What is hysterisis? Define the terms 'coercivity' and 'retentivity' of a ferromagnetic material.

Explanation

Hysteresis : The phenomenon of lagging behind the magnetic induction `(vec B)` with respect to the magnetizing field `(vec H)` is called hysteresis.
Retentivity : The property of the magnetic material to retain magnetism even in the absence of the magnetizing field is known as retentivity or remanence.
Coercivity : The magnetizing field (H) needed to demagnetize the magnetic material completely is known as corecivity.