The area of the $B-H$ hysteresis loop is an indication of the

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:

The coercivity of a small magnet is $4 \times 10^3 \ A/m$. It is placed inside a solenoid of length $1 \ m$ having $500$ turns to demagnetize it. The current that must be passed through the solenoid is .......... $A$.

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

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.

The only property possessed by ferromagnetic substances is