MadSci Network: Physics |
The moderator has suggested that it may involve the symmetry of the nail, and I would tend to agree that it may be part of the answer. Since the amount of strength would be dependent on the lines of flux divided by area, the larger area of the head of the nail should have the lesser strength. And this could be confirmed by cutting the tips off the ends and see if the intensities balance out. Of course, if it turns out that the pointed end was not the stronger end, I have (as usual) a back-up theory… Rubbing the nail is not the best way to produce a uniform field. In fact, if the entire length was not rubbed, then the magnetic field of the remainder might fall off significantly. Of course, if only one end (pole) of the original magnet was used to magnetize the nail, then the side rubbed would be of one magnetic orientation, with the unrubbed taking on the other. In fact, if only one side of the shank of the nail was rubbed, end to end, then the tips might have little polarity at all. The important thing to remember is that the intensity of the field are depended on the closeness, and orientation, of source of the magnetizing forces, whether a coil or a permanent magnet, and the cross-sectional area and geometry of the area of interest. BTW, the use of a compass to measure the strength was a creative way to do it. Another way is by seeing how many small ferromagnetic parts, such as paperclips, can be lifted by the magnet, preferably end to end. This is particularly applicable when determining the effect of the number coil- turns versus current versus voltage (determined by the number of batteries used in parallel or in series, respectively) on the magnetic field generated on a ferromagnetic rod.
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