As shown below, one plastic rod with length L and carrying a uniformly distributed charge +Q is placed on the x-axis such that one end is on the origin and the other end is on the point x = -L. Another plastic rod with length L and carrying a uniformly distributed charge -Q is placed right next to the positively charged line such that one end is on the origin and the other end is on the point x = L.
a. Find the magnitude and direction of the electric field at a point P a distance D away from the end of the negatively-charged rod as shown below. Express your answer in terms of Q, L, D and other known constants (i.e. ke). (Hint: Try using the result from an example we did in class and use superposition from the two individual rods).
b. Find the magnitude and direction of the electric force of an electron placed at point P. Express your answer in terms of the above constants, as well as the fundamental charge, e.