Electrical Engineering ⇒ Topic : Magnetic Hysteresis

Magnetic Hysteresis

When a magnetic material is subjected to a cycle of magnetisation (i.e. it is magnetised first in one direction and then in the other), it is found that flux density B in the material lags behind the applied magnetising force H. This phenomenon is known as hysteresis.The phenomenon of lagging of flux density (B) behind the magnetising force (H) in a magnetic material subjected to cycles of magnetisation is known as magnetic hysteresis.

The term 'hysteresis' is derived from the Greek word hysterein meaning to lag behind. If a piece of magnetic material is subjected to *one cycle of magnetisation, the resultant B-H curve is a closed loop abcdefa called hysteresis loop [See Fig. a (ii)]. Note that B always lags behind H.

Thus at point 'b', H is zero but flux density B has a positive finite value ob. Similarly at point 'e', H is zero, but flux density has a finite negative value oe. This tendency of flux density B to lag behind magnetising force His known as magnetic hysteresis.

                                                                              figure (a)