E field in a wire

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Discussion Overview

The discussion revolves around the electric field in a wire connected to a battery, comparing the electric field in air versus within the wire itself. Participants explore the implications of current flow, charge distribution, and the effects of resistance on the electric field in different scenarios.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions the electric field along a path from the positive to the negative end of a battery, particularly at large distances from the battery.
  • Another participant suggests that extending parallel wires from the battery alters the electric field and voltage due to surface charge distribution, indicating zero electric field inside the wire material.
  • A different viewpoint describes the electric field as resembling an electric dipole field that decreases with distance, influenced by the wire's material properties and Ohm's law.
  • It is proposed that the surface charge distribution within the wire shapes the electric field according to the wire's geometry and material properties.
  • One participant emphasizes that in the air, no current flows, resulting in a dipole field, while in the wire, the battery short-circuits, leading to a rapid decrease in the external electric field as the battery discharges.
  • Current flow is identified as a key factor causing the difference in electric fields between the two scenarios.

Areas of Agreement / Disagreement

Participants express differing views on the nature of the electric field in air versus in a wire, with no consensus reached on the implications of current flow and charge distribution.

Contextual Notes

The discussion includes assumptions about the behavior of electric fields in different media, the role of surface charge, and the effects of resistance, which remain unresolved.

Jonathan Apps
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1. What is the electric field along a path through the air that starts at the + end of a battery, ends at the - end, and goes a large distance from the battery? In particular, what is the E field at those large distances?

2. Replace the path in 1. by the same path but along a wire between the + and - ends. What is the E field at large distances now?

3. And the point of this post is...... what causes the difference?
 
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Say you extend parallel wires from the ends of battery, plus minus charges distribute on their surface and change E, V around from what they used to be. Zero E inside the wire metal material. Then say you short circuit at the ends of the wires with a resister, by Ohm’s law points on it undertakes voltage in accordance with V of space around. If loop wire has homogeneous resistance, another pattern of wire surface charge distribution and E, V in space take place.


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Last edited:
1. It is more or less an electric dipole field that decreases with distance

2. It is the value of electric field allowed by the constitutive relation in the material of the wire, that is Ohm's law in its local form. It could be very high if the conductivity of the wire is low (compatible with what the battery can supply due to its internal resistance)

3. Surface charge (and interface charge, if you change the material the wire is made of). It shapes the field inside the wires in such a way that it will follow the geometry and the constitutive relation.

See this https://electronics.stackexchange.c...ectric-field-in-a-wire-constant/532550#532550
 
Jonathan Apps said:
3. And the point of this post is...... what causes the difference?
1. In the first case, no current flows through air, so the E-field will be a dipole field, centred halfway along the axis between the battery terminals.
2. In the second case, the battery is short-circuited by the wire, so there is almost no external E-field, rapidly falling to zero as the battery becomes discharged.
3. What causes the difference? Current flow.
 
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