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| '''Magnetic reluctance''', or '''magnetic resistance''', is a concept used in the analysis of [[magnetic circuit]]s. It is analogous to [[Electrical resistance|resistance]] in an [[electrical]] [[Electrical network|circuit]], but rather than dissipating electric energy it stores magnetic energy. In likeness to the way an [[electric field]] causes an [[electric current]] to follow the [[path of least resistance]], a [[magnetic field]] causes [[magnetic flux]] to follow the path of least magnetic reluctance. It is a [[scalar (physics)|scalar]],
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| [[Intensive and extensive properties#Extensive quantity|extensive quantity]], akin to electrical resistance. The units for magnetic reluctance are inverse Henries, H<sup>–1</sup>.
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| ==History==
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| The term was coined in May 1888 by [[Oliver Heaviside]].<ref>Heaviside O., Electrical Papers, Vol 2 – L.; N.Y.: Macmillan, 1892, p.166</ref> The notion of “magnetic resistance” was first mentioned by [[James Joule]]<ref>Joule J., Scientific Papers, vol 1 – 1884, p.36</ref> and the term "[[magnetomotive force]]” (MMF) was first named by Bosanquet.<ref>Bosanquet, Phil. Mag., vol 15, 1883, p.205</ref> The idea for a [[magnetic flux]] law, similar to [[Ohm's law]] for closed [[electric circuit]]s, is attributed to [[Henry Augustus Rowland|H. Rowland]].<ref>Rowland H., Phil. Mag. (4), vol 46, 1873, p.140</ref>
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| Reluctance is usually represented by a [[cursive]] capital R.
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| == Definition ==
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| In a DC field, the reluctance is the ratio of the "[[magnetomotive force]]” (MMF) in a [[magnetic circuit]] to the [[magnetic flux]] in this circuit. In a pulsating DC or AC field, the reluctance is the ratio of the amplitude of the "[[magnetomotive force]]” (MMF) in a [[magnetic circuit]] to the amplitude of the [[magnetic flux]] in this circuit.. (see [[Phasor (sine waves)|phasors]])
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| The definition can be expressed as follows:
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| :<math>\mathcal R = \frac{\mathcal F}{\Phi}</math>
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| where
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| :<math>\scriptstyle \mathcal R</math> ("R") is the reluctance in [[ampere-turn]]s per [[weber (unit)|weber]] (a unit that is equivalent to turns per [[henry (unit)|henry]]). "[[Turn (geometry)|Turns]]" refers to the [[winding number]] of an electrical conductor comprising an inductor.
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| :<math>\scriptstyle \mathcal F</math> ("F") is the [[magnetomotive force]] (MMF) in ampere-turns
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| :''Φ'' ("Phi") is the [[magnetic flux]] in webers.
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| It is sometimes known as [[Hopkinson's law]] and is analogous to [[Ohm's Law]] with resistance replaced by reluctance, voltage by MMF and current by magnetic flux.
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| Magnetic flux always forms a closed loop, as described by [[Maxwell's equations]], but the path of the loop depends on the reluctance of the surrounding materials. It is concentrated around the path of least reluctance. Air and vacuum have high reluctance, while easily magnetized materials such as [[soft iron]] have low reluctance. The concentration of flux in low-reluctance materials forms strong temporary poles and causes mechanical forces that tend to move the materials towards regions of higher flux so it is always an attractive force(pull).
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| The reluctance of a uniform magnetic circuit can be calculated as:
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| :<math>\mathcal R = \frac{l}{\mu_0 \mu_r A}</math>
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| or
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| :<math>\mathcal R = \frac{l}{\mu A}</math>
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| where
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| :''l'' is the length of the circuit in [[metre]]s
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| :''<math>\scriptstyle \mu_0</math>'' is the permeability of vacuum, equal to 4π × 10{{sup|−7}} henry per metre | |
| :''<math>\scriptstyle \mu_r</math>'' is the relative [[magnetic permeability]] of the material (dimensionless)
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| :''<math>\scriptstyle \mu</math>'' is the permeability of the material (''<math>\scriptstyle \mu \;=\; \mu_0 \mu_r </math>)
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| :''A'' is the cross-sectional area of the circuit in [[square metre]]s
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| The inverse of reluctance is called ''[[permeance]]''.
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| :<math>\mathcal P = \frac{1}{\mathcal R}</math>
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| Its [[SI]] derived unit is the [[henry (unit)|henry]] (the same as the unit of [[inductance]], although the two concepts are distinct).
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| == Applications ==
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| *Constant air gaps can be created in the core of certain transformers to reduce the effects of [[Saturation (magnetic)|saturation]]. This increases the reluctance of the magnetic circuit, and enables it to store more [[energy]] before core saturation. This effect is also used in the [[flyback transformer]].
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| *Variable air gaps can be created in the cores by a movable keeper to create a Flux Switch that alters the amount of magnetic flux in a magnetic circuit without varying the constant [[magnetomotive force]] in that circuit.
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| *Variation of reluctance is the principle behind the [[reluctance motor]] (or the variable reluctance generator) and the [[Alexanderson alternator]]. Another way of saying this is that the ''reluctance forces'' strive for a maximally aligned magnetic circuit and a minimal air gap distance.
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| *[[Multimedia]] [[loudspeaker]]s are typically shielded magnetically, in order to reduce magnetic interference caused to [[television]]s and other [[Cathode ray tube|CRT]]s. The speaker magnet is covered with a material such as [[soft iron]] to minimize the stray magnetic field.
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| Reluctance can also be applied to:
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| *Reluctance [[electric motor|motors]]
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| *Variable reluctance (magnetic) [[Pick up (music technology)|pickups]]
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| ==See also==
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| *[[Dielectric complex reluctance]]
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| *[[Magnetic capacitivity]]
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| *[[Magnetic capacitance]]
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| *[[Magnetic circuit]]
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| *[[Magnetic complex reluctance]]
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| *[[Reluctance motor]]
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| ==References==
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| <references/>
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| == External links ==
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| {{DEFAULTSORT:Magnetic Reluctance}}
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| [[Category:Electric and magnetic fields in matter]]
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Wilber Berryhill is what his wife enjoys to call him and he completely loves this title. Office supervising is my occupation. My spouse and I live in Mississippi and I adore every day living right here. What me and my family members love is bungee jumping but I've been taking on new things recently.
Here is my blog post - psychic phone readings; mouse click the following article,