Dielectric Constant - Definition, Formula, FAQs

Edited By Vishal kumar | Updated on Jul 02, 2025 04:27 PM IST

What is Dielectric Constant?

The term "dielectric" refers to a substance with insulating qualities. It is a substance capable of transmitting electric force without conduction.
Many different types of electric and polarised materials have some combination property. You will come across several terminologies linked to dielectric and its applicability in today's real situations as you read this text. You'll also learn about unitless values and numbers that characterise how electric insulators behave when they're exposed to an electric field. Let’s learn the dielectric constant meaning.

This Story also Contains

What is Dielectric Constant?
What is Dielectric Constant Definition?
What are dielectric constant units?

Dielectric Constant - Definition, Formula, FAQs

What is Dielectric Constant Definition?

Dielectric constant, also known as relative permittivity or specific inductive capacity and it is ratio of capacitance of capacitor filled with particular material to capacitance of an identical capacitor in vacuum without dielectric material.

When a dielectric is introduced between the plates of a parallel-plate capacitor, the capacitance, or ability to store opposing charges on each plate, is always increased, compared to when the plates are separated by a vacuum.

Conductor Equilibrium

The dielectric constant is represented by the Greek letter kappa, which is simply stated as $\mathrm{k}=\mathrm{C} / \mathrm{C}_0$. Here, C is the capacitance of a capacitor filled with a specific type of dielectric. And $\mathrm{C}_0$ is the capacitance of an identical capacitor in a vacuum.

The dielectric constant is a one-dimensional quantity. The dielectric constant and permittivity are the same in the centimetre-gram-second system.

Dielectric constant symbol $=\kappa$
Permittivity symbol $=\boldsymbol{\epsilon}$

Dielectric constant refers to a dielectric's large-scale feature rather than the electrical behavior at the atomic level.

Any material's static dielectric constant is always greater than one, which is its value in a vacuum.

Because the dielectric constant of air is roughly equal to that of a vacuum, air does not change the capacitance of a capacitor in any practical sense. By comparing the capacitance when the dielectric is in place to the capacitance when the capacitor is filled with air, dielectric constants of liquids and solids can be established.

Also read -

What are dielectric constant units?

The dielectric constant has no unit as it is the ratio of the same quantity (capacitance).

Here are some examples of dielectric constant values of various materials:

Dielectric Materials	Dielectric Constant Value
The dielectric constant of vacuum	1.00
The dielectric constant of air	1.00059
The dielectric constant of water	80.4 at 20 degrees Celcius.
The dielectric constant of germanium	16
The dielectric constant of paraffin	2.25
The dielectric constant of glass	5-10 at 20 degrees Celcius

NCERT Physics Notes :

Define dielectric strength.

The ability of an insulating material to act as an insulator is known as dielectric strength. The highest electric field that an insulating material can withstand before dielectric breakdown and becoming electrically conductive is defined as its dielectric strength. The highest voltage required to create a dielectric breakdown in an electrically insulating substance is also known as dielectric strength.

Point to note:

When electric charges react with an electrical conductor, they do not flow through the materials; instead, they move in position and value, resulting in dielectric polarisation. Positive charges are moved towards the field, and negative charges are displaced away from the field because the substance is polarised.

If the field shifts on the x-axis, for example, the negative charges will be directed towards the negative x-axis. If the dielectric contains weak link molecules, they will become polarised and re-oriented, allowing the symmetric axes to align.

Dielectric

Related Topics,

NEET Highest Scoring Chapters & Topics

This ebook serves as a valuable study guide for NEET exams, specifically designed to assist students in light of recent changes and the removal of certain topics from the NEET exam.

Download E-book

Dielectric constant formula.

The dielectric constant is the ratio of the capacitance produced by two metallic plates in the presence of an insulator to the capacitance of the same region in the absence of an insulator.

Parallel plate capacitor

A low dielectric constant is required when a material is utilized for any insulating purpose.

The dielectric constant formula is as follows:

$
\mathrm{k}=\mathrm{C} / \mathrm{C}_0
$

$
\mathrm{C}_0=\varepsilon_0 \mathrm{~A} / \mathrm{t}
$

$\mathrm{C}=$ capacitance of the dielectric-capacitor material

$
\mathrm{C}_0=\text { capacitance of vacuum as dielectric. }
$

T is the sample thickness.

A is the plate's surface area.

$\epsilon_0=$ Free-space permittivity $8.85 \times 10^{-12} \mathrm{~F} / \mathrm{m}$

Relation between the dielectric constant and electric susceptibility.

