Field and Wave Electromagnetics 2nd Edition by David Cheng

Exercise 90

Three charges ( +q, - 2 q, and +q ) are arranged along the z -axis at z = d /2 , z = 0, and z = - d /2,respectively.
a) Determine V and E at a distant point P ( R, , ).
b) Find the equations for equipotential surfaces and streamlines.
c) Sketch a family of equipotential lines and streamlines.
(Such an arrangement of three charges is called a linear electrostatic quadrupole. )