A geometric method to determine the direction of electric field due to a   uniformly charged line segment
  A geometrical approach to calculate the electric field due to a uniformly charged rod is presented. The result is surprisingly simple and elegant. Using pure geometrical quantities like length and angle, the direction of the electric field in this charge configuration can be graphically defined. Understanding and application of this result can lead to a deeper appreciation of symmetry in a seemingly unsymmetric system. 
Fulin Zuo
physics.pop-ph