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Homework Help: How'd this happen in my experiment?

  1. Jan 8, 2005 #1
    How'd this happen in my experiment??!!

    Im at a total loss now. As some of u guys may know, Ive been doing a science fair project on light refraction. I did the experiment, and somehting most peculiar happened.

    It is by Density Order

    Liquid Weight Density Angle of Refraction
    (1) 170g 1.06 g/mL 29.5°
    (2) 164g 1.03 g/mL 31°
    (3) 160g 0.99 g/mL 32°
    (4) 150g 0.89 g/mL 28.5°
    (5) 139.5g 0.785 g/mL 30°

    Why the heck is the Angle of refraction so erratic? shouldnt it decrease gradually as density decreases??

    I did this experiment dozens and dozens of times (literally, I swear)

    How did this happen? Is there some variable I missed due to me being a grade 9 student with limited knowledge and cranial capacities? :approve:
    Last edited: Jan 8, 2005
  2. jcsd
  3. Jan 8, 2005 #2


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    Is your idea that the angle of refraction should decrease as density increse based on some equation or law? or is it simply dicted by your everyday life intuition?

    I found on the internet* that the density [itex]\rho[/itex] of a liquid and its refractive index [itex]n[/itex] are related through the equation

    [tex]\frac{n^2-1}{n^2+2}=\frac{4\pi}{3}\rho \alpha[/tex]

    Where [itex]\alpha[/itex] is something called the molecular polarizability. I have no idea what that means either, but it probably means that to each media is associated a different value of [itex]\alpha[/itex], so that the angle of refraction does not depend only on the density, making your results you obtained experimentally more plausible.

    I hope that helped somehow.

    *http://students.creol.ucf.edu/JunLi/JunLiDocuments/Opt%20Exp%2012,%202002.pdf [Broken]
    Last edited by a moderator: May 1, 2017
  4. Jan 9, 2005 #3
    Now that is hard stuff, well, it was actually based on everyday intuition, I mean, wouldnt anyone think at first that higher density would result in a lower angle of refraction?

    Thanks a bunch:) I am sure that Ill put it into good use :biggrin:
  5. Jan 9, 2005 #4


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    I'm not sure what you mean by correlating the angle of refraction (unless of course you have some specific angles of incidence) ? Wouldn't it make sense to calculate the refractive index, n instead ?

    Anyway, your intuition that the refractive index should be a function of density alone is wrong. Refraction is not a macroscopic mechanical phenomenon. It is a microscopic electromagnetic phenomenon. So it will depend on charge distributions in the media.

    If we could do physics based on intuition, there would be no need for research. Unfortunately, things don't work that way.
    Last edited: Jan 9, 2005
  6. Jan 9, 2005 #5
    Well, I made the Angle of Incidence to 45 degrees, and I did calculate the refractive index on another chart, that was like a rudementary one.

    I have been researching for the reason why Density does not affect the Angle of refraction, are there any good sites out there that can help me out? :cry:
  7. Jan 9, 2005 #6
    Guys plz help me out.. :cry: Its due the day after tomorrow and if I dont understand htis Molecular Polarizability by then Im friend!! :surprised :cry:
  8. Jan 9, 2005 #7


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    What is the aim of your experiment ? And what is it you want help with ?

    It wouldn't be right to say that the refractive index does not depend on density. It does. But it also depends on other things...and that's what throws the table out of whack.
  9. Jan 10, 2005 #8
    Yeah those "other things" are the ones I need to know + understand and that is what I have been tring to find out ever since I conducted my experiment, which is about 2 weeks ago, extremely startling... and to think that it is due tomorrow.. *gasp* :cry:
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