1. Dielectrics:

A dielectric material is a substance that is a poor conductor of electricity, but an efficient supporter of electrostatic fields. If the flow of current between opposite electric charge poles is kept to a minimum while the electrostatic lines of flux are not impeded or interrupted, an electrostatic field can store energy. This property is useful in capacitors, especially at radio frequencies. Dielectric materials are also used in the construction of radio-frequency transmission lines.

An important property of a dielectric is its ability to support an electrostatic field while dissipating minimal energy in the form of heat. The lower the dielectric loss (the fraction of energy lost as heat), the more effective is a dielectric material.

2. Electric dipole:

An electric dipole is two charged objects, with equal but opposite electric charges, that are separated by a distance. The electric field caused by a dipole falls off as the cube (third power) of the distance from the dipole, and has a directional variation that depends on whether you’re moving along the line separating the two charges or perpendicular to it. A dipole can be created, for example, when you place a neutral atom in an electric field, because the positively-charged constituents of the atom will be pulled one way, and the negatively-charged constituents the other way, creating a separation of charge in the direction of the field.

3. Polarizability:

When an external electric field is applied to a dielectric material this material becomes polarized, which means that it acquires a dipole moment. This property of dielectrics is known as Polarizability. Basically, Polarizability is a consequence of the fact that molecules, which are the building blocks of all substances, are composed of both positive charges (nuclei) and negative charges (electrons). When an electric field acts on a molecule, the positive charges are displaced along the field, while the negative charges are displaced in a direction opposite to that of the field. The effect is therefore to pull the opposite charges apart, i.e., to polarize the molecule. It is convenient to define the polarizability  of an atom in terms of the local electric field at the atom-

p=αE

where p is the dipole moment. For a non-spherical atom α will be a tensor.