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Current through the circuit with resistor and light bulb

  1. Aug 22, 2012 #1
    1. The problem statement, all variables and given/known data

    Problem is give in the image


    2. Relevant equations

    V=IR

    3. The attempt at a solution

    Since its a series circuit i tried that current should be the same so it's 9/20 since there is no resistance in the bulb which is 0.45 Ω somehow the answer is 0.3Ω. why is that the case? should be something to do with the graph but i have no idea what to do with it
     

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  2. jcsd
  3. Aug 22, 2012 #2
    In the image you've provided, it's difficult to tell what's being asked. I assume that you're supposed to finish the sentence: The current in the circuit is ______. Is that correct?
     
    Last edited: Aug 22, 2012
  4. Aug 22, 2012 #3

    lewando

    User Avatar
    Gold Member

    The resistance in the lamp is not zero. It is variable--described by the curved dashed line. The answer has units of "A", not "Ω". Try an iterative graphical approach--pick some starting value for the lamp resistance, say 20Ω, find the resulting current then use that current to determine a better value for lamp resistance. Repeat process until your lamp resistance converges.
     
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