Ampere's Law: Explained and the Role of Magnetic and Electric Fields

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Discussion Overview

The discussion revolves around Ampere's Law, particularly focusing on the nature of magnetic fields generated by current-carrying wires, the geometric configurations that influence these fields, and the implications of relativistic effects on electromagnetic fields. Participants explore various aspects of the relationship between electric and magnetic fields, including the right-hand rule and hypothetical geometric configurations.

Discussion Character

  • Exploratory
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • Some participants inquire about the geometric configuration of current-carrying wires and why magnetic fields exist in specific forms, questioning the nature of electric fields in different frames of reference.
  • There is a discussion on the right-hand rule, with some suggesting it is merely a convention and could have been defined differently without altering the underlying physics.
  • Some participants emphasize that the magnetic field is not directly observed but inferred from forces between currents and moving charges, suggesting that the rules for determining field direction are based on empirical observations.
  • Questions arise about the fundamental reason why moving charges produce magnetic fields, with some attributing this to relativistic effects.
  • Hypothetical scenarios are posed regarding alternative geometric configurations, such as hexagonal patterns, and their implications for symmetry and mathematical representation in physics.
  • One participant reflects on the scientific method, suggesting that understanding magnetism involves observation followed by mathematical description, drawing parallels to the development of relativity.

Areas of Agreement / Disagreement

Participants express multiple competing views regarding the nature of magnetic fields, the conventions used to describe them, and the implications of different geometric configurations. The discussion remains unresolved with no consensus on several key questions raised.

Contextual Notes

Participants highlight the dependence on geometric configurations and the implications of relativistic effects, but these aspects remain unresolved and are subject to further exploration.

physics user1
I know the ampere's law but I want an explanation on why it exist in that way, consider a wire where flows current, i know that when an observer is in relative motion to the current there is a magnetic field but why in this geometric configuration and not in another? What about the electric field outside? I guess is zero unless we don't move at the same velocity on the current so that our frame of reference is solidal with it, then the electromagnetic field is just electric field, is that TRUE? I mean, if we see current flowing all the field is magnetic, if we don't see current all the field is going to be electric due to Lorentz contraction law and all that stuff right?
Why the magnetic field outside a wire obeys to the right hand rule?
 
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Can you focus your question down to one most important key question? You have so many scattered questions that you will get scattered responses.
 
Dale said:
Can you focus your question down to one most important key question? You have so many scattered questions that you will get scattered responses.

Why does the magnetic field outside the wire carrying current obey to the right hand rule, why does it formes circumferences around the wire?
 
That is just a convention. We could have chosen a left handed convention and all of the physics would have worked out the same.
 
We don't observe the magnetic field directly. Instead we observe the forces between current-carrying wires and moving charges. Our rules for the direction of the magnetic field produced by a current (or moving charge), and the force exerted by a magnetic field on a current (or moving charge) were chosen so as to accommodate our observations of the forces between currents and moving charges moving at various angles with respect to each other.

As Dale noted, we could use a "left-hand rule" for the magnetic field if we also used a matching "left-hand rule" for the magnetic force exerted by that field. Mathematically, this would be equivalent to putting minus signs in the two equations, which would cancel out when we combine them.
 
Cozma Alex said:
Why does the magnetic field outside the wire carrying current obey to the right hand rule, why does it formes circumferences around the wire?

Back up a step - why does charge in motion cause a magnetic field at all ?
 
P
jim hardy said:
Back up a step - why does charge in motion cause a magnetic field at all ?
Is a relativistic effect
 
Cozma Alex said:
Is a relativistic effect

an observed trait of the universe

What if it'd been hexagonal instead of circular ? The formulas would be a little different, that's all..
 
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jim hardy said:
an observed trait of the universe

What if it'd been hexagonal instead of circular ? The formulas would be a little different, that's all..

So... it's like that because the universe is made this way
 
  • #10
jim hardy said:
What if it'd been hexagonal instead of circular ?
That would imply a very arbitrary case of symmetry. If it had to be a hexagon pattern, would the sides of hexagons for different wires all be parallel from wire to wire? It would imply 'preferred' directions in space which would be very unsatisfactory for Mathematicians, if nothing else (lol). The circle is the least arbitrary pattern in this case. Geometry is a pretty powerful argument here, as it is when you justify the Inverse Square Law.
 
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  • #11
Cozma Alex said:
So... it's like that because the universe is made this way
I think so.

Place iron filings around a wire and observe the pattern.
magneticfieldsaroundcurrents3.JPG

Then figure out what math describes it.
http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/biosav.html
upload_2016-7-22_16-31-15.png
Scientific method:
Observe something.
Then figure out what math explains the observations.
Then see if the math ever fails, and when it does adjust it.

Isn't that how relativity came about ?

I think if i understood what magnetism really is i'd have a nice lab at Princeton.

old jim
 
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  • #12
sophiecentaur said:
It would imply 'preferred' directions in space which would be very unsatisfactory for Mathematicians,

hmmmm would preferred directions infer that dreaded "absolute frame of reference" ?
 

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