Path of a conducting sphere through a uniform magnetic field

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Discussion Overview

The discussion revolves around the behavior of a conducting sphere, specifically aluminum, as it passes through a strong uniform magnetic field that is orthogonal to its direction of motion. Participants explore the effects of Lenz's law, eddy currents, and the nature of the magnetic field on the sphere's trajectory, considering various scenarios and assumptions.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • Some participants propose that the Lenz effect and eddy currents will create a magnetic field opposing the external magnetic field, potentially affecting the sphere's motion.
  • Others argue that while eddy currents may slow the sphere down, they do not foresee any other effects that would cause a deviation from a vertical path.
  • A participant draws an analogy to a magnet falling through a pipe, suggesting that the behavior would be similar if the sphere were to fall through a magnetic field.
  • One participant questions whether the scenario is well-defined, raising issues about the initial conditions of the magnetic field and the nature of the sphere (ferromagnetic vs. conducting).
  • Another participant mentions that there will be a small upward force as the sphere enters the magnetic field and a small downward force as it exits, but concludes that it will maintain the same velocity as if the field were absent.

Areas of Agreement / Disagreement

Participants express differing views on the effects of the magnetic field on the sphere's motion, with some emphasizing the role of eddy currents and others questioning the clarity of the problem. No consensus is reached regarding the overall impact on the sphere's trajectory.

Contextual Notes

Participants highlight limitations in the problem's specification, including the initial conditions of the magnetic field, the nature of the sphere, and the uniformity of the field after the sphere's passage. These factors contribute to the uncertainty in the discussion.

ccarleton
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Hello, could someone help answer this question for me:
How would the path of a conducting sphere (i.e. AL) be affected as it passes through a strong uniform magnetic field orthogonal to the direction of motion.
I believe the Lenz effect/Eddy currents will create a magnetic field opposing the orthogonal field as it passes through it, but will every thing cancel out and the sphere continue to move in the same direction unaffected? Or will it be pushed in the direction of the magnetic field? Or will it just start spinning on its access or is there another scenario?

Thanks
 
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The Eddy currents would slow the ball down but I can't think of any other effect that could make a neutrally charged object to deviate from a vertical path.
 
Look for videos of a magnet falling (slowly) through a pipe. Now if the magnet is spherical shape, it's the same. If the falling object is not magnatized, but the pipe shaped object is, the result is the same.
 
Thanks for the responses, I've seen those videos of the magnet falling through an aluminum tube. The reason I was wondering if this case would be different is because the magnet falling through the tube has the magnetic field wrapping around and hence has field lines going in the direction of motion. Would it be different in a situation with a uniform magnetic field where all field lines are orthogonal to the direction of motion?
 
Anything that creates eddy currents, puts energy into the eddies and takes energy out of kinetic energy. So qualitatively, they're all alike. Quantitatively, I don't know.
 
I don't think this problem is well-specified. Is the sphere moving from a zero field to a region initially at constant field? Is the sphere placed a region of constant field before the sphere is there and then the field lines allowed to become non-uniform due to the sphere? Is the sphere ferromagnetic or only conducting? Is the setup such that the field lines are uniform after the sphere is there? Without a very specific question there is no single correct answer,
 
Vanadium 50 said:
I don't think this problem is well-specified. Is the sphere moving from a zero field to a region initially at constant field? Is the sphere placed a region of constant field before the sphere is there and then the field lines allowed to become non-uniform due to the sphere? Is the sphere ferromagnetic or only conducting? Is the setup such that the field lines are uniform after the sphere is there? Without a very specific question there is no single correct answer,

Thanks for the response Vanadium, for this scenario, the pure Aluminum ball would be in free fall, starting from an area with no magnetic field. it would then cross a uniform horizontal magnetic field created between two vertically mounted plate magnets. Then exit the magnet field as it continues falling. So the question is will there be any net vertical movement of the sphere.
 
There will be vertical motion as it falls.

There will also be a small upward foce as it enters the field and a small downward force as it leaves, and it will end up with the same velocity as it would have had the field been zero.
 

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