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Homework Help: What is the resistance of the wire and its uncertainty?

  1. Jun 10, 2008 #1
    1. The problem statement, all variables and given/known data
    An experiment is done to measure the resistance of a wire.
    The current in the wire is [tex]1.0 \pm 0.2A[/tex] and the potential difference across the wire is [tex]8.0 \pm 0.4V[/tex].
    What is the resistance of the wire and its uncertainty?

    2. Relevant equations
    3. The attempt at a solution

    [tex]\frac{0.2}{1.0} \times 100 = 20\%[/tex]

    [tex]\frac{0.4}{8.0} \times 100 = 5\%[/tex]

    Total Percentage Uncertainty = [tex]25\%[/tex]

    How can I get the uncertainty?
  2. jcsd
  3. Jun 10, 2008 #2
    Do you have a lab manual for your course? Sometimes they cover this in the introduction. Also, in this course, do they use calculus, or is it precalc?
  4. Jun 10, 2008 #3
    I don't think this question need calculus! It is a multiple choice question and the choices are:
    (A) [tex](8.0 \pm 0.2)\omega[/tex]
    (B) [tex](8.0 \pm 0.6)\omega[/tex]
    (C) [tex](8 \pm 1)\omega[/tex]
    (D) [tex](8 \pm 2)\omega[/tex]
  5. Jun 10, 2008 #4
    [itex]\omega[/itex]?...I think You mean [itex]\Omega[/itex]. You have been given the Voltage (V) and the Current (I). Use Ohm's law R = V/I to find the resistance. You can't add the percentages like that. Hint: You have to include the tolerance value of the Current and voltage in the formula.
  6. Jun 10, 2008 #5


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    Homework Helper

    Okay, which of those answers has a 25% uncertainty?
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