Physics Help Forum Urgent?? line density??

 Light and Optics Light and Optics Physics Help Forum

 Nov 15th 2008, 07:36 AM #1 Junior Member   Join Date: Nov 2008 Posts: 4 Urgent?? line density?? Consider two monochromatic sources of light, blue light of wavelength λb = 460 nm and red light of wavelength 670 nm. The red light is shun upon a diffraction grating of density, nr = 10,000 lines per cm. A diffraction grating with what line density (lines/cm) is required to have the 2nd maximum (m=2) of blue light coincide with the 1stmaximum (m=1) of red light? I honestly doubt if I know how to do this question.... I'm blank, someone please help? Thanks
 Dec 7th 2014, 11:51 AM #2 Junior Member   Join Date: Sep 2014 Posts: 12 Answer λb = 460 nm λr = 670 nm Grating formula = m x λ = d (sin of entrance angle + sin of exit angle) I assume the entrance angle is 0°. For red: 1 x 670 nm = 10 000 / cm x (sin 0° + sin of exit angle) sin of exit angle = 0,67. Meeting at the same point means having the same exit angle for both light waves. So for blue: 2 x 460 nm = ? x (sin 0° + 0,67) ? = 13 731 l / cm __________________ Örsan Yüksek

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