Define retentivity and coercivity. Draw the hysteresis curve for soft iron and steel. What do you infer from these curves ?

Explanation

(1) Retenvity : The value of magnetic induction `vec(B)` left in the specimen, when the magnetising force (H) is reduced to zero is called Retenvity or Remanence or Residual magnetism.
(2) Coercivity : To reduce the retentivity to zero, we have to apply a magnetising force in opposite direction. This value of magnetising force is called coerivity or coercive force.
(3) Hysterisis curve : The curve represents the relation between magnetic induction `vec(B)` (or) intensity of magnetization (I) of a ferromagnetic material with magnetizing force (or) magnetic intensity `(vec(H))` is called Hystersis curve.
(4) Hysterisis curve for soft Iron and steel is shown below.
The hysterisis loops of soft iron and steel reveal that
(i) The retentivity of soft iron is greater than the retentivity of steel.
(ii) Soft Iron is more strongly magnetised than steel.
(iii) Coercivity of Soft Iron is less than coercivity of steel. It means soft Iron loses its magnetisation more rapidly than steel does.
(iv) As area of I -H loop for soft Iron is smaller than tha area of I-H loop for steel. Therefore hysterisis loss in case of soft Iron is smaller than the hysterisis loss in case of steel.