ELECTRIC POLARIZATION

What is electric polarization?When insulating material with relative permittivity (or dielectric constant) Eo is inserted into an initially charged parallel plates of a capacitor. Then negative charges appear on the left face and positive charges on the right face of the dielectric  The phenomenon is known as electric polarization and dielectric is said to be polarized under such condition. The charges on the dielectric faces are called induced charges; they are induced by the external field and appear on the dielectric faces only. The electric field from the free charges is left to right whereas the electric field due to induced charges is right to left.

Molecules in the dielectric material have their positive and negative charges separated slightly, causing the molecules to be oriented slightly in the electric field of the charged capacitor. As electric field due to induced charges is opposite to the external electric field so it reduces the intensity of external field due to oppositely charged plates of the capacitor.

electric polarization

We know that dielectric materials are made up of the two types of molecules polar and non polar molecules polar molecule behaves like a permanent dipole; although electrically neutral as a whole. For example in NaCl the end with Sodium ion is positive while the end with chlorine ion is negative.

On the other hand, a non-polar molecule like oil has no electric dipole moment in the absence of an external field. The centre of positive and negative charges coincide in the absence of an external electric field.

When a non polar dielectric material is placed in an external field, it gets polarized, that is, it displaces the

electrons to the opposite of electric field E.  Under the action of external field the centres of negative and positive charges shift and form dipoles (Two opposite point charge separated by a finite distance d constitutes a dipole).

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