A capacitor contains electrodes, which consist of two metal plates or metal films that face each other. An insulator (or a dielectric substance), which can be made of various materials, is placed between the electrodes. (In the diagram, air acts as an insulator.)
When voltage is applied to both electrodes by connecting the positive and negative terminals of a battery, the facing electrodes will become positively and negatively charged.
The electric charges will remain even after the power source has been disconnected, as the capacitor has a charging effect. When the electrodes of a charged capacitor are shorted, there will be a momentary flow of current, and the stored charge will become neutralized and disappear. Thus, the capacitor is discharged.
In addition to the charge storage function described above, a significant characteristic of a capacitor is that it prevents a direct current from flowing through.
The following are examples of circuits that utilize the charge storage function of a capacitor: A regulator circuit for the power supply, a backup circuit for the microprocessor, and a timer circuit that utilizes the length of time required for charging and discharging a capacitor. Also the circuits that utilize the characteristic of a capacitor to shut off a direct current are the filters that extract or eliminate specific frequency elements.
Using of these characteristics, capacitors are used in automotive electric circuits for many purposes, such as to eliminate noise or substitute for a power source or a switch.
A capacitor is also known as a condenser.
Charging Characteristics of Capacitor
When a direct current voltage is applied to a completely discharged capacitor, the current will initially flow at a rapid rate. After the capacitor starts to store electricity, the flow of the current diminishes. Ultimately, when the electrostatic capacity (the ability of the capacitor to store electricity) of the capacitor has been reached, the flow of the current will stop. The voltage of the capacitor at this time is equal to the applied voltage.