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To my understanding, the voltage supplies the potential, and free electrons are taken from ground? This makes somewhat sense to me, for example if something has a "positive" charge then it will attract negative electrons to it - which works out, however I am unsure if negative charge (relative to one specific point) means more free electrons.

Another question, so mains line provides the potential of 120/240VAC (ignoring AC) and the current does not actually "come" from it, only from ground?

This subject seems to be just taught quickly, it would be very nice to have an understanding that "works" in all aspects I throw at it.

Hobbyist
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    Well as far as I know it, in AC the electrons shouldn't even be moving. When the voltage changes direction, they go back to where they were, right? Also +1 for the question. – AndrejaKo Oct 29 '11 at 17:50
  • @AndrejaKo: Yes, except that they also move around randomly. I think the random motion is actually much larger than the drift in one direction caused by your AC voltage. – endolith Dec 16 '11 at 19:40
  • @endolith Could be. – AndrejaKo Dec 16 '11 at 19:46

2 Answers2

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To my understanding, the voltage supplies the potential

Voltage is the difference in electric potential between two points. It is analogous to a difference in pressure between two points of a hydraulic circuit.

and free electrons are taken from ground?

Free electrons are everywhere in metal. All matter contains electrons, and in metals, some of those electrons can flow freely. They won't flow until you apply a voltage, though. Applying a voltage causes them to flow, which we call an electric current.

http://amasci.com/miscon/eleca.html#batt

"Ground" is just a label for a point in a circuit. Any point can be considered ground. It's not special, it's just a common reference point for measuring.

Another question, so mains line provides the potential of 120/240VAC (ignoring AC) and the current does not actually "come" from it, only from ground?

Current doesn't "come from" anywhere. Current is a flow of charge, which already exists everywhere.

In electronics, electrons aren't usually important. What's important is flows of charge, waves in charge, etc.

Go read everything on this page: http://amasci.com/miscon/elect.html

Related: Why does a resistor need to be on the anode of an LED?

Also related: Why is the charge naming convention wrong?

Community
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endolith
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"the voltage supplies the potential, and free electrons are taken from ground?"

Stop thinking about "the voltage", the only usefull concept is "voltage difference". A voltage source has two connections, and it maintains a voltage difference between those two connections. For DC, electrons travel from the more negative connection the more positive one.

Often one of the connections of your voltage source is connected to the ground (earth), or is simply called ground. But that does not change the course of the electrons.

Wouter van Ooijen
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