In order to draw the electric field lines, we place positive test charges at different places. The electric field created by the source charges will exert a force on these test charges. The lines of force (or electric field lines) are drawn tangent to the net force vector at every point.
Use the presets below to visualize the classic patterns from your textbook image:
Field lines are directed radially outward.Field lines are directed radially inward.Field lines repel. Middle region shows a zero field spot (neutral zone).Field lines start from positive and end on negative. Attractive force.