Question

A transpoarent paper (refractive index = 1.45) of thickness 0.02 mm is pasted on one of the slits of a young's double slit experiment which uses monochromatic light of wavelength 620 nm. How many friges will cross through the centre if the paper is removed?

Answer 1

Given that :$\mu =1.45,t=0.02mm=0.02\times {10}^{-3}mandl=620nm=620\times {10}^{-9}m$
We know, when th etransparent aper is pasted in one of the slits, the optical path changes by (\mu - 1) f.
Again for shift of one fringe, the optical path should be changed by l.
So, Number of fringes crossing throuigh the centre is given by,
$n=\frac{(\mu -1)}{\lambda }=\frac{0.45\times 0.02\times {10}^{-3}}{620\times {10}^{-9}}=14.5$