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Capacitors
What They Are, How They Work, and Stuff
Anthony Bisceglia
What is a Capacitor
• It is a basic device of a circuit
used to store charge.
• It is constructed by placing
two conductors plates which
are separated by a dielectric
• A common conductor
material is Aluminum
• Common dielectrics are air,
glass, porcelain, paper, or
Teflon
Original Capacitors
•
•
•
The Leyden Jar
A first breakthrough in storing
charge.
Pieter van Musschenbroek, a
Dutch professor at the
University of Leyden
Parts to a Capacitor
• The Conductor plates are what attract the
charge.
• The dielectric is located between the plates
• The electric field is through the dielectric
• Capacitance is a measure of a capacitor’s
ability to store Charge, measured in the units
Farads (F)
How to Determine Charge
•
•
•
•
Q=CV
Q=Charge, Coulombs (C)
V=Voltage, Volts (V)
Q=VC, which becomes obvious that charge is
directly proportional to the voltage applied
and to the capacitance.
How to determine Capacitance of a
Capacitor
•
•
•
•
•
C=Є A/d
C= Capacitance, farads(F)
Є=permittivity, (F/m)
A=area, (m2)
d=distance, (m)
• Noting the equation it shows that capacitance
is directly proportional to Є and A. and
inversely proportional to d.
Permittivity
• Permittivity is equal to the Dielectric Constant
by the Relative Permittivity of the dielectric
being used.
• Є=Єо Єr
• Єо = 8.85x 10-12 F/m
Єr
• Relative Permittivity Table
Dielectric
Єr
Air
Teflon
Paper
Rubber
Oil
Porcelain
Glass
1
2
2.5
3
4
6
7.5
Comparison
• Capacitor with air as a •Capacitor with paper as
dielectric.
a dielectric
•C= Єо Єr A/d
• C= Єо Єr A/d
-12
2
• =(1 x 8.85x
F/m x
• =8.85 picofarads
10-12
1m2)/1m
•=(2.5 x 8.85x 10 F/m x 1m )/1m
•=22.1 picofarads
• In conclusion, this comparison shows that without
changing the dimensions of the capacitor the
capacitance can be increased by changing the
dielectric.
Use for Capacitors
• Capacitors main trait
is their ability to
charge and discharge
quickly.
• Capacitors are used in
the flash of a camera.
Its bright surge of
light comes from a
capacitor’s discharge.
Works Cited
• Boylestad, Robert L. Introductory Circuit
Analysis Eleventh Edition, NJ: Pearson
Education Inc, 2007
• Brain, Marshall. How Stuff Works, How
Capacitors Work. November 29, 2009.
http://electronics.howstuffworks.com/cap
acitor.htm