. One like ($+$), two unlike ($-$): $\dfrac{kq^2}{a}(1 - 1 - 1) = -\dfrac{kq^2}{a}$.
Answer. $-\dfrac{kq^2}{a}$ (Option A).
Solution by Sreeraj P, M.Sc Physics