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In am Electrical Generator, where do the Electrons come from?

  1. Jan 20, 2004 #1
    I have a question, somewhat of a curious nature. Say you have an electrical generator that keeps running and running, producing an electrical current continuously. Where do the Electrons come from? I have just asked (in another thread) about Electrons having mass (which evidently they do). Given that, where do the electrons keep coming from that are produced by the Generator? Do they come from the windings of the generator, and if so, wouldn't the generator soon run out of electrons? If not, then where are they coming from? Any information would be appreciated, I am quite curious about this.
  2. jcsd
  3. Jan 20, 2004 #2


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    They come from the windings of the generator and the wires the electricity flows through. A metal has chemical bonds often described as a "sea of electrons" - they can move from atom to atom with little resistance and little change to the properties of the metal. A generator just takes those electrons and gives them a shove. No electrons are created or destroyed.
  4. Jan 20, 2004 #3
    Are these "free" electrons?? Is there an endless supply of electrons in the metals? As long as the generator runs the electrons keep flowing. I still don't get the concept of a seemingly endless supply of electrons. What am I missing? thanks for helping.
  5. Jan 20, 2004 #4
    There isn't an endless supply of electrons in the sense that there is an infinite amount. You are just using the available electrons that happen to be present in your circuit. Think of a closed loop of pipe with ping-pong balls inside, continuously circling.

    A voltage applied across a conductor will just cause the available electrons to move, not create them.
    Last edited: Jan 20, 2004
  6. Jan 20, 2004 #5
    You could think of a generator as if its an electron pump. It pumps electrons around and around the circuit.
  7. Jan 20, 2004 #6


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    Good analogies, guys - much clearer than my explanation.
  8. Jan 20, 2004 #7
    Okay, keep helping me out. Does that mean that electrons leaving the source eventually retrn to the source? If a generator in, say, New York, is supplying power to, say, Ohio, do these electrons in Ohio return to New York? If so, okay. If not, then how does the electrons get replaced at New York? Thanks for everyones help.
  9. Jan 20, 2004 #8
    Essentially that is correct but there is a difference between direct current and the alternating current which is supplied by the power companies.

    In direct currents, the electrons move really slow in one direction. This is known as electron drift. When dealing with AC, the individual electrons are actually vibrating back and forth and really are not moving from the source to your home and back again.


    Think of a long pipe full of ping pong balls. You can push another ball in one end of the pipe relatively slowly but the ball at the other end will move out pretty fast. It didn't require the first ball to travel the entire length of the pipe.

    See this faq:

    Hope I didn't confuse you more than help. :smile:

    Basically, electric generators do not generate electrons. They generate a difference of potential or voltage which causes the electrons already present throughout the system to move. Just as a water pump does not create water but creates the pressure needed to move the water.
    Last edited: Jan 20, 2004
  10. Jan 24, 2004 #9
    The way it was explained to me was like this: You have a sea of electrons. A voltage is applied. Now, I gather this means that there is an electric field throughout (or just on the surface of) the wire? So with DC, as you get from a battery, the electric field rises to, say, 9 volts and stays there (as oppose to AC where the strength of the electric field rises and falls periodically). Now, I was given to understand that it isn't the electrons which travel at (near enough, anyway) light speed, it is the wave which propagates through the sea of electrons which travels so fast (which I am able to believe by visualizing that tube of ping pong balls where you shove one ball in one end and another one instantly pops out the other end, the energy of the first one reached the end of the tube that fast while the actual balls didn't move so fast -- pardon me for going excruciatingly slow with this). That is the picture I have so far, but I still don't get it. When I run a mental model, I see the electric field appear along the wire. So, with the DC circuit, there is a constant e field (I forget the other way it's designated now... some letter...). Ok, so when I asked about this I was told to imagine the waves of energy in the DC circuit as on long wave, one that was so long that it looked like a horizontal line. Unfortunately, that didn't help me. I guess I slammed up against my IQ ceiling, something for which I wish I had a dime of every occurance! It's easy enough to see AC waves; voltage going up and then having to go down and then up again. But with DC there is just one wave where you rise up to our 9 volts and stay there until falling again when the battery is disconnected. But I have trouble seeing how this one long wave moves energy through the ciruit. In my mental model I can see one wave when the battery is connected and then all I can see are the electrons having to poke their way through the wire but with no waves propagating through them at lightening speed. Maybe I'm visualizing this incorrectly. Thinking of the circuit as a bike wheel, where the brake is like a resistor, slowing down the entire circuit, not just the part it's applied to, if I push on it periodically, that is like AC and if I apply constant pushing, say with contact with another wheel, then that is like DC. Perhaps that tube of ping pong balls really is more useful (now I come to think of it after sitting here not typing for a few minutes). If I push in one end periodically, with varying pressure, that is like AC, but if I somehow apply constant pressure, a constant supply of pingpong balls, I guess you could say, then that is like DC. So the energy that is travelling through the circuit at lightening speed, is that the electric field that is being referred to? Voltage is what travells through the wire at lightening speed? And what heats the bulb? I've heard that it isn't really resistance caused by the electrons. The way I've heard it described goes; it is the energy coming down both wires, from the neg. and pos. poles, like having two slinkies stretched from both hands and you pull on one and make a wave travel out towards the end and you push on the other and a wave also travels from you out towards the bulb! Energy dives into the bulb from both sides (even though current is going in one direction). That's how it was explained to me but I still don't get exactly what is lighting the bulb. I know that all light is caused by electrons jumping and then falling back into their original orbits. But how is that being made to happen?

