A short bar magnet produces magnetic field B at a point P on its axial line at distance r from its centre. The magnet is rotated through 90° about its centre while P remains fixed. The new field magnitude at P is:
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Question

A short bar magnet produces magnetic field B at a point P on its axial line at distance r from its centre. The magnet is rotated through 90° about its centre while P remains fixed. The new field magnitude at P is:

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G1 Physics · Accepted Answer

Initially P is on the axial line: B = (μ₀/4π)·2M/r³. After rotating the magnet through 90°, P lies on its equatorial line: B' = (μ₀/4π)·M/r³. Therefore, B'/B = 1/2, so B' = B/2.