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DC Circuits Homework

  1. Sep 27, 2009 #1
    1. Eight lights are connected in parallel to a 119V source by two leads of total resistance 2.5 ohms. If 240mA flows through each bulb what is the resistance of each? What fraction of the total power is wasted in the leads?


    2. V=IR, P=I^2(R)



    3. V=.24(119)=495.83/8=62ohms
    P=(.24)^2(62)=3.57W
    These are the answers i got but according to my book they are wrong. Can anyone tell me what im doing wrong? thanks
     
  2. jcsd
  3. Sep 27, 2009 #2
    Well as for your first question you seem to have V=iV.

    Now you know the resistors are connected in parallel.

    To find the total resistance of all components, add the reciprocals of the resistances R of each component and take the reciprocal of the sum. :D.
     
    Last edited: Sep 27, 2009
  4. Sep 27, 2009 #3
    2.5ohms is the total resistence? I thought that was just the resitence in the wire going from the battery and the wire going to the battery
     
    Last edited: Sep 27, 2009
  5. Sep 27, 2009 #4
    In addition to what you already know about the circuit, you need (well, I suggest):

    1) An equivalent circuit where you include a 2.5 ohms series resistor to represent the loss in the wires.
    2) Kirchoff's Current Law
    3) Kirchoff's Voltage Law
    4) Ohm's Law
    5) The expression for power.

    Use them in that order, and see how that goes.
     
  6. Sep 27, 2009 #5
    what is Kirchoff's current law and voltage law? they're not in my book
     
  7. Sep 28, 2009 #6
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