1. Two identical slides in air are illuminated with monochromatic light. The slides are exactly parallel, and the top slide is moving slowly upward. What do you see in top view? 1. all black 2. all bright 3. fringes moving apart 4. sequentially all black, then all bright 5. none of the above The path length difference will be related to the separation distance between the two slides. When d = N you get constructive interference and when d = (N+1/2) you get destructive interference.

4. Example: A plano-convex lens (n = 1.523) of 1/8 diopter power is placed, convex surface down, on an optically flat surface as shown in fig 7-17a. Using a traveling microscope and sodium light ( = 589.3 nm), interference fringes are observed. Determine the radii of the 1 st and 10 th dark rings.