What is hysteresis ?

Hysteresis:

1. Hysteresis occurs in a system that involves a magnetic field. Hysteresis is the common property of ferromagnetic substances. Generally, when the magnetization of ferromagnetic materials lags behind the magnetic field this effect can be described as the hysteresis effect.
2. The hysteresis loop shows the relationship between the magnetic flux density and the magnetizing field strength. The loop is generated by measuring the magnetic flux coming out from the ferromagnetic substance while changing the external magnetizing field.

Looking at the graph, if B is measured for various values of H and if the results are plotted in graphic forms then the graph will show a hysteresis loop.

1. The magnetic flux density (B) is increased when the magnetic field strength(H) is increased from 0 (zero).
2. With increasing the magnetic field there is an increase in the value of magnetism and finally reaches point A which is called saturation point where B is constant.
3. With a decrease in the value of the magnetic field, there is a decrease in the value of magnetism. But at B and H are equal to zero, substance or material retains some amount of magnetism is called retentivity or residual magnetism.
4. When there is a decrease in the magnetic field towards the negative side, magnetism also decreases. At point C the substance is completely demagnetized.
5. The force required to remove the retentivity of the material is known as Coercive force (C).
6. In the opposite direction, the cycle is continued where the saturation point is D, retentivity point is E and coercive force is F.
7. Due to the forward and opposite direction process, the cycle is complete and this cycle is called the hysteresis loop.