1. The problem statement, all variables and given/known data Two optically flat glass plates, 16.0 cm long, are in contact at one end and separated by 0.0200 mm at the other end. The space between the plates is occupied by oil with index of refraction 1.45. The index of refraction of the glass plates is 1.55. The plates are illuminated at normal incidence with monochromatic light, and fringes are observed. If the dark fringes are spaced 2.00 mm apart, what is the wavelength of the monochromatic light? 2. Relevant equations n=c/v where n=index of refraction v= velocity in medium maybe y=(p * wavelength*L)/a y=position of dark fringe p=0,1,2,.... a=slit width L= length from slit to screen This is the equation for single slit diffraction. 3. The attempt at a solution I am not sure. Is this question to do with single slit diffraction. If so how do i use the refactive index of the glass and oil in the question. alltogether very confused. Help appreciated thanks. Also is the light source shining on the side of the glass plate?