Magnetic hysteresis is exhibited by magnetic materials which are

The $B-H$ curve for a ferromagnet is shown in the figure. The ferromagnet is placed inside a long solenoid with $1000 \text{ turns/cm}$. The current that should be passed in the solenoid to demagnetize the ferromagnet completely is

The area of the hysteresis loop of a material is equivalent to $250 \, J$. When $10 \, kg$ of the material is magnetized by an alternating field of $50 \, Hz$, what is the energy lost in one hour? (Given: density of the material is $7.5 \, g/cm^3$)

The area of the hysteresis loop of a substance indicates:

Hysteresis loops for two magnetic materials $A$ and $B$ are given below. These materials are used to make magnets for electric generators,transformer cores,and electromagnet cores. Then it is proper to use:

Answer the following questions:
$(a)$ Explain qualitatively on the basis of the domain picture the irreversibility in the magnetisation curve of a ferromagnet.
$(b)$ The hysteresis loop of a soft iron piece has a much smaller area than that of a carbon steel piece. If the material is to go through repeated cycles of magnetisation,which piece will dissipate greater heat energy?
$(c)$ '$A$ system displaying a hysteresis loop such as a ferromagnet,is a device for storing memory?' Explain the meaning of this statement.
$(d)$ What kind of ferromagnetic material is used for coating magnetic tapes in a cassette player,or for building 'memory stores' in a modern computer?
$(e)$ $A$ certain region of space is to be shielded from magnetic fields. Suggest a method.