question_answer 6)

A beam of light consisting of two wavelengths650 nm and 520 urn is used to obtaininterference fringes in a Young's doubleslit experiment. (a) Find the distance of the third brightfringe on the screen from the centralmaximum for wavelength 650 nm. (b) What is the least distance from thecentral maximum where the brightfringes due to both the wavelengthscoincide ? The distance between two slits is 2 mm anddistance between the plane of the slits and the screen is 1.2 m.  

Answer:

(a)    Distance of nth bright fringe from thecentral maximum is given by For Also (b) Let  Minimum distance of theposition from the central maximum wherebright fringes due to  and  coincide. Now i.e. or or