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…

Q:  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 without changing the length of the wire and current, the amount of work done in doing so is

Sol: W = find P.E – initial P.E

$\large U_f = – M_f B = – i A_f B $

$\large U_i = – M_i B = – i A_i B $