Question

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

• A. $3A$
• B. $6A$
• C. $9A$
• D. $12A$

Answer 1

The correct option is B $6A$

Length of solenoid $L=10cm=0.1m$
Number of turns $N=50$
So, number of turns per unit length $n=\frac{N}{L}=\frac{50}{0.1}=500$
Current to be passed $i=\frac{H}{n}$
$⟹i=\frac{3\times {10}^3}{500}=6A$