**Hysteresis Curve:**

**NCERT Class 12th Physics || Chapter-5 || Magnetism and Matter:**

The hysteresis Curve represent the relation between the magnetic induction B or intensity of magnetisation I of a ferromagnetic material with magnetic intensity H. The graph shows the behaviour of the material as we take it through one cycle of magnetisation.

**Formation of hysteresis Curve:**

**1. **We take an unmagnetised ferromagnetic material and keep it in a solenoid and increase the current through a solenoid that means magnetic intensity H.

As H increases, magnetisation I also increases until saturation is achieved.

That means all atomic dipoles are aligned with applied H (point a). On further increasing current there is no change in I as saturation is achieved.

So initially when current is 0, H=0 and I=0 at point O.

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**2. **Now if we decrease current that is H decreases, I also decreases, But it is observed that even when current is reduced to zero but there is still some magnetisation left.

**Retentivity:- **Tendency to retain property of magnetisation even when external field is removed.

**3. **Now to make I=0 that is to bring dipole to original configuration, Opposite current is applied (H= -Ve). On increasing H in negative direction (at point c) I become 0.

This is called** Coercitity.**

**Coercivity:- **The amount of -Ve H required to make I=0.

**4. **Now if reversed current is increased (H increased in -Ve), Dipole starts alligning in opposite direction to original. Now dipole allign with -Ve H untill all dipoles are aligned and saturation is achieved, in opposite direction (at point d).

**5. **Again current is decreased to 0 (H=0) still I is not equal to zero (at point e).

**6. **Now if again we reversed to current in opposite direction(+Ve), (at point f), I=0.

**7. **On further increasing current, at same point a, I get saturated.

This whole curve is called **Hysteresis Curve**.