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Ac circuit non inductive resistor and a coil

  1. Jan 29, 2011 #1
    1. The problem statement, all variables and given/known data
    A non inductive resistor takes 8A at 100 volts. What inductance of a coil of negligible resistance must be connected in series in order that this load can be supplied from a 220 volt 60 Hz mains.



    2. Relevant equations
    Z^2 = R^2 + XL^2
    R=V/I
    XL = 2pi(frequency) L(inductance)

    3. The attempt at a solution
    i have solve the resistance before the coil is added.. R=12.5 ohms....
    i am stuck on how to get the value of the coil since there is no given current..
     
  2. jcsd
  3. Jan 29, 2011 #2
    (Stipud educators. The correct answer to this question is that any finite inductance will "supply" the load!!)

    The implied question phrased in more than half-witted manner is, "What will supply the load at the same RMS current?

    You know the new voltage. It's 220 VAC. So it's not the same one you used to find R.

    Use the voltage divider rule for complex impedance in series. Remember the one for finding the voltage across one resistor that's in series with a second resistor? It looks the same.
     
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