Magnetic resistance

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Physical size
Surname magnetic resistance, reluctance
Formula symbol
Size and
unit system
unit dimension
SI H −1 = A · V −1 · s −1 M −1  L −2  I 2  T 2

The magnetic resistance or reluctance is the proportionality factor between the magnetic voltage and the magnetic flux in the form:

According to John Hopkinson, the equation is referred to as Hopkinson's law or Hopkin’s law and has a form similar to Ohm's law for the electrical circuit , if the magnetic flux is put in analogy to the electrical current strength and the magnetic voltage to the electrical voltage . The magnetic resistance is not to be confused with the magnetoresistive effect , which describes an electrical resistance that is influenced by a magnetic flux.

Due to the historical formation of the term, the magnetic voltage is sometimes referred to in the specialist literature as magnetic flux with the symbol .

The magnetic resistance for an element with uniform magnetic flux corresponds to the size:

This corresponds to

the length of the magnetic circuit in meters ,
the permeability of vacuum ( henry per meter),
the relative permeability of the material (dimensionless),
the cross-sectional area of the magnetic conductor in square meters .
Iron core with air gap
R m  =  R m, iron  +  R m, air

In the case of magnetic circuits with constant magnetic conductance values, cross-sections and lengths in sections, partial magnetic resistances can be determined according to the above relationship. The calculation rules for combining these resistances are analogous to those for connecting electrical resistors in series and in parallel .

The total resistance in the magnetic circuit is also decisive for its inductivity and magnetic flux density .

Magnetic resistances are used in the magnetic circuit theory developed by John Hopkinson and his son Edward Hopkinson at the end of the 19th century. The ideas developed at that time were a basis for the construction of electrical machines and are still used today to understand simple magnetic circuits.

The reciprocal of the magnetic resistance is the magnetic conductance or permeance .

The unit of magnetic resistance in the International System of Units (SI) is the reciprocal of the unit Henry and can be expressed as H −1 . The unit of magnetic conductance is Henry .

See also

literature

  • Karl Küpfmüller, Gerhard Kohn: Theoretical electrical engineering and electronics . 14th edition. Springer, 1993, ISBN 3-540-56500-0 .