In the following graph of flux density $(B)$ versus magnetizing force $(H)$,coercivity and retentivity are respectively represented by the points

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

$A$ ferromagnetic material of volume $10^{-3} \, m^3$ is subjected to a magnetic field with a frequency of $50 \, Hz$. The area of the hysteresis loop is $0.1 \, M.K.S. \, \text{units}$. Calculate the energy dissipated in $1 \, \text{sec}$.

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 figure illustrates how $B$,the magnetic flux density inside a sample of unmagnetised ferromagnetic material,varies with $B_0$,the external magnetic flux density in which the sample is kept. For the sample to be suitable for making a permanent magnet:

If the given figure shows the relation between magnetic field ($B$ - along $y$-axis) and magnetic intensity ($H$ - along $x$-axis) of a ferromagnetic material,then the point that represents the coercivity of the material is