1. The problem statement, all variables and given/known data In a Young's double slit experiment , the two slits are separated 0.5mm apart, Monochromatic light of wavelgnth 6.0x10^-7 m is used to illuminate the slits. When a piece of glass of thickness 0.024mm and refractive index of 1.5 used to cover one of the slits the whole intefrence pattern shifted in one direction. Find the distance shifted by the centre of pattern . 2. Relevant equations 3. The attempt at a solution OPD= (n-1)t = m λ (1.5-1)(0.024x10^-3) = m (6x10^-7) m = 20 i am going to find the distance between central max and first min which i have x = λD/ a a= separation of slit but i dont have D (distance of the slit from the screen ) .... how to proceed with this? is the question wrong ? or ????