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Encyclopedia > Permeability of free space

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 GA_googleFillSlot("encyclopedia_square");

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:

 Permeability (electromagnetism) - Wikipedia, the free encyclopedia (356 words) In electromagnetism, permeability is the degree of magnetization of a material that responds linearly to an applied magnetic field. Magnetic permeability is represented by the symbol μ. The permittivity of free space (the electric constant) and the magnetic constant are related to the speed of light (c) by the formula:
 Free space - Wikipedia, the free encyclopedia (360 words) Free space is considered the baseline state of the electromagnetic field. According to relativity, radiant energy in free space propagates at the speed of light, independent of the speed of the observer or of the source of the waves. Free space conveys that the region is absolutely devoid of matter and has no external fields or forces other than those considered in the problem at hand.
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