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Lightsorce through spectrometer

  1. Mar 3, 2015 #1
    1. The problem statement, all variables and given/known data
    A light hits a spektrometer perpendicular into a gitter with 300 slits/mm. You observes that a red and a blue line (in Visual light) coinciding. And the angle deflectionis 24.5°. What wavelenght have the red and the blue lines.
    No n is given.

    2. Relevant equations

    3. The attempt at a solution
    First i calculated d
    1/300000m = 3.33*10-6
    ((3.33*10-6)*(sin24.5))/625-9 2.5

    ((3.33*10-6)*(sin24.5))/500-9 2.5

    so the red wavelenght is 625nm
    so the blue wavelenght is 500nm

    Is this correct ? can it be 2.5?? the blue is closer to n3 and red n2
  2. jcsd
  3. Mar 3, 2015 #2


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    So, I take it that "gitter" is "grating".

    I get approximately 2.2 and 2.7 as shown above in RED.

    So, yes, use n = 2 for red & n = 3 for blue.
  4. Mar 3, 2015 #3


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    Hello, SwedishFred.

    You know that n must be an integer, so n cannot be 2.5. Think about this: Is it possible for two different wavelengths to overlap using the same value of n for each wavelength?
  5. Mar 3, 2015 #4
    No that was what i was thinking about, so I understand it now, its much easier to see it happend ;-)
  6. Mar 3, 2015 #5


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    What do you get for the two wavelengths?
  7. Mar 3, 2015 #6
    Red 690nm
    Blue 461nm

    True ?
    Last edited: Mar 3, 2015
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