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Homework Help: Theoretical electronics problem

  1. Nov 20, 2008 #1
    1. The problem statement, all variables and given/known data

    I have made a picture af a circuit that you can see in the attachment.
    My teacher told me that at the points (A,C) and (B,D) the voltage (potential) is equal.
    Because of that there won't be a current between A and C and B and D (Ohm's formule)
    However, he has made an extra connection between A and D and now he asks us to find, for a given resistance of that connection, the current going through that connection.
    The voltage between A and D is also given.
    Also the two connections between + and - have a different resistance.
    I would be very grateful if someone would be able to clear this up for me.
    My whole class is unsure about the problem and although i don't really need the grades, i would still like to know answer out of pure interest in it.

    2. Relevant equations
    parallel connection: 1/R1+1/R2+...=1/Rn
    serial connection: R1+R2+...=Rn
    3. The attempt at a solution
    Because there is difference in voltage (potential) between A and D, there should also be a current between A and D. However there are two different ways to get from A to -.
    Via B or going via D. So the current should split up because it is a parallel connection.
    But because i don't know the resistance between A and B ( i do know the resistance between A and D) i can't calculate the current through A and B.
    Example problem :
    resistivity: 49E-8
    length: 25 m
    A = 2E-6
    difference in voltage between A and D ( potential) 10 Volt

    Attached Files:

  2. jcsd
  3. Nov 21, 2008 #2
    I already managed to figure it out on myself so no help is needed anymore.
    If anyone is interested: the current is divided over the two connections but because your resistance is known, and your voltage as well you immediately find the current through it.
    It was actually the easiest question in the whole book! I still aced the test though :)
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