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Questionable resistance pictures included

  1. Feb 3, 2009 #1
    1. The problem statement, all variables and given/known data
    You would like to check if the battery voltage drops while it is supplying a current of 6A. You use a voltmeter designed to measure voltages up to 20V and having a resistance of 50,000 Ohms. Which of the two circuits below should be used?
    a.) How much current (in A) would flow through the headlight for Circuit a?
    b). How much current (in A) would flow through the headlight for Circuit b?


    2. Relevant equations
    delta(V) = IR

    3. The attempt at a solution

    Circuit a should be used because it has the least resistance.

    a.) I = 12/50000 = 2.4e-4
    b.) I = 12/50000 = 2.4e-4
  2. jcsd
  3. Feb 3, 2009 #2
    Before putting the voltmeter into the circuit the current passing in the headlight is 6 amps.
    What is the resistance of the headlight?
    How does that compare to the resistance of the voltmeter?

    The purpose of a voltmeter is to measure a voltage while actually disturbing that voltage as little as possible. Voltmeters are designed to draw as little current as possible.

    Now consider which diagram is appropriate.
    Last edited: Feb 3, 2009
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