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Homework Help: Optical difraction

  1. Nov 24, 2009 #1
    1. The problem statement, all variables and given/known data
    first question; Does a double slit also diffract light of different wavelength into different directions?

    second question; How would a diffraction grating for cm waves differ from an optical grating?

    2. Relevant equations
    sin (theta) = m.Lambda / d

    maybe, i am unsure if this is needed or not, i think it is for the 2nd question

    3. The attempt at a solution
    for the first question, i looked in my book and could not find anything which said that the light of different wavelengths difracted to different locations, but as the formula for the double slit includes the wavelength, i would guess that they would be diffrected to different places, but i am unsure.

    second question i couldnt really answer as i dont know what the difference between da diffrection grating and an optical grating is, if someone could tell me, or show me somewhere i can find out then it would be much appreciated.

    thanks in advance
  2. jcsd
  3. Nov 24, 2009 #2
    You are correct; if you increase the wavelength, you can change the angle at which the beam comes out. I found a nice http://phys.educ.ksu.edu/vqm/html/doubleslit/" online that shows how changing the energy (which is proportional to the wavelength) increases or decreases the number of peaks.

    Diffraction grating is very much like the double slit experiment, except there are 100's to 1000's of slits for light to pass through. I think all types of grating are considered optical grating as it will affect visible light just as well as infrared and ultraviolet light.
    My guess is that it's looking for a comparison of spacing necessary between (a) nm light (visible is in the range 350-750, depending on who you ask) and (b) cm electromagnetic waves (microwaves at this range)
    Last edited by a moderator: Apr 24, 2017
  4. Nov 24, 2009 #3
    thanks :)

    and i understand the second question a bit more now, but i am still unsure as to what the answer is, if i am thinking along the right lines, then for a beam of light and a microwave to have the same diffraction angle, then the space between the gratings would need to increase if the wavelength does.

    is this right? or have i gone wrong somewhere in my thinking.

    it has been a while since i was taught this, and it seems to have slipped away from me :(
  5. Nov 24, 2009 #4
    Given the form of the question, it seems to me they are asking for the difference in grating distances for some given angle [itex]\theta[/itex] and their respective wavelengths.
  6. Nov 24, 2009 #5
    thanks :)

    i've got my answer, and hopefully its right, if not then at least i'll learn something for next time :)
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