1. Not finding help here? Sign up for a free 30min 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!

A question on percentage uncertainty

  1. May 24, 2016 #1
    1. The problem statement, all variables and given/known data

    Say we have the equation D2 = C x N where C = A2.
    Using a graphical method to find the % uncertainty of C (from graph of D2 against N) which involves working out the gradient which equals C and so forth. This value is 25%.
    The question is "what is the percentage uncertainty of A?"

    This is actually a question that appeared in an A-level paper i did today and it was the only one that really bamboozled me :confused:.
    2. Relevant equations


    3. The attempt at a solution
    I realize you don't divide by two;my reasoning being that when asked to calculate the % uncertainty of r in say the equation V = 4/3 x π x r3 the question doesnt explicitly state r3.

    So i think that it is between doubling 25% or just leaving it. Now i think it was the latter but in the exam I did indeed double it to 50%.
     
  2. jcsd
  3. May 24, 2016 #2

    Simon Bridge

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    2016 Award

    You are propagating errors of form ##z=x^a## knowing ##x\pm xp_x/100## where ##p_x## is the known percentage error.
    So what is the rule for propagating the error on a power?
     
  4. May 24, 2016 #3
    Multiply the percentage uncertainty by whatever the variable is to the order of?
     
  5. May 24, 2016 #4
    Anyone else?
     
  6. May 25, 2016 #5

    Simon Bridge

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    2016 Award

    What's wrong with the reply you got so far?
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: A question on percentage uncertainty
  1. Percentage uncertainty (Replies: 4)

  2. Percentage uncertainty (Replies: 4)

  3. Percentage Uncertainty (Replies: 2)

  4. Percentage Uncertainty (Replies: 7)

Loading...