The B-H curve for a ferromagnet is shown in the figure. The ferromagnet is placed inside a long solenoid…
The B-H curve for a ferromagnet is shown in the figure. The ferromagnet is placed inside a long solenoid with 1000 turns/cm.. The current that should be passed in the solenoid to demagnetize the ferromagnet completely is:
$2 \mathrm{~mA}$
$1 \mathrm{~mA}$
$40 \mu \mathrm{A}$
$20 \mu \mathrm{A}$
Solution
Given Number of turns, $\mathrm{n}=1000$ turns $/ \mathrm{cm}=1000 \times 100$ turns $/ \mathrm{m}$ Coercivity of ferromagnet, $\mathrm{H}=100 \mathrm{~A} / \mathrm{m}$ Current to demagnetise the ferromagnet, $\mathrm{I}=?$
Using, $\mathrm{H}=\mathrm{nI}$
or, $\quad 100=10^5 \times \mathrm{I}$
$\therefore \quad \mathrm{I}=\frac{100}{10^5}=1 \mathrm{~mA}$
