Hysteresis Curve - Practice Questions & MCQ

Hysteresis-

It is the property of the Lagging of magnetic induction (B) behind magnetic intensity (H) in the case of the ferromagnetic substances.

Hysteresis Curve- This is nothing but the graph of (B Vs H )or (I Vs H) as shown below.

When a non-magnetized material is placed in the long solenoid which is carrying current i as shown in the below figure.

Initially     I.e at Point O.

Now if we increase i, it will result in an increase in B and H and I, till saturation point (a) I.e path 1 or Path Oa

Now we decrease H and reduce it to zero by decreasing i  I.e path 2 or Path ab.

So at point b, H=0 but  where B_r is called retentivity or remanence or residual magnetism.

This is happening because, For ferromagnetic materials, by removing the external magnetic field, i.e. H = 0, the magnetic moment of some domains remains aligned in the applied direction of the previous magnetising field, resulting in a residual magnetism.

Now we have to remove this residual magnetism of the material or demagnetize the material completely. For this, we will reverse the direction of the current in the solenoid.

So, the process of demagnetizing a material completely (i.e path bc)  by applying the magnetizing field in a negative direction is defined as Coercivity.

So At point c we have B = 0 and H = H_c   where H_c  is called coercivity.

Coercivity signifies  magnetic hardness or softness of substance:
 I.,e  Magnetic hard substance (steel) ——> High coercivity
        Magnetic soft substance (soft iron) ——> Low coercivity.

If, after the magnetization has been reduced to zero, the value of H is further increased in the 'negative' i.e. reversed direction, the material again reaches a state of magnetic saturation, represented by point d.

Next, the current is reduced (curve de) and reversed (curve ea) then The cycle repeats itself till point a.