Is there an electric field in a circuit and how is it created?

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Discussion Overview

The discussion centers around the existence of electric fields in circuits, particularly in relation to current-carrying wires and the influence of batteries. Participants explore whether electric fields are created by the battery or the wires themselves, and the implications of these fields in different contexts, including resistive components and high-frequency applications.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants note that a current-carrying wire has no net charge, suggesting that it does not create an electric field, while questioning whether the battery creates an electric field due to its positive and negative terminals.
  • Others assert that electric fields exist but can often be neglected outside circuit elements, prompting questions about the conditions under which they cannot be neglected.
  • One participant emphasizes that in a good conductor with current, there is no voltage drop along the wire, implying no electric field exists along it, but acknowledges that real wires have some resistance leading to slight voltage drops and electric fields.
  • Another participant mentions that electric fields become significant in high-frequency applications, particularly when the structure of the circuit is a significant fraction of a wavelength.
  • Concerns are raised about the distinction between voltage drops due to resistance and those arising from electric fields in high-frequency scenarios, indicating a potential misunderstanding of the original question posed.

Areas of Agreement / Disagreement

Participants express differing views on the presence and significance of electric fields in circuits, particularly regarding when they can be neglected. There is no consensus on the implications of these fields in various contexts.

Contextual Notes

Limitations include assumptions about the ideal behavior of wires as good conductors, the impact of resistance, and the specific conditions under which electric fields are relevant in high-frequency applications.

Jimmy87
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I was reading my physics textbook which says that a current carrying wire has no net charge and thus no electric field because the electrons cancel the protons in the atoms of the wire. Would there not be an electric field created by the battery as you have a positive and a negative terminal? As I thought this is what creates a voltage and makes the charges move? So is there an electric field in the space in and around the circuit but it is created by the battery not the wires? Would this field be inside or outside the wires of the circuit or both? Any help is much appreciated.
 
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There are electric fields, but outside the circuit elements you can usually neglect them.
 
mfb said:
There are electric fields, but outside the circuit elements you can usually neglect them.
When can you not neglect them ??
 
Jimmy87 said:
I was reading my physics textbook which says that a current carrying wire has no net charge and thus no electric field because the electrons cancel the protons in the atoms of the wire. Would there not be an electric field created by the battery as you have a positive and a negative terminal? As I thought this is what creates a voltage and makes the charges move? So is there an electric field in the space in and around the circuit but it is created by the battery not the wires? Would this field be inside or outside the wires of the circuit or both? Any help is much appreciated.

Remember the wire is assumed to be very good conductor, even though you have current through the wire, there is no voltage drop across the wire, so there is no electric field along the wire.

The circuit must have some resistive components that drop the voltage of the battery, that has nothing to do with the wires. Yes, if voltage developed on the resistive load, the wire at the +ve terminal is going to rise above ground ( if the -ve terminal of battery is grounded) and yes, there will be electric field coming out perpendicular to the wire. But I don't think that's what you are talking about.

In real life, there is always small resistance across the wire, that cause a slight voltage drop across the wire and a little horizontal electric field along the wire exist.
 
technician said:
When can you not neglect them ??
For antennas and for some high-frequency applications.
 
I don't think you can neglecting electric ( more EM) field in frequency above a few MHz which, applies to a lot of circuits these days. Particular above frequency that the structure becomes a significant fraction of a ##\lambda##. That's when voltage difference becomes apparent between two point of the line ( wire). This is a totally different mechanism from voltage drop due to resistance along the wire. But I don't think this is what OP is asking...I hope. Or else, that's another whole can of worms.
 
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