NOTE : only need to do one of these 2 questions, so whichever one is easier!

7) A diffraction pattern incident on a screen that is 6.9 m away is produced using light that passes through a single-slit of width 440 um. The central maximum is 1.5 cm wide. If the single-slit is replaced with a double-slit with a slit separation of 0.20 mm and the same light is used, what would be the distance from the central maximum to a fifth dark fringe?

8) Infrared light emitted by a cooling mass of radioactive material is incident on a diffraction grating with 6500 lines/cm and produces a first-order maximum at 17.How many maxima will occur in total?