Question

The coercivity of a magnet is $3\times {10}^{4}A{m}^{-1}$. 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. $60A$
• C. $9A$
• D. $12A$

Answer 1

The correct option is B $60A$

Here $H=3\ast {10}^4$

$l=10cm=0.1m$

n=no. of turns per unit length

$=\frac{50}{0.1}=500turns/metre$

Therefore, the current through the solenoid is,

$I=\frac{H}{n}=\frac{3\ast {10}^4}{500}=60A$