1. 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 101

2. Capacitor Construction
Parallel plates separated by a dielectric layer
EGR 101

3. Fixed Value Capacitors
Polarized Electrolytic Capacitors
Most electrolytic capacitors are polarized
EGR 101

4. Interleaved-Plate Capacitors
Variable Capacitors
Interleaved-Plate Capacitors
EGR 101

5. Charging a Capacitor Electrostatic Charge Develops on the Plates
Electrostatic Field Stores energy
EGR 101

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

7. Capacity (Capacitance) of a Device
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 101

8. Q = the total charge stored by the component
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
EGR 101

9. Example
EGR 101

10. Capacitor Ratings
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 = F
EGR 101

11. Variable capacitors used where exact values required
Capacitors in the nanofarad range are also commonly rated in microfarads:
68 nF = F
Tolerance
Usually fairly poor
Variable capacitors used where exact values required
EGR 101

12. Capacitor Value Codes
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 103 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

13. Capacitance of a Parallel Plate Capacitor
EGR 101

14. 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 (m2)
d = the distance between the plates, in meters (m)
EGR 101

15. 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
EGR 101

16. Capacitors in Series CT = the total series capacitance
Cn = the highest-numbered capacitor in the circuit
EGR 101

17. Capacitors in Parallel
Cn = the highest-numbered capacitor in the parallel circuit
EGR 101