1. The problem statement, all variables and given/known data A piece of paper is placed at the end of an air wedge 4 cm long. Interference fringes appear when the light of wavelength 639 nm is reflected from the wedge. A dark fringe occurs at both the vertex of the wedge and at its paper end, and 56 bright fringes appear between. Calculate the thickness of the paper. 2. Relevant equations delta X = L (lambda / 2t) where t is the thickness of the paper lambda = wavelength l = length of air wedge X = distance between fringes.