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Homework Help: Error analysis

  1. Dec 10, 2005 #1
    i have 5 values of slit width S

    0.0015m
    0.0158m
    0.00191m
    0.0021m
    0.00257m

    the standard error is plus or minus 0.0005

    however my teacher says she wants us to calculate ∆S error
    she says its ∆S=S(subscript 2) - S(subscript 1)

    she says the answer is 0.0007m

    WHY IS THIS SO?

    Fabian
     
  2. jcsd
  3. Dec 11, 2005 #2

    lightgrav

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    Homework Helper

    If you don't know what the "correct" value is for some quantity,
    but are pretty sure you've measured what should be the same thing 5 times, you have to presume that your average value is the "correct" one.

    How do you analyze your data (even after fixing #2 = 0.00158)
    and obtain a "standard error" of .0005 ?
    I got a mean of .001932 and a sample standard deviation of .00038 ...
    but the estimate of your error in the "correct" value is the population standard deviation of .00043 .
    If you have some reason to think that your variations are normally distributed, you can report the 50%-level rather than the 1-sigma ...
    that would get you pretty close to .0005 , I guess.

    The only way I can think of to get a .0007
    would be to use the two-sigma range (mean - sigma) to (mean + sigma),
    with the sample standard deviations. I'd call it unusual.
     
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