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

Magnetic hysteresis is exhibited by magnetic materials which are

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.

$A$ bar magnet has a coercivity of $4 \times 10^3 \text{ A m}^{-1}$. It is placed inside a solenoid of $12 \text{ cm}$ length and $60$ turns. The current that should be passed through the solenoid to demagnetize the bar magnet is: (in $\text{ A}$)

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