Question

The coercivity of a magnet is $3\times {10}^3{\text{Am}}^{-1}$. What current should be passed through a solenoid, of length $10\text{cm}$ and number of turns $50$, so that the magnet is completely demagnetized, when inserted in it ?

• A. $3\text{A}$
• B. $6\text{A}$
• C. $9\text{A}$
• D. $12\text{A}$

Answer 1

The correct option is B $6\text{A}$

Coercivity of magnet, $H_c=3\times {10}^3{\text{Am}}^{-1}$

Number of turn per unit length,
$n=\frac{N}{L}=\frac{50}{0.1}=500$

We know that,

$H=\frac{B}{{\mu }_0}$

As, $B={\mu }_{o}nI$

$\Rightarrow H=nI\left(\text{for Solenoid}\right)$

$3\times {10}^3=500\times I$

$\therefore I=6\text{A}$