Magnetic Permeability

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What Is Magnetic Permeability?

Magnetic permeability, also referred to as permeability in electromagnetism, is a property of a magnetic material which supports the formation of a magnetic field. The term was coined by Oliver Heaviside in the year 1885. Magnetic permeability is a property that basically allows magnetic lines of force to pass through a material.

In other words, the magnetic permeability of a material can also be said to be its magnetisation capability. This helps in determining how much magnetic flux can the material support, which will pass through it.

Magnetic Permeability Definition

Magnetic permeability is defined as the ratio of the magnetic induction to the magnetic intensity. It is a scalar quantity and is denoted by the symbol μ. Magnetic permeability helps us measure a material’s resistance to the magnetic field or measure the degree to which a magnetic field can penetrate through a material.

If the material has greater magnetic permeability, the greater will be the conductivity for magnetic lines of force.

Factors Affecting Magnetic Permeability

Permeability also depends on several factors, such as the nature of the material, humidity, position in the medium, temperature, and frequency of the applied force. Magnetic permeability is always positive and can vary with a magnetic field. On the other hand, the opposite of magnetic permeability is magnetic reluctivity.

Magnetic Permeability Formula

The magnetic permeability formula is given as follows;

Magnetic permeability (μ) = B/H

Where B = magnetic intensity and H = magnetising field.

The SI unit of magnetic permeability is henry per meter (H/m) or newton per ampere squared (N⋅A⁻²).

Types of Permeability

The different types of permeability include the following:

Permeability of Free Space

It is the ratio of magnetic intensity in a vacuum and magnetising field.

The permeability of free space, also known as the permeability of air or vacuum, is represented by μ₀ = B₀/H.

Permeability of Medium

It is the ratio of magnetic intensity in the medium and magnetising field.

It is expressed as,

μ = B/H

Relative Permeability

Relative permeability is a dimensionless quantity. It is the ratio of two quantities with the same units, so relative permeability has no unit. The relative permeability of free space is 1.

Its expression is given as,

μ_r= μ/μ_m

Relative permeability = (number of lines of magnetic induction per unit area in a material)/(number of lines per unit area in a vacuum)

Magnetic Permeability Materials

Materials may be classified on the basis of their permeability as follows:

Diamagnetic Materials

Diamagnetic materials have a constant relative permeability of slightly less than 1, and that’s why magnetic flux density inside diamagnetic materials is slightly reduced. Diamagnetic materials are feebly repelled in external magnetic fields. Bismuth is an example of diamagnetic material.

Read more about it here: Diamagnetic Materials

Paramagnetic Materials

Paramagnetic materials have a constant relative permeability slightly greater than 1, and that’s why when a paramagnetic material is placed in an external field, it gets feebly magnetised in the direction of the magnetic field. Platinum is an example of paramagnetic material.

Read more about it here: Paramagnetic Materials

Ferromagnetic Materials

Ferromagnetic materials do not have constant relative permeability.

Pure iron and many alloys have relative permeability greater than 100000; as the magnetising field increases, the relative permeability increases. Therefore, ferromagnetic materials have the strongest magnetic properties. Iron is an example of ferromagnetic material.

Relation between Relative Permeability and Magnetic Susceptibility

The relation between magnetic susceptibility and relative permeability is described as follows:

χ_m = μ_r − 1

Lets us understand how we can establish or derive this equation.

First, we take some relevant equations.

B = μ_o(H+M) and M=X_mH

Substituting the values, we get

B = μ_o(H+X_mH)

B = μ_oH(1+X_m)

So,

μH = μoH(1+Xm)

μ/μ_o = μ_r

X_m=1 – μ_r

Also Read:

• Dimensions of Permeability