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Power question

  1. Mar 25, 2012 #1
    Question is in paint doc... question c and d are what I am interested in...

    For both questions I used P=IV, this gave me a correct answer for d but not c. For c I got 9/2 the answer is 4.3. Is that close enough? Or am I using the wrong equation?
     

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  3. Mar 25, 2012 #2

    gneill

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    Staff: Mentor

    You should show more of your work. How did you arrive at 9/2 for (c)?
     
  4. Mar 25, 2012 #3
    P =iv = 0.5a(9.0v)
     
  5. Mar 25, 2012 #4

    gneill

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    Ah. Well the power supplied by the battery is the power as delivered to external connections at its terminals. The batteries each include an internal resistance, so the voltage at the "9V" battery's terminals is not going to be 9V...
     
  6. Mar 25, 2012 #5
    is there an equation to find the voltage at the 9V battery terminals?
     
  7. Mar 25, 2012 #6

    gneill

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    KVL, Ohm's law. What's the potential drop across the internal resistance?
     
  8. Mar 26, 2012 #7
    Would it be 3?
     
  9. Mar 26, 2012 #8

    NascentOxygen

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    Staff: Mentor

    Why did you guess 3?
     
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