Definition:

Capacitor is an electronic device which stores the charge in the form of an electric field, also known as condenser. Capacitor is also the passive component like resistor. Generally, it is used to store the charge.

Capacitor symbols:

Importance:

Capacitors are important because:

Construction:

It has two metal plates parallel to each other, which are not connected. These two plates are separated by non-conducting material (insulating material) which is commonly known as Dielectric medium.

There are many capacitors that are different in size and dimension but all of them are are used in storing the electrical charge in them.

The capacitors are present in different shapes like rectangle, square, circular, cylindrical shapes. An ideal capacitor, unlike resistor, does not dissipate energy.

Dielectric:

Dielectric is the material between the two plates. Dielectric is of different type of non-conducting material such as ceramic, mica, plastic or some type of a liquid gel and waxed paper. It plays an important in finding the value of capacitance of the capacitor. As, the insulated material or dielectric is placed between the plates in the centre of the capacitor then its value increases.

The value of dielectric constants are different for dielectric materials whatever, the value is greater than 1.

The following below table gives the value of dielectric constant for different materials.

Dielectric's types:

The two types of dielectrics are followings:

Polar dielectrics: These type of dielectrics have permanent movement.

Non Polar dielectrics: These types of dielectrics have temporary dielectric movement. They can be induced with the dipole moments by placing them in an electric field.

The insulated materials which are used in capacitors as a dielectric are as following:

Complex Permittivity:

It is the product of the relative permittivity of free space (εo) with the relative permittivity (εr) of the dielectric material, which is called complex permittivity of the dielectric material. The formula of the complex permittivity is given below,

ε = ε0 * εr

The value of the complex permittivity for the capacitor is equal to the relative permittivity, because the relative permittivity of free space is equal to ‘1’. The value of complex permittivity differs from one material to another. Some of the values of complex permittivity (ε) for different dielectric materials are'

 Pure Vacuum = 1.0000, Air = 1.0005, Mica = 5 to 7, Paper = 2.5 to 3.5, Wood = 3 to 8, Glass = 3 to 10 and Metal Oxide Powders = 6 to 20 and etc.

Working:

As capacitor consists of two conductors, separated by a insulated material, when there is any voltage or potential difference moves between the two conductors then the electric potential is developed then this causes the capacitor to both charge and discharge.

In the practical way, when the capacitor is connected to a a DC source, then the  current starts to flow through the circuit. Thus, -ve charge is stored on one plate and +ve charge is stored on the other plate. This whole process continuous until the voltage of capacitor reaches the supply voltage. When the voltage of the capacitor is equal to the input voltage, then the capacitor tends to stop charging further even when the battery is connected to the circuit. After this, when the battery is removed from the circuit the the two plates will be accumulated with +ve and -ve charges. Thus, the capacitor stores the charge. But, when the input supply voltage is of an AC source then, it both charges and discharges continuously.

Example

Below diagram shows the working of capacitor.

Capacitance:

Capacitance is the factor of the capacitor that describes the maximum amount of electrical charge that can be stored in it. The value of capacitance carries according to the shape of the capacitor. Its value can be calculated by determining the characteristics about conducting material and dielectric material. 

Capacitance can be defined as the ratio of charge (Q) on the plates to the potential difference (V) between them. 

C =Q/V,

The unit of capacitance is Farads (F).

The capacitance is inversely proportional to the voltage (V) and directly proportional to the charge (Q). Where, the capacitance increases by increasing the no. of plates, which keeps the same size of the capacitor.

Standard units of capacitance:

The capacitance can be expressed in Farads (F) and can also be expressed such as as micro farads(uF) , nano farads(nF) and pico farads(PF).

Where as,

Voltage Rating of a Capacitor:

It is the maximum voltage by which a capacitor charges to a maximum value also called as working voltage (WV) or DC working voltage (DC-WV). The figure below expresses the voltage rating of the capacitor.

If the large voltage is applied to the capacitor then it damages the capacitor by developing an arc between the plates due to the break down of dielectric.

The voltage rating plays important role, while designing the circuits with capacitors, and the capacitor's voltage rating should be greater than the voltage used in the circuit e.g. if the circuit operates at 12V then you should choose a capacitor with voltage rating of 12V or above. This voltage rating depends on the factors like thickness of dielectric, material used as dielectric between the plates and on the circuit.