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A bar magnet has a length much greater than its width and thickness. In a vibration magnetometer, its oscillation period is 2 s. The magnet is then divided lengthwise into three equal pieces, and the three pieces are stacked together so that like poles are in contact. What is the oscillation period of this arrangement?

1. 2√3 s
2. 2/3 s
3. 2 s
4. 2/√3 s

Correct answer: 2 s

Solution

The oscillation period of a magnet in a vibration magnetometer depends on its moment of inertia and the restoring torque, which are unchanged when the magnet is divided and reassembled with like poles together. Since the effective magnetic moment remains the same, the oscillation period remains at 2 s.

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