The coercivity of a small magnet where the ferromagnet gets demagnetized is 3 x $10^{3} {Am}^{- 1}$ . The current required to be passed in a solenoid of length 10 cm and number of turns 100, so that the magnet gets demagnetized when placed inside the solenoid is

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30 mA

3 A

60 mA

3 MA

answer is A.

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Detailed Solution

H is the demagnetizing field that comes from a solenoid

For solenoid $B = \frac{μ_{0} N i}{l}$ then $H = \frac{N i}{l}$

given $H = 3 \times 10^{3} A / m$ = $\frac{N i}{l}$ ,

$i = \frac{0.1 \times 3 \times 10^{3}}{100} = 3 A$

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