To visualize the complex geometry of cosmic magnetic fields it is useful to represent the field by means of magnetic field lines, that is, lines that are every where parallel to the magnetic field vector.

There are two sorts of magnetic dipoles we will consider: a dipole consisting of two magnetic charges p separated by a distance d (a true dipole), and a current loop of area A (an approximate dipole).

For the study of many phenomena connected with the Earth's magnetic field, the use of dipole or geomagnetic coordinates is more practical than the use of geographic ones.

Because of this similarity, we can refer to a small current loop of are S and current I as a Magnetic Dipole. Clearly, the analogous product to Qd for a magnetic dipole is SI. We can, in fact, define a …

electric dipole moment, p (or electric dipole for short), is a measure of the polarity of a system of electric charges. Here x is the displacement vector pointing from the negative charge to the positive charge.

On the x-axis, this force is maximum at the origin, the point midway between the two charges, and at large distances it decreases as r-3, because the inverse square repulsion and attraction are …

In these notes, I write down the electric field of a dipole, and also the net force and the torque on a dipole in the electric field of other charges.