Reluctance (S)

Reluctance (S)

• In an electric circuit, current flow is opposed by the resistance of the material, similarly there is opposition by the material to the flow of flux which is called reluctance                                                                                                                  

• It is defined as the resistance offered by the material to the flow of magnetic flux through it. It is denoted by 'S'. It is directly proportional to the length of the magnetic circuit while inversely proportional to the area of cross-section.

It is measured in amperes per weber (A/Wb) or ampere-turns per weber (AT/Wb) The reluctance can be also expressed as the ratio of magnetomotive force to the flux produced.

i.e. Reluctance = m. m.f/ flux

∴  S = NI/ϕ  A/Wb or AT/Wb

Review Question

1. Define reluctance and state its units.

Permeance

• The permeance of the magnetic circuit is defined as the reciprocal of the reluctance.

• It is defined as the property of the magnetic circuit due to which it allows flow of the magnetic flux through it.

∴   Permeance = 1/Reluctance

It is measured in weber per amperes (Wb/A).

Review Question

1. Define permeance and state its units.