1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Uncertainty as power.

  1. Dec 31, 2012 #1
    1. The problem statement, all variables and given/known data

    Book: Introduction to error analysis, Taylor

    In page 66, quick check 3.8

    If you measure x = 100[itex]\pm[/itex] 6, what should you report for [itex]\sqrt{x}[/itex]with its uncertainty.

    2. Relevant equations

    Rule for uncertainty as power:
    [itex]\frac{∂q}{|q|}[/itex] = |n|[itex]\frac{∂x}{|x|}[/itex]

    where [itex]q = x^{n}[/itex]

    3. Attempt

    So our function is q = [itex]x^{\frac{1}{2}}[/itex]

    then σq = 0,3. (as in solution)

    The problem that is killing me is if i decide to use the general rule for error propagation, the result is different.

    Using that rule:

    |σq| = |[itex]\frac{∂q}{|x|}| Δx = | \frac{1}{2\sqrt{x}} |Δx [/itex]
    That gives:

    |σq| ≈ 0,3

    After all, the problem is correct. It was just bad calculations.

    I do not to know how to delete topics. :/
    Last edited: Dec 31, 2012
  2. jcsd
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Can you offer guidance or do you also need help?
Draft saved Draft deleted