Answered>Order 1348

Two rectangular, optically flat glass plates (of index of refraction 1.54) are in contact along one end and are separated along the other end by a sheet of paper that is 49 µm thick. The top plate is illuminated by monochromatic light (of wavelength 590 nm). An interference pattern results from the reflection of this light by the bottom surface of the top plate and the top surface of the bottom plate. Calculate the number of dark parallel bands crossing the top plate including the dark band at zero separation along the line of contact. The last dark band is to be counted if and only if its center (where the intensity is zero) is present.