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Encyclopedia > Magnetic permeability

This article is in need of attention. Please improve it (http://en.wikipedia.org/w/index.php?title=Permeability_%28electromagnetism%29&action=edit) in any way you see fit.

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. is known as the Permeability of free space (absolute permeability below)

Permeability in linear materials owes its existance to the approximation:
Where is a dimensionless scalar called the Magnetic Susceptibility
According to the definition of the Auxillary Field,

Thus

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:

Relative permeability for some materials
Medium
Hydrogen 0.008 × 10-6
Copper −6.4 × 10-6
Water −8.0 × 10-6
Aluminium 22.2 × 10-6
Platinum 265 × 10-6

SI magnetism units

SI electromagnetism units

edit  (http://en.wikipedia.org/w/index.php?title=Template:SI_electromagnetism_units&action=edit)
Name Symbol Dimensions Quantity
ampere (SI base unit) A A Current
coulomb C A·s Electric charge, Quantity of electricity
volt V J/C = kg·m2·s−3·A−1 Potential difference
ohm Ω V/A = kg·m2·s−3·A−2 Resistance, Impedance, Reactance
ohm metre Ω·m kg·m3·s−3·A−2 Resistivity
farad F C/V = kg−1·m−2·A2·s4 Capacitance
farad per metre F/m kg−1·m−3·A2·s4 Permittivity
reciprocal farad F−1 kg1·m2·A−2·s−4 Elastance
siemens S Ω−1 = kg−1·m−2·s3·A2 Conductance, Admittance, Susceptance
siemens per metre S/m kg−1·m−3·s3·A2 Conductivity
weber Wb V·s = kg·m2·s−2·A−1 Magnetic flux
tesla T Wb/m2 = kg·s−2·A−1 Magnetic flux density
ampere per metre A/m m−1·A magnetic induction
ampere-turns per weber A/Wb kg−1·m−2·s2·A2 Reluctance
henry H V·s/A = kg·m2·s−2·A−2 Inductance
henry per metre H/m kg·m·s−2·A−2 Permeability
(dimensionless) - - Magnetic susceptibility

  Results from FactBites:
 
Magnetic permeability of magnetic shields a critical factor (1086 words)
It is defined as the ratio of the intensity of induced magnetization in the material to the intensity of the inducing magnetic force field that produced it.
For the most effective magnetic shield attenuation performance, the higher the magnetic permeability, the better.
Magnetically "hard" materials, on the other hand, make good magnets because they can retain a strong magnetic field even after the source of the magnetic energy has been removed.
  More results at FactBites »


 

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