Dielectric Constant

Introduction:

Take a small tour to your kitchen, did you ever notice the ceramic cookwares or utensils have some commonality with glass, plastic, mica or even the air? Did you ever think about building an electronic component out of them? Probably not! Because the property of these materials is often overlooked.

What is dielectric?

A dielectric is a material which has poor electrical conductivity but inherits an ability to store an electrical charge(due to Dielectric polarization). Thus exhibiting only displacement current making it ideal to build a capacitor; to store and return electrical energy.

What is Dielectric Constant?

Dielectric Constant of a substance can be defined as:

The ratio of the permittivity of the substance to the permittivity of the free space

It expresses the extent to which a material can hold electric flux in it.

Dielectric Constant Formula

It is mathematically expressed as:

\(\kappa =\frac{\varepsilon }{\varepsilon _{0}}\)

Where,

  • κ is the dielectric constant
  • 𝜺 is the permittivity of the substance
  • 𝜺0 is the permittivity of the free space

Dielectric Constant Units

As it is the ratio of two like entities, it is a unitless, dimensionless quantity.

Dielectric Constant Symbol

The relative permittivity of a dielectric substance is also called as Dielectric Constant, expressed using greek letter kappa ‘κ’.

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Theory behind Dielectric Constant

This is a prime parameter to characterizes a capacitor. A capacitor is an electronic component designed to store electric charge. This is widely built by sandwiching a dielectric insulating plate in between the metal conducting plates. The dielectric property plays a major role in the functioning of a capacitor.

The layer made up of dielectric material decides, how effectively the capacitor can store the charge. Picking the right dielectric material is crucial. Thus, we can also define it as ‘the ratio of the electric field without a dielectric(E0) to the net field with a dielectric(E).’

\(\kappa =\frac{E_{o} }{E}\)

Here, the value of E0 always greater than or equal to E. Thus, The value of a dielectric constant is always greater than 1.

Greater the value of κ more charge can be stored in a capacitor.

In the capacitor, the capacitance is given by C = κC0

Thus, filling the gap between the plates completely by dielectric material will increase its capacitance by the factor of dielectric constant value.

In the parallel plate capacitor, the capacitance is given by:

\(C=\frac{\kappa \varepsilon _{0}A}{d}\)

Where,

  • C is the capacitance of the parallel plate capacitor.
  • κ is the dielectric constant.
  • 𝜺0 is the permittivity of the free space.
  • A is the area of parallel conducting plates plates
  • D is the separation between parallel conducting plates plates

The capacitance value can be maximized by increasing the value of the dielectric constant and by decreasing the separation between the parallel conducting plates.

Dielectric Constant Value

Thus, the value of the dielectric constant is crucial in building various electronic components. The following table gives some of the typical values of Dielectric Constants:

Dielectric Materials Dielectric Constant Value
Dielectric Constant of vacuum 1.00
Dielectric Constant of air 1.00059
Dielectric Constant of water 80
Dielectric Constant of paper 3.6

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