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Homework Help: Resistance between two points in complex circuit

  1. Apr 14, 2014 #1
    1. The problem statement, all variables and given/known data
    I have attached a circuit scheme from old textbook. Basically, there are 17 resistors which every has resistance R and we need to find the resistance between points A and B. (I added numbers to each resistor so it would be easier to communicate).
    Extra question of mine - is the equivalent resistance equal to that between points A and B?

    2. Relevant equations
    R = R1 + R2 + R3 + ...
    1 / R = 1 / R1 + 1 / R2 + 1 / R3 +...

    3. The attempt at a solution
    I have solved some resistors circuits exercises, but this one is more complex. I simply added 1st resistor with 3rd and 2nd with 5th, because they are in series. Now I am stuck, because I am not sure which resistors are in parallel and which are not, because they are combining to each other. I would be grateful if someone would explain from where should I start or show an example of how to solve such type of circuits.

    Attached Files:

  2. jcsd
  3. Apr 14, 2014 #2


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    Staff Emeritus
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    Hello Anonimas. Welcome to PF !

    Use symmetry.

    If a voltage applied across A & B, then all of the following nodes will be at a voltage half way between the voltages at A and at B.
    the node joining R1, R2, and R4

    the node joining R4, R6, R7, and R9

    the node joining R9, R11, R12, and R14

    the node joining R14, R16, and R17

    If there is no potential difference between any of those, then what what does that say about the current R4, R9, and R14
  4. Apr 15, 2014 #3
    Thank you for information,
    I'll try to find out :)
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