The dielectric constant is a measurement of how well a material conducts electricity.

When a substance is held in an electric field, its electrical susceptibility determines how polarised it becomes. If the material becomes more polarised, it will create an internal field that opposes the external field, lowering the overall electric flux through it. As a result, the medium's electric permittivity is affected by its electric susceptibility.

The lower the electric permittivity, the higher the level of polarization.

Also, check-

Frequently Asked Questions (FAQs)

1. What is dielectric constant in chemistry?

A solvent's polarity is measured by its dielectric constant (symbol: ĸ). The higher a solvent's dielectric constant, the more polar it is.

2. What is the unit of dielectric strength?

The voltage necessary to create a dielectric breakdown through a material is referred to as dielectric strength. Volts per unit thickness is the unit of dielectric constant.

3. Define dielectric constant of a medium

The dielectric constant of a medium is equal to the ratio of the substance's permittivity to the permittivity of free space.

K=ε/ε0

4. What is dielectric constant of water?

The dielectric constant of water is 80.4 at 20 degrees Celcius.

5. What is the relation between permittivity and susceptibility?

According to physicists, permittivity is the ability to resist external electric fields. A substance with high permittivity requires a high electric field to get polarised.

On the contrary, susceptibility is the ability to get polarised, meaning a substance with high susceptibility is easy to polarise.

Mathematically, both of these quantities are linearly dependent on each other.

6. How does the dielectric constant affect the energy stored in a capacitor?

The dielectric constant affects the energy stored in a capacitor by increasing the capacitance. The energy (U) stored in a capacitor is given by:

7. How does the dielectric constant relate to the susceptibility of a material?

The dielectric constant (κ) is directly related to the electric susceptibility (χₑ) of a material by the equation:

8. How does the dielectric constant affect the speed of electromagnetic waves in a material?

The dielectric constant affects the speed of electromagnetic waves in a material by slowing them down. The speed of an electromagnetic wave (v) in a material is related to the speed of light in vacuum (c) and the dielectric constant (κ) by:

9. How does the dielectric constant of a mixture relate to the dielectric constants of its components?

The dielectric constant of a mixture is not a simple average of its components' dielectric constants. Various mixing rules exist to estimate the effective dielectric constant, depending on the structure of the mixture. For example, the Lichtenecker logarithmic mixing rule states that the logarithm of the mixture's dielectric constant is a weighted average of the logarithms of the components' dielectric constants. The exact relationship depends on factors like the volume fractions and how the components are distributed.

10. What is the significance of the complex dielectric constant?

The complex dielectric constant is used to describe the behavior of dielectric materials in alternating electric fields. It consists of a real part (ε'), which represents the energy storage capability, and an imaginary part (ε"), which represents the energy loss in the material. The complex notation is particularly useful for understanding and quantifying dielectric losses, which are important in applications like microwave engineering and material characterization.

11. What is the dielectric constant and why is it important?

The dielectric constant, also known as relative permittivity, is a measure of a material's ability to store electrical energy in an electric field. It's important because it determines how much a material reduces the electric field strength and increases the capacitance of a capacitor. Materials with higher dielectric constants are used to make more efficient capacitors.

12. What is the formula for calculating the dielectric constant?

The dielectric constant (κ) is calculated as the ratio of the permittivity of the material (ε) to the permittivity of vacuum (ε₀):

13. How does the dielectric constant affect the capacitance of a capacitor?

The dielectric constant directly increases the capacitance of a capacitor. When a dielectric material is inserted between the plates of a capacitor, the capacitance increases by a factor equal to the dielectric constant. This is because the dielectric material reduces the effective electric field between the plates, allowing more charge to be stored.

14. What's the difference between dielectric constant and dielectric strength?

While both relate to dielectric materials, they measure different properties. The dielectric constant measures a material's ability to store electric energy, while dielectric strength measures the maximum electric field a material can withstand before breaking down and conducting electricity. A high dielectric constant doesn't necessarily mean high dielectric strength, and vice versa.

15. Can the dielectric constant of a material be less than 1?

No, the dielectric constant of a material cannot be less than 1. The dielectric constant is defined relative to the permittivity of vacuum, which is assigned a value of 1. All materials have a dielectric constant greater than or equal to 1, with most common materials having values between 1 and 100.

