Q. Two point charges $A$ and $B$ of magnitude $+8 \times 10^{-6} C$ and $-8 \times 10^{-6} C$ respectively are placed at a distance $d$ apart. The electric field at the middle point $O$ between the charges is $6.4 \times 10^{4} NC ^{-1}$. The distance '$d$' between the point charges $A$ and $B$ is:
Solution: