Q.

Two charges q and 3q are separated by a distance ‘r’ in air. At a distance x from charge q, the resultant electric field is zero. The value of x is     [2024]

1 r(1+3)  
2 (1+3)r  
3 r(1+3)  
4 r3(1+3)  

Ans.

(1)

(Enet)P=0kqx2=k·3q(r-x)2

(r-x)2=3x2

r-x=3xx=r3+1