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Hysteresis Loop

Published on 24/2/2012 & updated on 27/7/2018
Hysteresis loop is a four quadrant B-H graph from where the hysteresis loss, coercive force and retentively of s magnetic material are obtained.
To understand hysteresis loop, we suppose to take a magnetic material to use as a core around which insulated wire is wound. The coils is connected to the supply (DC) through variable resistor to vary the current I. We know that current I is directly proportional to the value of magnetizing force (H) as  Where, N = no. of turn of coil and l is the effective length of the coil. The magnetic flux density of this core is B which is directly proportional to magnetizing force H. electro magnet Now, we should be familiar with some important terms related to hysteresis Loop.

Definition of Hysteresis

Hysteresis of a magnetic material is a property by virtue of which the flux density (B) of this material lags behind the magnetizing force (H).

Definition of Coercive Force

Coercive force is defined as the negative value of magnetizing force (-H) that reduces residual flux density of a material to zero.

Residual Flux Density

Residual flux density is the certain value of magnetic flux per unit area that remains in the magnetic material without presence of magnetizing force (i.e. H = 0).

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Hysteresis Loop

Definition of Retentivity

It is defined as the degree to which a magnetic material gains its magnetism after magnetizing force (H) is reduced to zero. Now, let us proceed step by step to make a clear idea about hysteresis loop. hysteresis loop

The path a – b – c – d – e – f – a forms hysteresis loop. [NB: The shape and the size of the hysteresis loop depend on the nature of the material chosen]

Importance of Hysteresis Loop

The main advantages of hysteresis loop are given below.
  1. Smaller hysteresis loop area symbolizes less hysteresis loss.
  2. Hysteresis loop provides the value of retentivity and coercivity of a material. Thus the way to choose perfect material to make permanent magnet, core of machines becomes easier.
  3. From B-H graph, residual magnetism can be determined and thus choosing of material for electromagnets is easy.

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