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Diffraction grating

  1. Mar 25, 2004 #1
    White light containing wavelengths from 405 nm to 760 nm falls on a grating with 7510 lines/ cm. How wide is the first-order spectrum on a screen 2.29 m away?

    Is this correct

    sin theta= (1)*(4.05e-7m)/(1.33e-6m)= 0.305 theta=17.8
    location= 2x(tan 17.8)= (2*2.29)*0.321=1.47m

    sin theta= (1)*(7.60e-7m)/(1.33e-6m)= 0.571 theta=34.8
    location= 2x(tan 34.8)= (2*2.29)*0.695= 3.18m

    so then should the answer to the question be
    3.18m+1.47m/2= 2.33m
     
  2. jcsd
  3. Mar 25, 2004 #2

    Doc Al

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    Staff: Mentor

    Why did you multiply by 2?
     
  4. Mar 25, 2004 #3
    so then should i multiply the angle by 2
     
  5. Mar 25, 2004 #4

    Doc Al

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    Staff: Mentor

    Why are you multiplying anything by 2??
     
  6. Mar 25, 2004 #5
    because the book states that with large angles you should multiply by two either way I don't get the correct answer based on the formula i used. Whether I multiply by 2 or not the answer still seems to be wrong. Am I not supposed to add at the end then divide by two for the answer?
     
  7. Mar 25, 2004 #6

    Doc Al

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    Staff: Mentor

    That makes no sense.

    Find the location of the first order maxima for each wavelength. Subtract those two numbers and you'll have the width of the first order spectrum.
     
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