Q 12-01-030JEE MainJEE Main 2026 (24 Jan, Shift 1)Easy
Three charges $+2q, +3q$ and $-4q$ are situated at $(0, -3a), (2a, 0)$ and $(-2a, 0)$ respectively in the $xy$ plane. The resultant dipole moment about origin is ______ .
Answer: (A) $2qa(7\hat i - 3\hat j)$
$\vec p = \sum q_i\vec r_i$:
$$\vec p = 2q(-3a\hat j) + 3q(2a\hat i) + (-4q)(-2a\hat i) = -6qa\hat j + 6qa\hat i + 8qa\hat i$$
$$\vec p = 14qa\hat i - 6qa\hat j = 2qa(7\hat i - 3\hat j)$$
Solution by Sreeraj P, M.Sc Physics