1. Capacitors
A basic capacitor has two parallel plates separated by an insulating material
A capacitor stores an electrical charge between the two plates
The unit of capacitance is Farads (F)
Capacitance values are normally smaller, such as µF, nF or pF

2. Capacitors Basic capacitor construction Dielectric material
The dielectric material is an insulator therefore no current flows through the capacitor
Plate 2
Plate 1

3. Capacitors Storing a charge between the plates
Electrons on the left plate are attracted toward the positive terminal of the voltage source
This leaves an excess of positively charged holes
The electrons are pushed toward the right plate
Excess electrons leave a negative charge _ + _ + - +

4. Capacitors Types of capacitors
The dielectric material determines the type of capacitor
Common types of capacitors are:
Mica
Ceramic
Plastic film

5. Capacitors
Some capacitors are polarised, they can only be connected one way around
Electrolytic capacitors are polarised

6. Capacitors
Variable capacitors are used in communication equipment, radios, televisions and VCRs
They can be adjusted by consumers by tuning controls
Trimmers are internal adjusted capacitors that a consumer cannot adjust

7. Capacitors
These variable capacitors would be difficult to squeeze into your mobile phone and iPod
Current technology uses semi-conductor variable capacitors called varactors (varicaps)

8. Capacitors
The capacitance in a varactor is created when a purpose diode is reversed biased
Adjusting the reverse bias alters the capacitance value
A simple radio receiver using varactor