A thin circular wire carrying a current I has a magnetic moment M. The shape of the wire is changed to a square and it carries the same current. It will have a magnetic moment

Iπr2=M                       2πr=lM=Iπl24π2=Il24π                         r=12πWhen it is made a square l = 4a.M1=Ia2=Il216                       a=14MM1 =Il2/4πIl2/16=164π=4πM1=πM4