# Permeability & Relative Permeability

In this post, we will discuss Permeability & Relative Permeability with their definition, relationship, equations, formula, the permeability of air, examples, etc.

## Permeability

The ability of a material to conduct magnetic lines of force through it is called the permeability of that material.

It is generally represented by **μ** (mu, a Greek letter). The greater the permeability of a material, the greater is its conductivity for the magnetic lines of force and vice versa.

The permeability of air or vacuum is the poorest and is represented as **μ**_{0} (where **μ**_{0} = 4 x pi × 10^{–7} H/m).

## Relative permeability

The absolute (or actual) permeability **μ** of a magnetic material is much greater than the absolute permeability of air **μ**_{0}.

**The relative permeability of a magnetic material is given in comparison with air or vacuum.Hence, the ratio of the permeability of material μ to the permeability of air or vacuum μ _{0} is called the relative permeability μ_{r} of the material.**

Therefore,**μ**_{r} =**μ**/**μ**_{0}

or, permeability of material **μ** = **μ**_{r}**μ**_{0}

## Relative permeability – values

- Obviously, the relative permeability of air would be 1.
- The value of relative permeability of all the non-magnetic materials is also 1.
- However, the relative permeability value is as high as 8,000 for soft iron.
- Whereas the relative permeability value for Mu metal (iron 22% and nickel 78%) is as high as 120,000.

The closed path followed by magnetic flux is called a magnetic circuit. A magnetic circuit usually consists of magnetic materials having high permeability (e.g., iron, soft steel, etc.).