Dipole Electric Field

	The plot shows the electric field vector E (green arrows) for a set of grid points (the black dots) for an electric dipole.  The field is due to two equal and opposite charges of strength q.  Successive plots show the x and y components of E for values of z from z = 0 (the plane of the charges) to a faraway distance, z = 0.2.  (We are using arbitrary units.)  These components are given by the (vector) equation

          ¬ 

where i = 1, 2, 3 stands for components of E along x, y, and z.  The charges are located at

        r1 = (x1=0.42, y1=0.47, z1=0) ,   q1 = +.1,   red dot
        r2 = (x2=0.58, y2=0.53, z2=0) ,   q2 =  -.1,   blue dot

near the middle of the unit square in which we are plotting.

	Note the curious effect that the electric field vectors, as projected in the x-y plane at various values of z, rotate slightly as one moves away from the z = 0 plane of the charges.  [Homework problem: why?]

	What are actually plotted are not the Ei themselves, but scaled values:

         ¬

Without the scaling, the vectors near the charges become very large (Emax/Emin is about 60 for this example) and are hard to grasp visually.

	The C-program which calculates the vector components, dipoleElectricField.c, is included and can be modified at your pleasure.  To display the changed field vectors, use the Open Panel to select the output file you create, dipoleElectricField.data, in the directory that you executed the code.

	Have fun!

		Dick Silbar
		silbar@cantina.lanl.gov