A dielectric, or electrical insulator, is a substance that is highly resistant to electric current. Vacuum is also an excellent dielectric

 

A dielectric tends to concentrate an applied electric field within itself. As the dielectric interacts with the applied electric field, charges are redistributed within the atoms or molecules of the dielectric. This redistribution alters the shape of the applied electrical field both inside and in the region near the dielectric material.

When a dielectric material is placed between two electric charges it decreases the effective force between them and, when an electromagnetic wave travels through a dielectric, the velocity of the wave will be reduced and it will behave as if it had a shorter wavelength.

 

 

When a static electric field is applied to a dielectric medium, a current flows. The total current flowing in a real dielectric is, in general, made up of two parts: a conduction and a displacement current. The displacement current can be considered the elastic response of the dielectric material to the applied electric field. As the magnitude of the electric field is increased, the additional displacement is stored as potential energy within the dielectric. When the electric field is decreased, the dielectric releases some of the stored energy as a displacement current. The electric displacement can be separated into a vacuum contribution and one arising from the dielectric by

where P is the polarization of the medium, E is the electric field, D is the electric flux density (or displacement), and ? its electric susceptibility. It follows that the relative permittivity and susceptibility of a dielectric are related,

 

 

The dielectric constant is a measure of the extent to which a substance concentrates the electrostatic lines of flux. It is the ratio of the amount of electrical energy stored in an insulator, when a static electric field is imposed across it, relative to vacuum (which has a dielectric constant of 1). The dielectric constant is also known as the static permittivity. Infact there is complex dielectric permittivity in dielectrics.

Mdeium having a high resistance to electric current is called dielectric, such as vaccum.

The dielectricconstant of a medium is the ratio of the Capacity of the condenser containing the given substance to that with vaccum between the plates of the condenser. C/C0.

In solvents with high dielectric constant , there is more ionization. Water has the highest dielectric constant and hence maximum ionization takes place in water.