# Cancelling bar magnet magnetic fields?

• posted

A wire carrying DC has static field.. similar to the one in bar magnets. How come when you put two parallel wires together in the DC circuit. The magnetic field cancels while in a bar magnet, it doesn't. If you do proper positioning of 2 bar magnets, do you think you can cancel the magnetic field from bar magnets? why and why not? If not, why can the magnetic field in DC carrying wire be canceled while in magnets it can't. Lory

• posted

--------------------------- The bar magnet has a field that varies due to the positions of all its iron atoms acting as tiny magnets. Its field can only be canceled locally to specific points where it is numerically zero. Since this field varies according to where along the magnet you are and where in space, it is not generally cancelable. The field around a wire is much more symmetrical and you can get them quite close together. Also an individual wire's field will be much smaller in intensity.

-Steve

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• posted

Both the bar magnet and the field around a wire COULD be cancelled i they were infinitely thin (an impossibility). Neither can b perfectly cancelled in real life because they are of finite size. Perfect cancellation could only be achieved by exact superposition o all elements of the wire or magnet with an element of the opposit polarity/current direction at the same point in space. Since you ca never achieve such exact superposition due to the physical size of th wire/magnet, you can never achieve perfect cancellation - onl approximate cancellation, for example, by placing two small wire very close together. Twisting two wires helps by averaging th imperfectly cancelled fields from the two wires, but this is als just an improved, imperfect cancellation

After all, the absence of a magnetic field around a non-magnetize

piece of iron is due to the micro-scale mutual cancellation of al the randomly oriented tiny magnetic domains of the iron. They cance "perfectly" on a macro scale because the domains are so small and w are normally sensing the average field of all those randomly oriente domains. But if you could probe with a micro probe, you would be abl to sense the magnetic field around each minute magnetic domain and yo would see that, at that scale, the cancellation is not perfect due t the non-infinitesimal size of the domains

Does this help, or just add to the confusion

awrigh

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