Q. Two point charges $+ 9e$ and $+ e$ are at $16\ cm$ away from each other. Where should another charge $q$ be placed between them so that the system remains in equilibrium
A) $24\ cm\ from + 9e$
B) $12\ cm\ from + 9e$
C) $24\ cm\ from + e$
D) $12\ cm\ from + e$
Explanation
(b) Suppose $q$ is placed at a distance $x$ from $+ 9e,$ then for equilibrium net force on it must be zero $i.e.\ \left| F_{1} \right| = \left| F_{2} \right|$
Which gives $x_{1} = \frac{x}{\sqrt{\frac{Q_{2}}{Q_{1}}}\ + 1} = \frac{16}{\sqrt{\frac{e}{9e}}\ + 1} = 12\ cm$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.