2 Batteries Mesh Circuit Polarity confusion

Discussion in 'Homework Help' started by LittleOldMan, Feb 11, 2009.

  1. LittleOldMan

    Thread Starter New Member

    Feb 11, 2009
    4
    0
    The attached mesh circuit problem is as shown in text.
    Text uses conventional current direction of positive to negative.
    Polarity of 6V battery and direction of current in the east circuit seem to be in conflict.
    Any insight will be greatly appreciated.
    Thank you
     
  2. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    Regardless of the direction of assumed current flow, you should be able to proceed with the your analysis based on that assumption. If the equations are formed correctly based on your assumptions you should obtain the correct results. The sign will alert you to differences between your assumed current direction and the conventional direction.

    hgmjr
     
  3. LittleOldMan

    Thread Starter New Member

    Feb 11, 2009
    4
    0
    OK, I'm working through the analysis.
    In following the current from the ground to point B, I believe voltage drops through the battery and then drops again through the resistor.
    Does this mean the voltage at Point B is negative relative to ground?
    Thank you for your help
     
  4. Ratch

    New Member

    Mar 20, 2007
    1,068
    3
    LittleOldMan,

    You never said what you are trying to calculate. Is it the current in the loops, the voltage across the resistors, the voltage at note "N", what is it? Always use conventional current protocol for calculations. Assume the loop currents exist in a clockwise direction. Decide whether you wnat to do loop, branch, or node analysis. Ratch
     
  5. LittleOldMan

    Thread Starter New Member

    Feb 11, 2009
    4
    0
    The problem is to determine the voltage drop across R2, which I believe is the same as the voltage at node N, using node-voltage analysis. I have solved my polarities confusion. My new confusion is why the current across R4 is the same as the current across R3. Is this simply because they are in series with each other, regardless of the rest of the circuit?

    Thanks again for all your help - much appreciated.
     
  6. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    Be sure to provide us with all of your work so that we can better assist you in identifying where you may have gone off the rail.

    hgmjr
     
  7. LittleOldMan

    Thread Starter New Member

    Feb 11, 2009
    4
    0
    My work is attached. The answer book says I2 is the same across R3 and R4. I am confused as to how we know that I2 is the same across both resistors.
    Thanks again
     
  8. Ratch

    New Member

    Mar 20, 2007
    1,068
    3
    LittleOldMan,

    Your posting is rotated 90 degrees.

    Certainly, R3 and R4 are in series.

    Your work did not give a voltage across R2.

    Ratch
     
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