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In electromagnetism, permeability is the degree of magnetisation of a material that responds linearly to a magnetic field. Absolute permeability is represented by the symbol μ. In SI units, permeability is measured in henrys per metre.
<math>\mu_0 \,<math> is known as the Permeability of free space (absolute permeability below)
- Permeability in linear materials owes its existance to the approximation:
- <math> \mathbf{M}=\chi_m\mathbf{H}<math>
- Where <math>\chi_m \,<math> is a dimensionless scalar called the Magnetic Susceptibility
- According to the definition of the Auxillary Field, <math>\mathbf{H}<math>
<math>\mathbf{B}=\mu_0 (\mathbf{H}+\mathbf{M})=\mu_0 (1 + \chi_m)\mathbf{H}<math>
- <math>\mu=\mu_0(1+ \chi_m) \,<math>
- Thus <math>\mu = \frac {B} {H} \,<math>
where
μ is the permeability, measured in henrys per metre
B is the magnetic flux density (also called the magnetic induction) in the material, measured in teslas
H is the magnetic field strength, measured in amperes per metre
Absolute permeability
Absolute permeability is represented by the symbol μ0 and is the permeability of the vacuum, where μ0 = 4π × 10−7 N A−2 (exactly).
Together with permittivity, permeability defines the speed of light.
Relative permeability
Relative permeability, sometimes denoted by the symbol μr, is the ratio of the permeability of a specific medium to the permeability of free space μ0:
- <math>\mu_{r} = \frac{\mu}{\mu_{0}} <math>
| Relative permeability for some materials
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| Medium
| <math>\chi_m = \mu_r - 1 \,<math>
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| Hydrogen
| 0.008 × 10-6
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| Copper
| −6.4 × 10-6
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| Water
| −8.0 × 10-6
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| Aluminium
| 22.2 × 10-6
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| Platinum
| 265 × 10-6
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SI magnetism units
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