Superposition theorem

Discussion in 'Homework Help' started by metelskiy, Nov 8, 2010.

  1. metelskiy

    Thread Starter Member

    Oct 22, 2010
    66
    3
    i have this circuit
    lab 7_1.png
    I got confused with positive and negative voltage supplies. In class we used only positive. I need to find voltage at point A using superposition theorem. Could someone please help me at least understand circuit? How would i redraw it in a more understandable way?
    To start i know i have to short 12V source and leave -12V and calculate Voltage at A.
    Than short -12v and leave 12v and calculate voltage at A again.
    Than add those two values and it should be voltage at A for original circuit.
    How would i treat that -12v souce? thanks.
     
  2. shteii01

    AAC Fanatic!

    Feb 19, 2010
    3,394
    497
    You have two cases.

    Case 1
    12 V is shorted.
    You have R1 parallel with R3, lets call it R1||R3.
    The R1||R3 is in series with R2 and in series with -12 V source.
    Draw this circuit, solve for what ever you need.

    Case 2.
    -12 V is shorted.
    You have R2 parallel with R3, lets call it R2||R3.
    The R2||R3 is in series with R1 and in series with 12 V source.
    Draw this circuit, solve for what ever you need.

    Like you said, add results from Case 1 and Case 2, that is your answer.
     
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  3. metelskiy

    Thread Starter Member

    Oct 22, 2010
    66
    3
    Thanks a lot. This circuit makes sense to me now. I found Va'=3.5V and Va''=-6.1V and Va=3.5v+(-6.1V)=-2.6V
     
    Last edited: Nov 8, 2010
  4. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    -2.6V matches my result.

    hgmjr
     
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  5. metelskiy

    Thread Starter Member

    Oct 22, 2010
    66
    3
    Ok here is another problem. I think i mainly understand it but if someone got time and patiance please check if i'm doing it right, first redrawing circuits. I'll need to find voltage at points A and B using superposition theorem.
    Original (A and B on ends of R3):
    lab 7_2.png
    5V and -12V shorted:
    lab 7_2_1.png
    12V and -12V shorted:
    lab 7_2_2.png
    12V and 5V removed:
    lab 7_2_3.png
     
  6. Georacer

    Moderator

    Nov 25, 2009
    5,142
    1,266
    Your circuit look good to me. You just didn't label the nodes A and B in the initial circuit so I can't comment on the correct node notation.
     
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