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