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Bernard Cleyet wrote on Mon, June 6, 2011 2:22:13 PM:
Am I correct? The field from a solenoid is the same as that of a dipole and on
axis ~ 1/r^3. (1)
Using a field calculator (2) I found (far field) the on axis field of a
cylindrical magnet ~ 1/r^2. Is this correct, and if so, would a cylindrical
coil be a correct model?
(1) the last equation of Magnetic Fields due to a Solenoid
(2) K&J Magnetics - Magnetic Field Calculator
The far field from of a cylindrical magnet must be the same as that of a
solenoid or just of a current loop, B ~1/r^3. In none of these cases can it fall
off with distance as ~1/r^2. The latter would be characteristic of a
hypothetical isolated magnetic charge (monopole), but not of the known sources
of a time-independent magnetic field. I do not know what could have caused the
result that you report. It might come from a computational error or some
erroneous initial expression in the input.
Moses Fayngold,
NJIT
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