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) $-\dfrac{kq^2}{a}$
Three pairs: one like pair ($+kq^2/a$) and two unlike pairs ($-kq^2/a$ each):
$$U = \frac{kq^2}{a}(1 - 1 - 1) = -\frac{kq^2}{a}$$
Solution by Sreeraj P, M.Sc Physics