Capacitor

Capacitor is a two terminal device capable of storing charges. It is similar to a battery. Battery produces electrons with the help of chemical reactions but capacitor stores charges that can be discharged. Another important difference between a battery and capacitor is that, the discharge time of capacitor is very less than that of battery. A capacitor is shown below:

The shorter terminal is to be connected to negative voltage and longer terminal to the positive voltage. It is usually written on the body of the capacitor.

The symbol of capacitor is shown below:

When a battery is connected to a capacitor, negative charges are accumulated on the plate nearer to the positive terminal of battery and positive charges are accumulated on the plate nearer to the negative terminal of the battery. Thus a capacitor stores charges.

The first capacitor symbol (a), means that the capacitor is non-polar, i.e current can pass through both sides. Whereas the secaond symbol (b) shows a polar capacitor. The voltage on the curved side should be more negative than the straight lineside.

The gap between the two plates is occupied by a dielectric and it determines the capacity of the capacitor.

Various types of dielectric materials used are:

• Air        - Mostly used in radio tuning circuits.
• Glass    - Can be used for high voltage applications.
• Mylar   - Mostly used in timer circuits.
• Ceramic- Mostly used in high frequency applications.

Types of capacitor:

Disk Capacitor
They are the smallest capacitor available on market. They are small and disk shaped. Their capacitance is measured in picofarads.

Film Capacitor
They are medium range capacitor. They are shaped like a rectangular box. Their capacitance are measured in microfarads.

Electolytic Capacitor
They can hold more than 1micofarad of charge. They are cylindrical in shape.

We will study more about capacitor later with the help of an experiment.