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dual electromagnets

jarvis2.0

Apr 29, 2015
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Hi. I'm new and I don't really have much experience with forums. I do however have a question about electromagnetism. I have two coils of wire of similar length with the same number of coils, one is small and one large, and I place the small one inside the large one so that they are not touching. Then I connect current that is one way for the small and the opposite way for the large, what would happen? Would they mutually cancel each other out? Please help me out.
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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Jan 21, 2010
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Assuming the same current flows in each, the answer is a qualified yes.

To cancel out completely the coils would have to be almost coincident. Having one inside the other would result in incomplete cancellation because the pattern of the magnetic field generated by each on its own would be different.
 

BGB

Nov 30, 2014
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Hi. I'm new and I don't really have much experience with forums. I do however have a question about electromagnetism. I have two coils of wire of similar length with the same number of coils, one is small and one large, and I place the small one inside the large one so that they are not touching. Then I connect current that is one way for the small and the opposite way for the large, what would happen? Would they mutually cancel each other out? Please help me out.

I think, it depends:
for the external net field, probably. the fields should mostly cancel out if they are opposite and fixed in place.

if the coils can move freely, and the field strength is high enough, one may see some movement.


the presence of a steel or iron core on the inner coil significantly increases the amount of movement observed. likewise, the inner coil need not be physically inside the outer coil, but may be wrapped around the core.

an example would be wrapping a coil around one end of a nail (fixed in place), with another coil free-sliding (such as around a piece of drinking straw), running current through the coils may cause the free-moving coil to move along the nail (pulling them together if they are in the same direction, or otherwise pushing them apart).

though, at the time, wasn't particularly impressed as the movement was fairly modest for the amount of wire and current used.


also observed in a few later tests with coils, if you make an incomplete circle of steel, then the free ends of the steel near the free ends is much more magnetic (than with a single straight core), however, if the loop is closed (a piece of steel touches both ends), then the external strength mostly drops off (very little else will stick to it), whereas with a single rod, you can get a big pile of random bits of steel with little reduction in strength.

however, for a pair of coils, a closed loop may somewhat increase the interaction of the coils (say, there is a second parallel nail, and some bits of steel on the ends of the nails).

also observed that some steel reacts strongly to the coils (becomes strongly magnetic), and other steel reacts hardly at all (soft white steel seems to work best here, whereas hard black or yellow tinted steel are not particularly magnetic).
 
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