Chapter 23, Problem 23.21E

A positive charge q is fixed at the point x = 0, y = 0, and a negative charge −2q is fixed at the point x = a, y = 0. (a) Show the positions of the charges in a diagram. (b) Derive an expression for the potential V at points on the x-axis as a function of the coordinate x. Take V to be zero at an infinite distance from the charges. (c) At which positions on the x-axis is V = 0? (d) Graph V at points on the .r-axis as a function of x ill the range from x = −2a to x = +2a. (e) What does the answer to part (b) become when x >> a? Explain why this result is obtained.