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Electrons flow from low potential to high potential in DC, i.e. from negative terminal to positive terminal.
But how do they flow in AC, as the polarity changes every 10ms for 50Hz?

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Possible duplicate of pattern of moving electrons in wire under AC – John Rennie 7 hours ago
    
You've asked my question. – Wrichik Basu 7 hours ago
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They flow as they would do in DC, if you turned around the battery all the time. In other words: They flow back and forth, instead of just forth. – Steeven 6 hours ago
    
cdn.sciencebuddies.org/Files/6651/9/… – endolith 1 hour ago
up vote 13 down vote

Electrons do not "flow" in AC unlike in DC, where they physically move from negative to the positive terminal of the EMF source. Observe that by definition current is rate of flow of charge. In alternating current, the electrons just oscillate about their mean position. Yet they constitute a current[alternating current here], because there is flow of charge through the cross section of the wire.

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initially I imagined they oscillate in the "vertical" plane (given a horizontal wire) and couldn't see how this creates flow of charge through the cross section. So they must be oscillating "along" the wire, right ? – Ciprian Tomoiaga 3 hours ago
    
@Tejas I had this same question. Thanks for the answer. – Wrichik Basu 2 hours ago
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@CiprianTomoiaga: yes, indeed. AC is a longitudinal wave. – Javier 2 hours ago
    
@Javier "AC is a longitudnal wave". This explains how AC transmits energy and so many other questions that people have. Very nice statement. It connects our intuition about waves with AC. I thought about it just now for the first time. Unfortunately its not 100% correct.. but still very nice. – Kartik 2 hours ago
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  • If you plug a battery to a circuit, you have direct current (DC). Charge starts moving and speeding up from positive towards negative terminal. At some point they reach maximum speed and we have a constant steady current.

  • If you now unplugged the battery, turned it around and reinserted it very quickly, the moving charge would slow down, stop shortly and start moving backwards, then speed up backwards and soon reach a steady flow.

If you could turn around the battery very, very fast, you would constantly see charges speeding up, slowing down, moving backwards, slowing down, moving forwards etc. Maybe so fast that the current never has time to becomes steady in any direction. You will then call it alternating current (AC).

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Well, a steady current is not necessary for AC, really. Consider an AC square wave: The current reaches a steady state in the positive half, then switches, then steady negative, then switches, and so on. Yes, in the context in this question a simple answer is good, this comment is merely a footnote. – Kroltan 3 hours ago

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