16. Why do some materials have very high dielectric constants?

Materials with very high dielectric constants, such as ferroelectric ceramics, typically have special molecular structures that allow for significant polarization in an electric field. These materials often have permanent electric dipoles that can easily align with an external field, or they may undergo phase transitions that result in large polarization changes. The ability to store more charge through this polarization leads to higher dielectric constants.

17. How does the dielectric constant relate to the refractive index of a material?

The dielectric constant is closely related to the refractive index of a material. For non-magnetic materials at optical frequencies, the square of the refractive index (n) is approximately equal to the dielectric constant (κ):

18. What is the difference between static and dynamic dielectric constants?

The static dielectric constant refers to the material's response to a constant (DC) electric field or very low-frequency alternating fields. The dynamic dielectric constant, also called the optical dielectric constant, describes the material's response to high-frequency electric fields, typically in the optical range. The dynamic constant is usually lower because at high frequencies, some polarization mechanisms can't respond quickly enough to the changing field.

19. What happens to the electric field inside a dielectric material?

When a dielectric material is placed in an electric field, the field inside the material is reduced. This reduction occurs because the molecules in the dielectric become polarized, creating an internal electric field that opposes the external field. The strength of the electric field inside the dielectric (E) is related to the external field (E₀) by:

20. Why is the dielectric constant important in the design of electronic devices?

The dielectric constant is crucial in electronic device design because it affects the performance of capacitors, which are fundamental components in many circuits. Higher dielectric constants allow for smaller capacitors with the same capacitance, enabling device miniaturization. It also influences signal propagation speed in transmission lines and the behavior of insulating materials in various components, impacting overall device efficiency and performance.

21. How does temperature affect the dielectric constant of a material?

Temperature can significantly affect the dielectric constant of a material. For most materials, the dielectric constant decreases as temperature increases. This is because higher temperatures increase molecular motion, making it harder for the material to maintain polarization in an electric field. However, some materials, like ferroelectrics, can show more complex temperature dependencies.

22. What is meant by dielectric polarization?

Dielectric polarization refers to the alignment of electric dipoles within a material in response to an applied electric field. In non-polar molecules, the electric field can induce a slight separation of positive and negative charges, creating temporary dipoles. In polar molecules, existing dipoles rotate to align with the field. This polarization is the fundamental mechanism by which dielectric materials increase capacitance and reduce electric field strength.

23. Can the dielectric constant of a material change?

Yes, the dielectric constant of a material can change under various conditions. It can be affected by temperature, pressure, frequency of the applied electric field, and in some cases, the strength of the electric field itself. Some materials, like ferroelectrics, can have their dielectric constant changed dramatically by external conditions, which is utilized in certain electronic applications.

24. What is meant by dielectric relaxation?

Dielectric relaxation refers to the delay in the polarization response of a dielectric material when an electric field is applied or removed. It occurs because the molecules or dipoles in the material need time to align with or return from alignment with the electric field. This phenomenon is frequency-dependent and can lead to energy dissipation in alternating fields, which is important in applications like microwave heating.

25. What is dielectric breakdown and how is it related to the dielectric constant?

Dielectric breakdown occurs when the electric field in a dielectric material becomes strong enough to cause it to conduct electricity, often resulting in physical damage. While not directly related to the dielectric constant, materials with higher dielectric constants often have lower dielectric strength (the field strength at which breakdown occurs). This is because the mechanisms that allow for high polarizability (high dielectric constant) can also facilitate electron movement under strong fields, leading to breakdown.

26. What is the difference between linear and nonlinear dielectrics?

Linear dielectrics have a constant dielectric constant regardless of the applied electric field strength. In these materials, the polarization is directly proportional to the electric field. Nonlinear dielectrics, on the other hand, have a dielectric constant that changes with the applied field strength. This nonlinearity can arise from various mechanisms, such as saturation effects or phase transitions, and is important in applications like frequency conversion and optical signal processing.

27. What is meant by dielectric anisotropy?

Dielectric anisotropy refers to the variation of dielectric constant with direction in a material. In anisotropic materials, the dielectric constant can be different along different crystal axes. This property is represented by a dielectric tensor rather than a single scalar value. Dielectric anisotropy is important in applications like liquid crystal displays, where the orientation-dependent dielectric properties are used to control light transmission.

