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Homework Help: Simple Parallel Circuit Problem

  1. Sep 7, 2010 #1
    1. The problem statement, all variables and given/known data
    I have to find V0 and I0.
    [PLAIN]http://img842.imageshack.us/img842/3058/resistor.png [Broken]

    2. Relevant equations
    I am having trouble identifying parallel resistors.

    3. The attempt at a solution
    So far I think that the 70 ohm and 30 ohm resistors are parallel but I am not sure. I know the share the same node at the top but don't they also have to share the same node as the bottom? Which is not the case (I don't think) due to that middle line that separates the top two resistors from the bottom two.

    I just need to know if those are parallel.
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Sep 7, 2010 #2
    Yes, the 70 ohm and 30 ohm resistors are parallel.

    Imaging that middle line to be shorter, would it matter? Since you are assuming the wires have no resistance it would not. So imagine that is was just a point, that should make it clear that the 70 ohm and 30 ohm resistors are parallel.
  4. Sep 7, 2010 #3
    Ok thanks. After figuring out those were parallel, I was able to find i, i1, and i2 using current division.

    Assuming my values are correct, how do I go about finding i0?
    I was thinking of using KCL but I think I have too many unknowns.

    Here's my current diagram:
    [PLAIN]http://img839.imageshack.us/img839/3058/resistor.png [Broken]
    Last edited by a moderator: May 4, 2017
  5. Sep 7, 2010 #4
    Just as you found i1 and i2 you could calculate an i3 and i4 through the two remaining resistor, and then use KCL to find i0
  6. Sep 7, 2010 #5
    would I do i3=(R4*i1)/(R3+R4) and i4=(R3*i2)/(R3+R4) ?

    edit. nevermind, i found i3 using KVL :)
    Last edited: Sep 7, 2010
  7. Sep 7, 2010 #6
    Yes you would
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