Capacitors
A capacitor is an electrical circuit element made out of two conductive surfaces placed
very close together without touching. A voltage difference is applied across them and
equal but opposite charges develop on the opposing surfaces.
The idealized version of this element is the
parallel plate capacitor
. It is
depicted to the right as a pair of identical metal plates of area
A
with a
nonconducting
dielectric
sandwiched in between of width
d
. The
dielectric improves the capacitor because of its high electrostatic
permittivity. Often, this permittivity is represented as the product of a
dielectric constant
,
κ
, and the permittivity of free space,
ε
₀
. The
capacitor’s parameters come together in a single physics quantity called
the
capacitance
, which simply measures how much charge the capacitor
can hold at a given voltage. The equation for the capacitance is
C=
ε
A/d
(or
C=
κε
₀
A/d
), where
C
is measured in
farads
(
F
).
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 Spring '11
 Tibbets
 Charge, Electric charge, permittivity.

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