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What defines a real negative voltage?

  1. Jan 20, 2012 #1
    This has been bugging me for a long time! Now if electrons are -Q and the V is basically what energy is added to that Q how do you define the voltage as being - or +. For example in a computer system, the data cable has + and - negative voltage, so is the polarity switch at ether end on the cable?

    I do apologise if this doesn't make much sense, I am not very good at explaining, what I am trying to ask.
  2. jcsd
  3. Jan 20, 2012 #2
    The reference point determines whether we have a positive or negative voltage.
    See this example

    Attached Files:

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