Explanation Of Terms Related To Magnetic Circuits In Electrical B.Tech.

explanation of :

  1. Reluctance
  2. Flux density or Magnetic flux density
  3. Coercive Force
  4. Magnetomotive Force (M.M.F.)
  5. Residual flux
  6. Magnetic circuit
  7. Permeability
  8. Electromagnetic Induction
  9. Magnetic field
  10. Field Intensity or Magnetising force (H)
  11. Permeance
  12. Leakage coefficient
  13. Flux


It is the name given to that property of material which opposes the creation of magnetic flux in it. It is measured in ampere-turn/Wb Or Amp/Wb.

Flux Density

The magnetic flux per unit area (A), measured in a plane perpendicular to the flux is defined as the flux density. It is denoted by (B).

Coercive Force

It is the amount of magnetizing force required to reduce the retained magnetism to zero.

Magnetomotive Force

It is defined as the force responsible for the flow of flux or generation of flux. The magnetic field strength (H) is decided by m.m.f.

m.m.f. = N x I (amp – turn)

Residual Flux

Residual Flux is the flux which remains in a sample of magnetic material after the magnetising force reduce to zero. It means that value of residual flux for a magnetic material is the same as the retentivity of the material.

Magnetic Circuit

It may be defined as the route or path which is followed by magnetic flux. The laws of magnetic circuit are quite similar to those of electric circuit.


If equal amount of m.m.f. is applied to different pieces of different magnetic materials, the amount of flux produced is found to be different. The material in which more flux is produced is known as good magnetic material. The ability of a material to conduct flux is known as permeability. More the permeability, more is the flux and hence, stronger is the magnet. Permeability is denoted by ‘ u ‘ and unit is Henry/meter (H/m). Value of is  different for different materials and is given by,

It gives the permeability of any magnetic material relative to air, e.g. if the permeability of a material is 500 times greater than that of air, then

Electromagnetic Induction

According to Faraday’s law, whenever the flux linked with a conductor or coil changes, an emf is induced in that coil and the amount of this induced emf is directly proportional to the rate of change of flux linked with the coil.

Magnetic Field

The space or region around the magnet which it extends its influence, i.e. it offers force of attraction or repulsion, is its magnetic field. At every point in the space surrounding the magnet, magnetic intensity acts in a particular direction. A continuous curve in a magnetic field, such that the tangent at any point of it gives the direction of magnetic intensity at that point, is known as ‘line of force’. The direction of each line is from N-pole to S-pole outside the magnet and S-pole to N-pole inside the magnet. These lines never intersect since the resultant force at any point can have only one direction as shown in figure.

Field Intensity Or Magnetic (H) Or Magnetic Field Strength

It is defined as m.m.f. per unit length or magnetic field strength.


The reciprocal of reluctance is known as permeance of magnetic circuit. It is similar to conductance in an electrical circuit.

Leakage Coefficient

It is defined as the ratio of total flux to the useful flux.

It is always greater than 1.


The term flux refers to the magnetic lines of force. The total no. of magnetic lines of force in a magnetic field is called flux. More the number of lines, more is the flux and hence greater magnetic field intensity. It is denoted by

Unit is weber. 1 weber = 108 lines of force.

The Next important topic from Magnetic Circuits of basic Electrical Engineering is :

Kirchhoff’s laws for Magnetic Circuits : flux Law (KFL) & magnetomotive force Law (KML)


  1. Introduction Of Magnetic Circuits In Electrical Engineering
  2. Explanation Of Terms Related To Magnetic Circuits In Electrical B.Tech.
  3. What is kirchhoff’s laws ? for magnetic circuit & How relate to electric circuit
  4. Compare Electric And Magnetic Circuit : Similarities & Dissimilarities
  5. Explain The Series Magnetic Circuit ? OR Composite Magnetic Circuits ?
  6. Kirchhoff’s laws for Magnetic Circuits : flux Law (KFL) & magnetomotive force Law (KML)
  7. what is Leakage Flux And Fringing in Magnetic Circuits
  8. B-H Curve Phenomena Of Magnetic Hysteresis With Effect And Loss

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