Three point charges are placed on the y-axis: a charge q at y=a, a charge -2q at the origin, and a charge q at y=-1 . Such an arrangement is a special case of what is called an electric quadrupole.
1) Find the magnitude of the electric field at points on the positive x-axis.
2 ) Find the direction of the electric field at points on the positive x-axis.
3) Use the binomial expansion to find an approximate expression for the magnitude of the electric field valid for .