Question

A bar magnet has coercivity $4\times {10}^{3}A{m}^{-1}$. It is desired to demagnetize it by inserting it inside a solenoid $12cm$ long and has $60turns$. The current that should be sent through the solenoid is:

• A. $8A$
• B. $10A$
• C. $12A$
• D. $14A$

Answer 1

The correct option is A $8A$

The coercivity of bar magnet is $4\times {10}^{3}A{m}^{-1}$ i.e., it required a magnetic intensity $H=4\times {10}^{3}A{m}^{-1}$ to get demagentised.
Let i be the current carried by solenoid having n number of turns per metre length, then
$H=ni$
Here $H=4\times {10}^{3}A{m}^{-1}$
and $n=\frac{N}{l}=\frac{60}{0.12}=500turn/m$
$\therefore i=\frac{H}{n}=\frac{4\times {10}^3}{500}=8.0A$