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Application of the properties of light

  1. Jan 21, 2015 #1
    1. The problem statement, all variables and given/known data
    Light with wavelengths of 520 nm and 630 nm passes through a diffraction grating that contains 6000lines/cm.
    a) Sketch a diagram of the image produced from m = 0 to m = 2. Label the order of each fringe.
    b) Calculate the angles for the first and second order maxima that would appear on the screen.
    c) What is the lowest value of m for which the 520 nm line no longer exists? Justify your answer.
    d) Compare the appearance of the fringe at m=0 with all the others.

    2. Relevant equations
    SinΘ= mΛ/d
    d= 1m/6.0x10^5lines

    3. The attempt at a solution
    I am taking a learn at home course and this material is very new to me. I don't want to be told answers I'm just having a lot of difficulty grasping the entire concept of light if I'm being honest.
    I have used the equation to solve for b and c.
    The issue I'm having, perhaps I am over thinking it, is that I do not know how to sketch the diagram of the maxima and fringes. How am I to know the distances between fringes and the maxima? I tried to look through other equations in previous chapters but they require another variable, L, which I do not have. Of course without the sketch I cannot solve D.
    I was just hoping someone could help guide me into figuring it out on my own.
    Last edited by a moderator: Jan 21, 2015
  2. jcsd
  3. Jan 21, 2015 #2

    Simon Bridge

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    Just draw what you'd expect to see on a screen. If you don't know what that is, you should look for some pictures of diffraction patters online.

    That's what the equations are for.
    You may want to use a little geometry - but your notes should have that done for you.
    However you don't need to know to draw a sketch. You just need to illustrate the important points.

    You don't need to be so exact. It's only a sketch to give the idea.
  4. Jan 21, 2015 #3


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    All distances will scale in the same way with L. For a sketch, you don't need exact distances, the scale can be arbitrary.
  5. Jan 21, 2015 #4


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    Hello Paige, welcome to PF :)

    This is a physics subject that can be nicely supported with internet stuff like here
    Google double-slit interference to find a ton more sites. Wikipedia has a nice animated picture.
    Hyperphysics is a good site too.
  6. Jan 21, 2015 #5
    I know what diffraction patterns look like but to sketch a diffraction pattern with two different wavelengths and label both maxima is what is throwing me off.
    Am I on the right track if I use my calculations for part B to help me locate the m0-2 on the sketch? As the angles for the first and second orders are different could I assume that would affect their distance to the central maximum? the 520nm wavelength, for example, is 18degrees at m1 where as the 630nm wavelength is 22 degrees.
    So, to sketch I would assume that means the 520nm would have a m1 closer to the central maximum?
    Of course doing this I feel the sketch is very vague and wont be scaled correctly.
  7. Jan 21, 2015 #6

    Simon Bridge

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    You can do it for either one?
    The combined pattern is the sum of the two by themselves.
    Have you seen the diffraction pattern for white light?
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