Page 24 - POLYMER TECHNOLOGY
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b. Dielectric constant
The dielectric constant of a plastic can be defined as the ratio of the charge stored
in an insulating material placed between two metallic plates to the charge that can
be stored when the insulating material is replaced by vacuum or air. It is also called
as electric permittivity or simply permittivity. In other words, dielectric constant
can also be defined as the ratio of the capacitance induced by two metallic plates
with an insulator between them, to the capacitance of the same plates with air or
a vacuum between them.
An insulating material with higher dielectric constant is needed when it is to be
used in electric and electronic applications where high capacitance is needed.
If a material were to be used for strictly insulating purposes, it would be better to
have a lower dielectric constant.
The dielectric constant formula is:
Where:
ε = Permittivity
C = capacitance (dielectric capacitor)
C0 = capacitance (vacuum)
ε0 = Permittivity of free space
A = Area of the sample cross section area
t = Thickness of the sample
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