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Chapter V Dielectric Study of ……
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electric field. For anisotropic dielectrics the relationship between P and E is
tensorical.
Usually, the dielectric constant for a given material is defined as the
ratio of a capacitance of capacitor containing a given dielectric (C) to a
capacitance of vacuum capacitor (C0) of identical dimensions. This can be
represented by the following relationship,
r = (5.7)
For a given charge distribution, the dielectric constant expresses the
ratio of electric field strength in vacuum to that in a dielectric, the later field
being reduced by the polarization of the dielectric medium.
5.2.1 Polar and Non-polar Dielectrics
Dielectrics can be divided into two classes
(i) Polar dielectrics
(ii) Non-polar dielectrics
This classification is extremely important when electrical, general physical
and chemical properties of materials are considered.
A molecule of any material consists of atoms or ions having definite
positive or negative electric charges. Even in the absence of external electric
field if the molecule exhibits electric dipole (figure: 5.1-c) with dipole moment
different from zero, it is referred to as a permanent dipole and the molecule is
called as polar dielectric. The magnitude of the electric dipole moment of a
molecule is,
µ = q.l (5.8)
Where, q is the magnitude of positive or negative electric charge of a
molecule and l is the length of the dipole. Here, µ is the intrinsic electric
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