The coercivity of a magnet is $5 \times 10^3 \text{ A/m}$. The amount of current required to be passed in a solenoid of length $30 \text{ cm}$ and the number of turns $150$,so that the magnet gets demagnetized when placed inside 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

Magnetic materials used for making permanent magnets $(P)$ and magnets in a transformer $(T)$ have different properties. Of the following,which property best matches the type of magnet required?

Magnetic hysteresis is exhibited by . . . . . . magnetic materials.

The $B-H$ curves $S_1$ and $S_2$ in the adjoining figure are associated with:

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.