Figure 5-5: Wave Interference (a) Electromagnetic radiation travels as waves. Thomas Young’s interference experiment shows that light of a single color passing through a barrier with two slits behaves as waves that create alternating light and dark patterns on a screen. (b) Water waves passing through two slits creates two overlapping waves on the right side of a ripple tank; the result is an interference pattern. Constructive interference occurs where the crests (high points) from waves combine together. Destructive interference occurs where the crest from one wave combines with the trough (low point) of another, leaving the water’s surface undisturbed. In the experiment with light, the bright bands result from constructive interference, and the dark bands, from destructive interference, which shows that light is made of waves.