capacitance demonstrations & notes. warning capacitors can act like high voltage batteries, but...
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Capacitance
Demonstrations & notes
Warning Capacitors can act like High
Voltage batteries, but more fatal! (unless it’s a flux capacitor)
Capacitor uses:1. store energy for later use
(like a battery)
2. Powerful discharge of current(spot welding, flash cameras)
3. Smooth/filter out current fluctuations (motors run better, less noise in sensitive
circuits, less interference pick-up)
Basic Capacitor
Extra + charge piles up on the left; other + charge is taken from the right
Dielectric adds capacitance
C= eA/d
= e permitivity (polarizability)
e= 1 air or vacuum 3 paper 10 glass 100 water 1000 ceramics
Types: paper
Cheap<500V
Low capacitanceSensitive to moisture
Types: ceramic
CheapCan handle 10kvLow capacitance
robust
Types: electrolyte
Polarized (if connect wrong,
might explode!)<500V
high capacitanceChemicals inside
Make your own
Capacitors
• stores energy in the E field• Capacitance is a measure of
the ability to store energy in the form of separated charges
• Capacitors take time to charge and discharge
Capacitance Equations
V
QC
Q = total charge
Units: farads = C/V
d
AC 0
0 = permittivity constant (C2/Nm2)
A = area of plate
d = Distance between plates
Energy and Capacitors Equations
VQPE 2
1
2)(2
1VCPE
C
QPE
2
2
Capacitors in Series: same charge, share the voltage
Capacitors in Parallel Same voltage, but share the charge
Q = Q1 + Q2 + Q3
CPV = C1 V + C2V + C3V
CP = C1 + C2 + C3
References:
http://www.sentex.net/~mec1995/circ/hv/hvcap/hvcap.html
www.answers.com/topic/capacitor