Question

Two positive point charges `q_1=16muC` and `q_2=4muC` are separated in vacuum by a distance of `3.0m`. Find the point on the line between the charges where the net electric field is zero.-

Answer 1

Correct Answer - A::B::C::D
Between the charges the two field contributions have opposite directions, and the net electric field is zero at a point (say P) where the magnitude of `E_1` and `E_2` are equal. However, since `q_2ltq_1` point P must be closer to `q_2` in order that the field of the smaller charge can balance the field of the larger charge.

At `P, E_1=E_2`
`1/(4piepsilon_0) q_1/(r_1^2)=1/(4piepsilon_0).q_2/r_2^2`
`:. r_1/r_2=sqrt(q_1/q_2)=sqrt(16/4)=2`
Also `r_1+r_2=3.0m`
Solving these equations, we get
`r_1=2m` and `r_2=1m`
Thus, the point `P` is at a distance of 2 m from `q_1` and 1m from `q_2`.