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Homework Help: Not sure how to do this complex circuit

  1. Feb 9, 2016 #1

    My friend told me the 2 24 are shorted. How do I know these are shorted and b) what do I do do make this question simple?
  2. jcsd
  3. Feb 9, 2016 #2

    jim hardy

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    1. Have you studied yet what is a "node" ?
    2. Have you studied that admittances in parallel add ?

    3. I see four 24 ohm resistors not two.

    4. How do you make the problem simple?
    Look at it. Which of the resistors is shorted out by wires connecting its two ends ? Replace it (or them) with wire. Then it's just four resisitors (or admittances) in parallel.

    Those are strong hints. If they do not make it obvious, repost in homework.
  4. Feb 9, 2016 #3
    Thanks for your reply Jim!

    1. Yes. A node is where 2 or more elements are connected to.

    2. I have not. I am a first year student and this is only my 4th week at school.

    3. Yes, my mistake.

    4. This is where I am not understanding. What are you meaning by a "short" ? Here is a little video I made to explain what I mean: https://vid.me/2W3D [Broken]
    Last edited by a moderator: May 7, 2017
  5. Feb 9, 2016 #4


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    A component is said to be shorted when potential difference across it becomes 0. Here, if the same wire is connecting both the ends of a resistor, the resistor is shorted. No current will flow through it. All the current flows through the wire, bypassing the resistor.Hence, it is replaced by a wire.
    Last edited: Feb 9, 2016
  6. Feb 9, 2016 #5

    jim hardy

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    A picture of what Mr cnh said


    AHA ! That diagonal 24 ohm resistor might as well not be there. It's two ends are connected by wire. So you could replace it by a wire. Or you could just erase it since (assuming no magnetic effects) no current flows through it.

    Solid Geometry thought experiment time-- Imagining things is part of figuring out circuits.
    Imagine that circuit actually built of wires and resistors in space, sitting on your tabletop.
    It might look like a 1 inch cube shaped framework with resistors forming the vertical legs..
    i see four dots in a plane at the top of that structure. Looks to me like they're a single 'node'.
    ow about the bottom ?

    Might be worth simplifying and re-drawing that circuit . That's how we solve complex circuits, simplifiy them one step at a time.
    Can you redraw it in one plane instead of three dimensional ?

    wow - a video ? You young folks are amazing. I fumble with Paint.....

    ps this is looking more and more like homework
    and there is a homework forum and mentors might move it there -
    i probably should have insisted on reposting there and following the rules
    the rules exist to encourage orderly thinking
    but you seem to be doing okay in that regard

    keep on truckin' -

    old jim
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