1. The problem statement, all variables and given/known data A Michelson interferometer is illuminated with a laser with a wavelength of 514.5nm. A Haidinger fringe pattern is photographed with a lens of focal length 55mm. The diameter of the two adjacent circular fringes in the image are 1.53mm and 2.62mm. How far would the mirror that is further away from the beamsplitter need to be moved in order to set the interferometer at zero path difference? 2. Relevant equations Haidinger Fringe rp rp=f*√[(p*λ)/d] where rp = Haidinger Fringe f = focal length p = order of interference λ = wavelength d = difference in distance between the two mirrors and beamsplitter Effective path difference 2d*cosθ = pλ 3. The attempt at a solution Trying to derive an equation for the two path differences from the Haidinger Fringe equation, which is independent of the p value, but I'm struggling... rp=f*√[(p*λ)/d] ( rp / f )2 = (p*λ)/d ( rp / f )2 = 2d*cosθ/d d = 2d*cosθ / ( rp / f )2 d = 2d*cos1.3644 / 1.31 mm/55mm d = 2*cos1.3644 / 0.02381818181 d = 17.2082026858 2 * 17.2082026858 * cos1.3644 = pλ p = 2 * 17.2082026858 * cos1.3644 / 5.145*10^-7 p = 7.05309334257 / 5.145*10^-7 p = 13708636.2344 5.145*10^-7 * 13708636.2344 = 7.05309334257 metres = difference in distance between the two mirrors and the beam splitter So would the mirror need to be moved 7.05309334257 metres in order to set the interferometer at zero path difference?