More Magnetic Field Questions
Does the strength of a 'permanent' magnetic field decrease with the
square of the distance or just as the distance increases? thanks atp
Actually, I think for a permanent dipole magnet the field
decreases as the fourth power of distance (I could be wrong though).
This is different from electric and gravitational fields in the
sense that there is no such thing as an isolated magnetic charge -
the field from an isolated electric charge does decrease as the
square of distance, and similarly for the gravitational field from
a mass. But you cannot have an isolated north pole of a magnet - it
must always be tied to a south pole nearby, producing a dipole
field pattern that (at longer distances) decays faster than the
simple inverse square law because the two nearby poles almost cancel out.
Actually, that should be inverse third power, not fourth, for
the decay of a magnetic dipole field at long distances.
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Update: June 2012