|MadSci Network: Physics|
If I have a permanent bar magnet, and I place a static charge in the middle, (Imagine a box -the magnet- and a point charge q embedded inside). Then the magnet will produce a static dipole magnetic field, and the static charge will produce a static electric field. If you calculate the direction of the Poynting vector S (ExB), it will seem to be circumferential, ie. it looks like it is circulating around the bar magnet. Now EM fields have a momentum associated with them, in the direction of this Poynting vector S. If you attach a solar sail that is attached to the bar magnet frictionlessly, placed so that it can rotate about the magnet in the same direction as S. Won't the sail be pushed? I understand that it takes work to place the charge inside the magnet, etc. But this is a finite amount of work, and since Magnetic field and Electric field are static, nothing is changing so none of the energy that is stored in their fields, (~Integral[E^2 +B^2]all space) is lost. So where does the energy come from? And does it seem to be infinite?
Re: Does the following situation violate conservation of energy?
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