    Many many thanks.
  11. Jan 24, 2004 #10
  12. Jan 25, 2004 #11

    Ivan Seeking

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    btw, the short answer: Electrons that flow in dc circuits come from ground - the earth. This was implied but I don't think anyone ever said it. The world's economy now depends on good ground rods.

    I always found the drift velocity funny to consider. In a 12 guage wire carrying ten amps, vd is about 0.036 cm/sec.
    Last edited: Jan 25, 2004
  13. Jan 25, 2004 #12
    Generator creates Photons

    An electric generator's purpose is to creat photons (electromagnetic energy).

    Electrons are forced to move.. but they're purpose is just to create current and thuse the magnetic field component of the EM energy.

    A flow of energy rushes down transmission lines (external to the wires) at the speed of light (slightly less usually), while electrons barely drift forwards (very random, some might even be moving backwards while the NET drift is forwards).

    Even in AC circuits/generators, the flow of energy is one way. Funny, the electronics near the generator might never read the load in AC circuits, yet energy travels at c.
  14. May 2, 2006 #13
    That doesn't explain it. Cars, planes, and emergency hand powered flashlights aren't conencted to the ground.
  15. May 2, 2006 #14
    Hold on a sec!

    Electrical current flow, DC or AC, is not necessarily dependent on a "ground", unless designed to use it, of course. A DC flashlight or AC generator in space will be most happy to generate flow without any "ground" to earth.

    Electron flow in a common electrical circuit is MUCH slower that the speed of light.
  16. May 2, 2006 #15


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  17. May 2, 2006 #16


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    Ivan, can you elaborate on that please. As pallidin stated a circuit could be designed without a ground. The only essential things needed for a current is a complete path and a force to push the electrons. I dont see how the ground thing comes into play. Am I missing something?

    EDIT: I just realized that this topic is really old.
    Last edited: May 2, 2006
  18. May 3, 2006 #17


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    In the case of a generator which does not have a return line, electrons are "pumped" from the ground to elevated potentials by the generator. The conductors then transport electrons and energy to a load, where the electrons then return to ground, returning the energy gained at the generator.

    If the generator is not connected to a "earth" ground then the return path must provided. In this case electrons are simply "pushed" through the circuit by the generator.

    Isolated circuits must have a means of moving electrons or a source of electrons. The source can be a chemical reaction as in a battery or a atomic change in state as in a Photovoltaic cell.

    Do not get the idea that only electrons can be current carriers, in ionic solutions the ions, both positive and negative can be current carriers.
  19. May 3, 2006 #18

    Ivan Seeking

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    Boy, my answer on this one really sucked.

    As Integral stated, the generator acts like an electron pump that moves the electrons along the circuit. All that is needed is a complete circuit or a capacitive reservoir to store the charge. In the case of an isolated generator running a load, the current is circulating in a closed loop, so this is like taking a water pump and connecting the discharge to the suction side; presumably with some kind of load in between such as an orifice in the case of a water pump, or a resistor in an electrical circuit. Valence electrons in the conductors - the circuit - is the source of the charge.
    Last edited: May 3, 2006
  20. May 3, 2006 #19
    Here's a diagram of what everone is saying. It's simple circut with a battery but it's the same effect as a generator. Bascially when the electorns go though the light bulb they lose energy form the energy conversion then they go back to the - side of the battery and get more energy form the battery. This will contuine until things 1) the battery dies 2) you noticed how there's a wire going back to the battery form the lightbulb if that wire gets disconnected there will be no constant supply of electorns to pump the energy into the light bulb.

    Attached Files:

  21. May 5, 2006 #20
    I always like to explain the ping-pong ball analogy with a pipe filled with water. When you turn on the 'switch' it's like putting a drop of water in one end of a water filled pipe. On the other end, out comes a drop, but overall the water in the pipe didn't really move. This can be applied to drift velocity because when the electricity flows through the wires, it isn't travelling like a car on a road....it's just "bumping other electrons down the line up a notch".
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