For substances,hysteresis $(B-H)$ curves are given as shown in the figures. Which of the following is best for making a temporary magnet?

Which of the following is represented by the area enclosed by a hysteresis loop?

In the hysteresis cycle,the value of $H$ needed to make the intensity of magnetisation zero is called

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:

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

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 .......... $A$.