A coil of ' n ' turns and radius ' R ' carries a current ' I '. It is unwound and rewound again to make another coil of radius ( R 3 ) , current remaining the same. The ratio of magnetic moment of the new coil to that of original coil is

Step-by-step solution

As the length of the wire remains the same, we can write aligned & N ₁ 2 R = N ₂ 2 R 3 & ~N ₁= N ₂ 3 & ~N ₂=3 ~N ₁ aligned array ll & Magnetic moment of coil = NIA & ₁=N₁ I A₁=N₁ I R^2 & ₂=N₂ I A₂=3 N₁ I R^2 9 & ₂ ₁ =3 N₁ I R^2 9 1 N₁ I R^2 = 1 3 array