DC Circuits
CAPACITANCE
Capacitance
Capacitance is the ability to store an electrical charge. Capacitance is equal to the amount of
charge that can be stored divided by the applied voltage, as shown in Equation (3-7).
C =
(3-7)
Q
V
where
C = capacitance (F)
Q = amount of charge (C)
V = voltage (V)
The unit of capacitance is the farad (F). A farad is the capacitance that will store one coulomb
of charge when one volt is applied across the plates of the capacitor.
The dielectric constant (K) describes the ability of the dielectric to store electrical energy. Air
is used as a reference and is given a dielectric constant of 1. Therefore, the dielectric constant
is unitless. Some other dielectric materials are paper, teflon, bakelite, mica, and ceramic.
The capacitance of a capacitor depends on three things.
1.
Area of conductor plates
2.
Separation between the plates
3.
Dielectric constant of insulation material
Equation (3-8) illustrates the formula to find the capacitance of a capacitor with two parallel
plates.
C =
(3-8)
KA
d
(8.85 x 1012)
where
C
=
capacitance
K
=
dielectric constant
A
=
area
d
=
distance between the plates
8.85 x 10-12
=
constant of proportionality
Rev. 0
Page 11
ES-03
