are the volumes on this site reliable? I have just read something I don't understand

Discussion in 'Homework Help' started by bll_dotson1, Sep 15, 2007.

  1. bll_dotson1

    Thread Starter New Member

    Sep 15, 2007
    I have been reading the first chapter (I think) in the DC volume. It is talking about voltage drop and comparing it to how if a rock falls or water falls from a certain height it has a more violent impact the higher the object is dropped from. This does not make sense to me because a voltage drop means (if I am correct) that the amount of voltage drops over a given distance. Also, maybe I misunderstood, but in the beginning of that chapter it was talking about static electricity and the origin of negative and positive.

    Benjamin Franklin hypothesized that the negative had a deficiency of fluid, while the positive had an excess of "fluid". However, since electrons have a negative charge, having an abundance of them makes the negative side negative. Then later on the text says something and then in parentheses (thanks Ben!) like the idea of positive and negative is incorrect. Also, when I was doing my really simple electronics project i.e. getting 2 IR LEDs to light when connected to a USB cable, I was calculating the voltage drop over the LED, which I cam to the conclusion that the voltage of the LED was the drop, so then I had to account for the remaining voltage with a resistor. Is the voltage drop only the voltage needed by the LEDs because the distance to the beginning of the circuit is not very big?

    Regardless, it might help to make the volumes (at least the DC one) not as confusing. I am a beginner and I am having a hard time.
  2. bll_dotson1

    Thread Starter New Member

    Sep 15, 2007
    also, it seems confusing to me that often electrons are refered to as electricity. Electrons have a negative charge, so it must be that the electrons that are moving are "exposing" the charge of the protons. Although, in non-solid conductors both protons and electrons move, but since the electrons are moving it is still "revealing" the protons. Is this correct?
  3. hgmjr


    Jan 28, 2005
    I think you will find that the accuracy of the ebooks is quite reliable. It is a work in progress and there are a few errors but they are rare. If you have any confusion on a given topic then you can google the Internet and compare the explanations from multiple sources.

  4. Eduard Munteanu

    Active Member

    Sep 1, 2007
    If you're doing a circuit analysis, it doesn't really matter whether you watch the flow of electrons or holes. AFAIK, the only place where this matters is semiconductor physics, but even then the difference is not that big.

    Protons almost never flow freely (maybe just in avalanche breakdown of hydrogen or electrolysis of acids, I think). Instead, holes are used as a model.
  5. bll_dotson1

    Thread Starter New Member

    Sep 15, 2007
    so what exactly is the voltage drop? The volumes make it seem like the voltage drop is the same as voltage. Also, about the positive and the negative. Am I right that the sides are not messed up (i.e. an abundance of electrons makes that end have a overall negative charge?)
  6. mOOse


    Aug 22, 2007
    Drop means "lose potential energy".
    Gravitational potential energy is lost "across" distance.
    Electrical potential energy is lost across resistance.
    To fit it to the analogy, you would have to see the wires as extremely short
    and the resistances as very long.

    In Franklin's day people of course knew nothing of electrons and protons.
    They thought that since there were two types of electrically charged states,
    there were two kinds of moveable particles (or "fluids").
    Ben theorized that electricity was made up of only one kind of moveable particle/fluid,
    and that an electrically charged state was caused by the uneven distribution, an excess
    or deficit, of this single particle.
    The only problem was to figure out which charge was which.
    When paraffin is rubbed with wool, the two materials develop opposite charges.
    Ben simply guessed that since the wool was rough, it was rubbing particles off of
    the paraffin, and so he dubbed the charge on the wool "positive" and that on the paraffin "negative".
    Later it was determined that the particles (electrons) actually go from the wool to the paraffin.
    Thanks Ben!

    It's not the distance but the resistance you must consider.
    The wires leading to the LED have very little resistance, so they drop/lose/waste very little voltage.

    The electron is moving because it's being pushed from behind by other electrons, so the "revealed"
    protons are not really revealed at all. The marbles-in-a-tube analogy helps here. Imagine a circlular
    tube packed with marbles: if one moves they all move. When a marble moves, you wouldn't expect
    it to expose the empty tube behind it. The very reason it moved was that it was being pushed by the
    marble behind it, so that marble fills any emptiness the first marble leaves behind.