A bar magnet has a coercivity of 4 x 10³ Am^-1. It is placed inside a solenoid of length 12 cm having 60 turns in order to demagnetise it. The amount of current that should be passed through the solenoid is [EAMCET 2015]

The coerctivity of bar magnet = 4 X 10³ Am^-1,
Length of solenoid = 12 cm = 12 X 10^-2 m
and number of turns = 60

For a solenoid

   B = $\mu nI$
The coercivity of 12 cm length of solenoid

= 4 x 10³ x 12 X 10^-2 = 480 Am^-1

Now, current through each turn to demagnetise  $=\frac{480}{60}=8 \mathrm{A}$