# Vacuum permeability

magnetic constantpermeability of free spacepermeability of vacuumpermeabilitypermeability constantμ 0 magnetic permeabilityvacuum magnetic permeabilityμ'' 0 magnetic permeability of free space
The physical constant μ 0, (pronounced "mu nought" or "mu zero"), commonly called the vacuum permeability, permeability of free space, permeability of vacuum, or magnetic constant, is the magnetic permeability in a classical vacuum.wikipedia
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### Ampère's force law

Ampère's lawAmpere's force lawAmpere's law
Ampère's force law states that the force per length L is given by
with μ 0 the magnetic constant, defined in SI units as

### Physical constant

constantconstantsfundamental constants
The physical constant μ 0, (pronounced "mu nought" or "mu zero"), commonly called the vacuum permeability, permeability of free space, permeability of vacuum, or magnetic constant, is the magnetic permeability in a classical vacuum.

### Centimetre–gram–second system of units

CGScgs unitsCGS unit
In the old "electromagnetic (emu)" system of equations defined in the late 19th century, k m was chosen to be a pure number, 2, distance was measured in centimetres, force was measured in the cgs unit dyne, and the currents defined by this equation were measured in the "electromagnetic unit (emu) of current" (also called the "abampere").
Furthermore, if we wish to describe the electric displacement field D and the magnetic field H in a medium other than vacuum, we need to also define the constants ε 0 and μ 0, which are the vacuum permittivity and permeability, respectively.

### Permeability (electromagnetism)

permeabilitymagnetic permeabilityrelative permeability
In particular, it appears in relationship to quantities such as permeability and magnetization density, such as the relationship that defines the magnetic H-field in terms of the magnetic B-field.
The permeability constant μ 0, also known as the magnetic constant or the permeability of free space, is a measure of the amount of resistance encountered when forming a magnetic field in a classical vacuum.

### Maxwell's equations

Maxwell equationsMaxwell equationMaxwell’s equations
The magnetic constant μ 0 appears in Maxwell's equations, which describe the properties of electric and magnetic fields and electromagnetic radiation, and relate them to their sources.
*the permeability of free space,

### Speed of light

clight speedspeed of light in vacuum
In SI units, the speed of light in vacuum,
This subscripted notation, which is endorsed in official SI literature, has the same form as other related constants: namely, μ 0 for the vacuum permeability or magnetic constant, ε 0 for the vacuum permittivity or electric constant, and Z 0 for the impedance of free space.

### Magnetic field

magnetic fieldsmagneticmagnetic flux density
The magnetic constant μ 0 appears in Maxwell's equations, which describe the properties of electric and magnetic fields and electromagnetic radiation, and relate them to their sources.
is a constant called the vacuum permeability, measuring 4 V·s/(A·m) and

### Fine-structure constant

fine structure constant137coupling constant
It is proportional to the dimensionless fine-structure constant with no other dependencies. Conversely, as the permittivity is related to the fine structure constant (\alpha), the permeability can be derived from the latter (using Planck's constant, h, and the electric charge on an electron, e):
is the magnetic constant or permeability of free space;

### Ampere

AmAamp
The ampere was that constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross section, and placed 1 meter apart in vacuum, would produce between these conductors a force equal to 2 newton per meter of length.

### Vacuum

free spaceevacuatedhigh vacuum
The physical constant μ 0, (pronounced "mu nought" or "mu zero"), commonly called the vacuum permeability, permeability of free space, permeability of vacuum, or magnetic constant, is the magnetic permeability in a classical vacuum.

### Mathematical descriptions of the electromagnetic field

Maxwell's equations in the potential formulationformulation of Maxwell's equationsgeometric algebra formulation of electromagnetism
where ρ is the charge density, which can (and often does) depend on time and position, ε 0 is the electric constant, μ 0 is the magnetic constant, and J is the current per unit area, also a function of time and position.

### Impedance of free space

Characteristic impedance of vacuumη 0 characteristic impedance of free space
The impedance of free space (that is the wave impedance of a plane wave in free space) is equal to the product of the vacuum permeability

### Vacuum permittivity

permittivity of free spaceelectric constantvacuum electric permittivity
, is related to the magnetic constant and the electric constant (vacuum permittivity),
where c is the defined value for the speed of light in classical vacuum in SI units, and μ 0 is the parameter that international Standards Organizations call the "magnetic constant" (commonly called vacuum permeability).

### Magnetization

magnetizedmagnetisationbound current
In particular, it appears in relationship to quantities such as permeability and magnetization density, such as the relationship that defines the magnetic H-field in terms of the magnetic B-field.
The vacuum permeability μ 0 is, by definition, 4 V·s/(A·m).

electromagnetic waveelectromagnetic waveselectromagnetic
The magnetic constant μ 0 appears in Maxwell's equations, which describe the properties of electric and magnetic fields and electromagnetic radiation, and relate them to their sources.
Thus Maxwell's equations connect the vacuum permittivity, the vacuum permeability \mu_0, and the speed of light, c 0, via the above equation.

### 2019 redefinition of the SI base units

2019 redefinition of SI base unitsredefinitionredefinition of the SI base units
In the new SI units, only the fine structure constant is an actual measured value in this formula.
Other consequences of the previous definition were that in SI the value of vacuum permeability (

### Committee on Data for Science and Technology

CODATACODATA 2018CODATA 2014
, the vacuum permeability μ 0 will no longer be a defined constant (per the former definition of the SI ampere), but rather will need to be determined experimentally; The 2018 CODATA value is given below.

### International Union of Pure and Applied Physics

IUPAPC-13 CommitteeIUPAP red book
In the 1987 IUPAP Red book, for example, this constant was still called permeability of vacuum.

### Dyne

dyndyne-centimeters
In the old "electromagnetic (emu)" system of equations defined in the late 19th century, k m was chosen to be a pure number, 2, distance was measured in centimetres, force was measured in the cgs unit dyne, and the currents defined by this equation were measured in the "electromagnetic unit (emu) of current" (also called the "abampere").

### Abampere

Bibiot
In the old "electromagnetic (emu)" system of equations defined in the late 19th century, k m was chosen to be a pure number, 2, distance was measured in centimetres, force was measured in the cgs unit dyne, and the currents defined by this equation were measured in the "electromagnetic unit (emu) of current" (also called the "abampere").

### International System of Units

SISI unitsSI unit
In 1948, international decisions were made by standards organizations to adopt the rmks system, and its related set of electrical quantities and units, as the single main international system for describing electromagnetic phenomena in the International System of Units.

### Electric field

electricelectrostatic fieldelectrical field
The magnetic constant μ 0 appears in Maxwell's equations, which describe the properties of electric and magnetic fields and electromagnetic radiation, and relate them to their sources.

### Planck constant

Planck's constantreduced Planck constantreduced Planck's constant
Conversely, as the permittivity is related to the fine structure constant (\alpha), the permeability can be derived from the latter (using Planck's constant, h, and the electric charge on an electron, e):

### Electric charge

chargeelectrical chargecharged
Conversely, as the permittivity is related to the fine structure constant (\alpha), the permeability can be derived from the latter (using Planck's constant, h, and the electric charge on an electron, e):