What is the Difference Between Dielectric Constant and Relative Permittivity?

The dielectric constant and relative permittivity are related but distinct concepts in the context of material properties. Here are the key differences between the two:

1. Definition: The dielectric constant is a dimensionless quantity that represents the ratio of the permittivity of a material to the permittivity of free space. Relative permittivity, on the other hand, is the permittivity of a material expressed as a ratio with the electric permittivity of a vacuum.
2. Unit and Dimensions: The dielectric constant is a dimensionless quantity and has no units. In contrast, relative permittivity is a synonym for permittivity and has the unit of Farad per meter (F/m).
3. Relationship: The relationship between dielectric constant and permittivity can be expressed mathematically as $$ε = κε0$$, where ε0 is the permittivity of free space (approximately 8.85 × 10^−12 F/m). This relationship shows that the dielectric constant is always greater than or equal to 1.

Both concepts are used to describe the ability of a material to store an electric field, and they are often used interchangeably in engineering applications. However, it is essential to understand the subtle differences when using these terms in specific contexts.

Comparative Table: Dielectric Constant vs Relative Permittivity

Here is a table that highlights the differences between dielectric constant and relative permittivity:

In summary, both dielectric constant and relative permittivity are related to the ability of a material to store an electric field, but they are expressed differently. The dielectric constant is a dimensionless quantity that directly compares a material's charge storage capacity to that of a vacuum, while relative permittivity is the ratio of a material's permittivity to the permittivity of a vacuum.