A steel wire of length 1 has a magnetic moment M. It is bent into a semicircular arc, what is the new magnetic moment?

Explanation

Pole strength,` m = (M)/(l)` where, M is magnetic moment and l is length of solenoid. When wire is turned into semi-circular arc then
`2 pi r = 2l implies r = (l)/(pi)`
New magnetic moment,
`M = m xx 2 r = ( m)/( l ) xx 2 xx( l)/( pi) = ( 2m )/( pi)`