A metallic wire is folded to form a square loop a side 'a'. It carries a current 'i' and is kept perpendicular to a uniform magnetic field. If the shape of the loop is changed from square to a circle withoul changing the length of the wire and current, the amount of work done in doing so is

Explanation

W = Find P.E - initial P.E
`W=-M_(f)B-(-M_(i)B)`
`W=iB(A_(i)-A_(f)) W=iBa^(2)[1-4/pi]`