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Capacitors

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. Capacitors.

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Capacitors

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  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 http://www.microst.it

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