Question

A 5.0*10^-6C point charge is placed at the 0.00 cm mark of a meter stick and a -4.0 *10^-6C point charge is placed at the 50 cm mark. At what point on a line joining the two charges is the electric field due to these charges equal to zero?

Answer 1

Write an equation for the E-field along the line joining the two charges. Let the position of the charge be x. Set the E-field equal to zero and solve for x. You can assume that x has to be > 50 cm, so that the fields due to the two charges oppose each other.

E = k*[(5.0*10^-6/x^2) -4*10^-6/(x-0.5^2]
= 0

k is the Coulomb constant, which you don't need to use since it cancels out.

Answer 2

1.35