HYSTERESIS LOOP
The variation of flux density with magnetic field intensity
is not linear. A graph plotted between B and Has shown in the Figure 2.13. is
called B-H curve. From this graph, it is clear that the curve rises rapidly at
first indicating big change in the value of B for a corresponding small change
in H. The slope of this curve gradually decreases indicating a small change in
3 for increasingly larger values of H. A stage is reached when the slope of the
curve becomes constant and this condition is known as saturation..
If we take ferromagnetic material in completely demagnetized
state and make it to undergo through a cycle of magnetization in which H is
increased from zero to a maximum, then decreases to zero, then reversed and
again taken to-H max and finally brought back to zero. The variation of B with
respect to H can be represented by a closed hysteresis loop shown in the
figure.
A study of hysteresis loop of different magnetic
materials helps us to know their magnetic properties. For example, the area of
the hysteresis loop for soft iron is smaller than for steel. Hence energy lost per cycle is
correspondingly less. So soft iron is preferred steel for cores of dynamos,
transformers, etc. which are subjected to a large number of cycles so that the loss of energy may be
minimum
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