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Diffraction orders seen

by clockworks204
Tags: diffraction, orders
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clockworks204
#1
Jul21-10, 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!
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rl.bhat
#2
Jul21-10, 09:09 PM
HW Helper
P: 4,439
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.
clockworks204
#3
Jul22-10, 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?

rl.bhat
#4
Jul22-10, 06:34 AM
HW Helper
P: 4,439
Diffraction orders seen

Quote Quote by clockworks204 View Post
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?
sinθ = nλ/d. if n = 3
sinθ = 3*λ/d = 3*0.3164 = 0.9492< 1. So n cannot be more than 3.
clockworks204
#5
Jul22-10, 09:44 AM
P: 25
Thanks, I understand now.


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