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Ohm's law

  1. Dec 12, 2012 #1
    In ohm's law for a receiver or generator I couldn't understood the difference between e/E and U(voltage).
    So please can anybody help me in this?
     
  2. jcsd
  3. Dec 12, 2012 #2

    gneill

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    Staff: Mentor

    Hi M&I. The use of e, E, V, U, etc., to represent potential difference is a choice made by the author of a diagram or document. Sometimes the choice is personal preference or local convention, or sometimes it's just to avoid duplication if a given variable is already in use for something else.

    No matter what variable name is used, all electric potential differences are treated the same way for analysis (Ohm's law, Kirchhoff's law, etc.).

    Do you have a particular example where the naming is causing confusion?
     
  4. Dec 12, 2012 #3
    In ohm's law for a generator:
    U=E-r.I
    U voltage
    E electro motive force
    r resistance
    I current

    And ohm's law for a receiver
    U=e+r.I
    e back electro motive force
     
  5. Dec 12, 2012 #4

    gneill

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    Staff: Mentor

    The U,E, and e are representing different potentials in a generator/motor situation. It seems that the author has decided to use U for the "line" potential, e for the back-emf created in the motor's windings (inductance), and E for the potential developed across a generator's windings. The naming convention is designed to help you keep track of what the values represent "in the real world".

    attachment.php?attachmentid=53860&stc=1&d=1355328795.gif

    The figures in your text might show the inductor potentials as dependent voltage supplies.
     

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