Question

A -2.8nC charge is on the x-axis at x1 = -8cmand a 3.5nC charge is on the x-axis at x2 = 16cm. At what point or points on the y-axis is the electric potential zero?

Answer 1

let the potential be zero at y units from origin

so this y is at distance of sqrt ( y^2 + 0.0064) units from -2.8 nC

or this point is at a distance of (sqrt(Y^2 + 0.0256) from 3.5 nC charge

for potential to be zero, potential due to both charges must be same

potential due to a point charge is given by V = Kq/r

here V1 = V2

Kq1/sqrt (y^2+ 0.0064) = Kq2/sqrt ( y^2 + 0.0256)

sqrt {(Y^2 + 0.0256)/(Y^2 + 0.064)} = 3.5/2.8 = 1.25

{(Y^2 + 0.0256)/(Y^2 + 0.064)}= 1.25^2 = 1.5625

Y^2 + 0.0256 = 1.5625Y^2 + 0.1

Y^2( 0.5625) = 0.0744

Y^2 = 0.1322

Y = +- 0.3636 m
so at a distance on either + 36 cm or - 36cm on Y axis net potential is zero