Permittivity and Permeability

In electromagnetic theory, there are two concepts known as permittivity and permeability. The concept related to the formation of an electric field is known as permittivity, and the one related to the magnetic field is known as permeability.

Definition of Permittivity

Permittivity can be explained as the ratio of electric displacement to the electric field intensity. It is the property of a material to measure the opposition generated by the material during the electric current development.

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The permittivity of a material is represented by the symbol ε. The SI unit of permittivity is Farad per metre. The approximate value for permittivity is 8.85 X 10-12 Faraday/metre, which is found in a vacuum medium. The permittivity measures the number of charges needed for generating a unit of electric flux in a specific channel.

Permittivity is expressed in relative terms in engineering applications instead of absolute terms. The permittivity of free space (that is, 8.85 x 10-12 F/m) is represented by eo and the permittivity of substance in question (also represented in farads per metre) is represented by e. Here, the relative permittivity dielectric constant er, is given by:

\[e_r  = \frac{e}{e_o} \]

= e (1.13  x  1011)

Definition of Permeability

The property of the material which supports the formation of magnetic flux when passed through a magnetic field is known as permeability. It is affected by the field frequency, temperature, field strength, and humidity. It is represented by μ.

The permeability of the material is defined as the ratio of flux density to the field strength of a material. It is also directly proportional to the conduction of magnetic lines of force. The permeability of free space is also known as the permeability constant and is represented by μ0, which is approximately equal to 4Π X 10-7Henry/metre.

The symbol for permeability is μ. It is also defined as the ratio of the intensity of magnetic field (simple magnetic field) to the magnetic field (i.e., the limit to which the magnetic field can magnetize a material).

\[\mu = \frac{\text{Intensity of Magnetic Field (B)}}{\text{Intensity of Magnetizing Field (H)}}\]

or, \[\mu = \frac{B}{H}\]

Unit of Permeability

The unit of measurement for the intensity of the magnetic field is Tesla (T) or Newton per Ampere metre (N/Am).

Ampere per metre (A/m) is the unit of a magnetizing field.

Magnetic reluctivity is the reciprocal of magnetic permeability. The SI unit of permeability is given as Henries-per-metre (H/m). It is measured in Newtons-per Ampere squared (N/A2)

So as per the above permeability formula, it becomes unit Newton per Ampere square.

\[\mu = \frac{Newton}{\text{ Ampere Square}}\]

Or \[\mu  = \frac{N}{A^2} \]

By calculating their equations and units, we will find the dimension of permeability to be

[M¹L¹T^-2I^-2].

Difference Between Permittivity and Permeability

The main differences between permittivity and permeability are explained below.

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From the above text, we understand that during the formation of electric fields, the obstruction produced by the material is measured by the permittivity. In contrast, the ability of the material to allow magnetic lines to conduct through it is known as permeability.