Can anyone suggest the best way to shape a single wire carring a current so that it's magnetic field cancels itself out? Completely if possible. I'm trying to optimize the idea for light weight and varying current values. All I can think of would be to bunch the wire into a tight zig-zag plane. (From:---------- To:||||||||) Would that work? Or would it produce the same field...and just be heavy? Any help would be great, thanks.
The cancellation will be nearly complete if half of the wire runs back along the same path as the other half. Twist the halves together and it will be better yet. Put a hole down the middle of one half, enlarge it, and run the other half back thru the hole, (coaxially), and the cancellation is as perfect as the coaxiality.
If the single wire has to carry current from one point to another in a different place, then you are chasing a rainbow. There will be a magnetic field created by that current, no matter what path it takes between the two separated points.
It would produce very nearly the same field, and just dissipate more heat to carry the same current.
You could get better help by stating more of your real problem and constraints.
-- --Larry Brasfield email: donotspam_larry_brasfield@hotmail.com Above views may belong only to me.
You're right, I meant to mention that it had to be between two points. Chasing a rainbow then. Are you sure? What if I wrapped it in a coil for half the distance, then wrapped it in the opposite direction for the other half? Like magnet/solinoid wraps. I just thought of it, but that would change the direction of the field and cancel out right? Or would that be the same as the zigzag? (This is for a math model that I gave up on a while ago when I realized that I would have to create and destroy electrons to have a single current between 2 points in a closed system. Now this is another idea how to make it realistic...unless it's impossible. Just trying to think and get knowledgable feedback. )
Well, I am sure that *if* you have a current not following its own return path back coaxially, *then* there will be a magetic field produced by that current.
Almost, but not quite. And the not quite is equivalent to what you get if the current does no spiraling around and just travels in a straight path along the axis of what was the spiral.
The same in the sense of no net improvement. Your zigzag is probably easiest to think about. Consider that each zig or zag can be broken into two vector components. One is in line with the net direction of the zig-zag, the other is transverse to it. The transverse components of the zigs cancel the transverse components of the zags, but the in line components all add in the same direction, as much as would the effect from a plain straight current flow.
Now you're on to the practical issue here. In the world we inhabit, there is no such thing as a current not flowing in a loop in appreciable amounts. You can imagine single or small numbers of charges being made to movie that way, but either they have to get back to their source, (an ever mounting positive or negative) region, or you have to have an unreal device to keep moving them indefinitely.
-- --Larry Brasfield email: donotspam_larry_brasfield@hotmail.com Above views may belong only to me.
Alright, if you're still following this, maybe you can think of a way to make this work: Just think of an x-y plane where the magnetic field is in the z direction. There are two battteries, DC generators, whatever at two points. Say (0,0) and (10,0). If two wires are connected between the two sources, there would be a current in both wires. Both would generate a magnetic field and cancel out. Can you think of a way to shape one of the wires so that it would not effect the forces on the whole system? So that it would not produce a net force in any direction and only the one wire (along the x-axis) would be in the math model? (eg. I think a tall triangle would make the effects in the y direction negligable, but then it would produce a large effect in the +- x direction...) Any ideas? Impossible?
They would cancel out, if the current flows were coaxial, at points outside the outer conductor. If the currents are not coaxial, there will be a net magnetic field at most points. There could be some cancellation, along some surfaces or lines, depending on the flow geometry.
Your question is too vague for me to understand. Only moving charges are subject to a force due to a DC magnetic field. And the closed system does not exert net forces upon itself, (at least not in the DC case. If it emits photons, it could.)
Sorry, I don't know at this point.
-- --Larry Brasfield email: donotspam_larry_brasfield@hotmail.com Above views may belong only to me.
The only way to cancel the magnetic field of a current is to have that current return by the same path. The best you can do is to use a coaxial wire, with the current going out in one conductor and coming back through the other. A twisted pair is pretty good. A twisted quad (two wires at the corners of the cross section carrying one way, the wires at the other two corners of the cross section carrying the other way), is better, etc.
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