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

VQC

= Q = total charge

Units: farads = C/V

dAC 0e=

e0 = permittivity constant (C2/Nm2)

A = area of plate

d = Distance between plates

Energy and Capacitors Equations

VQPE =21

2)(21 VCPE =

CQPE2

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