In Young's double slit experiment , the two slits 0.20 mm apart are illuminated by monochromatic light of wavelength 600 nm . The screen 1.0 m away from the slits .
(a) Find the distance of the second (i) bright fringe , (ii) dark fringe from the central maximum .
(b) How will the fringe pattern change if the screen is moved away from the slits ?

Explanation

Here , `d = 0.20 mm = 0.20 xx 10^(-3) m = 20 xx 10^(-5)` m
`lambda = 600 nm = 600 xx 10^(-9) m , D = 1.0` m
(a) (i) Distance of the second bright fringe
`x_(2) = (2 lambda D)/(d) " " [ because x_(n) = ( n lambda D)/(2d)]`
`= (2 xx 600 xx 10^(-9) xx 10)/(20 xx 10^(-5)) = 60 xx 10^(-4) = 6 xx 10^(-3) m = 6 mm`
(ii) Distance of the second dark fringe
`x_(2) = (3 lambda D)/(2d) [ because x_(n) = ((2n-1) lambdaD)/(2d)]`
`= (3 xx 600 xx 10^(-9) xx 1.0)/(2 xx 20 xx 10^(-5))`
`= 45 xx 10^(-4) = 4.5 xx 10^(-3) m = 4.5 `mm .