When the capacitor is connected to a voltage source (eg a battery or other voltage source) capacitor will store the charge. The amount of capacity charge stored in a capacitor is called the capacity of the capacitor. The amount of the capacity of the capacitor is called capacitance. The capacity of the capacitor is much charge stored in the capacitor when connected to certain potential difference. Capacitance of the capacitor is symbolized by the letter C capital, mathematically be written as follows:
Where:
Capacitor C = Capacity, measured in farads
q = charge stored in the capacitor, measured in coulombs
U = the potential difference between the capacitor plates, measured in volts
Parallel Plate Capacitor Gambar3.10
Let’s review the configuration of parallel plates as in Figure 3.8. When the switch S is closed, the space between the plates will arise electric field. After a few moments on the plate 1 will collect the charge + q and the plate 2 charge q. The phenomenon shown in Figure 3.11 below.
Figure 3.11 Parallel Plate Capacitor Symptoms
The charge in the plate reaches the maximum price q after potential plate 1 reaches the price of Us. Q The maximum charge collected on the plate is proportional to the voltage source Us. Strong electric fields that arise in the plate are:
With 
, The charge density per unit area. So that the potential difference
the plate is:
For the next C is called the capacitance of the capacitor system stating the capacity to store charge or electrical fields also. Price capacitance capacitors depending on the form of the system, namely the vast distance between the plate and the plate. Capacitance unit Farad (F).
The capacitive system is a system that can store a charge or an electric field. While the capacitor is a capacitive system created in order to have a certain capacitance prices. The usefulness of the capacitor in a variety of electrical circuit is:
a. stepping prevent electric sparks in the circuit containing the coil, when suddenly disconnected and connected to an electric current.
b. store charge or electrical energy in a series of electronic igniters
c. select the wavelength of the radio receiver
d. as a filter in a direct current power supply circuit.
Figure 3.13 Symbol Capacitors