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Homework Help: Current in a circuit

  1. Apr 2, 2014 #1
    1. The problem statement, all variables and given/known data

    The circuit is given as in the attachment. All resistors have known resistance and the inner resistance of the ammeter in known. The current which is measured by the ammeter is known. What is the current at the point T?

    2. Relevant equations

    Ohm's law: V=IR. Also at each junction, Iin=Iout.

    3. The attempt at a solution

    Let R0 be the resistance of the ammeter, I1 be the current at the point T, I2 be the current at resistor R2 and IA be the current at ammeter. It follows that IAR0=I2R2, from which I2 follows. Then I1=I2+IA.

    That is what I think is true. But, given the values of resistances of all resistors which I didn't use in the calculation, I start to wonder if I miss something. Am I right or wrong?

    Attached Files:

    Last edited: Apr 2, 2014
  2. jcsd
  3. Apr 2, 2014 #2


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    Staff: Mentor

    You are right so far, but not yet finished. You should end up with something like

    IT = k.IA where k is a value you determine
  4. Apr 2, 2014 #3
    Isn't IT=I2+IA? (conservation of charge at the junction)
  5. Apr 2, 2014 #4


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    Staff: Mentor

    Correct. But we don't know I2 so eliminate it from the equation.
  6. Apr 3, 2014 #5
    But I2=IAR0/R2...
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