Q. Two similar spheres having $+ q$ and $–q$ charge are kept at a certain distance. $F$ force acts between the two. If in the middle of two spheres, another similar sphere having $+ q$ charge is kept, then it experience a force in magnitude and direction as
A) Zero having no direction
B) $8F$ towards $+ q$ charge
C) $8F$ towards $- q$ charge
D) $4F$ towards $+ q$ charge
Explanation
(c) Initially, force between $A$ and $C$ $_{}$$F = K\frac{Q^{2}}{r^{2}\ }$
When a similar sphere $B$ having charge $+ Q$ is kept at the mid point of the line joining $A\ $and $C$, then Net force on $B\ $is $F_{net} = F_{A} + F_{C} = k\ \frac{Q^{2}}{(r/2)^{2}\ } + \frac{kQ^{2}}{(r/2)^{2}\ } = 8\frac{kQ^{2}}{r^{2}} = 8F$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.