1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Experimental Uncertainty and Error

  1. Mar 26, 2014 #1
    Hello all,

    I used the micrometer in my lab that has a resolution of 100 nm.
    so, my measurement looks something like,

    0.2345 mm, with an uncertainty of 0.00005 mm.

    But I don't want to write, (0.2345 +/- 0.00005)mm in my data table because it just looks a little awkward to have so many zeros inside my table.

    Is there a better way of writing the measurement above? (with it's uncertainty)?

    Also, I noticed that there are 2 types of error. One is standard error and then the second one being resolution error.

    How can I combine the two? so will my resolution error be 50 nm ? I'm subtracting the two measurements to yield delta d, so will my reading error be, sqrt (50^2+50^2)≈71 nm ?

    Thank you
     
  2. jcsd
  3. Mar 26, 2014 #2

    UltrafastPED

    User Avatar
    Science Advisor
    Gold Member

  4. Mar 26, 2014 #3

    Simon Bridge

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    2016 Award

    (0.2345 +/- 0.00005)mm = (234.5 ##\small{\pm}##0.05)μm = (234.5 ##\small{\pm}##0.05)x10-3mm

    better? You can put the 10^-3 or the units at the top of the column in the table (as part of the header).
     
  5. Mar 26, 2014 #4
    Use the standard concise notation 0.23450(5) mm where the number in parenthesis is the uncertainty of the last digit of the previous quantity
     
  6. Mar 26, 2014 #5
    Shouldn't it be 0.2345(5) mm?
    And if I want to write, 666.66 nm +/- 71 nm, how can I represent the uncertainty in parenthesis?

    Thank you
     
  7. Mar 26, 2014 #6
    No, 0.2345(5) indicates a range from 0.2346 to 0.2344. The actual range is 0.23455 to 0.23445
     
  8. Mar 26, 2014 #7
    No, 0.2345(5) mm represents (0.2345 +/- 0.0005)mm. You want 0.23450(5) mm which represents (0.2345 +/- 0.00005)mm. Note the extra zero. The number in parenthesis is not an extra digit. It is the uncertainty of the previous digit(s).

    666.66(7100) nm = 666.66 nm +/- 71 nm

    I would round it to the more practical 667(71) nm. There is no point in using more than 2 significant figures for the error.
     
    Last edited: Mar 26, 2014
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Experimental Uncertainty and Error
  1. Experimental error (Replies: 7)

  2. Experimental uncertainty (Replies: 10)

Loading...