View source for Permeance

{{Electromagnetism|Magnetic circuit}}

'''Permeance''', in general, is the degree to which a material admits a flow of [[matter]] or [[energy]]. Permeance is usually represented by a curly capital P: {{mathcal|P}}.

==Electromagnetism==
In [[electromagnetism]], '''permeance''' is the inverse of [[reluctance]]. In a magnetic circuit, permeance is a measure of the quantity of [[magnetic flux]] for a number of current-turns. A [[magnetic circuit]] almost acts as though the [[flux]] is conducted, therefore permeance is larger for large cross-sections of a material and smaller for smaller cross section  lengths. This concept is analogous to [[electrical conductance]] in the [[electric circuit]].

Magnetic permeance {{mathcal|P}} is defined as the reciprocal of [[magnetic reluctance]] {{mathcal|R}} (in analogy with the reciprocity between electric conductance and resistance):
<math display="block">\mathcal{P} = \frac{1}{\mathcal{R}}</math>

which can also be re-written:
<math display="block">\mathcal{P} = \frac{\Phi_\mathrm{B}}{NI}</math>

using [[magnetic circuit #Hopkinson's law: the magnetic analogy to Ohm's law|Hopkinson's law]] (magnetic circuit analogue of [[Ohm's law]] for electric circuits) and the definition of [[magnetomotive force]] (magnetic analogue of [[electromotive force]]): 
<math display="block">\mathcal{F} = \Phi_\mathrm{B} \mathcal{R} = NI</math>

where:
* {{math|Φ<sub>B</sub>}}, [[magnetic flux]],
* {{mvar|I}}, current, in amperes,
* {{mvar|N}}, [[winding number]] of, or count of turns in the electric coil.

Alternatively in terms of [[permeability (electromagnetism)|magnetic permeability]] (analogous to [[electric conductivity]]):
<math display="block">\mathcal{P} = \frac{\mu A}{\ell}</math>

where:
* {{mvar|μ}}, permeability of material,
* {{mvar|A}}, cross-sectional area,
* ℓ, magnetic path length.

The SI unit of magnetic permeance is the [[henry (unit)|henry]] (H), equivalently, [[weber (unit)|webers]] per [[ampere]].{{efn|The SI unit of [[magnetomotive force|mmf]] is the ampere, the same as the unit of current (analogously the units of [[electromotive force|emf]] and voltage are both the volt). Informally, and frequently, this unit is stated as the ampere-turn to avoid confusion with current. This was the unit name in the [[MKS system]].}}

==Materials science==
In [[materials science]], '''permeance''' is the degree to which a material transmits another substance.

==See also==
*[[Dielectric complex reluctance]]
*[[Reluctance]]

==Notes==
{{notelist}}

==References==
===Electromagnetism===
* [http://orca.phys.uvic.ca/~tatum/elmag/em12.pdf ''Properties of Magnetic Materials''] (units of magnetic permeance)

===Material science===
* Bombaru, D., Jutras, R., and Patenaude, A., "''Air Permeance of Building Materials''". Summary report prepared by, AIR-INS Inc. for [[Canada Mortgage and Housing Corporation]], Ottawa, 1988.

[[Category:Electric and magnetic fields in matter]]