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Circuit Theory: physics vs. convention?

  1. Apr 17, 2006 #1

    KCL

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    This bothers me every time I study circuits, currently introductory level.

    I can solve problems just fine, but something is just not "clicking" here. Mostly conventions for things like current, power absorption, etc...

    Is there some where an explanation of what actually happens in a circuit and how does it relate to conventions like taking the current to move from positive to negative? I keep staring at a diagram of currents and thinking "is this negative current just the opposite of the positive one 'we use' or the 'real' current of negative charges that's actually moving or or or" etc... :confused:


    I don't think I can even phrase the question correctly, I hope someone understood me from this post. :rofl:
     
  2. jcsd
  3. Apr 17, 2006 #2

    chroot

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    You can equally well consider current to be positive charges moving in one direction (this is conventional current), or negative charges moving in the opposite direction (this is how electrons actually move).

    - Warren
     
  4. Apr 17, 2006 #3

    Ouabache

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    Ben Franklin has often been credited with our convention of current flow from positive to negative poles.

    ref

    You're not the first to notice this. Many of us, myself included, found this convention disturbing. :grumpy: Perhaps the only way to change it now would be by international agreement amoung scientists and the technical community. :smile:
     
    Last edited: Apr 17, 2006
  5. Apr 17, 2006 #4

    KCL

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    stupid question:

    So if, let's say you're using the actual current - negative charges. Would the current be just 5 amps and a negative of that be the positive one in the opposite direction or would it be -5 amps with the negative of that be the positive one in the opposite direction? :redface:

    Thanks for any help.
     
  6. Apr 17, 2006 #5

    chroot

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    Current is always defined with respect to some convention. If you assume a direction, and you're right, the value is positive. If you assume a direction, and you're wrong, the value is negative.

    Really, forget about the signs on currents, and instead just look at the arrows on the schematics that indicate which direction the currents are flowing.

    - Warren
     
  7. Apr 17, 2006 #6

    KCL

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    Ok that's exactly what I needed to hear, thanks.
     
  8. Apr 18, 2006 #7

    Ouabache

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    What sort of questions are you having about power absorption?
     
  9. Apr 19, 2006 #8

    KCL

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    I was just rambling about everything because current signs/direction just confused everything in any circuit. Once I get "stuck" on any detail I just panic and become incapable of understanding anything, so that really screwed me up for a while. Texts explain it clearly but I just needed to make sure, to read the same thing I'm getting from the text but after I ask a question on it just to confirm that I'm really "getting" it.... Not sure if this makes sense. :redface:

    And yes I have a serious OCD problem. :rofl:
     
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