Capacitors and its Types

Capacitor:

The capacitor is an Energy storage device similar to a battery, although used in many applications. The capacitors made up of two plates separated by a dielectric medium like glass, mica, ceramic, paper, film, etc. The capacitor is a passive element which stores potential energy in an electric field.  The effect of a capacitor known as Capacitance. Dielectric is an insulating material; it does not separate the plates physically rather electrically. The capacitors are otherwise known as a Temporary battery.

                                                                                                   Symbols of Capacitor

Capacitor design:

In fact, Capacitor consists of two conducting plates, separated by a dielectric medium. The capacitance depends on the dielectric medium used. The conducting plates made up of Aluminium, Tantalum, Silver, foil, thin film, etc.,

Dielectric contains molecules that are polar which means they can change their orientation according to the charges in the plates. The molecules align themselves with an electric field, enabling more electrons to attract the negative plate and repelling away from the positive plate.

Capacitor Working:

The capacitor made up of metals; they have an equal amount of positive and negative charges. They are neutral.

The capacitor works based on Coulomb’s law. A charge on one conductor exerts a force the charge carriers within the outer conductor, attracting opposite polarity charge and repelling like polarity charges, thus an opposite polarity charge induced on the surface of the outer conductor.

Capacitance:

The capacitance defined as the ratio of charge Q on a conductor to a potential difference between them.

C=Q/V

The capacitance measured in Farad.

For example,

When connected to a power supply, current will try to flow i.e., electron flow will occur. But there is a dielectric medium; this prevents the flow between the plates. So they will start accumulating on the plates. Up to a certain level, the charges stored. This indicates that the capacitor fully charged.

The two plates have an equal amount of positive and negative charges creating a strong electric field which makes them hold the charge inside the capacitor.

If the capacitor fully charged and we remove the battery they can withstand for a long time. If the load connected to a capacitor, it will supply energy to load until it becomes, electrically neutral.

Parallel plate capacitor:

The capacitance of a parallel plate capacitor depends on Area A and inversely proportional to the distance between the plates. So, reducing the distance between the plates increases the Capacitance.

C = ε (A/d)

ε – The absolute permittivity of the dielectric material.

The permittivity of a vacuum, εo was also known as the “permittivity of free space” has the value of the constant 8.84 x 10-12 Farads per meter. The permittivity of its dielectric referenced to the base dielectric of free space, giving a multiplication factor known as “relative permittivity”, εr.

Therefore, The Capacitance has given as
C= εo εr A / d Farad

To increase the Capacitance,

  • The surface area of the plates is to be larger
  • The distance between the plates should be small
  • Dielectric material should have high permittivity.

This is the reason why the capacitor is in a cylindrical shape. If we keep on increasing the surface area means the size of capacitance will be large. So in order to increase the capacitance without the size, it’s better to roll the plates in a cylindrical shape.

Types of Capacitor:

Capacitors are available from small trimming capacitor used in tuning circuit to very large power metal type capacitor used in high power corrections.

The type of capacitor classified based on the dielectric material used between the plates.

S.NO Image Type Dielectric material Purpose Application
1 Dielectric Capacitor Plastic Film  (Mylar, polystyrene, polypropylene,

polycarbonate)

To maximize the charge Radio tuning

Receiver and Transmitter

2 Ceramic Capacitor Ceramic disc with silver High dielectric Constant Decoupling or By-pass capacitor
3 Electrolytic Capacitor The Thin layer of oxide

One plate will be a metallic film  and others will be semi-liquid electrolyte in the form of a paste

Polarised

Large capacitance

Coupling and decoupling, DC blocking

 

Capacitor block DC:

If a DC source connected, the capacitor will get fully charged up to the level of the source connected. Once the capacitor fully charged, no current will flow. The steady state reached. Even if the polarity reversed, this will be the same situation.

Whereas AC, there will be changes in polarity within a cycle. During the first half, the polarity will be +,-. In this case, the electrons on one plate attracted and repelled according to the charges on the plates. Next half cycle, polarities will be -,+. According to this, electron flow and repulsion will be there.


 

 

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