Question

What is the difference between dielectric permeability and permittivity?

Answer 1

The terms dielectric permeability and permittivity are closely related, but they are used in different contexts, and there's a subtle difference between them.

1. Permittivity (often denoted as \( \varepsilon \)):

1. Definition: Permittivity is a measure of how much electric field can be "spread out" or "permitted" to pass through a material. It essentially tells you how easily a material can be polarized in response to an applied electric field.
   

1. Units: Farads per meter (F/m)
   

1. Relation to Vacuum: Permittivity of free space (vacuum), denoted as \( \varepsilon_0 \), is a constant and represents the baseline value of permittivity in a vacuum.
   

  
    \[
    \varepsilon_0 \approx 8.854 \times 10^{-12} \, \text{F/m}
    \]

1. In Material: When a material is present, its permittivity \( \varepsilon \) is usually expressed relative to the permittivity of free space. The relative permittivity (also called the dielectric constant) \( \varepsilon_r \) is given by:
   

    \[
    \varepsilon = \varepsilon_r \cdot \varepsilon_0
    \]

    Where:
    - \( \varepsilon_r \) is the relative permittivity of the material.
    - \( \varepsilon_0 \) is the permittivity of free space.

2. Dielectric Permeability:

1. Definition: Dielectric permeability is a term sometimes used interchangeably with permittivity, but it is more specific to how materials respond to electric fields in terms of their ability to allow electric flux to pass through them. In many cases, dielectric permeability is essentially just another name for permittivity in certain contexts, especially in electromagnetics.
   

1. Relation: Dielectric permeability is a term used mostly in the context of how a material responds to an electric field, and it typically emphasizes the behavior of the material as a dielectric (i.e., an insulating material).
   

However, in standard physics and engineering terminology, we tend to use permittivity more than dielectric permeability, especially when we are talking about how materials interact with electric fields.

Key Difference:

1. Permittivity is the more widely used term and specifically describes how a material reacts to an electric field.
   

1. Dielectric permeability is less commonly used and tends to be applied in more specific contexts, but it's often synonymous with permittivity.
   

In most cases, when you're discussing materials and their electric properties, you can think of dielectric permeability as just another way of referring to permittivity, though the former term is less commonly used.