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Homework Help: Complex Circuit problems!

  1. Apr 7, 2009 #1
    1. The problem statement, all variables and given/known data
    Consider the circuit in the figure.
    Circuits 001.jpg
    Find the current in the 1.3 Ω resistor. Answer in units of A.
    Find the potential difference across the 1.3 Ω resistor. Answer in units of V.
    Find the current in the 10.0 Ω resistor. Answer in units of A.

    2. Relevant equations
    V = IR
    Req = 1/R1 + 1/R2 + 1/R3 ...

    3. The attempt at a solution
    First, I calculated the equivalent resistance.
    The top path - parallel circuit: 1/((1/7.7) + (1/7.7)) = 3.85 + 3.4 = 7.25​
    The middle path - parallel circuit: 1/((1/4.6) + (1/10.0)) = 3.150684932 + 1.3 = 4.450684932​
    Req = ? ​
    My teacher helped me at school and when I tried to do the problem on my own, using his steps, I forgot them all. Just yesterday I remember that I could get the equivalent resistance which is around 6.157 but I keep trying and trying but I can't seem to get that answer either. I need help on that part too.

    Here is the total current: I = V / R -> I = 18.0 / 6.157 = approx. 2.92

    I don't really understand how to find the current etc. It gives me headaches! Sorry the picture is kinda dark....
    Last edited: Apr 7, 2009
  2. jcsd
  3. Apr 8, 2009 #2
    Everything you have done is OK. Except the equation is

    1/Req = 1/R1 + 1/R2 +......

    Treat the top and middle paths as two parallel resistances and find their equivalent resistance before adding the final 3.4 Ohm. You will get the 6.157 Ohm value.

    Then to answer questions 1 and 2 you have to work out how much of that 2.92 amperes of current will go though the middle branch.

    For question 3 you conduct a similar investigation.
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