How can current flow in A/C circuits?

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Discussion Overview

The discussion centers on the behavior of current in alternating current (A/C) circuits, particularly how current can flow to a load despite the oscillating nature of voltage. Participants explore the mechanisms of current flow, the speed of electromagnetic waves, and analogies to explain the phenomenon.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant questions how current can reach the load in A/C circuits given that voltage alternates between positive and negative values.
  • Another participant asserts that current oscillates back and forth through the load, implying that this oscillation allows for effective current flow.
  • A different viewpoint suggests that even with an 80% velocity factor at 60 Hz, the current can travel significant distances before the polarity of the electromotive force (EMF) reverses, indicating that electrons can reach the load efficiently.
  • Another participant adds that multiple waves can travel down the wire simultaneously, further supporting the idea of effective current flow despite oscillation.
  • One participant uses a water flow analogy to illustrate that, similar to water in a hose, current begins to flow almost instantaneously when the circuit is activated, even if individual electrons may take longer to traverse the circuit.

Areas of Agreement / Disagreement

Participants express various viewpoints on the nature of current flow in A/C circuits, with no consensus reached on the best explanation or analogy. The discussion remains open to interpretation and further exploration.

Contextual Notes

Some assumptions about the behavior of electrons and the nature of current flow in A/C circuits are not fully explored, and the discussion relies on analogies that may not capture all aspects of the phenomenon.

Farlander
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How can current flow in A/C circuits!?

Hello everyone!

In alternating current circuits, such as the North American main power grid, voltage swings from 120V to -120V at a rate of 50-60 cycles per second, right? If that's true, than how can current ever reach the load?? It seems like the electromotive force would prevent any amps from actually moving...
 
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The current (everywhere in the circuit) oscillates back and forth through the load.
 


Assuming an 80% velocity factor and a system frequency of 60 Hz, the current leaving
the generator will travel well over 1000 miles before the polarity of the EMF reverses.
I think those electrons can get to any load and back to the generator quite handily.
 


In fact, even if the electrons don't move quite that fast or the distance is much further, you'll just have several waves traveling down the wire at the same time.
 


I'm not fond of the water flow analogy, but it works to answer this question.

Imagine a garden hose full of water, but the faucet is off. Then you turn the faucet on. Almost immediately, water starts coming out the end of the hose. Even though individual water molecules may take 10 seconds or so to travel the length of the hose, all water molecules begin moving as soon as the faucet is turned on, and the "current" is set up practically instantaneously.

Turning current on or off, or reversing current as part of the line cycle, works pretty much the same way.
 

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