Walker, Halliday & Resnick — Electric Potential: Problem 24

24 In Fig. 24-31a, a particle of elementary charge $+e$ is initially at coordinate $z = 20\text{ nm}$ on the dipole axis (here a $z$ axis) through an electric dipole, on the positive side of the dipole. (The origin of $z$ is at the center of the dipole.) The particle is then moved along a circular path around the dipole center until it is at coordinate $z = -20\text{ nm}$, on the negative side of the dipole axis. Figure 24-31b gives the work $W_a$ done by the force moving the particle versus the angle $\theta$ that locates the particle relative to the positive direction of the $z$ axis. The scale of the vertical axis is set by $W_{as} = 2.0 \times 10^{-30}\text{ J}$. What is the magnitude of the dipole moment?