Permittivity and Permeability: Learn Their Definitions, Differences, Relation

In electromagnetic theory, two distinct concepts, permittivity and permeability, are considered. Permittivity refers to the concept associated with the growth of an electric field, while permeability refers to the growth of a magnetic field.

Read on, to learn more about their definition, differences and their examples in detail.

What is Permittivity?

Permittivity is a measurement of a medium’s resistance to producing an electric field. The value of the electric displacement (D) in a medium is determined by comparing it to the intensity of the electric field that causes it. It is the ratio between these two quantities (E). It is a crucial electrical property of the materials, especially insulates.

SI Unit of permitivity- Permittivity is measured in farads per meter ().

Due to the high permittivity of the medium, a substantial amount of polarization occurs within it, necessitating a bigger quantity of electric flux to generate the opposing electric field. Therefore, if the permittivity of a dielectric media is high, the net field strength within the medium will be low.

A vacuum has a constant permittivity, and it is the permittivity with the smallest possible value. A vacuum’s permittivity has a value of 8.85410-54 . Occasionally, it is more convenient to represent the permittivity of a dielectric media as a multiple of the permittivity of a vacuum. This simplifies mathematical applications and makes it easier to compare the permittivities of a different material. This ratio of absolute () and vacuum permittivity () represents relative permittivity (). Absolute permittivity is the term for the real permittivity of the medium. No units exist for relative permittivity, which will always be greater than 1.

What is Permeability?

Permeability is defined as the magnetic field density (B) ratio inside a medium to the magnetic field strength outside the medium (H). This feature is essential to consider when considering a material’s magnetic properties.

SI Unit of permeability– Permeability is measured in SI units using the Henry per meter ().

Dimensional formula of permeability-

Inductance can also be used to define permeability when stated as a unit length function. When external magnetic fields are applied, it describes the magnetic flux created within the medium.

The permeability in space (vacuum), which has a value of represents the lowest achievable permeability.

Types of Permeability

There are three common types of permeability:

• Magnetic permeability
• Absolute permeability
• Relative permeability

Magnetic Permeabillity

This type of permeability is related to the ability of a material to respond to a magnetic field. It is denoted by the symbol "μ" (mu) and is usually measured in henries per meter (H/m). The formula for magnetic permeability is:

Absolute Permeability

Absolute permeability refers to the permeability of a material in the absence of any other substances. It is a fundamental property of the material itself and is denoted by the symbol μ₀. It is measured in henries per meter (H/m). The formula for absolute permeability is the same as magnetic permeability:

Absolute permeability is a constant value given as H/m

Relative Permeability

Relative permeability is a dimensionless quantity that describes the ability of a material to conduct magnetic flux compared to a vacuum or free space. It is denoted by the symbol μᵣ. It expressed as the ratio of the absolute permeability of the material (μ) to the absolute permeability of free space (μ₀). The formula for relative permeability is:

Permeability and Relative Permeability of Materials

Material	Permeability (μ) (H/m)	Relative Permeability (μᵣ)
Air		1.000
Copper		0.999
Vacuum		1
Water		0.999
Wood		1.00

Difference Between Permittivity and Permeability

The following are the distinctions between permittivity and permeability.

Permeability	Permittivity
Permeability is the capacity by which a material allows magnetic lines to pass through it.	Permittivity is the impediment caused by the substance during the creation of the electric field.
According to the SI system, permeability is measured in Henry/meters.	According to the SI system, permittivity is measured in Faraday/meters.
Magnetization determines the permeability of a substance.	Polarization determines the permittivity of a substance.
The free space of permeability is 1.26 H/m	The free space of permittivity is 8.85 F/m.
Permeability is accountable for the formation of the magnetic field.	Permittivity is responsible for the formation of the electric field.
The inductor and transformer cores are responsible for generating a high permeability.	The capacitor generates a high permittivity.

Relation Between Permittivity and Permeability

Permittivity (ε) and permeability (μ) are related to each other through a fundamental constant known as the speed of light (c) in vacuum or free space.

The relationship between permittivity, permeability, and the speed of light is given by Maxwell's equations, which describe the behavior of electromagnetic waves. These equations establish a fundamental connection between electric and magnetic fields.

In vacuum or free space, the relationship is expressed as:

This equation states that the product of permittivity and permeability is equal to the inverse of the square of the speed of light. It means that the value of permittivity and permeability determines the speed at which electromagnetic waves, including light, can propagate through a medium.

Example Showing Permittivity

Suppose two plates are separated by a distance “d”. A medium composed of air fills the area between these two plates.

The existence of molecules in the gap between these plates should be evident. This demonstrates the propensity of these molecules to generate electric dipole moments.

An electric dipole consists of two charges with identical magnitudes but opposite signs. One molecule may have a positive charge associated with one end and a negative charge attached to the other, with some distance between. This is an instance of what we call an electric dipole.

These molécules often arrange themselves randomly on the plates. When an electric field is applied from an external medium, these molecules begin to align themselves more efficiently. In addition, its dipole moment generates its electric field as a result.

This electric field pulls against the externally applied electric field. In contrast to the behaviour of the external electric field, the electric field created by dipole moments behaves in a manner that is antithetical to that of the external electric field.

Consequently, it is comparable to the same pole on two separate magnets. They continue to collaborate in opposition. Polarizability is the phenomenon that describes the ability of molecules to align themselves in response to the application of an external electric field. The more the molecules can polarise or align themselves, the more excellent their resistance to the impact of an external electric field.

This characteristic is known as permittivity. Suppose the permittivity of a medium is greater, the molecules polarise more effectively, and as a result, they offer more resistance to the impact of an external electric field. Similarly, if the permittivity of a medium is low, the molecules in the medium polarise very poorly, resulting in low resistance when exposed to an external electric field.

Example Showing Permittivity

Let us take a magnet. One can observe a magnetic field surrounding the magnet. It is unavailable for viewing. Nonetheless, we can indeed have that experience. And all that is required to do this is to get the iron object close to the magnet.

In the region of the magnet, the magnetic field will resemble elliptical lines. These lines demonstrate the magnetic field that this magnet generates.

What will occur if a person brings a piece of wood into proximity to this magnet or the magnetic field? Nothing occurs. Bring in some iron to examine at this time. Because the magnet is magnetic, one may assume it will attract the iron.

What led to this happening? Why doesn’t the magnet attract the piece of wood, but it does attract the iron? Permeability is the solution.

Consequently, this is the magnetic field we are experiencing. The magnetic field was attracted to the iron due to its appealing qualities. When the iron piece generates its magnetic field, it becomes magnetized. It was magnetically permeable and allowed the magnetic field to pass through. Wood has a low permeability, which is another way of saying it is impermeable.

Therefore, the property of a substance or medium to become magnetized in reaction to an external magnetic field is known as its permeability or magnetic permeability.

If you are checking Permittivity and Permeability, also check the related physics articles:
Dielectric Constant	Parallel Plate Capacitor
Impedance of Free Space	Electric Flux