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Physics/circular magnetic fields

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Question
A long straight vertical wire carrying a DC current will have circular magnetic field of line around described by the right hand rule. I would like to know where the North and South poles are? Thanks

Answer
There really are no such things as "north and south poles" in a magnetic field.  They always connect back.  If you look at the field inside the bar of a bar magnet itself, north and south connect in an opposite direction.  See the hyperphysics link http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/imgmag/mearthbar.gif Note that fields go from south to north inside the actual magnet itself.  We define north and south to define "poles" relative to the direction of field we're looking at.  If you look at the field outside the magnet, then you've got north and south poles as traditionally defined.  If you looked at the field inside the magnet, they're actually reversed by definition...but that field is not interesting to us, so we stick to the traditional definition.

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Dr. Stephen O. Nelson

Expertise

I can answer most basic physics questions, physics questions about science fiction and everyday observations of physics, etc. I'm also usually good for science fair advice (I'm the regional science fair director). I do not answer homework problems. I will occasionally point out where a homework solution went wrong, though. I'm usually good at explaining odd observations that seem counterintuitive, energy science, nuclear physics, nuclear astrophysics, and alternative theories of physics are my specialties.

Experience

I was a physics professor at the University of Texas of the Permian Basin, research in nuclear technology and nuclear astrophysics. My travelling science show saw over 20,000 students of all ages. I taught physics, nuclear chemistry, radiation safety, vacuum technology, and answer tons of questions as I tour schools encouraging students to consider careers in science. I moved on to a non-academic job with more research just recently.

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Ph. D. from Duke University in physics, research in nuclear astrophysics reactions, gamma-ray astronomy technology, and advanced nuclear reactors.

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