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Homework Help: Resistance of voltmeter

  1. Apr 17, 2010 #1
    1. The problem statement, all variables and given/known data
    a resistor of 600 Ω and one of 400 Ω are connected in series and their combination is being supplied by 90 V. A voltmeter that is connected on edge of the resistor of 600 Ω shows 60 V. a) what's the internal resistance of the voltmeter.


    3. The attempt at a solution

    i found the real V in the resistor of 600 V which is 54 V. But the voltmeter shows 60 V. Now I don't know how is this possible

    if they are in parallel could we just find the Rtot that will be Rv* Rs/(Rv+Rs) and then say I = V/R

    and from this equation find the Rv? but i find false results using this method, the book says 3000 Ω
     
  2. jcsd
  3. Apr 17, 2010 #2

    ehild

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    The voltmeter reads 50 V if its internal resistance is 3000 ohm. 60 V is impossible.

    ehild
     
  4. Apr 17, 2010 #3
    hm, so the book has it wrong?

    Im using the university physics by Hugh D. Young it's in chapter 27

    never mind, let's suppose that it reads 50, how can I find the resistance of the voltmeter? There isn't any method inside the book, and our teacher never explained us anything like that, I'm just curious how this can be solved

    thanks in advance
     
  5. Apr 17, 2010 #4

    ehild

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    Draw the circuit diagram first. Show me, please.

    ehild
     
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