1. The problem statement, all variables and given/known data If the apparatus for showing Newton's rings is illuminated with light at 6250 A (angstroms), what thickness of film underlies each of the first three light rings? 2. Relevant equations 2D (the thickness of the film) equals a multiple of 1/2 of a wavelength 1 angstrom = 1 x 10^-10 wavelength 3. The attempt at a solution I can't see how the angstroms connect to the fact that the thickness must be a multiple of 1/2.