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Voltage of battery through voltmeter

  1. Oct 14, 2008 #1
    1. The problem statement, all variables and given/known data

    A 85 V battery has an internal resistance of r = 5.73 ohms .

    (a) What is the reading of a voltmeter having a resistance of R_v = 482 ohms when placed across the terminals of the battery?
    ___________ V
    (b) What maximum value may the ratio r/R_v have if the error in the reading of the emf of a battery is not to exceed 5.0%?


    2. Relevant equations

    V=IR
    V=E-Ir
    V_v= I_fs ( R_c +R_s)

    3. The attempt at a solution

    i dont know where to start, the only thing i have tried was drawing the diagram of the circuit. please offer input on where to start thank you in advance
     
  2. jcsd
  3. Oct 15, 2008 #2

    Defennder

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    Homework Helper

    (a) Just treat the voltmeter as a resistor. Then find the current and calculate the potential drop across the voltmeter.

    (b) For this let the resistance of the voltmeter be R. Then using the same method above, determine the potential drop across the voltmeter in terms of R, f(R). Then we want 0.95(V)<|f(R)|<1.05(V) where V is the emf of the battery.
     
  4. Oct 15, 2008 #3
    thank you very much i got both answers correct thank you
     
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