# Dieletric Medium and non dielectric medium

In the  previous course in electromagnetism you have learnt the concept of electric field electrostatic energy and the nature of the electrostatic force however for reasons of simplicity reconfirmed the most part our consideration of this concept for charge that are placed in a vacuum for example coulomb’s law of electrostatic force is the electric field due to distribution of charge Refer to the situation the surrounding medium is vacuum. ofqual important is the situation in which the electrical phenomena occur in the presence of a material medium.

Hear  we must distinguish two  between two different situation as the physics of this situation is completely different the first situation is when the medium consist of insulating materials i.e material which do not conduct electricity the second situation correspond to the case when the median consists of conducting material materials which are conductors of electricity the conductive material containing electrons which are free to move within the materials these electrons move under the action of electric field and constitute current we shall study conducting material and electric field in conducting material at a later stage.

In the present units you will study the electric field in the presence of an insulator. in this material there are practically no free election or number of such election is so small that the conduction is not possible. in 1937, faraday experimentally found that when an insulating material also called dielectric such as niga, glass or polystyrene it is. is introduced between the two plates of a capacitor, it is found that the capacitance is increased by a factor which is greater than any one. this factor is known as dielectric constant of the material. it was also found that this capacitance is independent of the shape and size of the material but it varies from materials to  material. in the case of glass, the value of the dielectric constant is 6, why for water it is 80. all the election in this material are bound to their respective atom or molecule.

when a potential difference is applied to the insulator no electric current flow however the study of their behaviour in the presence of an electric field give us very useful information. the choice of a proper dielectric in a capacitor, the understanding of double refraction in quartz or calcite crystal is based on such study. natural materials such as wood, cottons, natural rubber, mica are some popular example of electric insulator. a number of varieties of plastic are also good dielectric.

Dielectric substance are insulator or non-conducting substance as they do not allow the conduction of electricity through them.

in this unit  we will study a simple model of dielectric

Simple model of dielectric material

you must be aware that

1. every material is made up of a very large number of atoms or more
2. an atom causes of a positively charge and negatively charged particles with electron revolving around it
3. d total positive charge of the nucleus is balanced by the total negative charge of the electron in the atom so that the atom as a whole is electrically neutral any point to present outside the atom
4. the molecule may be constituted by atom of same kind ore of different kind.

to understand the polarization we shall consider a crude model of the atom a simple model of an atom is shown below

Model of an atom