Two thin rods, each of length a, lie along the x-axis as shown in Fig. 20.34. The left-hand rod, which extends from x = -a to the origin, carries negative charge -Q distributed uniformly over its length. The right-hand rod extends from the origin to x = a and carries positive Q distributed uniformly over its length. (a) Find an expression for the magnitude of the electric field on the x-axis for x 7 a (that is, beyond the right end of the right-hand rod). (b) Show that, for x W a, the field exhibits the 1>x3 falloff of an electric dipole. (c) Compare the result of (b) with Equation 20.6b and write an expression for the magnitude of the dipole moment of this two-rod structure.