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Homework Help: Finding error.

  1. Oct 18, 2011 #1
    1. The problem statement, all variables and given/known data
    See photo 1

    2. Relevant equations

    3. The attempt at a solution
    See photo2

    I don't know why the error is lager than the area.
    Is it possible?

    Attached Files:

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    • 2.JPG
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  2. jcsd
  3. Oct 18, 2011 #2
    For each type of function there is a different error calculation

    for lets say x = tsin(sy) the error would be

    Δx = (Δy)tscos(sy) where t and s are some arbitrary constants

    and something like

    x = tzy were t is an arbitrary constant


    (Δx/x)2 = (Δz/z)2 + (Δy/y)2 + 2(Δzy)2/zy

    where 2(Δzy)2/zy is the covariance factor which i doubt you need to include.

    so Δx = x√(all error added together and squared individually)


    error calculations are a pain in the but in upper level physics studies but they are a necessity.

    I'll give you an different example in case it doesn't make a lot of sense

    Suppose that the area of a rectangle A=LW is to be determined from the following measurements of lengths of two sides:

    L = 22.1 ± 0.1cm W= 7.3 ± 0.1cm

    The relative contribution of ΔAL to the error in L will be

    ΔAL/A = ΔL/L = 0.1/22.1 = 0.005

    and the corresponding contribution of ΔAW will be

    ΔAW/A = ΔW/W = 0.1/7.3 = 0.014

    Thus ΔA will equal

    ΔA = A√( 0.0142 + 0.0052)

    ΔA = 0.015A
    Last edited: Oct 18, 2011
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