Sometimes it is also referred to as the magnetic susceptibility of a material

# Sometimes it is also referred to as the magnetic

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Sometimes it is also referred to as the magnetic susceptibility of a material. It is determined by the ratio of magnetic flux density to magnetizing force producing this magnetic flux density. It is denoted by μ. Hence, μ=B/H where, B is the magnetic flux density in material in Wb/m 2 H is the magnetizing force of magnetic flux intensity in Wb/ Henry-meter SI unit of magnetic permeability is Henry / meter Permeability of material is also defined as, μ = μ 0 μ r Where, μ 0 is the permeability of air or vacuum, and μ 0 = 4π X 10 -7 Henry / meter, and μ r is the relative permeability of the material. μ r = 1 for air or vacuum. A material selected for magnetic core in electrical machines should have high permeability, so that required magnetic flux can be produced in core by less ampere- turns. Retentivity When a magnetic material is placed in an external magnetic field, its grains get oriented in the direction of magnetic field. This results in magnetization of material in the direction of external magnetic field. Now, even after removal of external magnetic field, some magnetization exists, which is called residual magnetism. This property of a material is called magnetic retentively of the material. A hysteresis loop or B-H cure of a typical magnetic material is shown in figure below. Magnetization B r in hysteresis loop represents the residual magnetism of material.
~ Page 34 of 79 ~ Coercive Force Due to retentivity of material, even after removal of external magnetic field some magnetization exists in material. This magnetism is called residual magnetism of material. To remove this residual magnetization, we have to apply some external magnetic field in the opposite direction. This external magnetic motive force (ATs) required to overcome the residual magnetism is called “coercive force” of a material. In above hysteresis loop, - H c represents the coercive force. Materials having large value of residual magnetization and coercive force are called magnetically hard materials. On the other hand materials having very low vale of residual magnetization and coercive force are called magnetically soft materials. Magnetic reluctance From Wikipedia, the free encyclopedia Magnetic reluctance , or magnetic resistance , is a concept used in the analysis of magnetic circuits . It is analogous to resistance in an electrical circuit , but rather than dissipating electric energy it stores magnetic energy. In likeness to the way an electric field causes an electric current to follow the path of least resistance , a magnetic field causes magnetic flux to follow the path of least magnetic reluctance. It is a scalar , extensive quantity , akin to electrical resistance. The unit for magnetic reluctance is inverse henry , H −1 . Reluctance is usually represented by a cursive capital .

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