Permittivity and Permeability

What is Permittivity and Permeability?

In electromagnetic theory, there are two concepts known as the 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

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

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

er = e / eo

=e (1.13 x 1011)

Definition of Permeability

The property of the material which supports 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.

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The permeability of 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 permeability constant and is represented by μ0, which is approximately equal to 4Π X 10-7Henry/meter.

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

μ = intensity of magnetic field (B)/intensity of magnetizing field (H)

Or, μ = B/H

Unit of Permeability

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

Ampere per meter (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-meter (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.

μ = Newton / Ampere square

Or μ = N/ A2

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

[M L T ^ -2 I ^ -2]

Difference Between Permittivity & Permeability

The measurement of obstruction generated by the material in the formation of electric fields is done by permittivity. It is the major difference between permittivity and permeability, which also explains the ratio of electric displacement to electric field density.

Permeability, whereas measures the ability of the material to allow the magnetic lines of force to pass through it.

The property of material that supports the formation of the magnetic field is known as permeability and is affected by field strength, temperature, field frequency, and humidity.

Some other differences between permittivity and permeability are herewith explained below.

  • During the formation of electric fields, the obstruction produced by the material is measured by permittivity. In contrast, the ability of the material to allow magnetic lines to conduct through it is known as permeability.

  • Permittivity is represented by ε and permeability as μ.

  • Henry/meter is the SI unit of permittivity, and Faraday/meter is for permeability.

  • Due to polarization, there is permittivity, and due to magnetism, there is permeability.

  • 8.85 F/m is the free space of permittivity, and it is for permeability by 1.26 H/m.

  • The electric field is developed by permittivity and magnetic field by permeability.

  • A capacitor develops high permittivity, whereas inductors and cores of transformers develop high permeability.

FAQ (Frequently Asked Questions)

1. Is the speed of light dependent on the permittivity & permeability of space?

This is true.

Taking the inverse square of product of these two quantities, the speed of light is dependent. As the values of permittivity and permeability are different in different materials, the speed of light is different for those materials.

Considering there is no violation involved, and relativity only requires that the speed of light in a vacuum is constant in all reference frames.

2. What is the physical significance of permittivity?

The variation in the force experienced by a charge (test charge) in the medium (where the test charge stays) compared to force it (test charge) and having experience in vacuum space is determined by the permittivity of the medium.

In simpler terms, let's assume a force F is experienced by a positive charge in a vacuum space. Now, if the same charge is placed in a medium like water, whose relative permittivity is obtained by the formula Permittivity of water/Permittivity of Vacuum = 80, then the same test charge would experience a force F/80 due to the same electric field.

3. What is the application of permittivity?

When an external electric field is established, the amount of resistance being incurred by the medium as an imposing factor is known as permittivity.

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The above image shows a dielectric medium showing orientation of charged particles creating polarization effects. Compared to a space, such a medium shall have a lower ratio of electric flux to charge.

In electrostatics, the capacitance of a capacitor is determined by the permittivity.

In general, the permittivity is a thermodynamic function of state. It is affected by the frequency, magnitude, and direction of the applied field. Farad per meter (F/m) is the SI unit for permittivity.

4. What is the difference between permeability and relative permeability?

Not much.

The tendency of a vacuum to allow magnetic field and force to permeate through it is known as permeability and it is denoted by μo.

The neat way to say permeability of an object concerning vacuum is known as relative permeability. (It is written as μr, and you might obviously know why r is in subscript)