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Homework Help: Combination Circuit

  1. Feb 4, 2014 #1
    1. The problem statement, all variables and given/known data

    Determine the Req, IT, and the current and voltage across each resistor. Collapse each drawing into one resistor that equals Req. Find the total power used by the circuit. Also determine the voltage, current, and power for each individual resistor.

    The one I'm having trouble with:

    2. Relevant equations

    Req = R1+R2+R3...
    1/Req = 1/R1+1/R2+1/R3...
    V = IR
    P = IV

    3. The attempt at a solution

    I combined B and C into BC (4 Ω) and then combined that with F to make BCF (2 Ω). This would give me the following resistances: RA = 2 Ω, RE = 6 Ω, RBCF = 2 Ω, RG = 2 Ω, and RD = 5 Ω. That would make Req = 17 Ω since all these are now in series.

    When trying to calculate the current of the whole circuit... I = V/Req = 40/17 = 2.35 A

    My teacher posted that the total current should be 4 A. I'm not sure where I messed up.
  2. jcsd
  3. Feb 5, 2014 #2


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    Homework Helper
    Gold Member

    That's a fair start. :approve:

    There is where the problem is!

    You can't treat BC and F as being parallel with each other. There are resistors E and G in the way which prohibit that!

    However, what you can do is combine E, F and G, all in series.

    After that, you have parallel resistors that you can combine: BC and EFG. (And then deal with a couple more series resistors A and D even after that.)
  4. Feb 5, 2014 #3
    AH! That makes so much sense! Thanks!
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