Section A
The capacitance can be calculated if the geometry of the conductors and the dielectric properties
of the insulator between the conductors are known. For example, the capacitance of a
parallel
plate
capacitor
constructed of two parallel plates of area
A
separated by a distance
d
is
approximately equal to the following:
or
where
C
is the capacitance in
farads
, F
ϵ
s
is the static
permittivity
of the insulator used (or
ϵ
0
for a vacuum)
A
is the area of each plate, measured in
square metres
ϵ
r
is the
relative static permittivity
(sometimes called the dielectric constant) of the
material between the plates, (vacuum =1)
d
is the separation between the plates, measured in
metres
Coaxial Cable
C =
2 p
ε
0
ε
r
x
ln [ b/a ]
A = Area of plates
C = Capacitance (F)
D = Distance between plates (m)
a = Inner radius (m)
b = Outer radius (m)
q = Charge (Coulombs)
x = Length (m)
W = Energy (J)
ε
r
= Relative permittivity
ε
0
= 8.85 x 10
12
F/m
D.F. = Dissipation Factor = 1/q
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 Spring '10
 Hampton
 Permittivity, Fundamental physics concepts, Lowpass filter, Dielectric

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