What is Magnetic reluctance – Definition

magnetic circuit

The reluctance is the property of the magnetic material which provides opposition to  flow of magnetic flux through a given volume of space or material. The reluctance of magnetic circuit is analogous to the resistance of electric circuit. The lower is the reluctance, it is easier for the magnetic flux to flow through the magnetic material.The opposite of the reluctance is the permeability and permeability is analogous to the conductivity in the electric circuit. The magnetic materials have low reluctance and high permeability, and non magnetic materials have high reluctance and low permeability.

Comparison of Magnetic and Electric Circuit

comparision of magnetic and electric circuit
The above diagram shows analogy of electric and magnetic circuit. The magneto-motive force(MMF) is equivalent to emf in the electric circuit. Flux is analogous to the electric current and the reluctance is analogous to the resistance in electric circuit.

When voltage is applied to a coil which has N number of turns, the current  starts flowing through the coil. Let the magnitude of the current is I amps.

The Magneto-motive force MMF produced is equal to the product of the current and the number of turns.
MMF formula
The current flowing in the coil produce the magnetic flux (Φ) which travels through the magnetic core. The magnitude of the flux depends on the MMF and the reluctance of the magnetic circuit. If the reluctance offered by the magnetic material is more the magnitude of the magnetic flux will be less. The flux can be increased by lowering the reluctance of the magnetic material.

If the uniform section having the different value of length, cross section area and permeability are added, the non-uniform magnetic circuit can be made.

By adding the reluctance of the uniform section of the magnetic circuit, the reluctance of the non-uniform circuit can be calculated.

Formula of Magnetic Reluctance

The reluctance( Rm) of the magnetic circuit can be expressed as ;

MMF equation of magnetic circuit- Magnetic circuit MMF formula

SI unit of reluctance is AT / Wb (ampere-turns / Weber). The reluctance(Rm) of the magnetic circuit is directly proportional to the length of the conductor and inversely proportional to the cross-section area of the conductor.

The permeance is one of the parameter which measures the property of magnetic circuit to allow the magnetic flux passing through it. The permeance is inversely proportional of the reluctance. It is expression by following expression.

permeance formula of magnetic circuit

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