Magnetic field due to a current carrying conductor is___?

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Discussion Overview

The discussion revolves around the nature of current flow in conductors, specifically addressing the contributions of positive and negative charges to the magnetic field generated by a current-carrying wire. Participants explore the implications of charge movement on the derivation of magnetic field equations, referencing Biot-Savart's Law and Ampere's Law.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant questions whether the derivation of the magnetic field from a current-carrying wire is valid if it does not account for both positive and negative charge movement, suggesting a potential inconsistency in textbooks.
  • Another participant clarifies that the conventional definition of current considers the flow of negative charges (electrons), while positive charges (atomic nuclei) do not move, indicating that this is a matter of convention.
  • A different viewpoint suggests that the charge makeup of the current does not affect the outcome, as the magnetic field can be modeled regardless of whether it is due to electrons, ions, or a mix.
  • One participant acknowledges a misunderstanding regarding the movement of charges in a conductor, realizing that only electrons flow during current, not the positive charges.
  • Another participant introduces the concept of "holes" in semiconductors, which are positively charged vacancies that can also contribute to current flow, thus complicating the discussion of charge movement.

Areas of Agreement / Disagreement

Participants express differing views on the movement of charges in conductors, with some asserting that only electrons flow while others mention the role of holes in semiconductors. The discussion remains unresolved regarding the implications of these differing perspectives on the derivation of magnetic fields.

Contextual Notes

There is a lack of consensus on the implications of charge movement for the derivation of magnetic field equations, and the discussion highlights assumptions about charge flow that may vary depending on the context (e.g., metals vs. semiconductors).

peeyush_ali
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In an infinitely long current carrying wire (assuming zero resistance) say there is a definite current.
"Having current in it" means there is a flow of charge in it, which means if positive charge moves in one direction then negative charge moves in opposite direction. As we know that a charge in motion will have to produce a magnetic field which is precisely given by the famous "Biot-Savart 's Law" for a current carrying wire. But is it not this for a normal current carrying wire, that the magnetic field produced by positive charges is equal to that produced by negative charges.
So, when we derive the expression for magnetic field due to an infinitely long current carrying wire the magnitude is given by |B|=Uoi/2 (pi)d where d--->perpendicular distance of the point from the wire and i--->current in the wire.
And that's the expression derived without considering the fact that "in a current carrying wire both positive and negative charges flow" but "only positive charges flow"..there are many textbooks which say exactly the same.
So is this not a violation of obtaining result for something which is not the proclaimed one??
.............
warning..
the probability of this poster to contain irony is finite and maybe nearly one..(or even not)
 
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I don't really get your question, could you rephrase it a little?

One can get the magnetic field due to an infinitely long wire by applying Ampere's law, or Biot-Savart's law. The charges which flow in current are negative charges of the electrons. The positive nuclei of the atoms themselves don't move. The current is defined to move the opposite way as the electrons, but that is just a convention we use. We could redefine convention and change the current to the other direction, but we'd have to redraw every schematic, and redo all the positive/negative signs on all those equations. This turns out to be too big of a hassle.
 
It doesn't matter what the charge makeup of the current actually is. We can model the current as a flow of ions, electrons, or a mix of the two but the end result is still the same.
 
peeyush_ali said:
without considering the fact that "in a current carrying wire both positive and negative charges flow" but "only positive charges flow"..there are many textbooks which say exactly the same.
So is this not a violation of obtaining result for something which is not the proclaimed one??

I don't think that I fully understand what you are asking.

But, as has been posted above, I don't think that positive charges flow in a wire.
 
In semiconductors, positively-charged "holes" (vacancy in the valence band) can flow in electric fields. See

http://en.wikipedia.org/wiki/Semiconductor

The total sum current (electrons plus holes plus ions etc.) is continuous everywhere. It doesn't matter what the makeup of the current is.

Bob S
 
So, the flaw is there in my question..actually i thought that both positive charges(atomic nuclie) as well as electrons move in a conductor while there is a current in it..there i was wrong..
 

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