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A beam of light consisting of two wavelengths 6500A^(0)" and "5200A^(0) is used to obtain interference fringes in a Young.s double slit experiment. What is the least distance from the central maximum where the bright fringes due to both the wavelengths coincide? Distance between the slits is 2mm, distance between the slits and the screen L= 120 cm. |
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Answer» Solution :LET the nth bright fringe of wavelength `lambda_(m)` coincide at a distance y from the central maximum then `y= (m lambda_(m)L)/(d)= (n lambda_(n)L)/(d)""therefore (m)/(n)= (lambda_n)/(lambda_m)= (6500)/(5200)= (5)/(4)` i.e., 5th bright fringe of wavelength `5200A^(0)` COINCIDES with the 4th bright fringe of wavelength `6500A^(0)` `therefore y_(m)= (m lambda_(m) L)/(d)= (5(5200xx 10^(-10))xx 1.20)/(2xx 10^(-3))= 1.56 mm`. |
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