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Draw the approximate diffraction pattern oringinating in the case of the fraunhofer diffraction from a greating consisting of three identical slits if the ratio of the grating period to the slit width is equal to (a) two, (b) three. |
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Answer» SOLUTION :The general formula for DIFFRACTION from `N` slits is `I = I_(0) (sin^(2) alpha)/(alpha^(2))(sin^(2)N beta)/(sin^(2)beta)` where `alpha = (pi a sin theta)/(lambda)` `beta =(pi(a+b)sintheta)/(lambda)` and `N = 3` in the CASE here. (a) In this case `a + b = 2a` so `beta = 2 alpha` and `I = I_(0)(sin^(2)alpha)/(alpha^(2)) (3 - 4sin^(2)2 alpha)^(2)` (b) In this case `a + b = 3a` so `beta = 3 alpha` and `I = I_(0)(sin^(2) alpha)/(alpha^(2)) (2 -4sin^(2) 3 alpha)^(2)` This has `3` MINIMA between the principle maxima 
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