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Wheatstone bridge arrangement with an ideal wire in middle

  1. Jul 12, 2013 #1
    1. The problem statement, all variables and given/known data
    I came across this questions in one of the online entrance tests,so i do not remember the exact values,I remembered the arrangement.
    ________________
    |............ |...........|
    |............ A...........C
    2v............|--------| (Please ignore the dots,they are to prevent figure from getting
    |.............B...........D distorted)
    |________|_______|

    A,B,C,D are resistances connected to a 2v battery.Rest everthing are ideal wires.We have to find the current through the connecting wire(-----).

    Let A-20ohms,B-15ohm,C-5ohms,D-10ohms



    2. Relevant equations

    V=I*R

    3. The attempt at a solution

    The current flowing in ---- wire will be the difference in potential across it divided by the resistance.But since it is ideal it has 0 resistance which gives infinite current.I am totally confused.(The answer is a finite value.)
     
  2. jcsd
  3. Jul 12, 2013 #2

    NascentOxygen

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    Staff: Mentor

    Welcome to Physics Forums. :smile:

    Forget about the bridge, just concentrate on determining the current in each resistor, first. Obviously, resistors A and C are in parallel?
     
  4. Jul 12, 2013 #3
    Yes...but ignoring the bridge would mean (AseriesB)||(C series D) ri8?
     
  5. Jul 12, 2013 #4
    No. It would mean (A parallel C) in series with (B parallel D). Calculate the current through the resistors and from this you can find the current through the bridge.
     
  6. Jul 13, 2013 #5

    NascentOxygen

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    Staff: Mentor

    I'm not saying ignore anything, nor suggesting any alterations to the circuit. I'm suggesting that you not get hung up on it being any special arrangement or having any special name. Just analyse it as a 4 resistor circuit to determine the current in each of the 4 resistors. The connecting wire remains in place right where it is.

    Your first step could be to determine the current drawn from the source, once you have calculated the effective resistance of that bunch.

    Then we'll take a closer look ......
     
  7. Jul 13, 2013 #6
    A||C-4ohms B||D-6 ohms. Equiv. resis.=10 ohms.So current drawn is .2 ampere.Is this correct?
     
  8. Jul 13, 2013 #7
    Correct.Now find the current through C & D (or A & B) and hence you will get the current through the connecting wire.
     
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