Electric Fields for Three Point Charges
The electric field of a point charge at is given (in Gaussian units) by . The lines of force representing this field radiate outward from a positive charge and converge inward toward a negative charge. The composite field of several charges is the vector sum of the individual fields. In this Demonstration, you can move the three charges, shown as small circles, and vary their electric charges to generate a stream plot of the electric field.
Snapshot 1: one of the charges can be reduced to zero to give the field of two point charges
Snapshot 2: the field of a charge-dipole interaction
Snapshot 3: the field of a linear quadrupole formed by the closely spaced sequence of charges +1, -2, +1