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Homework Help: Open circuit armature voltage of dc machine?

  1. Jun 30, 2015 #1
    1. The problem statement, all variables and given/known data
    The book says that "the induced voltage E_a can be found by measuring the open circuit voltage at the armature terminals"

    2. Relevant equations

    3. The attempt at a solution
    But isn't there a voltage drop across the resistor so that they cant be equal? or is this ignored

    Attached Files:

  2. jcsd
  3. Jul 1, 2015 #2


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    Homework Helper

    There will only be a voltage drop over the resistor if current
    is drawn from the circuit. The voltmeter draws very little current
    so no voltage is lost over the resistor and the full induced voltage
    is measured. If the current is zero then the IR product is zero.
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