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Help understanding flow of electricity

  1. Mar 20, 2015 #1
    I know very little about electricity, but I'm trying to understand it better. I'm trying to wrap my head around something- I have heard it said that, "the flow of electricity through a circuit is due to the movement of electrons". While this explanation sounds simple enough, I have some questions:
    Let's look at electricity being passed through a copper wire from - to + on a battery. If I am correct, I believe that electricity flows from - to +, and current flows from + to -...is that right?
    1. If the atoms of the wire are comprised of N, P and e-, why don't the N and P move?
    2. If atoms make up mass, why isn't a portion (no matter how minute) of the mass moved over a long period of time?
    3. Or are we talking "free" electrons, as in static electricity?
    4. Or is it a collision of electrons (perhaps from free electrons "overloading" the shells in atoms of the copper wire) causing a chain reaction to transfer e- along a path (the wire)?
    5. Or is it the simple fact that we are hooked to a battery + on one side and - on the other?
     
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  3. Mar 20, 2015 #2

    phinds

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    Think of electricity as a bicycle chain. The energy in the voltage source causes a flow all the way around the circuit at the same time. Also you might find it interesting to Google "electron drift velocity"

    In a DC circuit, if the circuit is physically small the chain might make one revolution every few hours (thinking of the links in the chain as the electrons). In an AC circuit the chain makes tiny backwards and forwards motions, never going anywhere in the long run.
     
  4. Mar 20, 2015 #3
    Thanks for the response, but I still need more help with the questions I presented; in fact, it added yet another new question. After reading the article on edv, it said, "Copper has one free electron per atom", so is that free electron the one that is transferring the energy from atom to atom, like a pinball effect?
     
  5. Mar 21, 2015 #4

    Drakkith

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    Electricity is not a phenomenon in and of itself, but is more like a category of related phenomena. For basic circuits, you have three primary concepts: Voltage, Current, and Resistance.

    Current is the flow of charged particles. In a most electrical circuits you encounter in your everyday life, electrons are the charged particles that are flowing. Thus, current flows from negative to positive. However, because of historical reasons, you will often encounter something known as 'conventional current' which is where current is modeled as positive charges flowing from positive to negative. For most applications you can use either model as long as you are consistent and the results are the same.

    Voltage is a measure of the electric potential energy between two points. In other words, when you apply 10 volts to a circuit, the charges have a certain amount of potential energy that can be used. A higher voltage causes more current to flow through a circuit with a given resistance.

    Resistance is a measure of how difficult it is for current to flow. A simple explanation is that electrons collide with the nuclei and other electrons and give up some of their energy, which manifests as resistance to current flow and as heat.

    1. The neutrons and protons are located in the nucleus of the atoms that make up the material. These nuclei are locked into place and are immobile and cannot move at all. It is only some of the electrons that can move, typically the ones located in the highest energy levels which are the furthest away from the nucleus.

    2. Because atoms aren't moving, only electrons.

    3. We are talking free electrons, but we aren't talking about electrostatics.

    4. No, the electrons that make up the current occupy the conduction band of the material and can travel freely to any point in the material. The fact that charges are moving around does tend to cause other charges to move since they repel each other, but it isn't as simply as a chain reaction with each electron causing one other electron to move.

    5. A battery is simply a voltage source. There are many different voltage sources, and the way that a circuit works has little to do with the particular voltage source you are using.
     
  6. Mar 21, 2015 #5

    Drakkith

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    Not really. Each atom contributes one electron to the conduction band of the material. These electrons move about randomly thanks to their thermal motion. Applying a voltage causes electrons to move more in one particular direction, which means you have a net movement of charges, which is current flow. It's not a pinball effect with each electron impacting a neighboring electron and transferring energy to it.
     
  7. Mar 21, 2015 #6
    Thanks, that helped! So, if I understand you correctly, we are displacing electrons from one (Cu) atom in the metal to another when voltage is applied?
    Can you expound a little more on the electron contributed to the conduction band?
    Is this the single outer shell electron in copper? Also, please expound on what the "conduction band" is. Are you speaking of the Valence band?
     
  8. Mar 21, 2015 #7

    Drakkith

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    The free electron given up by the copper atoms is, in a way, already displaced simply by the atom bonding with other copper atoms. In effect, the free electron is shared by all other copper atoms in the metal.

    Yes, the electron shared in copper belongs to the outer shell. The conduction band does not always overlap with the valence band. In semiconductors and insulators the conduction band is a higher energy band than the valance band, and electrons have to be excited from the valance band into the conduction band. In metals both bands fall in the same energy range so the electrons naturally sit in the conduction band without being excited above their ground states.

    You can say that the conduction band only exists when the atoms are bonded together. A lone copper atom has no conduction band but it does have a valance band which consists of up to several energy levels corresponding to the energy of each valance electrons.
     
  9. Mar 21, 2015 #8
    Thank you very much!
     
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