Q.

A point charge +q is placed at the origin. A second point charge +9q is placed at (d, 0, 0) in Cartesian coordinate system. The point in between them where the electric field vanishes is:          [2025]

1 (4d/3, 0 , 0)  
2 (d/4, 0 , 0)  
3 (3d/4, 0 , 0)  
4 (d/3, 0 , 0)  

Ans.

(2)

Let EP=0

∴ kqx2=k9q(d–x)2 ⇒ d–xx=3 ⇒ x=d4

∴ co-ordinate of P is (d4,0,0)