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Need help with Kirchoff's law problem

  1. Sep 29, 2016 #1
    1. The problem statement, all variables and given/known data
    http://file:///Users/jarrettwingfield1/Desktop/Screen%20Shot%202016-09-29%20at%205.29.21%20PM.png [Broken] My professor told me my equations were correct, but I do not know how to find the current through each resistor mathematically, and every example I find online is too simple so it doesnt help me.
    My equations are: i1=i2+i3; -2i2 - 6i1 = -8 ; 2i2- 4i3 = -12
    An online calculator says i1=0.857 i2=-1.429 and i3= 2.286


    2. Relevant equations


    3. The attempt at a solution question 4a.jpg Screen Shot 2016-09-29 at 5.29.21 PM.png
    I question 4.jpg
     
    Last edited by a moderator: May 8, 2017
  2. jcsd
  3. Sep 29, 2016 #2

    gneill

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    Staff: Mentor

    Hi BirdK, Welcome to Physics Forums.

    Your image is not visible, likely because it's hosted on your machine. Can you upload it? (Use the UPLOAD icon at the bottom right of the reply edit window).

    You need to show some details of your attempt.
     
  4. Sep 29, 2016 #3
    Well I can't seem to figure out the upload thing, maybe because its a mac. But I am certain that my equations are set up correctly, so if someone can just show me how to do the math. I've attempted it several times, but my professor hasn't showed us how to do all the different types of these equations.
     
  5. Sep 29, 2016 #4

    gneill

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    Staff: Mentor

    If the image is in a file on your computer then the UPLOAD mechanism should be able to open a file list via your machine's operating system for selection. If not then perhaps the mechanism is blocked on your machine (security issue?). Otherwise, you should be able to cut and paste a "snipped" screen grab. Failing that, upload your image to a hosting side and paste a URL.

    Regarding your equations, helpers won't do the math for you or show you step by step. You need to show what you've attempted in detail and they will point out errors, make suggestions, give hints and so on.
     
  6. Sep 29, 2016 #5
    I attached the problem and my work. Where it says 3(4), that just means I multiplied equation 3 by 4, to add to the equation of 1+2
     
  7. Sep 29, 2016 #6

    gneill

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    Staff: Mentor

    I'm having difficulty interpreting your handwritten work, but I can see that the results you're getting are not correct.

    I've spotted one error in the first block of equations where you summed ##-6 I_3## and ##-16 I_3## and arrived at ##-24 I_3##, which is not right. I gave up after that.

    You should endeavor to make the math you present more clear for others to read, preferably with some commentary to describe what you're doing at each step. Ideally you'd type in your equations so that they can be quoted in replies. LaTeX is a wonderful thing :smile:
     
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