(1) When it come to change the strenght of magnetic field h,it would make intesity of magnetization of ferromagnetic material i and it to be controlled by just before magnetized condition and is changed irreverdibly.it's also called magnetism history or magnetic hysteresis and it's relation can be described as hysteresis curve
(2) Hysteresis is the maximum difference in output generated in the same test when a load increases from zero to the rated load and then decreases to the origin. It is expressed as a percentage of the rated output.
Glossary