324CHAPTER 24 24.42The grating spacing is 461 cm8.3310cm8.3310m1200−−==×=×dUsing sinmdλθ=and the small angle approximation, the distance from the central maximum to the maximum of order mfor wavelength is ( )tansinmyLLLdθθ=≈=m. Therefore, the spacing between successive maxima is 1mmyyyLd+∆=−=(. The longer wavelength in the light is found to be )( )( )368.4410m8.3310mnm0.150 m××469=longydL∆Since the third order maximum of the shorter wavelength falls halfway between the central maximum and the first order maximum of the longer wavelength, we have 32shortL01longLdd+=or ()1469 nm8.1 nm6short724.43The grating spacing is 1 mm2.5010mm2.5010m400×=×dFrom sindm=, the angle of the second-order diffracted ray is ( )1sin2dθλ−=. (a) When the grating is surrounded by air, the wavelength is
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