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Finding current in an electric circuit

  1. Nov 30, 2016 #1
    1. The problem statement, all variables and given/known data
    A voltmeter of resistance 50kΩ is used to measure the electric potential difference in a circuit, as shown. The cell has an electromotive force (emf) of 5.0 V and negligible internal resistance.

    upload_2016-12-1_8-38-49.png

    2. Relevant equations
    I=V/R
    V=IR

    3. The attempt at a solution
    I=5/150000 I=3.33E-5
    V=50000*3.33E-5=1.7 V

    But the answer is 1 V. How?
     
  2. jcsd
  3. Nov 30, 2016 #2

    Doc Al

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    Staff: Mentor

    You did not account for the internal resistance of the voltmeter.
     
  4. Nov 30, 2016 #3
    How do you account for the internal resistance of a voltmeter though? It's not provided. Plus isn't voltmeters purposefully created with high resistance so as to create as little change in the circuit as possible?
     
  5. Nov 30, 2016 #4

    NascentOxygen

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    Staff: Mentor

    You're told it is 50kΩ. (That's separate to the resistor of the same value in the circuit.)

    There may be reasons it can't always designed to be near "infinity".
     
  6. Nov 30, 2016 #5
    Ohhhh I see, I thought the 50kΩ is the resistance of the resistor! Maybe I should've read the question more clearly. :woot:
     
  7. Nov 30, 2016 #6

    NascentOxygen

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    Staff: Mentor

    See my amended reply.
     
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