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: Urgent help need on easy significant number question

  1. Oct 14, 2004 #1


    User Avatar

    Hello guys. I have a little problem here.. we are doing a colorimeter (sorry in advance for the english errors. I dont know if it is called like that in english im translating from french.) experience and I have to use this formula
    D = e* L * C
    e= D/ LC

    where L is a constant 1cm.

    L= 1 cm
    D= 0,783 (taken from colorimeter)
    C= 0,4841 (concentration I have calculated)

    Now I know I'm supposed to keep the same amount of significant numbers than the one that has the less but I know I can't keep only 1 (because of the 1cm which is only 1 number.)

    So do I keep my answer with 3 or 4 ? Is D (optical density) considered a constant?

    Thanks a lot
  2. jcsd
  3. Oct 15, 2004 #2
    What does the value of L represent? Was it given to you in the experiment outline, or did you measure it?
    Often if it's given to you in the experiment, they'll list the correct number of significant digits they'll want, such as 1.00cm. If you had to measure it yourself, my suggestion would be to measure it as accurately as you can to a few decimal places (ie: 1cm and 0mm = 1.0cm). If you do have to measure it yourself though, I'd suggest asking your teacher how many significant figures they want from that measurement.
  4. Oct 15, 2004 #3


    User Avatar
    Science Advisor

    From your statement "L is a constant 1cm.", I would guess that L is "given" as an exact number. If that is the case, D is the "limiting" measurement. Since it has 3 significant figures, your result should have 3 significant figures.
  5. Oct 15, 2004 #4


    User Avatar

    Thats what I did. Thank you for your help.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook