A coil of ' n ' turns and radius ' R ' carries a current 'I'. It is unwound and rewound to make a new coil of radius R/3 and the same current is passed through it. The ratio of the magnetic moment of the new coil to that of the original coil is (a) 3 (b) 2 (c) 1/3 (d) 1/2

Answer: (c). Fixed wire length: n(2π R) = n'(2π R/3) ⇒ n' = 3n. M ∝ nR²: M'/M = (3n(R/3)²)/(nR²) = 1/3 So the answer is (c) 1/3.

A coil of ' n ' turns and radius ' R ' carries a current 'I'. It is… | MHT CET 2024 (10 May, Shift 2)

Q33MHT CET 2024 · 10 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 to make a new coil of radius $\frac{R}{3}$ and the same current is passed through it. The ratio of the magnetic moment of the new coil to that of the original coil is

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Answer: (c)

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

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Current Loop as a Magnetic Dipole question from MHT CET 2024 (10 May, Shift 2)

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