Explain polarization, Electrical Engineering

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Explain Polarization.

Polarization: A dielectric has molecules the atomic nuclei of that are effectively fixed, related to each other. In absence of any external field all the electrons are distributed symmetrically round the nucleus at any time. While an electric field is applied the electrons of the atoms are acted on by that field. It causes a movement of the electrons that are displaced in a direction opposite to the electrons that are displaced in a direction opposite to the field. This movement is opposed through the attractive forces in between nuclei and electrons. And resultant effect is to separate the positive and negative charges in each molecule therefore they behave as electric dipoles. The strength of all dipole is specified by the dipole moment that in its simplest form, having two equal point charges of opposite sign ± Q separated, with a distance d.

As the dipoles are created the dielectric is said to be polarized or in a state of polarization seems the dielectric to be composed of many of elementary cylinders each of length l towards the applied field and of cross section δA. Assume that a uniform field of strength E is applied normal to the plates. It polarizes the dielectric inducing dipoles in all elementary cylinders, and charges δq appears on any end of the cylinder. The charge density, σ on the surface δA of the cylinder is specified by σ = (δq/ δA)(c/m2) = l (δq/ δA) = m/δV. Here m is the dipole moment and δV is the volume of the elementary cylinder. When the number of dipole per unit volume be N which is when N = 1/δV after that σ = Nm. The product Nm is termed as the polarization (P) of the dielectric and is the complete dipole moment established in unit volumes of the insulating medium. Therefore a dielectric subject to a homogeneous field carries a dipole moment P per unit volumes that may be written as P=Nm.


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