Question

What is the unit of reluctance in magnetic materials?

(a) Henry/m

(b) Weber/m^2

(c) Ampere-turns/Weber

(d) Ampere-turns/m

The question was posed to me in exam.

Question is from Magnetic Materials in chapter Electrical Engineering Materials of Design of Electrical Machines

Answer 1

The correct answer is:

(c) Ampere-turns/Weber

Explanation:

Reluctance is a measure of the opposition to the magnetic flux in a magnetic circuit, similar to resistance in an electrical circuit. It is defined as the ratio of the magnetomotive force (MMF) to the magnetic flux.

Mathematically, reluctance $\mathcal{R}$ is given by:

R=MMFMagnetic flux=Ampere-turnsWeber\mathcal{R} = \frac{\text{MMF}}{\text{Magnetic flux}} = \frac{\text{Ampere-turns}}{\text{Weber}}R=Magnetic fluxMMF​=WeberAmpere-turns​

Where:

• MMF (magnetomotive force) is measured in Ampere-turns.
• Magnetic flux is measured in Webers.

Thus, the unit of reluctance is Ampere-turns per Weber, which corresponds to option (c).