Consider two identical, thin, and nonconducting rods, a and b. on rod a, positive charge is spread evenly, so that there is the same amount of charge per unit length at every point. on rod b, positive charge is spread evenly over only the left half, and the same amount of negative charge is spread evenly over the right half. what is the direction of the electric field at a point that is located directly above the midpoint of each rod?