What is hysteresis? Draw a hysteresis loop for ferromagnetic material and explain various important parameters. A magnetic material has a magnetization of 2300 A/m and produces a flux density of $0.00314 wb/m^2$. Calculate magnetizing force and relative permeability of the material.

Mumbai University > First Year Engineering > Sem 1 > Applied Physics 1

Marks: 8M

Year: May 2016

Hysteresis:

• Hysteresis is the dependence of the output of a system not only on it current input, but also on its history of past inputs.
• The dependency arises because the history affects the value of an internal state.
• To predict its future output, either its internal state or its history must be known.

Hysteresis loop:

• The figure shows the behavior of a ferromagnetic core subjected to cyclically varying magnetic field.
• Initially, the core is demagnetized and the strength of magnetic field “H” is set to zero. Thus point “O” marks the starting point of the curve.
• On increasing magnetic strength the magnetic induction increases non-linearly, as shown, up to point P, after which it remains constant.
• Thus, point P is known as the saturation point.
• On reducing “H” to zero, the core still remains magnetized. The residual value of “B” at point “Q” is called remnant induction.
• On further reduction of “H”, at point R, the core gets completely demagnetized.
• The value of magnetic strength at that point is called coercive field.
• As the magnetic field increases in the negative direction, again the magnetic induction appears to remain constant after a certain point S.
• This is the saturation point in the negative direction.
• Similarly, points T and U correspond to Q and R respectively as the value of H is increased reaching point P again.
• The full cycle of magnetization and demagnetization of core is termed as Hysteresis loop