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Homework Help: Physics gen ed question

  1. Jun 2, 2004 #1
    Hi, I'm a senior graduating this spring and I'm doing horrible in my gen ed class- my last attempt to not fail the class (I have a very low D and a 3.7 gpa so you see why I'm nervous), is extra credit.

    we did not have an assigned book for this class and she's given very little information other than notes- which do not correspond with our EC assignments.

    the question asks:

    light from the air passes through plates of glass and plastic below. the speed of light in the different materials are shown to the right. Construct a rough sketch showing an appropriate path through the system of four plates.

    compared to the 50 degree incident ray at the top, what can you say about the angles of the ray in the air between and below the block pairs?

    i scanned and image that can be seen at this link: http://www.wright.edu/~gildenmeister.2/scan.jpg [Broken]

    i'm not asking anyone to do this for me, but what I need to do to solve it, I want to learn how to do it, I just don't have a clue how to go about the actual solving process.

    Thank you.
    Last edited by a moderator: May 1, 2017
  2. jcsd
  3. Jun 2, 2004 #2
  4. Jun 2, 2004 #3
    would I use snell's law to calculate or am I on the wrong path?

    or should i use n= c/v I know that hte v is given, but I don't understand why there are 7 of them on the right hand side.
    Last edited: Jun 2, 2004
  5. Jun 2, 2004 #4
    The speed of light changes in every medium is goes through. The speeds on the right tell you how fast it travels inide each medium. There are seven of them because there are seven mediums, although some of them are identical. In order to use Snell's law you need to know the refraction index of each medium, which is given by n = c/v. And then just calculate the different angels and plot the path of light.
  6. Jun 2, 2004 #5
    so do i plot the seven on four plates?

    and since there are seven-

    299, 792, 358 m/s

    v is either given or v(c)

    so for the first

    n = 299, 792, 358/ c = so the answer is 1?

    and then I plot 1?
  7. Jun 2, 2004 #6
    Yes, when v = c, n = 1. But you don't write the index itself, you were asked to make a rough sketch of the path light takes when going through the plates. If you read that page I linked you, you will see that light not only changes its speed when going from one medium to another, it also changes its direction - this is called refraction. Why is a question you probably don't need the answer of, but using Snell's law you can find the new direction of light in the new medium based on its direction in the old medium and based on the refraction index of the two mediums.
  8. Jun 2, 2004 #7
    well I still don't understand even after looking at that site. thanks for your help. I failed the test today too, so I have to get atleast a d on the final to pass the class which without this ec i can't see happening.
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