Effect of Dielectrics in Capacitors

Dielectric mediums like glass, mica, etc. are used while making capacitors to increase their capacitance. 

The effect of dielectrics in a capacitor is very important from the perspective of its capacitance. Electricity cannot pass through dielectrics because they are bad conductors of electricity, but they store the electric charge using their property of getting polarised.

Dielectrics are poor electrical current conductors, but they store electrostatic charges while releasing very little energy. The majority of this energy comes in the form of heat. Mica, polymers, porcelain, metal oxides, and glass are a few examples of dielectrics.

The major effect dielectrics have in capacitors is that they increase the capacitance of the capacitors.

Capacitors

A capacitor is an electricity storage device that operates in an electric field. It’s a two-terminal passive electrical component.

Capacitance is the word used to describe the capacity of the capacitor to hold electric charge at a specific voltage. While any two electrical conductors in close proximity in a circuit have some capacitance, a capacitor is a component that is specifically intended to impart capacitance to a circuit.

Dielectrics

A dielectric is an electrical insulator that may be polarised by an applied electric field (or dielectric medium or material). When an electric field is applied to a dielectric material, electric charges do not flow through it as they would in an electrical conductor because of the absence of any bound or free electrons to drift through it; instead, they move slightly from their normal equilibrium position, resulting in dielectric polarisation.

Regardless of the fact that the name insulator indicates minimal electrical conduction, dielectrics usually refer to materials that are highly polarisable.

Examples of dielectrics are: Glass, mica, plastic films, oxide layers, ceramic, porcelain etc.

The electric susceptibility and permittivity of a dielectric

The electric susceptibility of a dielectric is the measure of the ease for that material to get polarised. The more electric susceptibility of a dielectric means the easier it can get polarised. The electric susceptibility of a dielectric also determines the electric permittivity of that material.

The electric permittivity is usually denoted by ε. 

The capacitance of a capacitor

The capacitance denotes the capacity of the capacitor in consideration for holding the charge at a specific potential difference.

For measuring capacitance, we use two quantities. First is the amount of electric charge that is stored in a conductor whose capacitance is to be found, and second is the potential difference on which that electric charge is stored.

Capacitance is the ratio of the amount of electric charge stored by the capacitor to the electric potential difference.

If we denote capacitance by C, then we get:

C = qV

where, q = amount of electric charge held by the conductor

and V = electric potential difference the conductor is placed at

This shows that the more the capacitance of a conductor, the more electric charge it can store at the given difference in electric potential.

Effect of dielectrics in capacitors and the importance they possess

• When capacitors are manufactured for commercial use, they are manufactured with solid dielectric materials.

• The more capacitance of a capacitor, the more charge it can store at a given electric potential difference.

• Usually, capacitors use a dielectric material whose electric permittivity is high as the intervening medium between the stored negative and positive charges.

• The direct advantage of using such dielectric materials with high electric permittivity is that it prevents the conducting plates from coming into direct electrical contact on which the charges are stored.

• The higher permittivity of the dielectric material allows a larger amount of electric charge to be stored at a specific voltage. 

• If the distance between the conducting plates of a conductor be ‘d’, the electric permittivity of the dielectric be ε, the uniform electric charge density on those conducting plates be σε, then, the charge density is given by:

σ= Vd

where V denotes the difference in the electric voltage at which the plates are kept.

The capacitance per unit area on the plates is then evaluated as

C =σ /  V =d

Thus, it can be seen that as the electric permittivity of the dielectric material increases, the capacitance of the capacitor also increases. This is the importance of dielectrics in capacitors. This effect of dielectrics in capacitors is used to increase the capacitance of conductors.

Ionisation resistance is also included in dielectric materials used in capacitors. This permits the capacitor to run at higher voltages before the insulating dielectric ionises, allowing unwanted current to pass through.

Conclusion

The advantage of using dielectric materials with high electric permittivity is that it prevents the conducting plates from coming into direct electrical contact on which the charges are stored.

Examples of dielectrics are: Glass, mica, plastic films, oxide layers, ceramic, porcelain, etc.

The more the capacitance of a capacitor, the more electric charge it can store at the given difference in electric potential. 

As the electric permittivity of the dielectric material increases, the capacitance of the capacitor also increases. This effect of dielectrics is used to increase the capacitance of conductors.