Working principle capacitor, capacitance and it's types are full detail

Capacitor

A capacitor is nothing but that two conducting surface separated by an insulating mmedium called dielectric .
This conducting surface could be in the the form of rectangular, circular, spherical or cylindrical in the shape.

A capacitor is also called condenser the commonly used die electric in capacitor are paper, mica, air etc.

Capacitance

Capacitance is define as the amount of charge required to create a unit of potential difference between the plates.

Key point- 

The property of the capacitor to store and dielectric energy in the form of static charge is called its capacitance.

Relation between charge and applied voltage

"Charge on the capacitor is proportional to the voltage applies to it."
Let applied voltage V, the charge accumulated on the capacitor plate Q , then mathematically, it can be written as

Q ∞ V

Q = CV

The constant of personality ‘c’ is called capacitance of capacitor.

C = Q/V

From the above expansion
the capacitance is defined as the ratio of charge acquired to attend the potential difference between the plates . It is the charge required per unit potential difference it is measure in unit farads .

One Farad capacitance is defined as the capacitance of a capacitor which require a charge of one coulomb to stabilize a potential difference of 1 volt between it plates.

 for practical use, the  Farad  it is too long unit and hence micro Farad, and picofarad are commonly used.

How, Energy stored in a capacitor?

When the capacitor is charged, energy is expanded by the charging source this is because charging the capacitor means the transfer of charge from one place to the another . This transfer is against the opposition due to potential difference across the plates . Due to this , there is expenditure of energy on the part of charging source.  Energy is store in the capacitor in term of electrostatic field setup in the dielectric medium.  However, when the capacitor is charged,  the field collaoses and energy store in it is released.

Factors Affecting Capacitance

The ability of a capacitor to store charge (i.e. its capacitance) depends upon the following
factors :

(i) Area of plate.

The greater area of capacitor plates, the larger is capacitance of the
capacitor and vice-versa. It is because larger the plates, the greater the charge they can hold  for a given p.d. and hence greater will be the capacitance.

(ii) Thickness of dielectric.

 The capacitance of a capacitor is inversely proportional to thet thickness(i.e. distance between plates) of the dielectric. The smaller the thickness of dielectric, the greater the capacitance .

(iii) Relative permittivity of dielectric. 

The greater the relative permittivity of the insulating material (i.e., dielectric), the greater will be the capacitance of the capacitor.

 Types of Capacitors

Mostly, the capacitors are classified based on the size and shape of the plates used. eg
Parallel plate, cylindrical, concentric spherical ec. They may be clasified based on the nature of the dielectric used as follows-

1) Air capacitors:

This type of capacitor corsists of one set of fixed plates and another set of movable plates .Its capacitance can be changed by changing the position of the movable plates.

This type is mainly used fur radio wark where the capacitance is required
to be varied.

2) Paper capacitors:

This consists of metal foils interleaved with paper impregnated with wax or ol and it is rolled into a compact form.

These are used in power supplies

3) Mica capacitors:  

It consists of allernate layers of mica and metal foil cdamped together tightly. Use of mica makes its cost high.

 It is mainly used in high frequency circuits which requires greater accuracy, high voltages and less dielectric loss.

4) Poly carbonate capacitors:

This is a reoent development where a film of polycarbonate, metallised with aluminium is wound to form the capacitor elements. It has a relative permittivity of 28 and has a high resistivity with very low dielectrie loss.

5) Ceramic capacitors:

It has a metallic coatings on the opposite faces of a thin disc of ceramic material like barium tutanate, hydrous silicate of magresia, etc.

 It is used in high
frequency radio and electronic circuits.

6) Electrolytic capacitors :

These are most commonly used and consists of two aluminium foils, ane with an axide film and one without. The foils are interleaved with a material such as a paper saturabed with a suitable electralyle. The aluninium oxide film is formed on the one foil by passing it throagh an electrolytic bath. This oxide film acts as a dielectric. These are used where very large capacitance values are required so used in electronic and filter circuits. The main limitations of this type are the low insulation resistance and suitability only for those cireuits where the voltage applied to the capacitor never reverses its direction.

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