A type of insulator that gets polarised when it comes in contact with an electric field is called dielectric. These materials are very poor conductor of electric current. When these materials are kept in an electric field, unlike metals, they do not have free electrons that drift through the materials instead a process called polarisation occurs. Most of the dielectric materials are solids in nature but few are liquids and gases. Mica, ceramic, dry air and distilled water are few examples of dielectric
What is Dielectric Polarisation?
When the Dielectric material is kept in an external electric field the positive charges in the material are displaced in the direction of the electric field. The negative charges are drifted in the direction opposite to the electric field. This process of separation of charges in an electric field is known as Dielectric Polarisation. The quantity of energy stored in an electric field per unit volume is greater when a dielectric material is used as the medium. By using a dielectric in a capacitor the capacitance of the capacitor can be increased.
What is a Capacitor?
The device which is used to store energy Is called Capacitor. The capacitor consists of two capacitors kept close to each other and it is separated by an insulator. The effect of the capacitor is called capacitance. The capacitance is the amount of electric charge that can be stored in the capacitor per unit change in the electric potential.
Depending on the polarity there are two capacitor types
- Polar capacitor
- Non-Polar capacitor
Polar capacitors use electrolyte as the dielectric. The capacitance of this capacitor will be extremely high.
These are capacitors without positive and negative polarity. These capacitors are mainly used in the circuit to avoid leakage. The two types of the non-polar capacitor are a ceramic capacitor and a mica capacitor.
Depending on the shape, there are three capacitor types
- Parallel plate capacitor
- Spherical capacitor
- Cylindrical capacitors
Parallel Plate Capacitor
The parallel plate capacitor has two plates separated by a small distance. One of the plates gets positively charged while the other gets negatively charged when an electric field is applied.
Spherical Plate Capacitor
Spherical capacitors have two concentric spherical shells. The inner shell is given a positive charge and the outer shell negative charge when an electric field is applied
The cylindrical capacitor has a solid cylinder in the centre surrounded by a cylindrical shell. The capacitor is charged so that charge on the inner cylinder is positive and the outer cylinder is negative.
Application of Capacitors
Capacitors have many important applications. Few applications are listed below
- Capacitors are used in digital circuits to store a large amount of data in computer memory. The electric energy stored in capacitors maintains the information when there is a power failure.
- Capacitors are used as filters to protect the sensitive components from electric surges.
- Capacitors are used as sensors to measure air humidity, fuel levels etc
- The capacitors can effectively pass AC current and block DC current by a process called a capacitor coupling.
- Capacitors used in filtering unwanted signals.