One way to plot the electric field distribution graphically is by drawing lines that are everywhere tangent to the electric field, called field lines or lines of force. These lines are everywhere perpendicular to the equipotential surfaces and tell us the direction of the electric field. The magnitude is proportional to the density of lines. For a single line charge. the field lines emanate radially. The situalion is more complicated for the IWO line charges of opposite polarity in Figure 2-24 with the field lines always starling on the positive charge and terminating on the negative charge