1. The problem statement, all variables and given/known data The question is as follows, I'm truly stuck where to start here, any help would be much appreciated: A transparent paper of refractive index 1.45 and thickness 0.02mm is pasted on one of the slits of a double slit experiment. Monochromatic light of wavelength 620nm is passed through the slits. How many fringes will cross through the centre if the paper is removed? 2. Relevant equations I have been provided with one equation for this, which is as follows: Yo=β/λ(n-1)t Where n is the refractive index and t is the thickness. 3. The attempt at a solution Truly stuck where to even begin I'm sorry to say.