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Circuit Question - Combining/Redrawing Circuits

  1. Jan 16, 2014 #1
    Circuit Question -- Combining/Redrawing Circuits

    I dont understand how they the circuit on the left was redrawn to be the circuit on the right.

    1. How did they know R1 and E1 were parallel to R2 and E2 and the 6 ohm resistor?

    2. How did they know that E1 should be position as it is in the picture? Same question for E2.

    Attached Files:

    • QQ.jpg
      File size:
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  2. jcsd
  3. Jan 16, 2014 #2


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    Gold Member

    You think you could make the image just a little smaller? I can almost read this one.
  4. Jan 16, 2014 #3
    I hope this one is better

    Attached Files:

    • AA.jpg
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  5. Jan 16, 2014 #4


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    Take the nodes marked E1 and E2 in the first picture, and place ideal, constant voltage sources (or ideal batteries in this case) with the appropriate emf (voltage) between those nodes and ground. Connect all your grounds, and you should get the second picture (except without RL, since that wasn't in the blue part).

    For example, in the first picture, E1 is just hanging there at -6 V. Instead of letting it hang there like that, add in a 6 V source between E1 and ground, paying attention to the polarity such that the original point E1 is negative 6 V with respect to ground. Do the same sort of thing for E2 (except +10 V). Then connect all the grounds together.

    You can do that because when a node is "hanging" at a constant voltage like that, it is assumed that a voltage source is present, even though it's not in the diagram. So it's okay to put one in. You're not violating anything with lumped-parameter circuit theory by doing so.
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