Two particles A and B, each having a charge Q, are placed a distance d apart. Where should a particle of charge q be placed on the perpendicular bisector of AB so that it experiences maximum force? What is the magnitude of this maximum force?
Given:
Charge on particles A and B: q1= q2= Q
Separation between A and B : d
here ‘x’ is the distance at which particle C of charge ‘q’ is place on the perpendicular bisector of AB.
Formula used:
From the figure we can find sinθ :
The horizontal components of force cancel each other.
Total vertical component of force is: F’= 2Fsinθ
We use Coulomb’s Law:
Where F is the electrostatic force on b due to A, k is a constant .
k = 
= 9× 109 Nm2C-2 and r is the distance between the two charges.
Here r = 
Substituting we get,
The magnitude of maximum Force is:
Hence, the particle C must be placed at a distance of 
from the perpendicular bisector of AB so as to experience a maximum force of magnitude 