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Alternating violet and red fringes in Diffraction Grating

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huey910
#1
Aug6-11, 07:55 AM
P: 36
When white light is passed through the slits in the grate and hits a screen some distance away from the grate, different order spectra appear. My textbook tells me that violet light is always closer to the zeroth order bright fringe than red light because it has a shorter wavelength. However, other sources clearly state that the pattern that appears on the screen is of an alternating pattern of violet and red lights, forming different order spectra. So, why would there be violet fringes beyond red fringes even though their wavelengths remain unchanged?
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Bloodthunder
#2
Aug6-11, 08:07 AM
P: 174
Because you also have first order, second order....

http://en.wikipedia.org/wiki/Diffraction_grating
Find the word "order".
Redbelly98
#3
Aug7-11, 09:38 AM
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In other words, the 2nd-order violet fringe is beyond the 1st-order red fringe. The statement "violet light is always closer to the zeroth order bright fringe than red light" is only true for a violet and red fringe of the same order; so the 1st-order violet is closer than the 1st-order red, 2nd-order violet is closer than 2nd-order red, etc.


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