Question

A bar magnet has a coercivity of $4\times {10}^3{Am}^{-1}$. It is placed inside a solenoid of length $12cm$ having 60 turns in order to demagnetize it, the amount of current that should be passed through the solenoid is:

• A. $16A$
• B. $8A$
  
• C. $4A$
• D. $2A$

Answer 1

The correct option is B $8A$

Given: $H=4\times {10}^3{Am}^{-1}$

$L=12cm$

$N=60$

Bar magnet requires a magnetic intensity ($H=4\times {10}^3{Am}^{-1}$) to become demagnetized.

Let $n$ be the number of turns per unit length.

$\Rightarrow n=\frac{N}{L}=\frac{60}{0.12}=500turns/metre$

Now, $H=nI$

$\Rightarrow I=\frac{H}{n}=\frac{4\times {10}^3}{500}=8A$