A slit of width 0.6 mm is illuminated by a beam of light consisting
of two wavelengths 600 nm and 480 nm. The diffraction pattern is
observed on a screen 1.0 m from the slit. Find

(i) The distance of the second bright fringe from the central
maximum pertaining to light of 600 nm.

(ii) The least distance from the central maximum at which bright
fringes due to both the wavelengths coincide.

given, width =a=0.6 mm=0.6*10-3 m
and first wavelength =600 nm  
now for diffraction, we know, the distance of second bright fringe from central maximum =   5β2                                                        

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