At a point P at distance r, a short bar magnet produces an axial magnetic field Bₐ. The point is then placed on the equatorial line at the same distance r, and simultaneously the magnetic moment of the magnet is doubled. The new magnetic field magnitude is:
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Question

At a point P at distance r, a short bar magnet produces an axial magnetic field Bₐ. The point is then placed on the equatorial line at the same distance r, and simultaneously the magnetic moment of the magnet is doubled. The new magnetic field magnitude is:

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G1 Physics · Accepted Answer

Initially, Bₐ = (μ₀/4π)·2M/r³. After doubling the magnetic moment, M′ = 2M. At the same distance on the equatorial line, B′ = (μ₀/4π)·M′/r³ = (μ₀/4π)·2M/r³. Thus, B′ = Bₐ.