Basic knowledge of capacitor

Here present the article about the basic knowledge of Capacitor.

Capacitor is a passive element that stores energy in the form of electrical charge. Like a small rechargeable battery.
The capacitor is a device whose use can increase the capacitance of the driver.
S.I unit of Capacitance is Faraday's it is denoted by F.
Capacitors are capable of storing charges. They are used for coupling AC signals from one circuit to another circuit and for frequency selection etc.
An capacitor consists of 2 metallic plates separated by a dielectric.

The capacitance is defined as:
C=ε₀ε_r A/d,
where A is the area of plates,
d is plates separation,
ε₀ is permittivity of free space and
εr is relative permittivity.

A important parameter for capacitors is its voltage handling capacity beyond which the capacitor dielectric breaks down.
The value of a capacitor depends upon the dielectric constant (K = ε₀ ε_r) of the material.
Also capacitance is the change in electric charge with respect to time.

C= dQ/dt

Circuit diagram of capacitor

there are three main classes of capacitors :

(I) Non electrolytic or normal capacitors and
(ii) electrolytic capacitor and
(iii) variable capacitor.

The Normal capacitors are mostly of parallel plate type and can have mica, paper, ceramic or polymer as dielectric. the paper capacitors two rectangular metal foils are interleaved between thin sheets of waxed paper and the whole system is rolled to form a compact structure.

each metal foil is connected to an electrode. in the mica capacitors alternate layers of mica and metal are clamped tightly together.

In the capacitor mostly a thin metal - oxide film is deposited by means of electrolysis on axial electrode. thats now it derives its name. during electrolysis the electrode acts as anode whose cathod is a concentric can. the dielectric layer is very thin hence this require special precaution for their use: i.e. they have to connected in the right polarity failing which the dielectric breaks down. besides this fixed value capacitors we also have variable capacitors whose value depends upon the area of cross section. they have an fixed set of plates and movement set of plates which can be moved through the shaft. this movement a changes the area of overlap of the two sets of plates which changes its capacity.