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Homework Help: Equivalent Resistance between A and D

  1. Aug 26, 2015 #1
    1. The problem statement, all variables and given/known data
    I came across a problem and I was unable to understand how the effective resisitance of this circuit is to be calculated.
    (Please refer to image uploaded)
    2. Relevant equations

    3. The attempt at a solution
    Well I assumed that current tends to flow through wires without resistances preferrably.
    So I traces out a path such that the current flows from A to C without going theough B, then divides into 2 pathways, one containing 3ohm. The other, 1ohm.
    Can somebody guide me with the correct equivalent resistance between A and D
    Plus, lets say there were capacitors instead of the resistors, the values of their capacitances being same in magnitude as the resisitances in the image below. What would be the overall capacitance then?

    Attached Files:

  2. jcsd
  3. Aug 26, 2015 #2
    What you could try doing is simplifying the circuit.
    Draw a diagram in which the points are placed separate enough, and draw the resistances in between.

    Now pass current from A to C. You'll see that there will have to be current in more than just one path from A to D.

    Hope this helps.
  4. Aug 26, 2015 #3
    Thank you for your response, but I really have no clue as to how I can simplify this diagram more than this, if only I could do that, this would be easier to solve
  5. Aug 26, 2015 #4
    Mark points A, B, C and D, at the corners of say, a square. Now join the points appropriately using the wires/resistances.
  6. Aug 26, 2015 #5


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    Staff: Mentor

    It's a bit like a game of snakes and ladders. Imagine that A has some positive voltage and you are a positive charge and you have to move from A to D while always dropping down in voltage. Use a different colour pencil and trace out all the alternative paths you can find that take you from A to D while descending the voltage gradient. Every alternative path here represents a resistance in parallel.

    You'll recognize, too, that point B is really just point D with another name, and point C is electrically identical to A.
  7. Aug 26, 2015 #6


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    Gold Member

    you can redraw this circuit to make it VERY simple.
    hint: what is the definition of resistors in parallel and resistors is series.
  8. Aug 26, 2015 #7
    The rules for
    adding resistors in series : Rtotal = R1 + R2 + R3 + ....
    adding resistors in parallel : Rtotal = 1 ÷ (1/R1 + 1/R2 + 1/R3 + .....)


    how does this differ for
    adding capacitors in parallel?
    adding capacitors in series?
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