The magnetic moments associated with two closely wound circular coils A and B of radius r_A = 10 cm  and r_B  = 20 cm respectively are equal if :(Where ${\mathrm{N}}_{\mathrm{A}},{\mathrm{I}}_{\mathrm{A}}$ and ${\mathrm{N}}_{\mathrm{B}},{\mathrm{I}}_{\mathrm{B}}$ are number of turn and current of A and  B  respectively)