1. The problem statement, all variables and given/known data Consider a double slit experiment with a light source of 540nm. Slit separation is 4mm. A thin glass plate is placed in front of one of the slit,, resulting in each bright fringe moving to the location of the adjacent bright fringe. Find the minimum thickness of the glass. Refractive index of the glass is 1.56. Ignore reflections caused by the glass. 2. Relevant equations 2nt= +- mλ (bright fringe) 2nt= +- m+½λ (dark fringe) 3. The attempt at a solution I think I should be using the thin lens formula since they emphasised the thin glass plate as "thin". Bright fringe moves the distance of a dark fringe to take the position of the adjacent bright fringe. It seems too simple to just use t= (m+½λ)/2n Is there something I am missing?