Electric Dipole
The electric dipole moment for a pair of opposite charges of magnitude q is defined as the magnitude of the charge times the distance between them and the defined direction is toward the positive charge.
It is a useful concept in atoms and molecules where the effects of charge separation are measurable, but the distances between the charges are too small to be easily measurable.
It is also a useful concept indielectrics and other applications in solid and liquid materials.
There are two kinds of dipoles
1. An electric dipole is a separation of positive and negative charges. The simplest example of this is a pair of electric charges of equal magnitude but opposite sign, separated by some (usually small) distance. A permanent electric dipole is called an electret.
2. A magnetic dipole is a closed circulation of electric current. A simple example of this is a single loop of wire with some constant current through it .