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Physics/Question regarding magnetic field.....


QUESTION: There is an interesting question that has been boggling my mind and am really trying to just understand the concept. I am no longer taking the course as  I passed Physics 2 last year but am still trying to grasp the idea. Just the idea. The question mentions a wire of mass/length with current I to the south and then asks what is the minimum magnetic field required to lift the wire VERTICALLY UPWARD. I am thrown off by the VERTICALLY UPWARD. Do they mean to lift it off the ground and stand it up vertically? What does this mean. Also, they state in the solution that the magnetic force is equal to the weight of the wire. This makes no sense as the magnetic force would have to lift it VERTICALLY of the ground while it lays HORIZONTALLY. Please clarify the meaning of vertically upwards to me and how is it possible that the Mag force is equal to the weight?

ANSWER: Heh.  No, it just means up, perpendicular to the ground.  The wire doesn't turn, think of it as hovering.

---------- FOLLOW-UP ----------

QUESTION: That means the magnetic force is lifting it up in the vertical position from the horizontal position. The wire is lying down horizontally, so if it ends up being perpendicular to the ground, that means it was lifted from the horizontal position to the vertical position. If it is only hovering horizontally vertically upward, than its PARALLEL. I'm lost.  This doesn't make sense. It should just state levitating. Here is the question, "A wire having mass per unit length of 0.420 g/cm carries a 2.50 A current horizontally to the south. What are the direction and magnitude of the minimum magnetic field needed to lift this wire vertically upward?" I'm not looking for answers, just an explanation.

NO!  Read what I wrote.  The WIRE DOES NOT TURN.  The wire remains horizontal.  The force is vertical.  Everything remains that way.  Horizontal wire.  The force doesn't just act on one end of the wire, it acts on the center of mass.  The wire stays horizontal, the current stays horizontal (and therefore perpendicular to the magnetic field).


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Dr. Stephen O. Nelson


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.


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.

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

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