1. Not finding help here? Sign up for a free 30min 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!

Error Propagation calculation

  1. Oct 27, 2008 #1
    1. The problem statement, all variables and given/known data
    Estimate the absolute and relative standard deviations of the following calculations. The number in parentheses is the standard deviation of the preceding value.

    a) z=5.64(s=0.14)*log(138)(s=3)

    2. Relevant equations
    Sx/x =SQRT((Sp/P)2+(Sq/q)2+(Sr/R)2

    Sx=0.434(Sp/P)

    3. The attempt at a solution

    I thought of two ways to go about the problem I am not sure which way is correct here are both attempts:

    log(138)= 2.139
    Z=12.069
    SZ=SQRT((0.14/5.64)2+(3.0/2.139)2)=1.40
    Z=12.07 LaTeX Code: \\pm 1.40

    RSD=(1.4/12.07)*100 =11.6%

    Or my other attempt:

    Z=12.07
    (0.14/5.64)2+(0.434*(3.0/138))=0.01
    Z=12.07LaTeX Code: \\pm 0.01
    RSD=(0.01/12.07)*100=0.08%

    Are either of these ways correct? Any help would be appreciated. Thanks.
     
  2. jcsd
  3. Oct 27, 2008 #2

    LowlyPion

    User Avatar
    Homework Helper

    I would choose a different approach. For:

    z=5.64(s=0.14)*log(138)(s=3)

    Certainly the RSS of the relative uncertainties is a good method. But in that regard I would prefer to treat the relative error of the 3/138 as really the relative uncertainty of the range of Log(138 ±3) which looks to me more like 2.14±.01, because that is the effect on the final result, as opposed to the 3/138.

    Then I would choose to take the RSS of these relative terms according to the product rule.

    ((.14/5.64)2 + (.01/2.14)2)1/2

    And calculate the absolute uncertainty from that expression.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Error Propagation calculation
  1. Error propagation (Replies: 1)

  2. Error propagation (Replies: 1)

  3. Error Propagation (Replies: 0)

  4. Error propagation (Replies: 1)

Loading...