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!

Homework Help: Simple Experimental Error Problem

  1. Aug 19, 2009 #1
    I have two values:

    r = 12.3 ± 0.2m
    d = 0.57 ± 0.03mm

    I want to divide the two values to find theta (d/r = theta), how do I go about this?
    I assume that I add the experimental error margins together after the division of 12.3 and 0.57? Giving me:

    4.63 x 10^-5 ± 2.0003m
  2. jcsd
  3. Aug 19, 2009 #2


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    I cannot figure out what you've done here but 2.0003 m does not look like an appropriate uncertainty for an angle. The way this is usually done is through fractional uncertainties. The fractional uncertainty for the radius is

    [tex]\delta_{r}= \frac{\delta r}{r} = \frac{0.2}{12.3} [/tex]

    and for the arclength

    [tex]\delta_{d}= \frac{\delta d}{d} = \frac{0.03}{0.57} [/tex]

    Then the fractional uncertainty for the angle is

    [tex]\frac{\delta\theta}{\theta} = \sqrt{\delta^{2}_{r}+\delta^{2}_{d}}[/tex]
  4. Aug 19, 2009 #3


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    For division of variables on would normally treat the erros like so.

    [tex]\frac{\delta q}{q} = \sqrt{\left(\frac{\delta r}{r}\right)^2 + \left(\frac{\delta d}{d}\right)^2}[/tex]
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook