Two point charges `Q and -Q //4` placed along the x - axis are separated by a distance `r`. Take `-Q//4` as origin and it is placed at the right of Q. Then the potential is zero.

Options

A. `(2//3) a`
B. `a//2`
C. `3a//2`
D. none of these

Answer

A

Explanation

`E_(1)=E_(2)`
`therefore" "1/(4piin_(0))xxq_(1)/r_(1)^(2)=1/(4piin_(0))xxq_(2)/r_(2)^(2)`
`r_(1)/r_(2)=sqrt(q_(1)/q_(2))=sqrt((4q)/q)=2`
since `r_(1)+r_(2)=a`
`therefore" "r_(1)=2/3a`