Answer & explanation
Correct answer: option 4
$\text{Bar magnet should require a magnetic intensity of 4000A/m to demagnetize.}$
$ H = nI$
$n = \frac{N}{L} = \frac{60}{0.12} = 500 $
$\Rightarrow I = \frac{H}{L} = \frac{4000}{500} = 8A$
Correct answer: option 4
$\text{Bar magnet should require a magnetic intensity of 4000A/m to demagnetize.}$
$ H = nI$
$n = \frac{N}{L} = \frac{60}{0.12} = 500 $
$\Rightarrow I = \frac{H}{L} = \frac{4000}{500} = 8A$