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# Capacitors Capacitance is the ability of a component to store energy in the form of an electrostatic charge. A Capacitor is a component designed to provide.

## Presentation on theme: "Capacitors Capacitance is the ability of a component to store energy in the form of an electrostatic charge. A Capacitor is a component designed to provide."— Presentation transcript:

Capacitors Capacitance is the ability of a component to store energy in the form of an electrostatic charge. A Capacitor is a component designed to provide a specific measure of capacitance. EGR 1011

Capacitor Construction EGR 1012 Parallel plates separated by a dielectric layer

Fixed Value Capacitors Polarized Electrolytic Capacitors Most electrolytic capacitors are polarized EGR 1013

Variable Capacitors Interleaved-Plate Capacitors EGR 1014

Charging a Capacitor EGR 1015 Electrostatic Charge Develops on the Plates Electrostatic Field Stores energy

Discharging a Capacitor EGR 101 6 Apply a discharging component (here a short circuit) across the capacitor. (Safer to use a resistor!)

Capacity (Capacitance) of a Device EGR 1017 Capacity is the amount of charge that a capacitor can store per unit volt applied. Capacity is directly proportional to charge and inversely proportional to voltage

EGR 1018 where C = the capacity (or capacitance) of the component, in coulombs per volt, or Farads Q = the total charge stored by the component V= the voltage across the capacitor

Example EGR 1019

Capacitor Ratings EGR 10110 Most capacitors rated in the picofarad (pF) to microfarad (  F) range Capacitors in the millifarad range are commonly rated in thousands of microfarads: 68 mF = 68,000  F Capacitors in the nanofarad range are also commonly rated in microfarads: 68 nF = 0.068  F

EGR 10111 Capacitors in the nanofarad range are also commonly rated in microfarads: 68 nF = 0.068  F Tolerance Usually fairly poor Variable capacitors used where exact values required

Physically large capacitors usually have their values printed directly on the case Smaller capacitors are generally labeled using a code: –2-digit code: the number represents the value of the component in pF Example: 15 = 15 pF –3-digit code: the code is interpreted like the first three digits of a resistor code Example: 473 = 47 x 10 3 pF = 47 nF –The numbers 6 and 7 are not used as multiplier values –The numbers 8 and 9 are decoded as follows: 8 = 0.01 and 9 = 0.1 Example: 158 = 0.15 pF Capacitor Value Codes

Capacitance of a Parallel Plate Capacitor EGR 10113

EGR 10114 C = the capacity of the component, in farads (8.85 X 10 -12 )= the permittivity of a vacuum, in farads per meter (F/m)  r = the relative permittivity of the dielectric A= the area of either plate, in square meters (m 2 ) d = the distance between the plates, in meters (m)

EGR 10115 Plate Area: capacitance is directly proportional to plate area Dielectric Thickness: capacitance is inversely proportional to dielectric thickness Dielectric Permittivity: the ease with which lines of electrical force are established in the dielectric material Relative Permittivity: the ratio of a material’s permittivity to that of a vacuum

Capacitors in Series EGR 10116 C T = the total series capacitance C n = the highest-numbered capacitor in the circuit

Capacitors in Parallel EGR 10117 C n = the highest-numbered capacitor in the parallel circuit

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