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Uncertainty (Measurements)

  1. Mar 31, 2016 #1

    averycasille

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    Hello, guys! (And girls, but.. you know..)
    There are several things I do not quite understand, so, can you help me clear my doubts? ^^

    1) How do I know when to multiply the value of calculated data when it comes to determining the uncertainty of the data?

    2) When do I multiply the percentage of accuracy with given data when determining uncertainty?
     
  2. jcsd
  3. Mar 31, 2016 #2
    I have no idea what you are asking, Perhaps you could give an example of your issue.
     
  4. Mar 31, 2016 #3

    averycasille

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    Sorry for being unclear!
    • The manufacturers of a digital voltmeter give, as its specification, accuracy +-1% with an additional uncertainty of +-10mV. The meter reads 4.072V. How should this reading be recorded, together with its uncertainty?
     
  5. Mar 31, 2016 #4
    You record the reading as is 4.072 V. The uncertainty should be 1% of that reading + 10 mV.= 0.0407 V + .01 V = .0.0417 V =0.042 V ( rounding )
     
  6. Mar 31, 2016 #5

    averycasille

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    Ohh. So, when the specific accuracy is given, I should always multiply with the data and add it with the additional uncertainty? Is that it?
    Also, regarding the rounding off, that should be based on significant figures/decimal place of the data? O.O
     
  7. Mar 31, 2016 #6
    yes
     
  8. Mar 31, 2016 #7

    jbriggs444

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    0.0407V + 0.010 V = 0.0507V which is 0.051 after rounding to an appropriate precision.
     
  9. Mar 31, 2016 #8

    averycasille

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    Thanks, peeps! But, significant figure OR decimal place? Sorry for asking a lot
     
  10. Mar 31, 2016 #9

    jbriggs444

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    As a general rule, significant figures are not appropriate in the real world. They are a toy for the classroom. The reporting conventions for your organization should be followed. One recommendation from http://web.mit.edu/fluids-modules/www/exper_techniques/1.Recording.Uncertainty.pdf is:

    "As described above, to determine a quantity x, we make a measurement, report our best estimate, and report the range over which we are reasonably confidant the actual value lies: (measured value of x) = xbest ± δx ."

    e.g. 4.072 ± .051 V
     
  11. Mar 31, 2016 #10

    averycasille

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    Thanks for the assistance, everyone. Means a lot Really appreciate it!
     
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