Chapter 23, Problem 23.20P

Review. Two identical particles, each having charge +q, are fixed in space and separated by a distance d. A third particle with charge −Q is free to move and lies initially at rest on the perpendicular bisector of the two fixed charges a distance x from the midpoint between those charges (Fig. P22.13). (a) Show that if x is small compared with d, the motion of −Q is simple harmonic along the perpendicular bisector. (b) Determine the period of that motion. (c) How fast will the charge −Q be moving when it is at the midpoint between the two fixed charges if initially it is released at a distance a << d from the midpoint?

Figure P22.13