Energy lost when current is induced in a loop

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Discussion Overview

The discussion revolves around the energy dynamics of protons passing through a loop of wire and the resulting electromagnetic effects, including induced currents and energy loss. Participants explore whether a proton or a stream of protons can induce a current in the wire and the implications of such induction on the protons' energy and motion.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Exploratory

Main Points Raised

  • Some participants propose that a proton passing through a loop of wire induces a tiny current, potentially causing the proton to lose energy.
  • One participant suggests that the energy lost by the proton can be calculated using the I²R formula.
  • Another participant questions the initial premise, arguing that a proton does not induce a current due to the absence of an electric field and suggests that a magnet would be more appropriate for inducing a current.
  • A later reply acknowledges the misunderstanding about the proton's role, stating that it is merely a current and will not slow down if the loop remains uniformly neutral.
  • Participants discuss the scenario of a stream of protons and whether it behaves similarly to a magnet, raising questions about the neutrality of the loop and the potential for energy loss in successive protons.
  • Some argue that a steady stream of protons creates a static magnetic field, which does not induce a current due to the lack of changing magnetic flux.
  • One participant references a diagram from another post, discussing the nature of the magnetic field generated by a moving charge and its implications for magnetic flux and current induction.
  • Another participant notes that while the magnetic field is static in the reference frame of the moving charge, it may still affect the charge's motion when interacting with the loop.

Areas of Agreement / Disagreement

Participants express differing views on whether protons can induce a current in the wire and the conditions under which energy loss occurs. The discussion remains unresolved, with multiple competing perspectives on the electromagnetic interactions involved.

Contextual Notes

There are limitations regarding assumptions about the neutrality of the loop, the definitions of current in the context of single protons versus streams, and the conditions required for inducing magnetic flux. These aspects remain open for further exploration.

Northprairieman
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Hi there,

If a proton passes through a loop of wire, it induces a tiny current in the wire. Will the proton lose energy and slow down as a result of this?

If so, by how much?
 
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The proton will slow down.

I think I2R will be the energy lost by the proton.
 
If a proton passes through a loop of wire, it induces a tiny current in the wire.
Forgive me, but I am finding this statement hard to accept. Thanks to the proton there will be an E field, axially symmetric and forward pointing, with a radially outward component. There will also be a B field, axially symmetric and pointing along the circumference. I don't see how either of these fields will induce a current in the wire.

If you tried the same experiment using the pole of a magnet instead of the proton, *then* you will induce a current in the wire. Is that what you're thinking of??
 
oh yeah. i had it wrong.
proton is just a current. it'll induce a magnetic field around. no electric field. you're right. it won't slow down assuming the loops is uniformly neutral.
 
Thanks for the responses. So what if you had a stream of protons? Would that be equivalent to the pole of a magnet?

In this stream of protons, will each successive proton be slowed down because the proton before it passing through the loop made the loop of wire no longer uniformly neutral?
 
Northprairieman said:
Thanks for the responses. So what if you had a stream of protons? Would that be equivalent to the pole of a magnet?

In this stream of protons, will each successive proton be slowed down because the proton before it passing through the loop made the loop of wire no longer uniformly neutral?

Whether it's a stream of protons or a single proton, it won't make any difference will it? There will still be no current induced because there is no changing magnetic flux through the loop.
 
ya if you just had a steady stream of protons, you would have a static B field and it wouldn't induce a current. And if you had just one proton moving I am not sure if this counts as a current, I think i remember reading something about this in Griffiths.
 
So according to this post:

https://www.physicsforums.com/showthread.php?t=487014

In the little diagram there, it shows a B field generated by a moving charge. So if I understand this correctly, that's a "static" B-field (not a moving B-field) and hence does not produce a magnetic flux?

What if the charge were accelerating?
 
Northprairieman said:
So according to this post:

https://www.physicsforums.com/showthread.php?t=487014

In the little diagram there, it shows a B field generated by a moving charge. So if I understand this correctly, that's a "static" B-field (not a moving B-field) and hence does not produce a magnetic flux?

The B-field is static in the reference frame of the electron. For a stationary object, the B-field
will increase if the electron approaches, and decrease when it moves away again.
You will get a current that slows down the electron, but if the electron goes through the loop of wire, there won't be any magnetic flux at all going through the loop.
 

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