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What is hysteresis loop and what is its purpose?
asked Nov 13, 2015 in Electro-Communication by T.PRATHIBA | 228 views

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Actually hysterisis is a greek derived word which means late or lag behind.

The loop is generated by measuring the magnetic flux of a ferromagnetic material while the magnetizing force is changed. 

the greater the amount of current applied (H+), the stronger the magnetic field in the component (B+)

A ferromagnetic material that has never been previously magnetized or has been thoroughly demagnetized will follow the dashed line as H is increased.

At point "a" almost all of the magnetic domains are aligned and an additional increase in the magnetizing force will produce very little increase in magnetic flux.

The material has reached the point of magnetic saturation.

When H is reduced to zero, the curve will move from point "a" to point "b." At this point, it can be seen that some magnetic flux remains in the material even though the magnetizing force is zero.

This is referred to as the point of retentivity on the graph and indicates the remanence or level of residual magnetism in the material.

Some of the magnetic domains remain aligned but some have lost their alignment.

 As the magnetizing force is reversed, the curve moves to point "c", where the flux has been reduced to zero. This is called the point of coercivity on the curve.

The force required to remove the residual magnetism from the material is called the coercive force or coercivity of the material.

As the magnetizing force is increased in the negative direction, the material will again become magnetically saturated but in the opposite direction (point "d"). Reducing H to zero brings the curve to point "e." It will have a level of residual magnetism equal to that achieved in the other direction.

Increasing H back in the positive direction will return B to zero. Notice that the curve did not return to the origin of the graph because some force is required to remove the residual magnetism.

The curve will take a different path from point "f" back to the saturation point where it with complete the loop.

Main purpose of hysterisis loop is to study the magnetic property of materials.

Hysterisis loops are also called as BH curve ,concept is simple - as we increase magnetic force ,the flux is also increase !

Ferromagnetic : ferro- "iron" + magnetic.

Reference :
https://www.nde-ed.org/EducationResources/CommunityCollege/MagParticle/Physics/HysteresisLoop.htm

answered Nov 13, 2015 by kevin
edited Nov 13, 2015 by kevin