**Magnetic reluctance** is the resistance of a material to a magnetic field. It is defined as the ratio of magnetomotive force (SI unit: ampere-turns) to magnetic flux (SI unit: weber).

The reluctance *R* of a uniform magnetic circuit can be calculated as:

where

**R** is the reluctance, measured in ampere-turns per weber. This unit is equivalent to the reciprocal henry (*H* ^{- 1}) multiplied by the number of turns

**l** is the length of the circuit, measured in metres

**μ** is the magnetic permeability of the material, measured in henry per metre (*H*.*m* ^{- 1})

**A** is the cross-sectional area of the circuit, measured in square metres

## Applications

The variation in the reluctance of a magnetic circuit, in which part of the circuit is moving, is used in measuring instruments called reluctance sensors.

Increasing the reluctance of a magnetic circuit enables it to store more energy. This effect is used in the flyback transformer.

Last updated: 02-08-2005 12:44:51

Last updated: 05-03-2005 17:50:55