Fabry-Perot fringes are projected on to a screen using a lens of focal length 1.00 m. Calculate the order number mc of the bright central fringe (which is the highest order), and use this to calculate the diameter of the 21st bright fringe of the pattern.
Assume that light of wavelength 500 nm is incident at an angle q near normal incidence (i.e. q is small), that the etalon plates are 5.00 mm apart, and that air is the medium between the plates. Draw a diagram to illustrate the geometry of the set-up.