Monichromatic lightof wavelenght 600 nm is used ina Young's double slilt experient. One of the slits is covered by a transparent sheet of thicknes `1.8xx10^-5` m made of a material of refractive index 1.6. How many fringe will shift due to the introduction of the sheet?

Explanation

Optical path difference introduced at the centre of pattern can be written as follow:
`Deltax = (mu - 1) t`
In n fringes cross the centre , then we can write as follows:
`Deltax = n lambda`
`implies (mu - 1)t = n lambda` `implies n = ((mu - 1)t)/(lambda) - ((1.6 - 1) xx 18 xx 10^(-6))/(600 xx 10^(-9)) = 18`.