Permeance
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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: Template:Mathcal.
ElectromagnetismEdit
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 Template:Mathcal is defined as the reciprocal of magnetic reluctance Template:Mathcal (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 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:
- Template:Math, magnetic flux,
- Template:Mvar, current, in amperes,
- Template:Mvar, winding number of, or count of turns in the electric coil.
Alternatively in terms of magnetic permeability (analogous to electric conductivity): <math display="block">\mathcal{P} = \frac{\mu A}{\ell}</math>
where:
- Template:Mvar, permeability of material,
- Template:Mvar, cross-sectional area,
- ℓ, magnetic path length.
The SI unit of magnetic permeance is the henry (H), equivalently, webers per ampere.Template:Efn
Materials scienceEdit
In materials science, permeance is the degree to which a material transmits another substance.
See alsoEdit
NotesEdit
ReferencesEdit
ElectromagnetismEdit
- Properties of Magnetic Materials (units of magnetic permeance)
Material scienceEdit
- 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.