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R circuit (pretty simple) need checked - full working - please

  1. Jul 19, 2010 #1
    R circuit (pretty simple) need checked - full working - please!!!

    1. The problem statement, all variables and given/known data

    see attachment

    2. Relevant equations
    P=IV
    P_loss=I^2 R
    V=IR


    3. The attempt at a solution
    ok
    36=I^2*12

    I_12Ω=√3 A
    V=20.8V
    That is the same for the 3 resistors in parallel (I hope)
    so I18Ω=1.15A
    I36Ω=0.577A
    the sum of these will give me the current through the unknown resistor
    Iunknown=3.46A
    net voltage = 60
    60=Vunknown + 20.8
    Vunknown=39.2V
    V=IR
    R=11.3Ω

    can someone please check this - wouldn't ask if I dint need it.
     

    Attached Files:

  2. jcsd
  3. Jul 19, 2010 #2

    rl.bhat

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    Re: R circuit (pretty simple) need checked - full working - please!!!

    Your answer is correct.
     
  4. Jul 19, 2010 #3
  5. Jul 19, 2010 #4
    Re: R circuit (pretty simple) need checked - full working - please!!!

    Sorry, I forgot the second half of the question,

    P_loss=I^2 R
    P=〖3.46〗^2*((1/12+1/18+1/36)^(-1)+11.3)
    P_loss=207.6W
    This seems big to me, could you please check that too.
     
  6. Jul 20, 2010 #5

    rl.bhat

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    Re: R circuit (pretty simple) need checked - full working - please!!!

    your answer is correct.
     
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