The coercive force for a certain permanent magnet is `4.0 xx 10^4 A m^(-1)`. This magnet is placed inside a long solenoid of 40 turns/cm and a current is passed in the solenoid to demagnetize it completely. Find the current.

Explanation

`B=(mu_0)n//l`
` implies(n/l)=(B)/(mu_0) [ Given n=40 turns //cm]`
`=4000turns//m`
`Given H=4xx 10 A//m`
` impliesH=(n)/(l)i`
` implies i-(Hl)/n`
`=(4xx10^(4))/4000=10A.`