Q.

A point particle of charge Q is located at P along the axis of an electric dipole 1 at a distance r as shown in the figure. The point P is also on the equatorial plane of a second electric dipole 2 at a distance r. The dipoles are made of opposite charge q separated by a distance 2a. For the charge particle at P not to experience any net force, which of the following correctly describes the situation          [2025]

1 ar~20  
2 ar~10  
3 ar~0.5  
4 ar~3  

Ans.

(4)

 1(ra)21(r+a)2=2a(a2+r2)3/2

         4ar(r2a2)2=2a(a2+r2)3/2