Maximizing Magnetic Levitation: Factors Affecting Ring Height Experiment

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Discussion Overview

The discussion revolves around an experiment involving the levitation of metal rings using a solenoid. Participants explore the theoretical aspects of which type of ring, aluminum or copper, would levitate higher under fixed current conditions, as well as the influence of factors such as ring diameter and material properties on levitation height.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions whether an aluminum or copper ring would levitate higher at a fixed current, considering other factors like ring diameter.
  • Another participant states that the force on the ring is inversely proportional to its resistance, suggesting that height depends on the ratio of mass to resistance (1/mR).
  • A participant seeks clarification on the derivation of the relationship between force, mass, and resistance.
  • It is mentioned that pure aluminum has a high ratio of electrical conductivity to density, potentially making it favorable for levitation compared to copper.
  • Discussion includes the concept of superconducting materials, which exclude magnetic fields, contrasting with eddy current levitation where eddy currents oppose magnetic fields.
  • One participant expresses confusion about the forces at play in the levitation of a copper ring and the role of a ferromagnetic core, asking about the electromagnetic laws involved.
  • Another participant challenges the correctness of an equation presented, arguing that the current does not become infinite if resistance is zero, but rather adjusts to cancel the inducing magnetic field.
  • There is a question regarding the presence of magnetic field lines when an iron core is involved in the setup.

Areas of Agreement / Disagreement

Participants express differing views on the factors affecting levitation height, the role of resistance, and the implications of using different materials. The discussion remains unresolved with multiple competing perspectives on the underlying physics.

Contextual Notes

Participants have not fully agreed on the equations governing the behavior of the rings, and there are unresolved questions regarding the influence of material properties and configurations on the levitation phenomenon.

SuperAcid
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In an experiment I am carrying out I am levitating metal rings using a solenoid with a clamp stand going through the solenoid acting as a support for the ring and a core for the solenoid (seen in the attachment). I have one simple question? Theorectically, should an Aluminium or Copper ring levitate higher (at a fixed current through solenoid) ? Would any other factors like ring diameter etc. affect the height of levitation (I am keeping the voltage/current constant)?

Thanks in advance!
 

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The force on the ring is inversely proportional to its resistance. The ring will rise to a height where F=mg, so its height will depend on 1/mR. Calculate this ratio for each ring.
 
clem said:
The force on the ring is inversely proportional to its resistance. The ring will rise to a height where F=mg, so its height will depend on 1/mR. Calculate this ratio for each ring.

Thanks for the reply, but:

How do you know this ? Is it derived from an equation?
 
Last edited:
There is a complete equation, but the dependence on R is simple. The current in the ring is given by I=EMF/R. The EMF depends on the area of the ring, which I assume is the same for each ring.
 
Pure aluminum is the best of all. I think it is called 2S aluminum. The reason is that it has the highest ratio of electrical conductivity to density for any metal. Its conductivity is about as good as copper, and its density is about 1/3 that of copper. For a given dB/dt, higher frequencies generally are better.

There is another form of levitation, using superconducting materials. Superconducting materials exclude dc magnetic fields from the metal entirely, while in eddy current levitation, the eddy currents near the surface are cancelling the ac magnetic fields inside. The depth of the eddy current penetration varies inversely with frequency (I don't think is like skin depth which is sqrt(frequency)). Look at transformer laminations.
 
how does it come that the copper ring is levitating? I have seen a demonstration which is very alike with your drawing but the "clamp" was a ferromagnetic material.
I understand that an induced eddy current opposes the magnetic field, but i don't understand which force is working on it and why it comes to an equilibrum whitout oscillating.. Which electromagnetic laws are involved? And what has the ferromagnetic core to do with it?
 
clem said:
There is a complete equation, but the dependence on R is simple. The current in the ring is given by I=EMF/R. The EMF depends on the area of the ring, which I assume is the same for each ring.

This equation isn't correct. The ring will not have an infinite current if the resistance is zero. The current attains the value needed to cancel the inducing magnetic field.
 
Antiphon said:
The current attains the value needed to cancel the inducing magnetic field.
but if there is an iron core within, there are still magnetic field lines going through... ?
 

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