The geometry of this example is the same as in Example 3, except the charge at x = -a is replaced by -Q.
Note that the expressions for the potential and the field are given by Equations (13) and (14) by making one of the charges negative.
The equipotential surfaces and the electric field lines are sketched below.
The arrangement of two opposite charges demonstrated in this example is called an electric dipole.
Ready to learn more? Go explore a dipole using our field applet.