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!

Significant figures

  1. Nov 3, 2015 #1
    1. The problem statement, all variables and given/known data
    Mass of copper = 321.5 g
    Volume = 36 cm3
    What is the density?
    How many significant figures should you give your density? Explain.

    2. Relevant equations


    3. The attempt at a solution
    The BOOK says two significant figures = 8.9 g/cm3 "since the volume is given to only two significant figures".


    YES the volume is to two significant figures but the mass of copper 321.5 g is to four significant figures.

    The full value for density of copper is 8.9305 which is five significant figures. So why did the book decide that 2 significant figures is appropriate (8.9) and not four significant figures (8.930)?
     
  2. jcsd
  3. Nov 3, 2015 #2

    SteamKing

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper

    Why should the calculated density of copper be more accurate than the quantity with the least precision, here the volume?

    The reference value for the density of copper was calculated from more precise data than what is presented in the problem statement.
     
  4. Nov 3, 2015 #3
    The book says the electronic balance measures to the nearest 0.1g
     
  5. Nov 3, 2015 #4

    SteamKing

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper

    You don't measure volume with an electron balance, though. Remember, density = mass / volume.

    If the volume is measured or calculated with less accuracy, it doesn't matter that the mass is measured to a greater precision. The precision of the density calculation is still governed by the precision of the least accurate component.
     
  6. Nov 3, 2015 #5
    i.e the volume that is measured to two significant figures.

    Thank you

    Straight talking from Steam King. No riddles (further questioning and interrogation trying to get you to work out the answer).
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted