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Standard Deviation Problem in Physics. Help?

  1. Feb 26, 2007 #1
    Standard Deviation Problem in Physics. Help!?

    1. The problem statement, all variables and given/known data

    In working with Wheatstone bridge one student chose the value for R1 so that the bridge is balanced at L1 = 48.5 cm and L2 = 51.2 cm. If Each measurement has an uncertainty of +/- .05, what would be the minimum value for the uncertainty in the calculation of Rx?

    Given Equation: Rx = (L2/L1)*R1

    3. The attempt at a solution

    I know that R1 can be eliminated when looking at this question. However, my main concern is how to find the deviation using the Division rule? I have been exposed to several methods of finding the deviation. It confuses me a lot!

    My guess is that, regardless of the sign (multiplication, division, subtraction, addition), the deviation +/- .10 . it's just a sum of the two .05 uncertainties in measurements.

    I just need confirmation. I don't want to end up screwing up this problem...It's kind of a crucial step for the next few problems. Thanks for any help I can get!
  2. jcsd
  3. Feb 26, 2007 #2
    How does the formula for calculating the deviation in Rx look like?
  4. Feb 26, 2007 #3
    Rx = (51.2 +/- 0.050 cm)/(48.5 +/- 0.050 cm)

    im ignoring R1 because a random value was chosen for it. anyways, it just comes down to the uncertainties. how to solve it? im thinking about adding them up, which would be 0.10 cm. what do you think?
  5. Feb 26, 2007 #4
    I don't think this is correct. You said that you know of some methods to find the deviation. Do you know a method where you have to take partial derivatives?
  6. Feb 26, 2007 #5
    nope, we never learned that. I'm taking the trig-algebra based physics. we will never learn anything that involves calculus. what is the other way?
  7. Feb 26, 2007 #6
    Hmm...I thought it was about "Propagation of errors". Can you show some of the methods to determine the deviation?
  8. Feb 26, 2007 #7
    it is, but i'm confused because there are many ways to do it. the many ways to do it often end up with different answers...i mean WAY different! that's why im asking this board. it's cool. thanks for the help. i appreciate it!
  9. Feb 27, 2007 #8
    Show at least one way how to calculate it and some other that yields a different result as you say.
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