Question

A transparent 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 fringes will cross through the centre if the paper is removed ?

Answer 1

Given that, μ= 1.45, t = 0.02 mm = 0.02x10^–3 m and λ= 620 nm = 620x10^–9 m

We know, when the transparent paper is pasted in one of the slits, the optical path changes by (μ – 1)t.
Again, for shift of one fringe, the optical path should be changed by λ.
So, no. of fringes crossing through the centre is given by,