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An insulating thin rod of length l has a linear charge density ρ (x) = ρ 0 l x on it. The rod is rotated about an axis passing through the origin (x = 0) and perpendicular to the rod. If the rod makes n rotations per second, then the time averaged magnetic moment of the rod is -

1. 3 π n ρ l 3
2. 4 π n ρ l 3
3. n ρ l 3
4. π n ρ l 3

Correct answer: 4 π n ρ l 3

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