The key difference between dielectric constant and relative permittivity is that dielectric constant refers to the relative permittivity of a dielectric substance whereas relative permittivity refers to the permittivity of a substance in comparison to the permittivity of a vacuum.
The terms permittivity and dielectric constant are used in capacitor technology; for example, using capacitors with different dielectric constants. However, in most contexts, we use these terms as synonyms.
CONTENTS
1. Overview and Key Difference
2. What is Dielectric Constant
3. What is Relative Permittivity
4. Side by Side Comparison – Dielectric Constant vs Relative Permittivity in Tabular Form
5. Summary
What is Dielectric Constant?
The term dielectric constant refers to the property of an electrical insulating material that is equal to the ratio between the capacitance of the material to the capacitance of vacuum. Most often, we use this term interchangeably with relative permittivity, though they have slight differences. An electrical insulating material is known as a “dielectric”. In the definition of dielectric constant, the term capacitance of material refers to the capacitance of a capacitor that is filled with the particular material. When determining the capacitance of vacuum, it refers to the capacitance of an identical capacitor without dielectric material.
Figure 01: Defining Dielectric Constant in a Diagram
In a capacitor, there are parallel plates in between that can be filled with the dielectric material. Presence of a dielectric material between these two plates always increases the capacitance. That means; it increases the ability of the capacitor to store opposite charges on each plate, compared to its ability to hold the charges when there is a vacuum between two plates. For the vacuum filled capacitor, the capacitance is considered to be one as a reference standard. Therefore, any dielectric material shows a dielectric constant that is more than one.
What is Relative Permittivity?
Relative permittivity is the permittivity of a substance with reference to the permittivity of vacuum. The permittivity is a property of a material that describes the Coulomb force between charged points of the substance. It is a factor by which the electric field (between two charged points) is decreased relative to the vacuum.
Figure 02: Relative Permittivity of Water in a Graph
We can give relative permittivity as follows:
εr= ε/ ε0
where εr is the relative permittivity, ε is the complex-dependent permittivity of the material, and ε0 is the permittivity of the vacuum. The relative permittivity is a dimensionless value, and it is usually unique to a material. For example, the relative permittivity of diamond is 5.5, for concrete it is 4.5, etc.
What is the Difference Between Dielectric Constant and Relative Permittivity?
The key difference between dielectric constant and relative permittivity is that the term dielectric constant refers to the relative permittivity of a dielectric substance whereas relative permittivity refers to the permittivity of a substance in comparison to the permittivity of a vacuum.
The following table summarizes the difference between dielectric constant and relative permittivity.
Summary – Dielectric Constant vs Relative Permittivity
The terms permittivity and dielectric constant are used in capacitor technology. The key difference between dielectric constant and relative permittivity is that the term dielectric constant refers to the relative permittivity of a dielectric substance whereas relative permittivity refers to the permittivity of a substance in comparison to the permittivity of a vacuum.
Reference:
1. “Relative Permittivity.” Relative Permittivity – an Overview | ScienceDirect Topics, Available here.
2. “Dielectric Constant & Relative Permittivity.” Electronics Notes, Available here.
3. “Relative Permittivity.” Wikipedia, Wikimedia Foundation, 5 Dec. 2019, Available here.
Image Courtesy:
1. “Dielectric-constant” By Lejla peace – Own work (CC BY-SA 3.0) via Commons Wikimedia
2. “Water relative static permittivity” By Stan J Klimas – Own work (CC BY 3.0) via Commons Wikimedia