Dielectric Constant: Learn its Value, Formula, Factors Affecting it & Applications

You must have noticed when any electrician comes to repair your electric supply system he always wears a different kind of pair of gloves which are totally different from the one you used to wear in winter. A question pops up: why is this so? This is because the nature of the material of gloves he wears depends upon the kind of work he is performing (like he is dealing with electricity in this case). The dielectric constant or relative permittivity of material gives a proportion of its impact on a capacitor.

Read on to learn more about its formula, value, factors affecting it, applications and its relationship with electric susceptibility which is similar to magnetic susceptibility.

Dielectric Constant

Dielectric constant or Relative Permittivity or sometimes referred to as specific inductive capacity is the property of insulating material equals to the ratio of capacitance of a capacitor with a dielectric medium and its capacitance without any dielectric medium(in vaccum).

Dielectric constant is represented by the greek alphabet (kappa).

Units: Dielectric Constant is the ratio of two similar terms that is the ratio of capacitance with and without dielectric material. Hence, Dielectric Constant is a unitless quantity. Hence, dielectric constant has no dimension or we can say they are just dimensionless.

To understand what dielectric constant is, let’s build an understanding of Dielectric first. In a dielectric material,there are no free electrons; hence, their behaviour in the electric field is entirely different from that of conductors. Thus, when any dielectric material is placed in an electric field, a dipole moment appears in any volume in it. This phenomenon is termed as the polarization of the material. The polarization vector,P, can be defined as the electric dipole moment (p) per unit volume(V)

Dielectric Constant Formula

Mathematically dielectric constant is expressed as,

Where

• is the dielectric constant
• is the permittivity of the substance
• is the permittivity of the free space

Factors Affecting Dielectric Constant

Dielectric of a material is affected by various factors such as

• Frequency: The frequency of voltage is one of the very important factors influencing the value of the dielectric Constant. As we keep increasing the value of the frequency of voltage, the value of the dielectric Constant will take a nonlinear turn.
• Applied Voltage: The value of the dielectric constant is determined by the type of applied voltage that is whether it is alternating current (A.C.) or direct current (D.C.). For D.C. voltage the value of the dielectric constant decreases while for the A.C. voltage the value of the dielectric constant increases.
• Temperature: At lower temperature it is difficult to maintain the alignment of molecules in the dielectric material. As the temperature rises the dominance of the dipole increases resulting in an increase in the value of dielectric constant, till the threshold value of temperature known as transition temperature. Afterwards there is a constant decrease in the value of dielectric constant.
• Humidity and Moisture: There is an inverse relationship between humidity and moisture and dielectric constant. That means if any humidity or moisture increases the value of the dielectric constant decreases.
• Heating effect: Heating a material will result in dielectric loss due to dissipation of energy in the form of heat because of the movement of molecules in the material.

Dielectric constant of a material depends on some other general Factors like structure and morphology and also on weathering and deterioration.

Relationship between Dielectric Constant and Electric Susceptibility

Dielectric constant is the property of material which clearly defines the extent to which any substance can allow the electricity to pass through it.

Electric Susceptibility is a quantitative measure of extent of applied electric field which will cause polarization (slight separation of positive and negative charge within the material) of the material.

Hence, the established relationship between dielectric constant and electric susceptibility tells that higher the polarization of material, lower will be its dielectric constant and vice versa.

Relation between Dielectric constant and Electric susceptibility:

We clearly aware of the fact that,

D = (E+P). ………(1)

We also have,

Also,D = . ………..(2)

and P = XeE ………..(3)

Now substituting the value of D and P from equation 2 and 3 to equations 1 will give us,

Dividing both sides by Electric field E, we obtain

Dividing both side by we obtained,

…………(4)

But from the definition of Dielectric constant we have,

…………(5)

Now substitute the value of equation 5 in equation 4 we obtained,

This is the required relation between, Dielectric Constant,K and Electric susceptibility,

Here, we have,

D = Displacement

E = Electric field

= Electric Susceptibility

K = Dielectric Constant

= Permittivity of the medium

= Permittivity of the free space

Dielectric Constant Value of Material

Below is the list of the values of dielectric constant for various materials.

S.no.	Material	Dielectric Constant Value
1.	Vacuum	1
2.	Air (1 atm)	1.00059
Air (100 atm)	1.0548
3.	Glass	5-10
4.	Water	80
5.	Paper	3.5
6.	Polythene	2.25
7.	Metal	∞(infinite)
8.	Oil	2.1-2.4
9.	Mica	3-6
10.	Metanol	32.70

Application of Dielectric Constant

Dielectric materials have numerous applications in our day to day life. Some of the application of dielectric is mentioned as follows:

• Dielectric is used in capacitors that help us to decrease the value of electric field inside it that further lowers the value of Voltage which in turn finally increases the capacitance of the material.
• Dielectrics are used to store energy between the plates of capacitors.
• High Permittivity dielectrics materials are used in semiconductors to enhance its performance.
• To assist the cooling process in the electrical transformer, we use mineral oil as a liquid dielectrics that lowers the temperature of the transformer.
• Dielectrics are used in LCDs(Liquid Crystal Display) to enhance the performance of the display.
• Electrest is an electrostatic equivalent to magnets is a specially processed dielectric material
• Castor oil are used to increase the capacitance value of high voltage capacitors.
• Dielectrics are used in capacitance to filter out noise from the signals.

Hope this article was able to clear your doubts regarding this topic and help you understand it. There are many such interesting Physics topics and their real-life application to learn about, just download the Testbook app and start browsing.