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 (a) 3: 1 (b) 1: 3 (c) 9: 1 (d) 1: 9

Answer: (b). Fixed wire length: radius R/3 gives 3n turns. M ∝ nR²: M'/M = (3n(R/3)²)/(nR²) = 1/3 So the answer is (b) 1: 3.

A coil of ' n ' turns and radius ' R ' carries a current ' I '. It is… | MHT CET 2023 (12 May, Shift 2)

Q44MHT CET 2023 · 12 MAY · SHIFT 2Medium

Current Loop as a Magnetic Dipole

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

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Answer: (b)

Fixed wire length: radius $R/3$ gives $3n$ turns.
$M \propto nR^2$ : $\frac{M'}{M} = \frac{3n(R/3)^2}{nR^2} = \frac{1}{3}$
So the answer is (b) $1 : 3$ .

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Current Loop as a Magnetic Dipole question from MHT CET 2023 (12 May, Shift 2)

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