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If i have a=exp x, and i know that my uncertainty in a is 3% ( at all

  1. Nov 21, 2013 #1
    if i have a=exp x, and i know that my uncertainty in a is 3% ( at all points). At a point where a=2, how do we calculate the uncdrtainty in x.

    is the absolute value = (3% of ln 2)/ln 2, which equals 0.03mm, which equals 1% (if x is 3mm)

    thanks
     
  2. jcsd
  3. Nov 21, 2013 #2

    mfb

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    x cannot have units of mm in that equation, and a=2 does not correspond to x=3.

    Use error propagation - write the expression as x=ln(a), the derivative with respect to a is easy to find then.
    The formula looks good, but the result has the problem mentioned above.
     
  4. Nov 21, 2013 #3
    so dx = da/a?

    so the absolute uncertainty in x is equal to the percentage uncetainty in a?
     
  5. Nov 21, 2013 #4

    mfb

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    Right.
     
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