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Regarding electricity and electric generators

  1. May 14, 2015 #1
    Please note, this is a question, and not a guide or instructional article.

    While learning about electrical-engineering, I realized that I did not really know what electricity was.
    So I decided to read into it, and what I found was quite confusing. A lot of articles I read conflicted with my original understanding of electricity. Eventually, I formed a new understanding, and as of now, this is what I know:

    Atomic Structure
    Atoms
    contain electrons, protons and neutrons. Atoms are usually electrically neutral.
    Neutrons hold atoms together. They're electrically neutral (They have no charge).
    Protons determine what element the atom is. These carry a positive charge, and they weigh almost as much as neutrons.
    Electrons are primarily what flows in electric current. These carry a negative charge, and they weigh much less than protons or neutrons.
    Ions are atoms that do not have a neutral charge.
    Anions are atoms that are negatively charged because they have more electrons than protons. (Due to gaining an electron)
    Cations are atoms that are positively charged because they have more protons than electrons. (Due to losing an electron)
    c1b1359ee2f424de1873dde3187d4108.png

    Conductors
    Certain elements conduct electricity well because they give up electrons easily. We call these elements conductors. Now, copper for instance is a conductor because it has one free electron in its outer shell. Notice in the image above that the 29th electron is all alone in the fourth outer shell, this allows it to break off from the atom relatively easily.

    Electrical Current (DC)
    Electrical current is what we call a flow of electric charge. When an electron breaks free of its atom, that can start a chain reaction and cause other electrons to also jump from atom to atom.
    electricity_flow.gif
    The electrons themselves move relatively slowly. And the reason your lights turn on nearly instantly is because the chain reaction, the "wave" or "energy" moves very fast. This is analogous to pushing water in a large pipe. If you apply pressure to one end, water at the other end will move instantly, the water at your end of the pipe didn't have to move far at all for the water at the other end to move.

    Electrical Circuit (DC)
    An electrical circuit is a closed loop made of a conductive element. Electrons flow from one end of the circuit to the other and may optionally pass through a "load" which consumes the power.
    87a7ead707e71e0e982f0cdaec708f3c.png
    In this image, the electrons flow from the anode(negative terminal) to the cathode(positive terminal). The electrons flow in this circuit because the anode contains anions which are attracted to cations in the cathode.

    Generating Electricity (DC)
    An electric current can be generated by moving a magnetic field through a conductor. By moving a magnetic field through a conductor, "free" electrons on the outer shell can be knocked from their atoms and start flowing in one direction.

    PhysicsForums would not load the gif, so I linked to it instead:
    http://s27.postimg.org/5wtz8hdu9/c30babe5806875c930f51520db2f367f.gif

    Using Electricity
    We can use electricity in many ways. One way we can use electricity is to pass it through a metal with high resistance producing heat. We can use this heat to excite certain gasses that in turn, produce visible light. Note that the electrons are not consumed when this happens, they simply lose some of that "energy" we talked about earlier.


    Now my question...

    Nowadays we use AC so the electrons in the coils that generate electricity at power plants do not go anywhere. But in Edison's day when DC was being used commercially, did the coils need to be replaced when the electrons were knocked free of their atoms? How were the electrons in the coils replenished? If the direct current flowed to my house, would it also flow back to the same power plant?

    Also, please correct me if I'm thinking about electricity or atoms in the wrong way, I am still learning, and what I wrote above is what I understand so far. This is by no means a guide or instructional article.

    Thanks! :)
     
    Last edited: May 14, 2015
  2. jcsd
  3. May 14, 2015 #2

    Dale

    Staff: Mentor

    DC circuits still form circuits, with the current going around in a closed loop. The electrons that are lost on one side of a section of wire are replenished on the other side.
     
  4. May 14, 2015 #3
    This makes perfect sense, but what I don't understand is how a closed circuit is formed.
    The electricity from the power plant is traveling to my house, if the electrons do not travel back, how is a closed circuit formed?
     
  5. May 14, 2015 #4

    Drakkith

    User Avatar

    Staff: Mentor

    Electrons in conductors are not 'knocked free' of their atoms. When metal atoms bond together, their outermost electrons are shared throughout the entire structure (structure meaning a wire, metal bar, etc). An electron that originally belonged to an atom in one corner travels allllllll over the structure relatively freely. So when you have a great many atoms bonded together, as you do in a wire, there is a 'sea of electrons' moving about that easily respond to electric fields.

    Consider a broken wire that causes an open circuit. When a voltage is initially applied to the circuit, electrons throughout the metal try to flow. But the open in the circuit prevents electrons on one side of the circuit from reaching the other side. This causes a pileup of electrons on the negative side, and a reduction in electrons on the positive side, until the charge separation provides enough counter-emf to prevent more current flow (current isn't flowing across the gap, it's just that the electrons that already exist in the metal on both sides are flowing). To close the circuit you need to provide a path for these electrons to get from one side of the open to the other.
     
  6. May 14, 2015 #5
    I'm not sure if you're saying that a circuit is formed between my house and the power station.
    It would make a lot more sense if my house was the "load" and if the electrons traveled back in the circuit towards the power station.
     
  7. May 14, 2015 #6

    Drakkith

    User Avatar

    Staff: Mentor

    Whoops, I missed part of your question, about how the electrons make it back to the station.

    It's typically very difficult to tell when someone is being rhetorical or not when interacting through text. Lack of verbal and non-verbal signals and all that.

    Yes, a closed circuit is formed between your house and the power station.

    That's a good way to think about it. The simplest way of setting up a DC circuit is to just use two conductors like we do in AC power. One wire would provide the current to your house, the other conductor would provide the return path to the power station.
     
    Last edited: May 14, 2015
  8. May 14, 2015 #7
    Ah, okay. Thank you very much for that explanation, I was searching for an answer online but no one seemed to mention this part. :)
     
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