BCalculate Speed of Electrons/Current in Circuits - Sparky_B

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Discussion Overview

The discussion centers around calculating the velocity of electrons and current in electrical circuits, exploring how resistance and different conductors and dielectrics affect these speeds. Participants delve into concepts such as drift velocity and the propagation of electric fields.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant suggests that the question of calculating electron velocity and current speed is relevant to electro-magnetics.
  • Another participant introduces the concept of "drift velocity," noting that electrons in a wire move slowly, and emphasizes the distinction between electron speed and current speed.
  • It is mentioned that while drift velocity is slow, the electric field propagates at near the speed of light, causing conduction electrons to begin moving almost simultaneously.
  • A participant questions why electrons do not travel freely and seeks to understand the atomic-level effects of resistance on electron motion.
  • Another participant explains that while electrons can move, their motion is influenced by random thermal fluctuations, and that drift velocity refers to the net displacement when an electric field is applied.
  • Discussion includes the idea that resistance causes electrons to collide with atomic nuclei, converting kinetic energy to thermal energy, likening it to a car stopping at red lights while accelerating.

Areas of Agreement / Disagreement

Participants express varying views on the nature of electron movement and the effects of resistance, with no consensus reached on the implications of these concepts or the specifics of electron behavior in different materials.

Contextual Notes

Participants highlight the complexity of electron motion, including the influence of thermal fluctuations and the distinction between drift velocity and the speed of the electric field. The discussion does not resolve the implications of resistance at the atomic level.

Sparky_
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Greetings,

I would think this question belongs in a "Electro-magnetics" section, if it is not relevant in this section please move it accordingly.

How can I calculate the velocity of the electrons or the current within a circuit?

Meaning, how can I show how resistance affects the speed of the current?

How can I show how various conductors affect the speed of individual electrons or current?

Likewise for various dielectrics?

Thanks
Sparky_
 
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Sparky_ said:
How can I calculate the velocity of the electrons or the current within a circuit?

How can I show how various conductors affect the speed of individual electrons or current?

You might want to note that the speed of the current is not the same as the speed of the electrons.

The drift velocity of the electrons mentioned by Ben Niehoff is *snails pace*. It would take something like a year or so for a single electron to cover the distance from the plug to the household applicant, assuming it runs on DC. In an AC circuit the average drift velocity of the electrons are zero.

But the electric field that drives the electrons propagates through the wire at near speed of light, so *all* conduction electrons in the wire begins to move at nearly the same instant, and thus the speed of the current would be the speed of light in the appropriate medium.

Also, it doesn't really make sense to speak of electron speed or current speed in dielectrics, as a dielectric by definition is a insulator. Still, the electric field propagates with the speed of light in the given dielectric.
 
why don't the electrons themselves travel , aren't they free to travel or are they only free to "roam" about their atoms ?

what does resistance do in the atomic level?

i hope sparky doesn't consider this as high jacking his thread...?!
 
AhmedEzz said:
why don't the electrons themselves travel , aren't they free to travel or are they only free to "roam" about their atoms ?

what does resistance do in the atomic level?

THe electrons are free to move, but their motion is by far dominated by the random thermal fluctuations, but these average to zero, so it is net displacement of an electron when you apply the electric field that is referred to as the drift velocity

As for resistance, the electrons colide with the massive nuclei as the move through the wire, transfering their kinetic energy to thermal energy as they go. Picture it, if you like as you driving your car with constant acceleration, but being forced to stop at red light at every 50 meters
 

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