4. (Waves and Light) When light of wavelength 640.0 nm passes through a single slit, the central maximum produced on a screen 2.0 m away is 8.0 cm wide. a. What is the fringe separation (the distance between dark fringes)? [1 mark] b. Find the angle from the central bright fringe to the first dark fringe. [1 mark] c. What is the width of the slit? [2 marks] d. If the system (consisting of the slit and screen) were submerged in water (n=1.33), what would be the width of the central maximum? [1 mark]