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Determination of direction in AC Power Flow

Discussion in 'Electrical Engineering' started by Beachcomber, Nov 11, 2006.

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  1. Beachcomber

    Beachcomber Guest

    Gernerally speaking, current DOES flow from the positive to the
    negative terminal. You are bringing up a special case. Charging was
    not mentioned in the original puzzle.

    But, even so, in order for the battery to charge, the charger +
    terminal needs to be even more positive than the battery + terminal.
    for charging current to flow.
    Don't know. Unless you are a research scientist, your boss and
    co-workers might think you are nuts.
     
  2. hob

    hob Guest

    I really jumped from AC to DC without thinking on this one - After reading
    your comments on DC, it occurred to me I have an old field-driven DC meter
    that does exactly that in my lab.

    If it is DC, I just put that DC current meter in the line and read off the
    direction.

    Sorry bout that...
     
  3. krw

    krw Guest

    Ok, change that to "current flows from the *most* positive terminal
    to the "least" positive terminal.
    What changes, other than the dielectric constant? The speed of an
    individual electron is still slow compared to the SoL.
     
  4. hob

    hob Guest

    The problem in my physics book (example problem solving for electron drift)
    has it in inches per hour.
     
  5. Guest

    | |>
    |> |>
    |>
    |> >
    |> > That convention has stayed with us today, even though we know that
    |> > electrons are moving from negative to positive and the actual speed of
    |> > any one individual electron in this flow is very slow, the current is
    |> > effectively traveling at/near the speed of light.
    |> >
    |>
    |> The drift velocity is very slow. The actual speed of an electron is often
    |> on the order of 10^6 m/s as it pinballs its way through the lattice.
    |
    | The problem in my physics book (example problem solving for electron drift)
    | has it in inches per hour.

    Coulombs is a specific number of electrons. Amps is coulombs per second.
    Figure in the electron density (figured from mass, atomic number, etc) and
    conductor cross-section and you should be able to get into the right ballpark.
     
  6. hob

    hob Guest

    Coulombs is a unit of charge, not a specfic number of electrons. While a
    given number of electrons have a specific charge, a certain charge does not
    have a specific number of electrons.

    the formula for drift speed is

    v= j/ne, where n = dN/M , where

    j=current density, e = electron charge, d =density of atoms, N= Avagadros
    number, M =atomic weight

    e.g., the drift speed in a copper wire 1.6 mm dia which is carrying 10 amps
    is 3.6 x 10^-2 cm/sec.

    per Halliday and Resnick.
    |------------------------------------/-------------------------------------|
     
  7. krw

    krw Guest

    Think about this again.
    Really? Have you thought through what you just said?
    Ok. so what don't you get about 'e'? Hint: You've just hoisted
    your own petard.
    They knew what they were talking about, anyway.

    <snip trailing stuff>
     
  8. krw

    krw Guest

    I understood your point, but the electron doesn't go banging
    *through* the lattice at 1E6M/S.
    Ok, from one atom to the next, perhaps. How do you tag an electron
    to measure its individual velocity?
     
  9. krw

    krw Guest

    But the individual electron doesn't go "pinballing" at 1E6M/S.
    Again, how would you tag the individual electron to see?
    Typical == drift velocity.
    It ma be 1E6M/S over 1E-10M. ;-)
     
  10. hob

    hob Guest

    What is there to think about?
    Are you confused because there are a fixed number of electron charges
    that make up a coulomb's worth of charge?

    Do you go around saying I would like a quart of hot water's worth of sugar
    because a quart of hot water weighs about that of a bag of sugar?

    To look at it another way - if find out that a dark matter electron has
    half a coulomb of charge, which electron are you going to use?

    And still another way - where in the definition of coulomb is the
    electron?
    I don't think you understand charge.
     
  11. krw

    krw Guest

    What is the charge of an electron?
    I'm not confused at all.
    Don't be stupid.
    In what universe do you live in?
    You flunk. Show me an electron with a different charge.
    If that's what you think you don't think.
     
  12. hob

    hob Guest

     
  13. JoeBloe

    JoeBloe Guest


    To answer the post title:

    It flows BOTH ways, and it dissipates as heat in loads.
     
  14. JoeBloe

    JoeBloe Guest


    Within the frame of the definition of the word Ampere.

    One Ampere Second is a count of electrons passing a point of
    reference per unit time because one ampere is a rate of electron flow.

    High repeat rate pulse lasers need cap banks charged by high output
    power supplies to keep up with the pulse rate.

    That's-a-lotta coulombs.

    Every element in a series circuit loop has that same flow as well.
    What comes out must go back in.

    Yes, the coulomb is directly related to electron flow.
     
  15. krw

    krw Guest

    Tag one and measure its speed then.
    The "average"? The average would be the drift velocity.
     
  16. krw

    krw Guest

     
  17. krw

    krw Guest

    Are we talking AC now? What relevance does this have to the
    discussion at hand?
     
  18. krw

    krw Guest

    Define "average speed" then. Seems to me this would be the average
    of the speed of the valence electrons along the wire (a.k.a. "drift
    velocity").
    Speaking of broken record...
    So the electrons are moving at right angle to the conductor?
     
  19. krw

    krw Guest

    Sometimes it's useful to turn the problem around and look at it
    from the other end? Definitions are made by people. The universe
    isn't.
     
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