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Combined Circuit problem

  1. Oct 24, 2011 #1
    1. The problem statement, all variables and given/known data
    I am having trouble with the placement of the voltmeter in this particular problem


    2. Relevant equations
    What is the reading on the voltmeter V?

    Image in link below:
    http://imageshack.us/photo/my-images/52/photouko.jpg/"

    3. The attempt at a solution
    I found that the resistance of R is 8 ohms and the current flowing through it is 7.5 A. But I don't know how to find the voltage when the voltmeter is placed in that way :confused: I have only done voltage when the voltmeter is placed in parallel with a singular resistor only.
     
    Last edited by a moderator: Apr 26, 2017
  2. jcsd
  3. Oct 24, 2011 #2

    lewando

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    Gold Member

    The voltage at the left side of the 4 ohm resistor is 100.0V, relative to Y. What is the voltage at the right side of the 4.0-ohm resistor, relative to Y? This will be the voltage appearing at the "+" terminal of your voltmeter.

    The voltage at the left side of the 1 ohm resistor is also 100.0V relative to Y. What is the voltage at the right side of the 1.0 ohm resistor, relative to Y? This will be the voltage appearing at the "-" terminal of your voltmeter.

    Now your voltmeter is measuring the difference of these 2 voltages (V4-ohms, right side - V1-ohms, right side)
     
  4. Oct 24, 2011 #3
    Well said, except that there is no indication as to which terminal of the voltmeter is positive and which is negative. Therefore, the answer may be either positive or negative, depending on the orientation of the voltmeter (how the probes are connected).
     
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