(c) Length of steel wire =l Magnetic moment, M=ml.......(i) Where, m is pole strength when steel wire is bent into semicircular wire, then l‌=πR ⇒‌‌R‌=‌
l
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∴‌ length of wire ‌=‌ diameter ‌ ⇒l′=2R=‌
2l
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⇒l′=‌
2l
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New magnetic dipole moment, M′‌=ml′ ‌=m‌