Question

Four charges $+a,+2q,+q$ and $-2q$ are placed at the corners of a square $ABCD$ respectively. The force on a unit positive charge kept at the centre ' $O$ ' is

• A. Along the diagonal AC
• B. Perpendicular to side AB
• C. Zero
• D. Along the diagonal BD

Answer 1

Answer: (B)

Force due to charge at $D$ and $B$ is along $\overrightarrow{F_O}\overrightarrow{D}$ towards $\overrightarrow{B}$.
Force due to charge at $A$ and $C$ is along $\overrightarrow{F_{A}O}$ towards $\overrightarrow{A}$.
$\therefore$ Resultant displacement will be along $\overrightarrow{F}$ which is perpendicular to $AB$.