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Diffraction orders seen 
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#1
Jul2110, 07:30 PM

P: 25

1. Light of wavelength 632.8nm is normally incident upon a grating of 5000 lines/cm. How many different diffraction orders can be seen in transmission?
2. m(lambda)=d(sintheta) 3. According to my text, d=1/5000lines/cm = 2x10^6m and sintheta= lambda/d = 632.8x10^9/ 2x10^6 = .3164 If I take sin^1(.3164), I get 18 degrees. From here, I don't know what to do because the answer is that 7 beams exist, corresponding to 4 orders, and I don't know how to get to that answer! 


#2
Jul2110, 09:09 PM

HW Helper
P: 4,433

sinθ = mλ/d.
λ/d = 0.3164. sinθ cannot be more than 1. So m should be 3. Hence there are 3 beams on either side and one central beam. 


#3
Jul2210, 06:01 AM

P: 25

Thanks for your reply. Although I understand what you are saying about the 3 beams on each side with one central, how do you derive that explanation from 0.3164?



#4
Jul2210, 06:34 AM

HW Helper
P: 4,433

Diffraction orders seen
sinθ = 3*λ/d = 3*0.3164 = 0.9492< 1. So n cannot be more than 3. 


#5
Jul2210, 09:44 AM

P: 25

Thanks, I understand now.



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