# reluctance

(redirected from reluctant)
Also found in: Dictionary, Thesaurus, Idioms.
Related to reluctant: reluctantly, unreluctant

## reluctance

(less commonly), reluctancy
Physics a measure of the resistance of a closed magnetic circuit to a magnetic flux, equal to the ratio of the magnetomotive force to the magnetic flux
Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005

## Reluctance

A property of a magnetic circuit analogous to resistance in an electric circuit.

Every line of magnetic flux is a closed path. Whenever the flux is largely confined to a well-defined closed path, there is a magnetic circuit. That part of the flux that departs from the path is called flux leakage.

For any closed path of length l in a magnetic field H, the line integral of H cos α dl around the path is the magnetomotive force (mmf) of the path, as in

(1)
Eq. (1), where α is the angle between H and the path. If the path encloses N conductors, each with current I, Eq. (2) holds.
(2)

Consider the closely wound toroid shown in the illustration. For this arrangement of currents, the magnetic field is almost entirely within the toroidal coil, and there the flux density or magnetic induction B is given by

(3)
Eq. (3), where l is the mean circumference of the toroid and μ is the permeability. The flux Φ within the toroid of cross-sectional area A is given by either form of
(4)
Eqs. (4), which is similar in form to the equation for the electric circuit, although nothing actually flows in the magnetic circuit. The factor l/μA is called the reluctance of the magnetic circuit. The reluctance is not constant because the permeability μ varies with changing flux density.

A toroidal coil
McGraw-Hill Concise Encyclopedia of Physics. © 2002 by The McGraw-Hill Companies, Inc.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

## Reluctance

a characteristic of a magnetic circuit; the reluctance R m is equal to the ratio of the magnetomotive force F acting on a magnetic circuit to the magnetic flux Φ developed in the circuit. For a uniform section of a magnetic circuit the reluctance can be calculated from the formula Rm = l/μμ0S, where l and S are the length and cross section of the section of the magnetic circuit, respectively; μ is the relative magnetic permeability of the material in the circuit; and μ0 is the magnetic constant.

In the case of a nonuniform magnetic circuit composed of successive uniform sections having different values of l, S, and μ, the reluctance is equal to the sum of the values of Rm for the uniform sections. Such a computation is approximate, since the formula does not take into account “magnetic leakage” (the diffusion of magnetic flux into the space surrounding the magnetic circuit), the nonuniformity of the magnetic field in the circuit, and the nonlinear dependence of the reluctance on the field. In a variable magnetic field the reluctance is a complex quantity, because in this case μ, is a function of the frequency of the electromagnetic oscillations. The unit of reluctance in the International System of Units is the ampere or ampere-turn per weber (A/Wb), and in the cgs system of units, the gilbert per maxwell (Gb/Mx); 1 A/Wb = 4 × 10-9 Gb/Mx ≈ 1.2566 × 10-8 Gb/Mx.

## reluctance

[ri′lək·təns]
(electromagnetism)
A measure of the opposition presented to magnetic flux in a magnetic circuit, analogous to resistance in an electric circuit; it is equal to magnetomotive force divided by magnetic flux. Also known as magnetic reluctance.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
We can glean from the story of Peter's call some of the key elements not just of a reluctant leader, but a successful one.
The government used Sh6 billion to import maize under the subsidy programme to lower flour shelf prices that had hit Sh153 for a 2kg packet before coming down to Sh90 following the intervention.Millers are reluctant to purchase maize from the board and are instead opting for cheap produce from Uganda going for as low as Sh1,500 per 90kg bag.
The Federal Board of Revenue (FBR), however, is reportedly reluctant to register a criminal case against the Huaneng Fuyun Shipping Company, thus highlighting the challenge and complexities faced by authorities in Pakistan when it comes to dealing with Chinese firms operating on its soil since 2013.
Diary of a Reluctant Dreamer is an eye-opening glimpse into a mostly hidden way of life.
A great way of getting reluctant readers to have a go at a story is to read short stories with them that get to the point quickly but are entertaining at the same time.
He said India is reluctant because it knows that it would have to discuss the core issue of Kashmir in talks with Pakistan.
David Moyes has also been touted for the job, but the former Manchester United manager is reluctant to drop below the Premier League.
I believe far more crime is about now because the police are reluctant to fight a lot of crime.
Global Banking News-October 16, 2013--Vietnamese banks reluctant to develop new banking services(C)2013 ENPublishing - http://www.enpublishing.co.uk
Criteria: An elegantly crafted novel, "The Reluctant First Lady" clearly documents author Venita Ellick as an exceptionally accomplished writer able to skillfully weave memorable characters into an riveting story line from beginning to end.
TOMMY'S TIPS SHAWFIELD Race 1 - Delmonte Town; Race 2 - Reluctant Ebony; Race 3 - Lynway Marina; Race 4 - Kilkenny Franco; Race 5 - Lemon Karen; Race 6 - Reluctant Jinty; Race 7 - Glenside Jen; Race 8 - Lagile Maldini; Race 9 - Moorfoot Lizzie; Race 10 - Moorfoot Bob; Race 11 - Nadurra Cartier.
RELUCTANT RITA (9-4) got up close home to land the re-run PS1,000 final of the Winning Lines British Bred Puppy Derby over 480m at Newcastle on Saturday, writes Jonathan Kay.

Site: Follow: Share:
Open / Close