Question

Two point charges `+8q` and `-2q` are located at `x=0` and `x=L` respectively. The location of a point on the x axis at which the net electric field due to these two point charges is zero is
A. `8L`
B. `4L`
C. `2L`
D. `(L)/(4)`

Answer 1

Correct Answer - c
The net field will be zero at a point outside the charges and near the charge which is smaller in magnitude.

Suppose `E.F` is zero at `P` as shown.
Hence, at `P, k.(8q)/((L+l)^(2))= (k.(2q))/(l^(2))implies l=L`
So distance of `P` from origin is `L+L= 2L`