28. How does the dielectric constant relate to the concept of displacement current?

The displacement current, introduced by Maxwell to complete his electromagnetic theory, is directly related to the dielectric constant. In a dielectric material, the displacement current density (J_D) is given by:

29. What is the relationship between dielectric constant and ferroelectricity?

Ferroelectric materials typically have very high dielectric constants, especially near their Curie temperature (the temperature at which they transition from ferroelectric to paraelectric). This is because ferroelectrics have permanent electric dipoles that can be reoriented by an external electric field, leading to very high polarizability. The dielectric constant of ferroelectrics is often nonlinear and can be tuned by external factors like temperature or stress, making them useful in various electronic applications.

30. How does the dielectric constant affect the force between charges in a material?

The dielectric constant reduces the force between charges in a material. According to Coulomb's law, the force (F) between two charges (q₁ and q₂) separated by a distance r in a medium with dielectric constant κ is:

31. What is the Clausius-Mossotti relation and how does it relate to the dielectric constant?

The Clausius-Mossotti relation connects the microscopic properties of a material (polarizability of its molecules) to its macroscopic dielectric constant. It's expressed as:

32. How does frequency affect the dielectric constant of a material?

The dielectric constant of a material generally decreases with increasing frequency of the applied electric field. This is because different polarization mechanisms respond at different timescales. At low frequencies, all polarization mechanisms (electronic, ionic, and orientational) contribute to the dielectric constant. As frequency increases, slower mechanisms (like molecular rotation) can't keep up, reducing their contribution. This frequency dependence is described by dielectric dispersion curves and is crucial in high-frequency applications.

33. How do piezoelectric materials relate to dielectric constants?

Piezoelectric materials exhibit a coupling between mechanical stress and electric polarization. They typically have high dielectric constants because the mechanisms that allow for piezoelectricity (the ability of charges to shift within the crystal structure) also contribute to high polarizability. However, the dielectric constant of piezoelectric materials can be highly anisotropic (direction-dependent) and can change significantly under mechanical stress, which is utilized in various sensor and actuator applications.

34. How does the dielectric constant affect capacitor leakage?

While the dielectric constant itself doesn't directly determine capacitor leakage, there's often a correlation. Materials with very high dielectric constants tend to have lower resistivity, which can lead to higher leakage currents. This is because the mechanisms that allow for high polarizability can also facilitate charge movement through the material. However, the actual leakage is more directly related to the material's resistivity and any defects or impurities present.

35. How does the dielectric constant affect the capacitance of a parallel plate capacitor?

For a parallel plate capacitor, the capacitance (C) is directly proportional to the dielectric constant (κ) of the material between the plates:

36. What is the role of the dielectric constant in electromagnetic wave propagation?

The dielectric constant plays a crucial role in electromagnetic wave propagation by affecting the wave's velocity, wavelength, and impedance in the medium. The velocity of an electromagnetic wave in a medium is inversely proportional to the square root of the dielectric constant. This property is used in the design of waveguides, antennas, and other electromagnetic devices to control wave propagation and matching.

37. What is the significance of the dielectric constant in electrostatic shielding?

The dielectric constant is important in electrostatic shielding because it affects how electric fields penetrate and are distributed within a material. Materials with high dielectric constants can effectively redirect electric field lines, making them useful for shielding sensitive components from external electric fields. However, for complete shielding, conductive materials are typically used in conjunction with dielectrics.

38. How does the dielectric constant affect the energy density stored in an electric field?

The energy density (u) stored in an electric field within a dielectric material is given by:

39. How does the dielectric constant affect the boundary conditions for electric fields at interfaces?

The dielectric constant plays a crucial role in determining the behavior of electric fields at the interface between two materials. The boundary conditions state that the tangential component of the electric field is continuous across the interface, while the normal component of the electric displacement field (D = κε₀E) is continuous. This leads to a discontinuity in the normal component of the electric field at the interface, with the field being stronger in the material with the lower dielectric constant.

40. What is the significance of the dielectric constant in the design of transmission lines?

The dielectric constant is crucial in transmission line design because it affects the characteristic impedance, propagation velocity, and losses of the line. A higher dielectric constant reduces the propagation velocity, which can be used to miniaturize components. However, it also affects impedance matching and can increase dielectric losses. Designers must balance these factors to optimize transmission line performance for specific applications.

41. How does the dielectric constant relate to the concept of polarization charge density?

The polarization charge density (σp) at the surface of a dielectric in an electric field is related to the dielectric constant (κ) by:

42. What is the role of the dielectric constant in the phenomenon of dielectric absorption?

Dielectric absorption, also known as dielectric relaxation, is closely related to the frequency dependence of the dielectric constant. It occurs when the polarization of a dielectric can't keep up with rapid changes in the applied electric field. This leads to a phase lag between the fiel