Halliday, Resnick & Walker — Electric Fields: Problem 1

1 Two charged particles are fixed to an x axis: Particle 1 of charge \( q_1 = 2.1 \times 10^{-8} \text{ C} \) is at position \( x = 20 \text{ cm} \) and particle 2 of charge \( q_2 = -4.00q_1 \) is at position \( x = 70 \text{ cm} \). (a) At what coordinate on the axis (other than at infinity) is the net electric field produced by the two particles equal to zero? (b) What is the zero-field coordinate if the particles are interchanged?