Figure 2 Figure 3 double slit screen Figure 1: an incoming wave goes through 2 slits and interferes resulting in bright and light pots projected on a screen. The distance, Ay, measures the distance between 2 neighboring bright spots (or likewise, 2 neighboring dark spots). Figure 2: two light rays, one from each of the holes (two solid lines), interfere to produce a bright spot at the screen an angle 6 away from \"straight through\". This picture is not drawn to scale since the distance to the screen D is much bigger than slit separation d, D >> 0!. Figure 3: Zoomed in on box in Figure 2. Since D >> d , a good approximation is to treat the two light rays as parallel, as shown in Figure 2