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Error Propagation

  1. Sep 27, 2015 #1
    1. The problem statement, all variables and given/known data
    Suppose you measure three numbers as follows:

    2. Relevant equations
    x= 200. +-2.
    y= 50. +-2.
    z= 40. +-2.

    where the three uncertainties are independent and random. Use step-by-step propagation to find the quantity
    q= x/(y-z) with its uncertainty.
    3. The attempt at a solution
    I do not know what to do. The only thing I am thinking of doing is taking the derivatives of the func., q= x/(y-z), with respect to x, y, and z, .... and .... that's it. I'm stuck. Help, please?
  2. jcsd
  3. Sep 27, 2015 #2


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    How is error propagated in the (y-z) part? That will produce some new uncertainty a, which you then propagate for x/a. How far have you actually gotten?
  4. Sep 27, 2015 #3
    I didn't get very far.
    I skipped that problem and continued with my other homework problems.
  5. Sep 27, 2015 #4


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    Do you know how error is propagated in subtraction?
  6. Sep 27, 2015 #5
    You add them?
  7. Sep 28, 2015 #6


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    You add the sum of the uncertainties squared, then take the square root. Is it apparent why?

    So what's the uncertainty of a?
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