2. Capacitance
Capacitance
Ability to store electrical energy in an electrostatic field
Basic unit is the farad (F)
Represented by letter C
Capacitor
Possesses a specific amount of capacitance
Either fixed or variable
3. Capacitance (cont’d.)
Figure 11-1. A capacitor consists of two plates (conductors)
separated by a dielectric (insulator or nonconductor).
4. Dielectric
A dielectric material (dielectric for short) is an
electrical insulator that can be polarized by an applied
electric field. When a dielectric is placed in an electric
field, electric charges do not flow through the
material as they do in a conductor
5. Capacitors
Factors that affect capacitance
Area of the plate
Distance between the plates
Type of dielectric material
Temperature
12. RC Time Constants (cont’d.)
RC circuit time constant formula:
t = RC
where: t = time in seconds
R = resistance in ohms
C = capacitance in farads
13. The RC time constant, also called tau, is the
time constant (in seconds) of an RC circuit, is equal to
the product of the circuit resistance (in ohms) and the
circuit capacitance (in farads), i.e.
14. It is the time required to charge the capacitor, through the
resistor, by ≈ 63.2 percent of the difference between the
initial value and final value or discharge the capacitor to
≈36.8 percent.
15. RC Time Constants (cont’d.)
Figure 11-8. Chart of time constants required to charge and discharge a capacitor.
16. Summary
Capacitance (C) allows for the storage of energy in an
electrostatic field
The unit of capacitance is the farad (F)
Capacitor types include: electrolytic, paper, plastic,
ceramic, and variable
Total capacitance in series circuits:
17. Summary (cont’d.)
Total capacitance in parallel circuits:
RC circuit time constant formula:
t = RC
It takes five constants to fully charge and discharge a
capacitor