Question

A magnet has coercivity of $3\times {10}^3$ $A{m}^{-1}$. It is kept in a $10$cm long solenoid with a total of $50$ turns. How much current has to be passed through the solenoid to demagnetize it?

Answer 1

${\mu }_{\circ }H={\mu }_{\circ }nI$

Given:

where $H=3\times {10}^{-3}A{m}^{-1}=$coercivity

$n=$number of turns per unit length $=\frac{50}{0.1}=500m^{-1}$

To find: $I=$ current

Now

$H=nI$

$3\times {10}^{-3}A{m}^{-1}=500m^{-1}\times I$

$I=6\times {10}^{-6}A=6\mu A$