Capacitors A basic capacitor has two parallel plates
Capacitors A basic capacitor has two parallel plates separated by an insulating material n A capacitor stores an electrical charge between the two plates n The unit of capacitance is Farads (F) n Capacitance values are normally smaller, such as µF, n. F or p. F n
Capacitors n Basic capacitor construction Plate 2 Dielectric material Plate 1 The dielectric material is an insulator therefore no current flows through the capacitor
Capacitors Storing a charge between the plates n Electrons on the left plate are attracted toward the positive terminal of the voltage source n This leaves an excess of positively charged holes n The electrons are pushed toward the right plate n Excess electrons leave a negative charge + + + _ _ -
Capacitors Types of capacitors n The dielectric material determines the type of capacitor n Common types of capacitors are: n Mica n Ceramic n Plastic film
Capacitors n n Some capacitors are polarised, they can only be connected one way around Electrolytic capacitors are polarised
Capacitors n n n 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
Capacitors n n These variable capacitors would be difficult to squeeze into your mobile phone and i. Pod Current technology uses semi-conductor variable capacitors called varactors (varicaps)
Capacitors n n n 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 http: //www. microst. it
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