In Young's inteference experiment, two narrow parallel slits 0.2 mm apart are illuminated with monochromatic light of wavelength 600 nm, to get grige pattern on a screen 0.8 m away from the slits. Calculate the distance of
(a) third dark fringe from the central fringes and
(b) second bright fringe from the central fringe

Explanation

Slit separation d=0.2 mm
Wavelength of light `lamda=600 times 10^-9 m`
Distance between the slits and the screen, D=0.8 m
Fringwidth, `beta=(lamda D)/d=(600times10^-9 times0.8)/(0.2times10^-3)=2.4 mm`
(a) Distance of `n^(th)` order dark frings from the central
fringe is `x_(nd)=((2n-1))/2beta,n=1,2,3` for the second
bright fringe, n=2
`thereforex_(2b)=2beta=2 times2.4=4.8 mm`
Result `x_(3d)=6mm:x_(2b)=4.8mm`